Freshwater Triclads (Turbellaria

of North America,

VI: The Genus Dendrocoelopsis

ROMAN KENK

wlu.

SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY • NUMBER 138
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SMITHSONIA N CONTRIBUTION S T O ZOOLOG Y • NUMBE R 138

Freshwater Triclads (Turbellaria)

of North America,

VI: The Genus Dendrocoelopsis

Roman Kenk

SMITHSONIAN INSTITUTION PRESS

City of Washington

1973
ABSTRACT

Kenk, Roman. Freshwater Triclads (Turbellaria) of North America, VI: The

Genus Dendrocoelopsis. Smithsonian Contributions to Zoology, number 138,

16 pages, 12 figures, 1973.—Five species of Dendrocoelopsis occur in North

America, D. vaginata Hyman, D. piriformis Kenk, D. alaskensis Kenk, D. hymanae

Kawakatsu, and D. americana [=Sorocelis americana Hyman]. Dendrocoelopsis

vaginata, D. piriformis, and D. americana are described in detail. The taxonomic

significance of multiple eyes in freshwater triclads is discussed.

Official publication date is handstamped in a limited number of initial copies and is recorded

in the Institution's annual report, Smithsonian Year.

COVER DESIGN: Montastrea cavernosa (linnaeus).

Library of Congress Cataloging in Publication Data

Kenk, Roman, 1898-

Freshwater triclads (Turbellaria) of North America, VI: the genus Dendrocoelopsis.

(Smithsonian contributions to zoology, no. 138)

Bibliography: p.

I Dendrocoelopsis. 2. Turbellaria—North America. I. Title. II. Series: Smithsonian Institution. Smithsonian contributions to zoology, no. 138.

QL1.S54 no. 138 [QL391.T75] 591'.08s [595M23] 72-10035

For tale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402 - Price 45 cents (paper cover)
Contents

Page

Introduction 1

Dendrocoelopsis vaginata Hyman, 1935 . 2

Dendrocoelopsis piriformis Kenk, 1953 6

Dendrocoelopsis alaskensis Kenk, 1953 8

Dendrocoelopsis hymanae Kawakatsu, 1968 9

Dendrocoelopsis americana (Hyman), 1939 10

Literature Cited 15

i n

Freshwater Triclads (Turbellaria)

of North America,

VI: The Genus Dendrocoelopsis

Roman Kenk

Introduction

The genus Dendrocoelopsis was established by

Kenk (1930:296) for a European species, Dendrocoelum spinosipenis Kenk (1925). The original

definition of the genus was as follows: Dendrocoelidae without adenodactyl; penis with well-developed papilla, penis bulb not composed of two

muscle layers separated by a glandular layer; oviducts uniting to a common terminal duct without

embracing the bursa stalk; testicular zone extending

to behind the copulatory apparatus; anterior end

with subterminal true sucker; eyes not multiple.

This definition had to be modified as more

species, undoubtedly close relatives of D. spinosipenis, were discovered and described. The genus

Amyadeniurn de Beauchamp (1931:159) was merged

with Dendrocoelopsis (Kenk, 1953:177), although

some European workers still keep it separate. Today

Dendrocoelopsis comprises some 14 species distributed over Europe, North America, and Asia. They

show all transitions between highly developed

adhesive organs and a lack of adhesive structures

at the anterior end; the testicular zone may terminate at the level of the copulatory complex or

extend to the tail end; and several species show a

multiplicity of eyes while others have only two or

are blind. Thus, the species placed today in the

genus Dendrocoelopsis exhibit the following characters (cf. Hyman, 1935:338): Dendrocoelidae

Roman Kenk, Department of Invertebrate Zoology, National

Museum of Natural History, Smithsonian Institution, Washington, D. C. 20560.

without adenodactyl; penis with well-developed

papilla, penis bulb of ordinary construction; oviducts uniting to a common oviduct without embracing the bursal stalk; eyes two, lacking, or

multiple.

Dendrocoelopsis, thus described, can hardly be

separated from the poorly defined Asiatic genus

Sorocelis. The crucial distinction concerns the interpretation of the multiplicity of the eyes in the

two genera. The use of the number and arrangement of the eyes for taxonomic purposes is of

limited value (Kenk, 1930:152). Complete absence

of eyes is generally correlated with ecological factors

such as life in subterranean habitats or in deep

lakes, while the occurrence of supernumerary or

accessory eyes is observed frequently in two-eyed

species of various genera of dendrocoelids and

planariids. Such supernumerary eye spots may be

of various size and structure, often confined to

simple specks of eye pigment lacking any retinal or

nervous elements. Sorocelis has what we may call

a true, genetically determined, pluriocularity, while

the multiple eyes of some Dendrocoelopsis species

appear to be more closely related to accessory eyes.

More evidence supporting this interpretation will

be given in the section on D. americana.

The holotypes of the five North American species

of Dendrocoelopsis are deposited in the American

Museum of Natural History (AMNH) and the

National Museum of Natural History, Smithsonian

Institution (USNM: United States National Museum collections).

ACKNOWLEDGMENTS.—This study was supported in

1
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

part by National Science Foundation Grant GB6016 to the George Washington University. The

kind cooperation of many persons who served as

guides in the field work or furnished material or

information is gratefully appreciated: Dr. C. J. D.

Brown (Montana State University), Dr. Jerry H.

Carpenter (Northern Kentucky State College),

Frank P. Crowley, Mrs. Virginia Erickson, Leslie

Hubricht, Dr. Masaharu Kawakatsu (Fuji Women's

College, Sapporo, Japan), Robert E. Olson, Dr.

Robert L. Rausch (Arctic Health Research Center,

College, Alaska), and Richard Whitten (Powell

Laboratories, Gladstone, Oregon).

I wish to express my thanks to Mr. Walter R.

Brown, Dr. Kenneth M. Towe, and Mr. Charles R.

Obermeyer II, all of the Smithsonian Institution,

who kindly took the scanning electron photomicrograph and who performed the X-ray diffraction test

and the X-ray concentration mapping on the spines

of D. americana, respectively.

Dendrocoelopsis vaginata Hyman, 1935

FIGURES 1A, 2A, 3A, 4

Dendrocoelopsis vaginatus Hyman, 1935:339.

Dendrocoelopsis vaginata.—Kenk, 1953:177.

