Fossil Bryozoa from 

Drill Holes on 

Eniwetok Atoll 

By D. A. BROWN 

BIKINI AND NEARBY ATOLLS, MARSHALL ISLANDS 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 260-EE 

Fi'l!e bryozoans from the Tertiary 

(stages b, f, and g) ·are described 

and figured 

UNITED STf\TES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 

CONTENTS 

Page 

Abstract------------------------------------------------------------------- 1113 

Introduction_______________________________________________________________ 1113 

Systematic descriptions______________________________________________________ 1113 

'References----------------------------------------------------------------- 1116 

ILLUSTRATIONS 

Page 

FIGURE 321. Specimen A. Diastopora?________________________________________ 1113 

322. Specimen B. Diastopora?________________________________________ 1113 

323. Specimen Ct. Nellia aff. oculata Busk_____________________________ 1114 

324. Specimen D. Escharoides?, encrusting zoarium_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1115 

325. Specimen D. Escharoides?, secondary orifice_______________________ 1115 

326. Specimen E. Suborder Ascophora ________________________________ 1116 

327. Specimen F. ?Family Reteporidae ____ ,____________________________ 1116 

III 
BIKINI AND NEARBY ATOLLS, MARSHALL ISLANDS 

FOSSIL BRYOZOA FROM DRILL HOLES ON ENIWETOK ATOLL 

By D. A. BROWN I 

ABSTRACT 

One cyclostome and four cheilostome 'bryowans a re described 

and figured from drill holes into the Tertiary (stages b, f, g) of 

Eniwet<>k •A:toll. None of the specimens is well-enough preserved 

to permit specific idenltification. 

INTRODUCTION 

Specimens of organisms from drill holes E-1 and F-1 on Eniwetok 1

Atoll (l.iadd a nd ()lthers, 1953) were received from Ruth 

Todd of the U.S. Goological iSurvey. F1rom these, four species of 

Bryowa 2 were obtained, comprising one cyclostome ·and four 

cheilost<>mes as detailed in .this repol"t. 

SYSTEMATIC DESCRIPTIONS 

Order CYCLOSTOMATA 

Family DIASTOPORIDAE 

Genus DIASTOPORA Lamouroux 

Diastopora sp 1 

Figures 321, 322 

Specimens A and B belong most probably to the same 

species and originate from core 9 at 3,655-3,665 feet in 

the Tertiary b section of drill hole F -1 which is described (Ladd and others, 1953, p. 2266) as "Firm to 

hard white foraminiferal limestone; corals as molds; 

some mollusks (Pecten) retain original shell." Specimen A is a curved fan-shaped laterally concavo-convex 

zoarium from core sample F - 1-9-2, and specimen B is 

a thin section cut from a similar zoarium found in core 

sample F - 1-9-3. 

Specimen A at its greatest width is 3.0 mm, stands 

2.38 mm in height, and has a narrow base 0.40 mm in 

width. Its distal part is curved and fan shaped with a 

flattened distal surface approximately 0.42 mm in 

width, along which is a median ridge giving the zoarium a bilaminate appearance (fig. 321). At a magnification -of 216 diameters this surface is seen to be 

perf-orate. Both lateral surfaces of the oolony are 

perforate also, with the zooecial tubes directed obliquely 

distally, their distal ends projecting as a series of papillae arranged in flabellate rays. These tubes extend almost t-o the base of the specimen. 

Specimen B (fig. 322) a thin section, has a maximum 

width of 2.0 mm and a height of 1.62 mm. The section 

shows a series of tubes diverging from the base so as to 

remain approximately normal to the upper distal edge 

1 The Australian National University, Canberr a City, Australia. 2 This name is used to conform to the U.S. Geol. Survey practice; the 

author believes the name Polyzoa to be more correct for this phylum. 

of the fan-shaped oolony. The tubes, which are all of 

the same general dimensions, average about 0.08 mm in 

diameter and are without diaphragms. N e.:'tr the base 

of the zoarium may be seen what appear to be cross 

sections of zooecial tubes normal to the lateral surface. 

Neither specimen p-ossesses an identifiable g-onozooecium, nor are any details of the -orifices discernible in 

FIGURE 321.-Specimen A. Diastopora sp? Concav~ lateral aspeet of 

fan-shaped zoarium showing pa pillate surface, X 35. 

lmm 

FIGURE 322.---,Specimen B . Diastopora sp? Thin section of zoarium 

showing arr angement of zooecial tubes, X 75. 

111 3 
1114 BIKINI AND NEARBY ATOLLS, MARSHALL ISLANDS 

'the papillate surface of the zoarium. The arrangement of the zooecial tubes in a bilamellar pattern with 

many tubes opening on the narrow distal extremity of 

the zoarium is an unusual one, although a somewhat 

similar arrangement may be observed in F asaipora 

pavonina Michelin sp., 1846, a Cenomanian species. 

Borg's ( 1944) classification of the Stenolaematous 

Bryozoa is not applied here, chiefly because of the absence of any gonozooecium in this material. However, 

in Bassler's ( 1953) classification which is chiefly morphological and more adapted to fossil forms, the genus 

Diastopora seems an appropriate designation. Diastopora is first recorded in Jurassic strata and is an abundant genus, encrusting or in foliate expansions, among 

Recent cyclostomes. 

