Diplocardia macdowelli

ABSTRACT

A new quadrithecate earthworm, Diplocardia macdowelli is described from Mississippi.

This species is morphologically similar to D. michaelseni, differing from that earthworm

in size, number of segments, number of calciferous gland lamellae, form of the spermathecae,

and the absence of modified spermathecal setae (ab) in IX.

This description is based upon earthworms collected June 17, 1959, along

Route 18, six miles west of Bay Springs, Smith County, Mississippi. The holo-

type has been placed in the U. S. National Museum: USNM Cat. No. 32615.

The species is named in honor of the late Harold D. McDowell, Ph.D.

Diplocardia macdowelli sp. n.

Unpigmented, clitellum yellowish to buff (Formalin preservation). Size, 31 to 47 mm by

1.0 to 1.5 mm, with averages of 42 by 1.2 mm for length and width respectively (17 clitellate

specimens). Somites 95 to 111, average 102. Small in size for genus, swollen in vm and ix

tapered anteriorly. Prostomium epilobic J4 to %. Secondary annulations strongest anterior

to clitellum. Setal formula: aa:ab:bc:cd = 10:3:7:4 (segment xxm); dd = ca lA ix. Clitellum

Xlll-xvii; of cingulum type, anterior and posterior margins distinct. Tubercula pubertatis

absent. Glandular tumescences ventrally developed in vin and anterior one-half of ix.

Spermathecal pores 2 pair; variable in position, usually on vin and ix, in varying combina-

tions, even including segments vn and x. Spermathecal setae of vin modified, tip hastate,

distal half of shaft is sculptured; seta 0.420 mm in length. Reserve setae of vin are 0.252

mm in length, shaft completely sculptured, tip hastate. Spermathecal setae of ix unmodified.

Male field flattish, seminal grooves nearly straight to slightly sinuous from ^ x v i n to Hxx;

edges of grooves somewhat glandular. Male pore in anterior quarter of xix; on outer edge

of seminal groove. Prostatic setae not visible externally. Female pores paired, antero-

median to setal line a-a in xiv. Female field weakly developed. Nephropores are inter-

segmental at d.

Pharyngeal gland masses ending in iv. Esophagus narrow vn through xin, and in xvi;

swollen in xiv and xv. Calciferous gland-like development in xiv and xv; widest in xv; in-

FIGURE 1

A. Ventral surface of D. macdowelli.

1. glandular tumesence of VIII.

2. spermathecal pore in IX.

3. oviducal pore in XIV.

4. position of male pore in seminal groove.

B. Spermatheca of VIII.

1. ampulla

2. diverticulum

3. duct

C. Prostate gland of XX.

1. duct

2. body of gland

D. Ectal portion of spermathecal seta a of

VIII.

E. Reserve seta a of VIII.

F. Spermathecal seta a of VIII.

G. Regular seta a of XII.

H. Prostatic setae of XVIII.

I. Cross section of calciferous gland in XIV

ternally with 35-40 lamellae, inner edges of these lamellae not joined to form wall of lumen;

ventral lamellae longest. Gizzard in v and vi. Intestine expands abruptly at % ; esophageal-

intestinal valve at % . Typhlosole simple fold, begins in xix, diminishes in height posteriorly,

reduced to near-vanish ing point ca. XLVIII. Last hearts in xn. Supra-esophageal vessel in

x-xn. Lateral parieto-esophageal vessel joins ventral esophageal wall in xin. Dorsal vessel

doubled intra-segmentally from ix into xvn. Sub-neural vessel absent.

Testes paired, from ventro-median wall in x and xi (from jKo and MKi), small, rather flat.