HOLOTYPE.—From shores of Flathead Lake, Montana, set of sagittal sections (AMNH 665).

The species was originally described from preserved specimens sent to Dr. Hyman by Dr. R. T.

Young of the University of Montana, two of which

were sexually mature. Kenk (1953) changed the

ending of the specific name to vaginata to agree in

gender with the feminine genus Dendrocoelopsis.

Sexually mature specimens are up to 21 mm long

and 2.8 mm wide. The anterior end is truncate, the

frontal margin, bearing the subterminal adhesive

organ, in the quietly gliding animal is either slightly

bulging or centrally retracted (Figures 1A, 2A). In

locomotion this central portion is elevated somewhat above the substrate. The rounded corners of

the head protrude gently laterally so that a slight

narrowing or neck appears behind them. The margins of the body then diverge gradually for about

one-fourth the body length, become parallel, and

converge again in the region of the copulatory

complex, forming a bluntly pointed posterior end.

The color of the animal in life is dark chocolate

brown dorsally and a little lighter ventrally. A pair

of oval fields above the eyes, a spot at the mouth

opening, and a circular field around the gonopore

are free of pigment. Two indistinct lighter fields

extend from the eyes toward the frontal margin,

flanking the adhesive organ, and two short, light,

longitudinal streaks parallel the body margins at

the level of the neck. Occasionally a dark middorsal

line is seen, beginning some distance behind the

eyes and extending to the region of the pharynx,

and a less distinct line, behind the pharynx to the

posterior end. In her original description, Hyman

(1935:339) reported that the species, collected in

Montana, was white and, hence, without body pigment; in a later paper (1963:4) she stated that the

dark color seen in another population, from

Oregon, was due not to body pigment but to in1 mm l m m l m m

FIGURE 1.—Outline drawings of living specimens: A, Dendrocoelopsis vaginata; B, D. piriformis; C, D. alaskensis; D, D.

americana from Brown Springs, Mt. Magazine, Arkansas.
NUMBER 138

A

FIGURE 2.—Photographs of living animals: A, Dendrocoelopsis i>agmata from Nigger Creek,

Washington, x 9-6; B, D. ezensis from Tomikawa-cho, Hokkaido, Japan, x 8.4; c, D. americana

from Brown Springs, Mt. Magazine, Arkansas, x 7-2.

elusions in the cells of the gastrodermis, presumably

originating from ingested food. It appears that

Hyman had studied only preserved specimens. The

pigment of D. vaginata is diffused in the mesenchymal tissue and is not the granular pigment confined

to special mesenchymal cells that occurs in some

other triclads and that can be identified in microscopic sections. Furthermore, it bleaches easily in

preserved specimens and then cannot be recognized.

Live worms from both of Hyman's localities show

clearly that the pigment is not confined to the intestinal system.

The two eyes are situated at a distance from each

other equal to about one-third the width of the

head and their distance from the frontal margin

is slightly greater than that from the lateral margin.

The adhesive organ, located in the center of the

frontal margin of the head, appears in the sections
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

lmm lmm

B

FIGURE 3.—Outline drawings of young (recently hatched)

animals: A, Dendrocoelopsis vaginata from Yellow Bay Creek,

Montana; B, D. americana from Brown Springs, Arkansas.

as a convex or concave field of infranucleate epithelium lacking cilia or rhabdites and perforated by

numerous gland ducts filled with a granular, eosinophilic secretion. The cell bodies of these glands are

scattered in the mesenchyme of the anterior third

of the prepharyngeal region, predominantly dorsal

to the intestinal branches. Muscle fibers attach to

the adhesive area, chiefly extensions of the internal

longitudinal layer of the ventral integumental musculature. The adhesive organ may be interpreted as

a modification of the submarginal adhesive zone,

which has a similar infranucleate and rhabdite-free

epithelium. The organ and the zone are not continuous but are interrupted on either side at what

appears to be the location of the lateral auricular

lobes, which are covered with a nucleate, ciliated

epithelium, in part lacking rhabdites, presumably

a sensory epithelium.

The digestive system shows no peculiarities. The

pharynx, measuring in length about one-sixth the

length of the body, is inserted at the middle of the

body length. Its internal muscle layer consists of

intermingled longitudinal and circular fibers as is

typical for the family Dendrocoelidae. The anterior

intestinal ramus bears five to six pairs of branches

and each posterior ramus about 12 to 14 lateral

branches.

The reproductive system has been well described

by Hyman (1935). The two ovaries are located

below or behind the second pair of intestinal

branches. The numerous, rather small testicles are

ventral, arranged in longitudinal rows extending

from some distance behind the ovaries to the level

of the copulatory complex. Four rows are developed

in the prepharyngeal region, one pair lateral and

one pair medial to each of the ventral nerve cords.

The medial rows terminate as they approach the

level of the pharynx while the lateral rows continue

along the sides of the pharynx and the copulatory

apparatus.

In the copulatory apparatus (Figure 4) the

genital atrium may be divided into a large anterior

male atrium (am) and a smaller common atrium

(ac), but frequently there is no constriction visible

between the two cavities. Apparently the shape of

the atrium is subject to deformation by muscular

contraction at the moment of killing. The wall

of the male atrium is lined with an epithelium of

tall, glandular cells, that of the common atrium

with a cuboidal epithelium. Below the lining of

both divisions is a layer of circular muscle fibers,

followed by a layer of longitudinal fibers.