Order CHEILOSTO·KATA 

Suborder ANASCA 

Superfamily KEMBRANIPORIDAE 

Genus NELLIA Bus·k 

Nellia aJl'. oculata Busk 

Figure 323 

Specimen C1 is a fragment of an internode 1.87 mm 

in length from cuttings at a depth of 990-1,000 feet in 

drill hole E-1 in beds referred to Tertiary f (Cole, 1957, 

p. 745). The section is described (Ladd and others, 

1953, p. 2264) as "Buff to tan coralliferous limestone 

·with well-preserved, shallow-water mollusks and 

smaller Foraminifera." 

The specimen (fig. 323) has an internode almosi 

square in cross section, about 0.40 by 0.40 mm. Edges 

of the aperture are not raised, and no development of 

cryptocyst is shown. The floor of the zooecium is 

open V -shaped with a deep medial longitudinal trench 

with evenly sloping s!des. No fertile zooecia were 

observed. 

Measurements: 8 £~=0.80-0.85 mm; l.=0.37-0.40 mm; h,.= 

0.54-0.70 mm; l,.=0.25-0.30 mm. 

This specimen very closely resembles N ellia oculata 

Busk var. quadrilatera d'Orbigny var., 1851, described 

and figured in detail by Harmer (1926, p. 242). The 

following differences are noted. 

1. There is but a single triangular avicularium ( av) 

present, located in one of the proximal angles of 

the gymnocyst. 

2. The lateral communication pores of the zooecia ( cp2 ) 

(Harmer, 1926, p. 243, text fig. 3A) are clearly 

visible, but there is no definite indication of the 

other pair of lateral pores ( ap1) . On the other 

hand, the area in the vicinity of Harmer's cprn 

8 The symbols used in this report for measurements are as follows : 

L~, length of zooecium; z~,· width of zooccium; hr, length of orifice ; lr, width of orifice ; Lo.,, length of ovicell ; hu., length of 

aperture ; lu., width of aperture. 

.05mm 

FIGURE 323.-Specimen C1• Nellia aft'. oculata Busk. Mature internode 

showing zooecia. av, single avicularium; av l, aVicularium of lateral 

rooecium; cp', lateral communication pores- of zooecia (c/. Harmer, 

1926, p. 243, text fig. 3A) ; t, tunnellike opening near distal end of 

zooecium. 

(terminal communication pore between zooecia) 

is occupied by a large tunnellike opening ( t) 

which may perhaps include and obscure the pores 

ap1 • Harmer ( 1926, p. 245) was also unable to 

detect these pores ~n the zooecia of N. tenuis 

Harmer. 

3. On two zooecia a circular pore passes through the 

proximal edge of the gymnocyst near the median 

line, in both cases slightly truncating the distal 

edge of the proximal zooeci urn. This opening may 

have accommodated an articulating fiber, though 

such a mode of branching is unusual in this genus. 

On account of the small amount of material, this 

specimen is unnamed. --- Specimen C2 is another internodal fragment of the 

same variety froin the same location, but in this case the 

zooecia are aborted, that is, the apertures are greatly 

reduced in size and there are no avicu]aria pre·sent. 

N ellia oculata is a common species, both Recent and 

fossil, being found in moderately shallow waters in the 

temperate .and tropical regions. It is recorded from 

Eocene beds (Jackson) in the Eastern United States. 

N.· ocu.lata var. quadrilatera is known only from Recent 

seas. 
FOSSIL BRYOZOA FROM ENIWETOK ATOLL 1115 

Suborder ASCOPHORA 

Family EXOCHELLIDAE 

Genus ESCHAROIDES Milne-Edwards 

Escharoides sp? 

Figures 324, 325 

Specimen Dis a part of an encrusting zoarium from 

cuttings at a depth of 990-1,000 feet in drill hole E-1 

(Tertiary f) as described under specimen C1 . The 

zoari urn (encrusting a pelecypod shell) consists of 

about 20 zooecia, 4 of which are ovicelled. Immature 

distal zooecia are represented by proximal side walls. 

Zooecia are elongate-quadrate, arranged in radiating 

rows, and separated by shallow but strong furrows 

along which lie thin salient wa.Ils between the rows 

of marginal areolae. Secondary orifice is subquadrate, 

rounded and narrows proximally; the proximal lip is 

concave; the peristome is slightly salient and urceolate 

distally. Frontal wall is convex and consists of a perforate granular pleurocyst; the pores are partly obscured by granular calcification and overlie a smooth 

olocyst with pores confined to the lateral margins. 

Marginal areolae are in a single prominent row. 

Ovicells are large, finely perforate, embedded deeply 

in and occupying a large area of the distal zooecium 

and bordered by a single row of marginal areolae (fig. 

324). A vicularia were not seen. 

FIGURE 324.--,Speclmen D. Escharoldes ap? Encrusting zoarlum, 

some zooecia-bearing ovlcells. The ovicells are more strongly perforate than the photograph suggests, X 53. 