Male funnel compact, folded with strong iridescence. Sperm duct direct, on internal surface

of parietes, contiguous, dorsal to setal line b. One pair of ovaries in xin, with multiple strands

of ova. Ovarian funnel auriculate, small, compact. Oviduct direct. Ovisac present, above

and median to funnel, in xiv (from % ) . Prostate glands compact, U-shaped, two pair, in

xviii and xx, extending into xix and xxi respectively; muscular duct about one-half total

length of gland. Prostatic setae vestigial, confined to surface of ectal portion of prostatic

duct; hair-like, unsculptured; nearly straight, with curved distal portion, from 0.117 to 0.12

mm in length. Spermathecae two pair, in VIII and ix; elongate, ampulla cordate, duct very

thin especially the distal half; diverticulum digitiform, from anterior aspect of duct at mid-

point; duct widening above point of origin of diverticulum; duct at least twice as long as ampulla.

Meganephridial, avesiculate. Septa %, %o, and 10/u somewhat thickened; septa 7/s and %

thickened.

The species Diplocardia macdowelli belongs to the "michaelseni-group" of

diplocardians with: (1) doubled dorsal blood vessel, (2) last hearts in xn, (3)

quadrithecate condition, (4) simple lamellar typhlosole, (5) calciferous gland

lamellae not joined internally, (6) prostatic setae inconspicuous, and (7) sperma-

thecal setae modified and hastate. This species differs from D. michaelseni Eisen

(1899) in size, number of segments, form of the prostomium, number of calciferous

gland lamellae, shape of the spermathecae, gland development in the spermathecal

and prostatic regions, and the absence of modified setae in ix (ab). Unfortunately,

Stephenson (1933) gives no information on his findings with regard to the cal-

ciferous gland lamellae in michaelseni, and sections made by Frank Smith (1924)

do not permit any proper evaluation of the numbers. I have, however, his-

tological preparations of both species at hand which show that, while the lamellae

in michaelseni may approach 60 in number, a maximum of 40 would be found in

macdowelli.

Similarities in setal structure between Diplocardia macdowelli and michaelseni

are strong, but no stronger than those obtaining between michaelseni and eiseni

(Michaelsen, 1894): indeed, if prostatic setae alone were considered, all of these

would be considered conspecific. The distinctiveness of eiseni and michaelseni

can scarcely be doubted if a number of somatic factors are compared, as for ex-

ample, the last pair of "hearts" in eiseni occur in xin, and in michaelseni, in xn.

It seeks unlikely that this constant difference (among others) in a somatic feature

would be due to local variation.

The external spermathecal region is considerably more variable in macdowelli

than in michaelseni; the spermathecal pores, considered as a pattern of two pair,

rarely open in exactly the way way. While usually lined up between setal lines

a and b, they may occur on various parts of segments VIII and ix, even extending

onto VII or x. Such variability in itself cannot be considered as necessarily a

definitive condition. The absence of modified spermathecal setae in ix, and the

fact that glandular development of ix is confined to the ventral region anterior

to the setal arc (fig. 1-A) are constant among the examples of macdowelli studied.

Internally, the spermathecae are markedly different from those of michaelseni.

In the latter species, the duct is strongly swollen above the point of origin of the

diverticulum, so swollen, in fact, that it appears to be a second ampulla or at

least a lower section of that region. In macdowelli, the duct shows no such pro-

nounced swelling (fig. 1-B). The pattern of glandular tumescences in the region
No. 1 NEW EARTHWORM FROM MISSISSIPPI 53
just behind the field differs. In michaelseni, glands are present on xxi and xxii,
mid-ventrally; this area is unmodified in macdowelli. The spermathecal region on
the other hand is glandular in both species, involving the entire mid-ventral areas
between setal lines c and c. In macdowelli, this glandular swelling does not extend
posteriorly beyond the setal arc of ix and, in segments vm and ix of that species,
the tumescences are somewhat more fused across % than in michaelseni.
Diplocardia macdowelli was collected from a moist, heavy clay-loam soil of a
river forest area. Tree cover was quite heavy, with a forest comprised of oak,
tulip poplar, elm, red maple, and pine trees. Associated with macdowelli in this
somewhat swampy situation was the earthworm Pheretima diffringens (Baird) 1869.
I wish to thank Dr. Marian H. Pettibone of the U. S. National Museum for
making available Frank Smith's slides of Diplocardia michaelseni for comparative
study. This research was carried out during the tenure of NSF Grants G-6378
and G-20353.