The penis consists of a large spherical bulb and

an elongated conical papilla. The bulb, which is

formed by the usual concentric layers of muscle

fibers, contains a voluminous cavity, the seminal

vesicle (vs). The cavity is lined with a secretory

epithelium and has villus-like extensions projecting

inward. The cavity continues into the penis papilla

as a narrower canal, the ejaculatory duct (de),

running in the axis of the papilla and opening at its

tip. The lining of this canal is a cuboidal epithelium. Below the flattened external epithelium of
NUMBER 1S8

m ode

FIGURE 4.—Copulatory apparatus in sagittal section of Dendrocoelopsis vaginata (after Kenk,

1972). [Abbreviations used in figures: a —genital atrium, ac=common atrium, am — male

atrium, i> = copulatory bursa, fad = bursal duct or stalk, fcp:=penis bulb, <ie—ejaculatory duct,

f= fibrous layer, g/—gland ducts, gp=gonopore, w —mouth, ofic = common oviduct, phz=.

pharynx, pp=zpenis papilla, «;—false seminal vesicle or spermiductal vesicle, fdzzvas deferens,

i'dc = common vas deferens, 1/5—seminal vesicle.]

the penial papilla is a thick layer of fine circular

fibers which do not stain like muscle fibers, the

fibrous layer (/); presumably this is of an elastic

nature and seems to impart a certain rigidity to

the papilla. This layer is followed by a sheet of

longitudinal muscles which in part attach to the fibrous layer. The two sperm ducts or vasa deferentia

(vd), which at the sides of the pharynx had enlarged

to form the tortuous false seminal vesicles or spermiductal vesicles, approach the penis bulb, enter it

from the sides, and open separately into the seminal

vesicle. Numerous gland ducts, with a granular,

faintly eosinophilic secretion, penetrate the penis

bulb from the surrounding mesenchyme and empty

into the posterior part of the seminal vesicle and

the ejaculatory duct.

The two oviducts or ovovitelline ducts converge

toward the midline and unite in the space between

the atrium and the bursal stalk to form a common

oviduct (ode) which opens into the atrium at the

transition between the male and common atria. The

terminal parts of the paired oviducts and the

common oviduct receive many outlets of strongly

eosinophilic glands, the so-called shell glands.

The sac-shaped copulatory bursa (b) is well-developed. Its outlet or stalk (bd) originates from its

posterior wall, first ascends dorsally, proceeds above

the penis and the genital atrium in the midline or

somewhat to the right side, and finally bends ventrally to open into the atrium close to the genital

aperture (gp)- In its proximal part, above the penis,

the duct is rather narrow and smooth, but it progressively widens distally, and is thrown into irregular folds. Its muscular coat consists of interlaced

circular and longitudinal fibers and gradually increases in thickness toward its posterior opening.

Dendrocoelopsis vaginata is an inhabitant of cool

streams and lakes in some of the northwestern

states. So far it is known only from a few localities,

but it will probably be found to be more widely

distributed upon further collecting. The following

are the records that have come to my attention:

MONTANA. GALLATIN COUNTY: (1) Spring north of Belgrade, in outlet crossing the county road about 4 miles north

of junction with U. S. Highway 10. 2 September 1967: water

almost stagnant, with much vegetation, temperature 10.4°

C, pH 7.5; 5 immature specimens under stones. (2) Tributary of Thompson Creek, crossing county road north of Belgrade, 4.3 miles from junction with U. S. Highway 10. 2

September 1967: water with fast current, 10.8° C, pH 7.6;

about 15 specimens under stones, 5 of them mature. 4 September 1967: 10 specimens of various sizes, 4 of them mature,

under stones. 4 June 1970: 14.0° C, 4 specimens under

stones, 2 of them mature (Polycelis sp. also occurs in this
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

locality). (3) Tributary of Gallatin River, opening into the

river above the bridge on U. S. Highway 10, 5.3 road miles

northwest of Belgrade. 2 September 1967: water fast, clear,

16.6° C, pH 8.8; 2 Dendrocoelopsis under stones, one of

them mature. LAKE COUNTY: (1) Along shore of Flathead

Lake and in tributary of the lake, type-locality of D. vaginata (Hyman, 1935:344) . (2) Yellow Bay Creek, about 10

yards from the mouth of the creek in Flathead Lake (possibly the same locality as that mentioned by Hyman). 10

August 1969: several specimens collected by Mr. Frank P.

Crowley and shipped to me alive [Polycelis coronata coronata

(Girard) also present]. MISSOULA COUNTY: Greenough Park,

Missoula, feeder spring and creek for Rattlesnake Creek (1

mile from Clark Fork River) . 21 May 1968: water slightly

muddy, 10° C, 8 specimens collected by Mr. F. P. Crowley,

most of them sexually mature.

OREGON. MULTNOMAH COUNTY: Woodbury Spring in

Crystal Springs area of Eastmoreland District of Portland,

one-half block south of Holgate on 28th Avenue. 12 September 1967: water almost stagnant, clear, 11.2° C, pH 6.3;

many D. vaginata taken on liver bait, both young and mature (the spring contains also Phagocata oregonensis Hyman

and Polycelis sp.). This is possibly the same locality as that

mentioned by Hyman (1963:1).

WASHINGTON. WHITMAN COUNTY: Nigger Creek, 18

miles south of Cheney. 1 August 1970, 5 D. vaginata collected by Mrs. Virginia Erickson and sent to me alive, one

of them mature.

Sexually mature specimens of D. vaginata were

taken in the field at all seasons, when collections

were made, from March to September; no data are

available for the winter months. It is possible that

the species breeds the year round. No indications of

asexual reproduction were observed. The temperature of the water varied from 10° to 16.6° C, with

an average of 12.2° C (6 measurements), the pH

from 6.3 to 8.8. Further observations on the physicochemical parameters of the habitats are lacking.

Specimens were kept in the laboratory in coldwater cultures (14° C) for several months, fed beef

liver or Tubifex worms, but could not be maintained indefinitely. Three cocoons were deposited

in the aquaria, all within the first weeks after the

collections. The cocoons were unstalked, spherical,

with a diameter of 1.6 to 1.8 mm, attached to the

substrate by a copious amount of colorless jelly.

Two cocoons hatched several weeks after deposition

and yielded seven and five young. They were of

different sizes, the largest being about 3.5 mm long

and 0.7 mm wide. They showed the adhesive organ

as a transverse, opaque field in the center of the

frontal margin (Figure 3A). On both sides of the

organ the margin sloped backward to the region of

the feebly developed rounded auricles, behind

which a slight constriction or neck was visible. The

young were initially pigmentless, white, but had

acquired body pigment by the time they were four

weeks old.

