Alomasoma nordpacificum Zenkevitch 1958

Alomasoma nordpacificum Zenkevitch, 1958 (Fig. 1 C-E)

MATERIAL EXAMINED. — East Equatorial Atlantic Ocean. GulfofGuinea,BIOZAIRE3,CP13, stnZB-C, 7°39.7530’S, 10°1.2916’E, 3991 m, 23.XII.2003, 2 ♀♀.

DESCRIPTION

Colour of trunk of preserved specimens is beige. Probosces missing in both specimens.Posterior end of trunk damaged in one female.In other specimen trunk is pear-shaped (Fig. 1C), 35 mm long and 17 mm across broadest part.Integument is thick and opaque in anterior half of trunk but thin and transparent in posterior half. Round to oval papillae closely arranged only on anterior half of trunk, posterior half is smooth and devoid of papillae. Single genital pore is located about 5 mm away from anterior end of trunk (Fig. 1C). Ventral setae absent.

Gonoducts one pair (Fig. 1D), small, spherical, unite proximally beneath nerve cord and open to exterior by a single genital pore. Gonostomes set on long stalks, basal in position. Gonostomal lips petaloid (Fig. 1D). Only foregut is intact, rest of intestine is missing including blood system. Pharynx is bulbous, clearly demarcated from oesophagus (Fig. 1E). Gut contents moulded into oval faecal pellets.Anal vesicles are branching tubules terminating in ciliated funnels and opening into rectum.

REMARKS

The genus Alomasoma is distinguished in possessing two gonoducts which unite proximally to form a common duct which opens to the exterior by a single genital pore. The gonostomes are basal and set on long stalks. Anal vesicles are branching tubules terminating in ciliated funnels. The genus Alomasoma is closely related to the genus Amalosoma Fisher, 1948. In the latter genus the two gonoducts open to the exterior separately. Furthermore, a specialized genital slit is present anterior to the genital pore in Amalosoma but absent in Alomasoma.

The species A. nordpacificum has been described by DattaGupta (1981) and Biseswar (2005) from the North Atlantic. The discovery of this species in the East Equatorial Atlantic Ocean considerably extends its range of distribution.