Achaetobonellia maculata Fisher, 1953

Achaetobonellia maculata Fisher, 1953

( Fig. 3 View FIG D-F)

MATERIAL EXAMINED. — Porcupine Abyssal Plain, BEN- GAL 3, Discovery 229, stn 13200#94, 48°47.29’N, 16°32.23’W, 4851 m, 26.VII.1997, 1 ♀.

DESCRIPTION

Colour of preserved specimen is light pink. Proboscis is 22 mm long, bilobed distally; right lobe is damaged as well as major part of stem ( Fig. 3D View FIG ). Proximally, lateral margins of proboscis unite to form narrow lower lip ventral to mouth. Trunk is cylindrical, 79 mm long and 11 mm at broadest part. Integument is opaque.To unaided eye integument appears smooth but under magnification, minute papillae are visible at anterior end of trunk. Single genital pore is located a few millimetres away from mouth ( Fig. 3D View FIG ). Ventral setae absent.

Internally, single oval gonoduct is located on left side of nerve cord ( Fig.3E View FIG ). Gonostome is sub-basal in position with small lobes around margin. Only foregut is intact, rest of alimentary canal is missing including blood vascular system. Anal vesicles branch at least three times before terminating in ciliated funnels ( Fig. 3F View FIG ).

REMARKS

The genus Achaetobonellia is distinguished by the following characters: presence of a bifid proboscis; single gonoduct with a sub-basally located gonostome; anal vesicles numerous arborescent structures and the absence of ventral setae. This genus contains a single species, namely, Achaetobonellia maculata described by Fisher (1953) from a single specimen collected from Gilbert Islands in the South Pacific.

Except for differences in the size and shape of the gonoduct and the structure of the proboscis, the specimen on hand conforms with the description provided by Fisher (1953). The genus Torbenwolffia Zenkevitch, 1966 seems to be close to Achaetobonellia but differs from the latter in possessing anal vesicles that are tubular and unbranched. Furthermore, the gonoduct in Torbenwolffia is located on the right side of the nerve cord ( Zenkevitch 1966).

Achaetobonellia maculata of the present collection is the first report since its discovery and first record of is occurrence in the Atlantic.

Torbenwolffia galatheae Zenkevitch, 1966 is another species that has been recorded at this station ( Biseswar 2005).