The three pigmented species of the genus Dendrocoelopsis, i.e., D. vaginata, D. piriformis Kenk

(1953) from Alaska, and D. ezensis Ichikawa and

Okugawa (1958) from Hokkaido, Japan, resemble

each other rather closely in their external appearance. Dendrocoelopsis vaginata may be distinguished from D. piriformis by having a slightly

different outline of the body, the lateral margins

running parallel when the animal is gliding quietly,

while in D. piriformis the greatest width is in the

last third of the body. Furthermore, the pigmentation of the two species is different, D. vaginata

lacking the accumulation of dark pigment between

the eyes and on the sides of the adhesive organ

and not showing any pattern of longitudinal stripes,

such as are seen frequently in D. piriformis. Dendrocoelopsis ezensis (Figure 2B), which in its pigmentation appears to be close to D. vaginata, has

the eyes set farther apart (about one-half the

width of the head) than D. vaginata. Anatomically

the three species may be separated by the location of

the testes: in D. vaginata they are ventral, extending

to the copulatory apparatus; in D. piriformis, dorsal, extending to the posterior end; and in D.

ezensis, ventral and dorsal, extending to the posterior end of the body. The anatomy of the penis

also furnishes good distinguishing characteristics:

D. piriformis lacks a fibrous layer in the wall of

the penis papilla; and D. ezensis has a plug-shaped

penis papilla and a thick muscular layer surrounding the seminal vesicle and the ejaculatory duct.

Dendrocoelopsis piriformis Kenk, 1953

FICURFS 1B, 5

Dendrocoelopsis piriformis Kenk, 1953:174.

HOLOTVPE.—From Moose Creek, on Glen Highway, Alaska, near mile-post 186, set of sagittal

sections (USNM 22334).

Since the original description (Kenk, 1953), the

species has been collected in a number of arctic

lakes in Alaska and western Canada by C. Holmquist (1967a, 1967b). The following description

is based on these three publications.

The species is up to 16 mm long and about 3
NUMBER 138

mm wide. The head is truncate, with a bulge on

the frontal margin corresponding to the position

of the subterminal adhesive or grasping organ, and

a pair of rounded auricles which project slightly

laterally (Figure 1B). Behind the head the lateral

margins gradually diverge to reach the greatest

width at the beginning of the last third of the body.

The pigmentation is very variable even within the

same population. The dorsal side may be almost

uniformly brown or brownish gray, or may appear

somewhat spotted; there is often a dark median

stripe which may be flanked by a pair of lateral

longitudinal stripes. The area between the eyes is

very dark and the pigment extends toward the

frontal margin along both sides of the adhesive

organ. The periocular spaces and a rounded field

above the adhesive organ are free of pigment. A

pair of indistinct, light-colored streaks, presumably

the auricular sense organs, may be seen on the lateral margins of the head. The ventral side is gray.

There are normally two eyes, a little more than

one-third the width of the head apart and nearer

to the lateral margins than to the frontal margin.

Accessory or supernumerary eyes may occur on one

or on both sides.

The adhesive organ is similar to that of D. vaginata. It consists of a subterminal adhesive field

perforated by numerous gland ducts filled with an

eosinophilic secretion, and of muscle fibers, presumably serving as retractors.

The ovaries, situated at the level of the second

pair of intestinal branches, show no pecularities.

The numerous testes are dorsal, forming a pair of

broad bands extending from the level of the ovaries

to the posterior end.

The copulatory apparatus (Figure 5) generally

resembles that of D. vaginata. The genital aperture (gp) leads directly into the male atrium (am)

as there is no common atrium developed. The penis

consists of a rounded muscular bulb and an elongated, conical or finger-shaped papilla. The bulb

contains a large cavity, the seminal vesicle (vs),

the walls of which form villus-like processes projecting into the lumen. From this cavity a smooth,

narrow ejaculatory duct (de) proceeds into the

penis papilla and opens at its tip. The penis bulb

has, as is usual, concentric layers of interlaced

muscle fibers in its peripheral part and a parenchymal zone surrounding the seminal vesicle. The

penis papilla is covered by a cuboidal epithelium

m b vd de am

I \

bd ode gp

FIGURE 5.—Copulatory apparatus in sagittal section of Dendrocoelopsis piriformis (after Kenk, 1953), X 49. [See Figure

4 for abbreviations.]

below which is a muscular zone consisting of several

layers; first, a thin longitudinal layer developed

chiefly in the proximal (anterior) part of the papilla, followed by a strong sheet of circular fibers

and, finally, a second, internal, longitudinal layer.

An elastic fibrous layer, such as is developed in

D. vaginata, is lacking in D. piriformis. The ejaculatory duct has a coat of longitudinal fibers.

The two vasa deferentia (vd) enter the penis

bulb anterolaterally and open into the bulbar

lumen separately, but close together, each on a short

conical papilla.

The two oviducts approach the midline at the

level of the copulatory complex, the right one

passing between the wall of the male atrium and

the outlet of the copulatory bursa. They unite to a

common oviduct (ode) which empties into the

atrium from the dorsal side close to the gonopore.

The copulatory bursa (b) is a lobate sac lined

with a tall secretory epithelium. Its outlet or duct

(bd) runs posteriorly above the penis bulb and the

male atrium. Its anterior part is a rather narrow

canal, but it widens gradually in the posterior half,

curving ventrally and opening into the atrium

(or almost independent of it) very close to the

gonopore. Both parts of the duct have a muscle

coat consisting of intermingled circular and longitudinal fibers.

Holmquist (1967a:456) reports that the cocoons

of /). piriformis, collected in the field, are round,

brown to almost black, and have a diameter of

1-3 mm.

Dendrocoelopsis piriformis has been collected by

Kenk in four lakes and two streams in subarctic
SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Alaska, by P. F. Scholander in a lake near Umiat on

the Arctic Slope of Alaska (Kenk, 1953:178), and

by C. Holmquist (1967a:454-455 and table 1) in 21

lakes in arctic Alaska, both north and south of the

Brooks Range, in the arctic sections of Yukon Territory, and in the Mackenzie District of Northwest Territories of Canada.

Dendrocoelopsis piriformis is a eurythermic species living in lakes and their outlets under a

considerable variety of environmental conditions.

Physicochemical measurements of some parameters

of its habitats were furnished by Holmquist (1967a;

table 1). The temperature range at the time of the

collections was between 5.5° and 15.5° C in arctic

localities and between 11.5° and 26.6° C in subarctic habitats (Kenk, 1958:178). The values of pH

(not measured in the field) varied between 7.0 and

9.2. Other parameters measured were: Cl~, 1.78-

26.6 mg/liter; CaCO3, 16.1-114.8 mg/1; and conductivity, 12-277 micromho (at 25° C). The worms

were collected at depths of 0-15 m. Holmquist

(1967a:455) points out that very shallow lakes that

freeze solid in winter contain no triclads.