Measurements: £.=0.90--1.05 mm; l.=0.65-0.75 mm; h.=0.24-

0.25 mm; lr=0.22-0.23; £ •• =0.35-0.37 mm. 

The generic affinities of this species are not clear particularly since the orifices ·are for the most part blocked 

by deposits, so that no distinct view of the ·primary orifice may be obtained. The external features, however, 

such as the perforate granular pleurocyst with marginal 

areolae and the perforate immersed ovicells -also with 

marginal areolae, strongly suggest affinities to Escharoides Mi·lne-Edwards. No trace of spine bases '<!:long 

the distal margin of the orifice was detected. 

The distal wall of 'the zooecium, which projects 

slightly along the distal margin of the orifice, shows 

(fig. 325) a marked tendency to split apart along the 

lateral lines near the distal end of the orifice. 

.10 mm 

FIGURE 325.-Specimen D. Escharoides sp? DetaUs of secondary orifice showing curved line, X on both aides, along which zooecla tend 

to split. 

Genus and species undetermined 

Figure 326 

Specimen E was taken from cuttings at 830-840 feet 

(Tertia·ry g) in dril'l hole E-1 and consists of a small 

coral with parts of two zooecia cemented to its underside. The section of the drill hole from which this 

specimen comes is described (Ladd and others, 1953, 

p. 2264) as 

Buff, weakly cemented limestone made up of coral (slender , 

branching forms •an'd more massive types, dncluding Porites and 

Millepora), s'hallow-wa.ter ga:str.opods with original shell (Poli,.. 

nices, Oerithium, Oypraea, Trivia, Conus, Bulla) and beach-type 

Fomminifer.a. 

The bryozoan remains compromise two zooecia with 

their basal walls removed exposing an internal view of 
1116 BIKINI AND NEARBY ATOLLS, MARSHALL ISLANDS 

evenly ·perforate frontal walls and a semicircular orifice 

(fig. 326) with concave ·proximal margin. In the absence of any details of the external frontal aspect, such 

as ovicells or avicularia, it is difficult to determine the 

identity of the specimen either generically or specically. 

However, it may be stated definitely that this is ·an 

Ascophoran Cheilostomatous bryozoan with a hippoporine orifice. In the sha·pe of the orifice and the evenly 

perforate convex fronta1 wall, there is a resemblance to 

the type species of Oosoiniopsis, 0. coelatus Canu and 

Bassler, 1927, a Recent species from the Sulu Archipelago, Philippine Islands . 

.lOmm 

FIGURE 326.-Speclmen E. Suborder Ascophora. Shape of orifice. 

7FamUy RETEPORIDAE 

Genu.s and species undetermined 

Figure 827 

Specimen F, obtained ·from cuttings taken at :a depth 

of 2,830-2,840 (Tertiary b) feet in drill hole E-1, is a 

part of a dendritic growth ·rising wbout 2.5 mm above a 

flattened subcircular base 1.75 mm in greatest width. 

The branches are subcylindrical, about 0.5 mm in diameter, and have irregular tubules arising on aU sides and 

with some degree of regularity. Some of the tubules 

a·re long, others are short and .merely salient openings 

on the main branches, aH with terminal. subcircular 

openings ( ori1

fices ~) with strongly thickened margins. 

A number of these openings are su!btended by smaller 

subtriangular openings, which may be avicularia. Both 

the main branches and the tubules are imperforate and 

prominent vibices appear in several places on the 

surface of the main branches ('fig. 327). 

The nonperforate nature of the zooarium and the 

presence of subsidiary structures resembling a vicularia 

suggest affinities with the Cheilostomata. Vibices are 

a common feature of reteporidans. On the other hand, 

the arrangement of the "oriifices" on all sides of the 

"trabeculae" is not that generally observed in the Reteporidae, and in the present specimen there is no certain 

indication that the branches fused to ·form the network 

so typical of that family. 

2mm 

FIGURE 327.-Speclmen F. ?Family Reteporldae. Sketch of colony. 

REFERENCES 

Bassler, R. S., 1953, Treatise on invertebrate paleontology, pt. 

G, Bryozoa: Geol. Soc. America and Univ. Kansas Press, 

p. G1-G253, 175 figs. 

Borg, F., 1944, The Stenolaematous Bryozoa: Further Zool. 

Research, Swedish Antarctic Exped. 1901-03, v. 3 (5), 276 

p., 16 pls. 

Cole, W. S., 1957, Larger Foraminifera from Eniwetok Atoll 

drill holes: U.S. Geol. Survey Prof. Paper 260-V, p. 743-748 

[1959]. 

Harmer, S. F., 1926, The Polyzoa of the Siboga expedition, pt. II, 

Cheilostomata Anasca: Siboga Exped. Rept. 28B, p. 188-501, 

pls. 13-34. 

Ladd, H. S., Ingerson, Earl, Townsend, R. C., Russell, Martin, 

and Stephenson, H. K., 1953, Drilling on Eniwetok Atoll, 

Marshall Islands: Am. Assoc. Petroleum Geologists Bull., v. 

37, p. 2257-2280.