Xenobrochus rotundus, Bitner, 2008

Bitner, Maria Aleksandra, 2008, New data on the recent brachiopods from the Fiji and Wallis and Futuna islands, South-West Pacific, Zoosystema 30 (2), pp. 419-461 : 429-431

Xenobrochus rotundus n. sp.

( Fig. 6 A-H)

TYPE MATERIAL. — Fiji. BORDAU 1, stn DW 1469, holotype ( MNHN BRA-3075 ; Fig.6 A-D). — Same data, 2 paratypes ( MNHN BRA-3076-3077 ; Fig. 6 E-H) .

TYPE LOCALITY. — Fiji Islands, Lau Ridge, BORDAU 1, stn DW 1469, 19°40.01’S, 178°10.24’W, 314- 377 m.

ETYMOLOGY. — From the Latin rotundus , round, referring to rounded outline.

DIAGNOSIS. — Xenobrochus rounded in outline with small foramen, prominent cardinal process, outer hinge plates rudimentary to absent, and transverse band anteriorly convex with a slight median fold.

MATERIAL EXAMINED. Wallis and Futuna. MUS- ORSTOM 7, Futuna, stn DW 516, 1 complete specimen. — Wallis, stn DW 610, 1 complete specimen, 1 ventral valve. — Stn DW 612, 1 ventral valve.

Fiji. BORDAU 1, Lau Ridge, stn DW 1469, 7 complete specimens. — Stn DW 1496, 3 complete specimens.

DEPTH RANGE. — 255- 550 m.

MEASUREMENTS. — See Table 7.

DESCRIPTION

Shell small (maximum observed length is 9.4 mm), rounded in outline and strongly biconvex. Shell surface smooth with numerous indistinct growth lines. Lateral commissure is slightly ventrally curved; anterior commissure rectimarginate. Beak suberect with a small mesothyrid foramen.Symphytium small and wholly visible. Pedicle collar short. Teeth wide, short. Inner socket ridges erect. Cardinal process broad, transversely semi-elliptical. Outer hinge plates rudimentary to absent. The crural processes are short, bluntly pointed and run upward, nearly parallel to each other. Loop very short; transverse band anteriorly convex, rounded with a weak median fold. Muscle scars well visible.

REMARKS

The investigated specimens display all the characters, such as small size, smooth surface, short loop with transverse band anteriorly convex, typical of the genus Xenobrochus ( Cooper 1981) . Until now seven species have been assigned to this genus ( Cooper 1981, 1983; Hiller 1986, 1994a, b), and specimens from Fiji differ from all of them in rounded outline and much smaller foramen. From X. africanus (Cooper, 1973) , X. australis Cooper, 1981 and X. naudei Hiller, 1994 , X. rotundus n. sp. differs in having rounded transverse band with a slight median fold; the first three species have angular transverse band. In X. translucidus ( Dall, 1920) , X. agulhasensis (Helmcke, 1938) , X. africanus and X. naudei outer hinge plates, although narrow, are distinct ( Cooper 1973b; Hiller 1986, 1994a), while in the studied specimens outer hinge plates are rudimentary to absent. Xenobrochus indianensis (Cooper, 1973) , having similar loop with a median fold and rudimentary outer hinge plates, has a more incurved beak with partly concealed symphytium. In the specimens from Fiji the symphytium is wholly visible. In turn, X. anomalus Cooper, 1981 from the waters around Marion Island is characterized by the extravagantly developed tubular pedicle collar ( Cooper 1981; Hiller 1994b), a feature not observed in the specimens described here.

Superfamily TEREBRATULOIDEA Gray, 1840 Family TEREBRATULIDAE Gray, 1840

Figures

FIG. 6. — A-H, Xenobrochus rotundus n. sp., Fiji, Lau Ridge, BORDAU 1, stn DW 1469, 314-377 m, SEM: A-D, ventral, dorsal, lateral and anterior views of complete specimen,holotype (MNHN BRA-3075);E, F, inner views of ventral and dorsal valves,paratype (MNHN BRA-3076); G, H, dorsal view of complete specimen (G) and enlargement of dorsal interior (H) to show brachial skeleton, paratype (MNHN BRA-3077);I-L, Abyssothyris wyvillei (Davidson,1878),complete specimen (MNHN BRA-3074),Fiji,Viti Levu,MUSORSTOM 10, CP 1361; I-K, dorsal, lateral and anterior views; L, SEM micrograph of dorsal interior to show cardinalia and brachidium. Scale bars: A-G, 2 mm; H, L, 1 mm; I-K, 0.5 cm.