The reproduction of the species is presumably

only sexual, by egg capsules, as no evidence of

fission has been observed. The species has not been

kept in laboratory cultures and little is known

about its food habits. It probably feeds on a variety

of aquatic invertebrates, for Holmquist (1967a:463)

has identified remains of copepods in its gut. This

observation is of interest as it may explain the

presence of cestode plerocercoids in some of her

specimens.

TAXONOMIC POSITION.—By its external appearance,

as well as its anatomical characters, D. piriformis is,

without doubt, closely related to D. vaginata and to

the Japanese D. ezensis. The differences between

the three species have been discussed in the section

on D. vaginata.

Dendrocoelopsis alaskensis Kenk, 1953

FIGURES lc, 6

Dendrocoelopsis alaskensis Kenk, 1953:178.

HOLOTYPE.—From creek crossing Elliot Highway,

Alaska, at milepost 31, set of sagittal serial sections

(USNM 22335).

The original description of this species was based

on the study of only a few specimens, none of

which was at full sexual maturity. Through the

courtesy of Dr. Robert L. Rausch of the Arctic

Health Research Center at College, Alaska, I received several additional samples of the species,

only one of which had the reproductive system

developed but not fully differentiated. The following description is taken chiefly from the original

publication.

The largest specimen measured was 20 mm long

and 4 mm wide (Figure lc). The anterior end is

truncate, with a convex frontal margin and rounded

auricular lobes which protrude both anteriorly and

laterally, causing a slight narrowing of the lateral

margins to appear behind them. There is no

adhesive organ visible in live specimens. The body

is unpigmented, white. The two principal eyes

are about one-third the width of the head apart

and the distance of each eye from the frontal

margin is equal to, or slightly longer than, the

distance from the lateral margin. Supernumerary

eyes may appear either anterior or posterior to the

principal eyes.

As no fully mature animal could be studied, the

description of the reproductive system must be

considered to be preliminary, lacking definite

morphological and histological details. The testes

are predominantly ventral, but individual follicles

may be located in the mesenchymal "septa" between

the intestinal branches farther toward the dorsal

side. The testicular band on either side extends

posteriorly to the level of the copulatory complex.

The ovaries are situated below the third or fourth

pair of intestinal branches. The copulatory organs

(Figure 6), though not in their final shape, show

the essential characteristics of the genus Dendrovd vs a ode gp bd

Fif;URF. 6.—Copulatory apparatus in sagittal section of Dendrocoelopsis alaskensis (after Kenk, 1953), x 57- [See Figure

4 for abbreviations.]
NUMBER 138

coelopsis. The penis has a round, muscular bulb

containing a cavity, the seminal vesicle (ys). The

penis papilla in the original specimen is plump and

short; in the second specimen, sent by Dr. Rausch,

it is slightly more developed and is conical and

pointed. The latter also shows the penial lumen

better differentiated, into a bulbar seminal vesicle

and a narrower ejaculatory duct which opens at

the tip of the penis papilla. The two sperm ducts

or vasa deferentia (vd) empty into the seminal

vesicle separately. The genital atrium (a) is a

single cavity, not divided into separate compartments. Its wall, as well as the outer wall of the

penis papilla, has the usual circular and longitudinal muscle layers developed below the epithelium. The two oviducts unite above the atrium to

form a common oviduct (ode) which opens into

the posterior part of the atrium from the dorsal

side. The copulatory bursa (b), situated dorsally

anterior to the penis bulb, is rather small in both

specimens and contains only a small cavity lined

with a columnar epithelium. At full maturity the

bursa will presumably be much larger and extend

farther ventrally. Its bursal duct (bd) consists of

a narrower anterior portion running in the dorsal

midline above the penis and atrium, and a w

T

ider

terminal portion, which bends ventrally and connects with the posterior part of the genital atrium.

The musculature of the duct consists of intermingled circular and longitudinal fibers.

Dendrocoelopsis alaskensis, a stenothermic and

rheophilic species, has been collected so far only in

cold, fast streams in the White Mountains, a

mountain range north of Fairbanks, Alaska. It

generally occurs in the company of another white

planarian, Phagocata nivea Kenk.

ALASKA. (1) and (2) Two streams on Steese Highway,

at miles 82.5 and 84.0 (Kenk, 1953:180). (3) Stream crossing

Elliot Highway at milepost 31.0, type-locality of the species

(Kenk, 1953:180). (4) Stream on Elliot Highway at mile

25, several specimens collected by Dr. Robert L. Rausch, 27

August and 12 September 1971.

TAXONOMIC POSITION.—The majority of the

species placed in the genus Dendrocoelopsis (in its

wider sense, including Amyadenium) are devoid of

body pigment, as is D. alaskensis. The five unpigmented species reported from France, i.e., D.

brementi (de Beauchamp, 1919), D. vandeli (de

Beauchamp, 1931), D. chattoni (de Beauchamp,

1949), D. garmieri (de Beauchamp, 1950), and D.

beauchampi (Gourbault, 1969), as well as the

species living in Lake Tahoe, D. hymanae Kawakatsu (1968), are blind and are equipped with

adhesive organs. Four white species with eyes, i.e,

D. spinosipenis (Kenk, 1925), D. americana

(Hyman, 1939a), D. lactea Ichikawa and Okugawa

(1958), and D. oculata (Porfir'eva, 1958) (originally

described as a subspecies of D. brementi), differ

from D. alaskensis in the anatomy of their reproductive systems, and some differ in the number and

arrangement of the eyes and the development of

grasping or adhesive organs. The nearest relative

of D. alaskensis appears to be D. hymanae from

Lake Tahoe in California and Nevada.

Dendrocoelopsis hymanae Kawakatsu, 1968

FIGURE 7

Dendrocoelopsis hymanae Kawakatsu, 1968:11.

HOLOTYPE.—From Lake Tahoe, Placer County,

California, at depth of 1554-1623 feet, set of sagittal

sections (USNM 42004).

This species is known only from Kawakatsu's

description based on the study of two specimens,

one sexually mature and the other immature. The

specimens, collected by Ted C. Frantz and collaborators in the course of a joint California and

Nevada fisheries study of Lake Tahoe, were dried

up when they reached the describer. They were

carefully softened but did not permit a thorough

histological analysis of their anatomy. The following are the essential characteristics of the species.

The larger preserved specimen was 14 mm long

and 2 mm wide, somewhat distorted and probably

contracted. The species appears to be unpigmented

and is blind. The shape of the head in the living

animal is not known but is presumably truncate,

as in other species of the genus. The anterior end

has a subterminal adhesive organ consisting of a

depression lined with a rhabdite-free epithelium

perforated by numerous eosinophilic gland ducts

and equipped with muscle fibers (apparently retractors) which attach to the epithelium. The

ovaries are posterior to the second pair of intestinal

branches, the numerous testes are ventral in position, forming on either side of the body a band

extending from the level of the ovaries to the insertion of the pharynx. In the copulatory apparatus

(Figure 7) the gonopore leads into an undivided
10 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

de pp

FIGURE 7.—Copulatory apparatus in sagittal section of Dendrocoelopsis hymanae (after Kawakatsu, 1968). [See Figure 4

for abbreviations.]

atrial cavity corresponding chiefly to the male

atrium. The penis has a large, highly muscular

bulb and a rather slender conical papilla (pp). The

bulb contains a pair of elongated cavities (seminal

vesicles, vs) which communicate at the base of the

penis papilla and continue as a narrow canal, the

ejaculatory duct (de), to the tip of the papilla. The

lining of the seminal vesicles and the ejaculatory

duct is a tall, glandular epithelium which decreases

in thickness toward the tip of the penis papilla.

The bulb is pierced by many eosinophilic gland

ducts coming from the surrounding parenchyma.

The common oviduct (ode) enters the posterior

part of the genital atrium from the dorsal side. The

copulatory bursa (b) is an elongated sac. Its duct

(bd) runs posteriorly, gradually widening, and

opens into the atrium behind the mouth of the

common oviduct, close to the gonopore. The muscle

coat of the bursal canal consists of intermingled

circular and longitudinal fibers.

The species is known only from Lake Tahoe,

California and Nevada, where it was collected by

an Ekman grab from a depth of between 1554 and

1623 feet (474 and 495 m).

Dendrocoelopsis hymanae appears to be very

closely related to D. alaskemis. It differs mainly in

the development of a grasping organ, the absence

of eyes, and the presence of a paired seminal vesicle.

Both species are in need of more detailed study

based on additional material.

Dendrocoelopsis americana (Hyman), 1939

FIGURES ID, 2C, 3B, 8A, B, 9-12

Sorocelis americana Hyman, 1938:137 [nomen nudum]; 1939a:

422.

Dendrocoelopsis aniericatia.-K.enk, 1972:62

HOLOTYPE.—From Bat Cave, Adair County, Oklahoma, whole mount (USNM 20403).

The species was first mentioned in the literature

by Chase and Blair (1937:220) as "a new species

of white turbellarian" occurring in a cave five miles

south of Kansas, Oklahoma, i.e., Bat Cave in Adair

County. Specimens were sent to Hyman (1938:137)

who first reported on them in a meeting of the

American Society of Zoologists. Hyman's (1939a)

original description was based on sexually immature specimens. Subsequently (1939b) she obtained

additional material from A. P. Blair and from C. E.

Mohr and K. Dearolf, including mature animals,

and completed the description by adding an analysis

of the reproductive system. Further data on the

behavior of D. americana in the laboratory, including food, temperature tolerance, and regeneraFIGI'RE 8.—Photographs of anterior ends of whole mounts, X^4: A, Dendrocoelopsis americana

from Bat Cave, Oklahoma; B, D. americana, young specimen from Brown Springs, Arkansas;

c, Sorocelis nigrofasciata (Grube) from Lake Baikal, Siberia; D, S. (Baikalobia) guttata (Gerstfeldt) from Lake Baikal, Siberia.
NUMBER 138 11

tive ability, were given by Levengood (1940). Mohr

(1950:7) published a photograph of the species

taken in Bat Cave, showing the great abundance of

the animals in the shallow stream of the cave in

the vicinity of a deposit of bat guano. He also listed

additional locality records in northwestern Arkansas.

Dearolf (1953:226) reported the species from three

caves and one spring in Oklahoma and Arkansas.

Dendrocoelopsis americana was again mentioned in

an article by Nicholas (1955:100), using Mohr's

photograph of the specimens. Carpenter (1970:117-

127), who collected his materials in Bat Cave, discussed the external features of the immature animal

and the structure and function of its adhesive organ

and furnished a beautiful photograph of a gliding

specimen. I received a dozen preserved specimens

from Mr. Leslie Hubricht who had collected them

in Brown Springs, Mount Magazine, Arkansas. In

1970 I visited this locality and obtained about 20

animals, which were taken to the laboratory for

further study.

Dendrocoelopsis americana (Figures ID, 2C) may

be up to 23 mm long and 3 mm wide, but usually

is smaller, even at sexual maturity. The head is

truncated, with a slightly bulging frontal margin

and rounded auricular borders projecting slightly

laterally. The subterminal adhesive pit is visible

below the center of the frontal bulge. Behind the

auricular projections the head narrows to a neck,

then the body widens again. The animal is unpigmented, white. The pharynx, measuring about

one-sixth the body length, is inserted at the middle

of the body or slightly more posterior. The copulatory complex occupies approximately one-half the

length of the postpharyngeal region. The eyes are

multiple, arranged in two almost parallel longitudinal rows at a distance from each other of onefourth to one-third the width of the head. The

most anterior pair of eyes is farther removed from

the frontal margin than from the lateral edges of

the body. The eyes are of different sizes, are somewhat irregularly spaced, and are variable in number, usually between three and ten in each row.

Carpenter (1970:118) observed a maximum of over

20 eyes on either side. There seem to be differences

in the average number of eyes in populations of

different provenances, the worms from Brown

Springs having fewer eyes than those of Bat Cave.

Smaller (younger) specimens (Figure 3B) also have

a smaller number of eyes than larger ones. Besides

the fully developed eyes, frequently there are

irregular clumps of eye pigment scattered in the

parenchyma of the ocular region.

The adhesive organ is rather weak, consisting

mainly of a small pit lined with a nucleate

epithelium lacking rhabdites and pierced by many

ducts filled with eosinophilic secretion originating

from parenchymal gland cells. The organ appears

to be an extension of the marginal adhesive zone

from which it is separated by two areas, right and

left, covered with normal surface epithelium.

The two ovaries are situated behind the second

i !

vd vdc f vs de ode gp

FIGURE 9.-Dendrocoelopsis americana, semidiagrammatic view of copulatory complex in sagittal

section (after Kenk, 1972) . [See Figure 4 for abbreviations.]

bd
12 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

or third lateral branches of the anterior intestinal

trunk. The testes, of moderate number, are arranged in a pair of bands beginning a short distance

behind the ovaries and extending posteriorly to a

level about half-way between the copulatory complex and the tail end of the body. They are rather

large and predominantly dorsal, although individual testes may be located close to the ventral side.

The copulatory apparatus (Figure 9) has several

distinguishing characteristics. The gonopore (gp)

leads into a small common genital atrium, not

always well denned, into which the bursal duct

(bd) opens from the dorsal side. Anteriorly the

common atrium connects with the male atrium

from which it is separated by a stricture. The penis

consists of a muscular bulb and a well-developed

conical papilla. The bulb contains a cavity of

lobate outline, the seminal vesicle (vs), which is

lined with a tall glandular epithelium. This cavity

continues into the penis papilla as a narrower canal,

the ejaculatory duct (de), lined with a nonglandular cuboidal epithelium. The outer covering of the

papilla consists of an epithelium which forms

wart-like protuberances packed with short, pointed

spines (Figures 10-12). Each wart represents one

large epithelial cell with a basal nucleus. The distal

part of the cell contains the bases of perhaps two

dozen spindle-shaped spines, pointed at both ends,

each with a small swelling in the middle, about 10

microns long and 2 microns thick in the widest part.

These spines give the impression of mineral bodies,

not accepting any stain when treated with hematoxylin, eosin, and phloxine-B. They have a higher

refractive index than the surrounding protoplasm

and are optically isotropic. They are insoluble in

diluted acetic, hydrochloric, and sulfuric acids applied for 30 minutes, and are not affected by

potassium hydroxide nor by chitinase. Dr. Kenneth

M. Towe kindly subjected a specimen of a freezedried penis to the Debye-Scherrer powder X-ray

diffraction test and found the spines to be

amorphous. Analysis of a section through the penis

by X-ray concentration mapping in the electron

microprobe, carried out by Mr. Charles R. Obermeyer, revealed that the spines contained no appreciable amounts of magnesium, calcium, aluminum, silicon, phosphorus, or sulfur. Their composition is, therefore, still open to further investigation.

The musculature of the penis bulb consists of

the usual concentrically arranged layers of interlaced fibers. The penis papilla has a layer of

circular fibers below the external epithelium,

followed by longitudinal fibers which, in part, also

enter the bulb. At the base of the papilla the external circular layer is modified, consisting of fine

fibers (/), much thinner than muscle fibers and not

FIGURE 10. — Dendrocoelopsis

americana, penial armature in

sagittal section of penis. [cm =

circular muscle layer, ep = epithelial cell, lm = longitudinal

muscle layer.]

staining like muscles. This is apparently a fibrous

layer of an elastic rather than contractile nature,

such as is frequently seen also in other species

(e.g., 1). vogiruita). The ejaculatory duct has a coat

of circular muscles. Many gland ducts with a granular eosinophilic secretion enter the penis bulb from

the surrounding parenchyma and open into the

seminal vesicle.

The sperm ducts or vasa deferentia (vd), which

lateral to the pharynx are expanded to form the

tortuous false seminal vesicles, unite outside the

penis to a common vas deferens (vdc) that retains

its sinuous expansion until it enters the penis bulb

FIGURE 11.—Dendrocoelopsis americana, view of squashed

freshly extirpated penis in the light microscope,

to open into the seminal vesicle (vs). The two

oviducts unite above the male atrium, and the

common oviduct (ode) empties into the atrium

from the dorsal side, near the transition between

the male and common atria.
NUMBER 138 13

There is no copulatory bursa developed. A thickwalled bursal duct (bd), opening into the common

atrium dorsally, then curving anteriorly and ending

blindly above the male atrium, obviously corresponds to the expanded terminal portion (vagina)

FIGURE \2.—Dendrocoelopsis americana, scanning electron

micrograph of surface of freeze-dried penis papilla,

of the bursa stalk of other species of the genus. This

duct is lined with a columnar, secretory epithelium.

Its thick muscle coat consists mainly of circular

fibers with less numerous interspersed longitudinal

muscles.

Dendrocoelopsis americana inhabits subterranean

streams and epigean springs in the Ozark region of

eastern Oklahoma and northwestern Arkansas:

ARKANSAS. LOGAN COUNTY: Brown Springs, on Mt. Magazine, Ozark National Forest. 26 May 1966 and 21 May 1968:

several specimens collected by Mr. Leslie Hubricht, some of

them mature. 12 June 1970: trickle of water forming a shallow pool at the spring, 14.5° C, about 20 specimens, 3 of

them sexually mature, under fallen leaves. WASHINGTON

COUNTY: (1) Watson Cave, near Prairie Grove (Hyman,

1939b:283; Mohr, 1950:7; Dearolf, 1953:226) . (2) Spring

near Watson Cave (Hyman, 1939b:283; Mohr, 1950:7).

OKLAHOMA. ADAIR COUNTY: (1) Bat Cave, in northwest

coiner of the county, type-locality of the species (Chase and

Blair, 1937:220; Hyman, 1939a:423, 1939b:283; Mohr, 1950:6;

Dearolf, 1953:226; Carpenter, 1970:119). (2) Spring near

Bat Cave (Hyman, 1939b:283). (3) Ozark Cave spring

(Dearolf, 1953:226). (4) First Cave (Dearolf, 1953:226) .

The species must be considered a troglophile

rather than an obligate troglobite. Levengood

(1910), who studied its behavior in the laboratory,

reports that it is more photophobic than the

epigean species Dugesia dorotocephala. It accepted

as food pieces of beef liver, of cave isopods, snails,

and earthworms. Levengood stated that in the cave

the specimens appeared to be feeding on bat feces.

Chase and Blair (1937:220) pointed out that in Bat

Cave the planarian habitat is shared by numerous

isopods (Caecidotea macropropoda), which may

be the natural food of Dendrocoelopsis. Levengood

demonstrated the great tolerance of the species to

variations in the osmotic pressure by keeping them

in mammalian Ringer solution and in distilled

water for six days without observing any signs of

disintegration. When exposed to a temperature

gradient from 14° to 23.5° C, the species showed no

perference for any specific temperature, but disintegrated at temperatures above 28° C. It may live

indefinitely at 24° C and for at least four weeks

at 6°-10° C.

I have kept specimens of D. americana in cultures

at 14° C for 27 months, feeding them beef liver.

The animals, which were immature when collected,

developed sexual structures and, in the course of

several months, deposited seven cocoons. The

cocoons are spherical or subellipsoidal, with a

diameter of 1.7-2.3 mm. Three of the cocoons

hatched about six weeks after deposition and released one, two, and three young. The freshly

hatched young (Figures 3B, 8B) were up to 6 mm

long and 1 mm wide, similar in shape to the adult,

bearing 2-1 eyes on either side. They matured, or

at least developed indications of a copulatory complex, in 4-5 months. No asexual reproduction was

observed.

The species has considerable regenerative ability.

In the course of this study, the postpharyngeal

regions of several specimens were removed for the

investigation of the armature of the penis. All

animals operated on survived and regenerated the

severed parts. Levengood (1940:34) had already

shown that specimens cut transversely into fifths

are capable of regeneration, though the process of

reconstitution is slower than in Dugesia dorotocephala.

TAXONOMIC POSITION:—Hyman (1939a:423) had

placed the species in the genus Sorocelis, based

principally on the combination of a dendrocoelid

type of pharynx with multiplicity of the eyes, which

are arranged in two rows or clusters in Sorocelis.

It must be kept in mind, however, that Sorocelis in

the classical sense (Kenk, 1930:298), the geographic

range of which is confined to the area of Lake
14 SMITHSONIAN CONTRIBUTIONS TO ZOOLOGY

Baikal in Siberia, is a very extensive and diversified

genus, still incompletely known, which is only now

being intensively studied by N. A. Livanov and

N. A. Porfir'eva of the University of Kazan. The

crucial point in the placement of D. americana is

the interpretation of the great number of eyes. In

Sorucelis (and Polycelis) the multiple eyes are of

about equal size (Figures 8c, 8D) and are more or

less evenly spaced, with hardly any rudimentary

eye spots or pigment clumps between them.

Dendrocoelopsis americana shows all intergrades

between fully differentiated eyes and apparently

nonfunctional accumulations of ocular pigment

granules, characteristic of some supernumerary or

accessory eye spots (cf. Ghisalberti, 1919; Balazs,

1962). One frequently sees a certain variability in

the number of eyes in various species of triclads:

Procotyla fluviatilis Leidy regularly has several

pairs of eyes in the northern parts of its distributional range and generally a single pair in southern

areas; Anderson (1951:83) and Stewart (1972:542)

observed two eye spots in freshly hatched young

and usually about six in adults of this species.

Other instances of multiple eyes in usually two-eyed

genera are Phagocata nenoi Okugawa (1939:157),

Dendrocoelum album (Steinmann, 1910), and

Dendrocoelum romanodanubiale (Codreanu, 1949).

I cannot agree with Codreanu (1951:618-619,

636-637) who considers the multiplicity of the eyes

to be of generic value and uses it in the characterization of his genus Palaeodendrocoelnm. A case quite

analogous to the condition of D. americana is the

development of two longitudinal rows of eyes in

Phagocata morgani polycelis Kenk (1935:103),

while the nominate subspecies normally has a

single pair. Within the genus Dendrocoelopsis the

occurrence of occasional accessory eyes is known in

the species D. alaskensis and D. piriformis and

regular pluriocularity occurs in D. lactea Ichikawa

and Okugawa (1958:10), D. chattoni (de Beauchamp, 1949:60), and D. oculata (Porfir'eva,

1958:46, described as Amyadenium brementi oculatum) where the eyes are arranged in a pair of

longitudinal rows. Dendrocoelopsis americana fits

well into this series.

Another peculiarity of D. americana is the development of a spiny armature on the penis surface.

Similar structures have been described in various

freshwater triclads: the European Polycelis nigra

(O. F. Miiller), P. tennis Ijima, and Dendrocoelopsis

spinosipenis (Kenk) and the Baikal planarians

Armilla armata (Zabusov), A. pardalina (Grube),

Protocotylus jlavus Korotnev, P. fungiformis,

(Zabusov), and Planaria (?) adhaerens Korotnev

(see discussions by Kenk, 1925:143-144; Livanov,

1961:280; Porfir'eva, 1970:106-108, 1971:89). The

penial spines must have developed in several genera

and even some species independently as they differ

widely in their shape, composition, and relation to

the tissues in which they originate. At first glance,

the spines of Dendrocoelopsis americana resemble

those of D. spinosipenis to some extent, but upon

closer examination this resemblance proves to be

only superficial. In D. spinosipenis the rather

large, club-shaped spines consist of calcium carbonate in the form of crystalline aragonite (Schmidt,

1942) while in D. americana they are amorphous

and of unknown composition, not containing any

calcium. Functionally the penial armatures of the

various species probably coincide, serving either for

the fastening of the penis in the vagina of the

partner during copulation, or for sexual stimulation, or possibly performing both functions at the

same time.

The third outstanding characteristic of D.

americana is the absence of a bursal sac, which it

shares with two other quite unrelated freshwater

triclads, Citra foremanii (Girard) (see Kenk, 1935:

81) and Rimacephalus arecepta Porfir'eva (1969:

1305). In Cura foremanii the bursal stalk is well

developed and opens into the posterior intestinal

ramus of one side. Rimacephalus arecepta apparently has only the terminal portion of the bursal

duct differentiated as a blindly closed, highly

muscular posterior extension of the genital atrium,

very similar in structure to the duct of D. americana

(Porfir'eva considers this outgrowth to be part of

the atrium although in its position it corresponds

to the enlarged distal section or vagina of the bursal

duct of the closely related R. pulvinar [Grube]). In

all instances the close relatives of the three species

are provided with a normal sac-shaped copulatory

bursa. The absence of the bursa can, therefore, not

be given any taxonomic significance beyond being a

good species characteristic.

The combination of pluriocularity, presence of

penial spines, and absence of a copulatory bursa

distinguishes D. americana from all other species of

the genus Dendrocoelopsis.
NUMBER 138 15

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v V.