Rhamphobrachium (Spinigerium) ehlersi Monro 1930

“Rhamphobrachium ehlersi, n.sp.

St, 172. 26. ii. 27. Off Deception Island, South Shetlands. 62° 59' 00" S, 60° 28' 00" W. 525 m. Gear DLH. Bottom: rock. Two speci­mens.

DESCRIPTION. Two fragments incom­plete posteriorly. The larger measures 28 mm. by 4 mm. including the feet and has 35 chaetigers. In spirit there are no colour markings. There is a pair of globular anterior tentacles. All the re­maining tentacles are short and thick. The outer laterals are spindle-shaped with massive tentaculophores : the inner laterals are more slender and subulate. They reach to the anterior border of the 2nd chaetiger. The median tentacle is a little shorter. The stout tentacular cirri are inserted on the anterior border of the 1st segment.

The first three pairs of feet are much enlarged and carried forward beneath the body. In addition to a stout dorsal cirrus and a small conical ventral cirrus, there are a small papilla on the inner and anterior face of the chaetal lobe and two papillae, a ventral and a dorsal, at the apex of the chaetal lobe. Behind the first three modified chaetigers the feet are of the usual onuphid shape (Fig. 46, a). The dorsal cirrus is rather short and thick, just surpassing the end of the chaetal lobe. The ventral cirrus is a rounded lobe and it is transformed into a pad by the 6th chaetiger. The cirriform prolongation of the posterior lip of the chaeta sac disappears by the 10th chaetiger. The gills begin as a single filament on the 10^th-11th chaetiger (Fig. 46, b) and at the 20th are bifila­mentous (Fig. 46, c). In the present specimens there arc never more than two filaments. The fully developed gill is two or three times as long as the dorsal cirrus.

All the bristles of the first three modified chaetigers are broken off. The 4th foot contains a dorsal bundle of capillary bristles (Fig. 46, d) and a ventral bundle of com­pound bristles with knife-like blades (Fig. 46, e). There are three long pointed yellow acicula supporting the feet. At the 10th foot there are, in addition to the two types of bristles already described, two or three dorsally situated comb chaetae (Fig. 46, f). At about the 20th foot a pair of yellow hooded bidentate subacicular hooks (Fig. 46, g) appear and take the place of the compound bristles.

The dental formula is 7-9 : 9 + 6-6, and the details of the jaws are shown in the figure (Fig. 46, h). The anterior part of the lower jaws (Fig. 46, i) is calcareous.

REMARKS. There are three known species of this rare abyssal genus, R. agassizi, R. brevibrachiata and R. chuni. The present species is distinguished by the low number of filaments to the gills and the character of its bristles. Fauvel apparently does not accept the genus Rhamphobrachium, for he redescribes (1923, p. 417) the Diopatra brevibrachiata, Ehlers (1875, p. 49), under the generic name Onuphis. Ehlers (1908, p. 78) has himself recognised that this species falls within the genus Rhamphobrachium.”

(Monro, 1930)

“Rhamphobrachium ehlersi, n.sp.

St, 172. 26. ii. 27. Off Deception Island, South Shetlands. 62° 59' 00" S, 60° 28' 00" W. 525 m. Gear DLH. Bottom: rock. Two speci­mens.

DESCRIPTION. Two fragments incom­plete posteriorly. The larger measures 28 mm. by 4 mm. including the feet and has 35 chaetigers. In spirit there are no colour markings. There is a pair of globular anterior tentacles. All the re­maining tentacles are short and thick. The outer laterals are spindle-shaped with massive tentaculophores : the inner laterals are more slender and subulate. They reach to the anterior border of the 2nd chaetiger. The median tentacle is a little shorter. The stout tentacular cirri are inserted on the anterior border of the 1st segment.

The first three pairs of feet are much enlarged and carried forward beneath the body. In addition to a stout dorsal cirrus and a small conical ventral cirrus, there are a small papilla on the inner and anterior face of the chaetal lobe and two papillae, a ventral and a dorsal, at the apex of the chaetal lobe. Behind the first three modified chaetigers the feet are of the usual onuphid shape (Fig. 46, a). The dorsal cirrus is rather short and thick, just surpassing the end of the chaetal lobe. The ventral cirrus is a rounded lobe and it is transformed into a pad by the 6th chaetiger. The cirriform prolongation of the posterior lip of the chaeta sac disappears by the 10th chaetiger. The gills begin as a single filament on the 10^th-11th chaetiger (Fig. 46, b) and at the 20th are bifila­mentous (Fig. 46, c). In the present specimens there arc never more than two filaments. The fully developed gill is two or three times as long as the dorsal cirrus.

All the bristles of the first three modified chaetigers are broken off. The 4th foot contains a dorsal bundle of capillary bristles (Fig. 46, d) and a ventral bundle of com­pound bristles with knife-like blades (Fig. 46, e). There are three long pointed yellow acicula supporting the feet. At the 10th foot there are, in addition to the two types of bristles already described, two or three dorsally situated comb chaetae (Fig. 46, f). At about the 20th foot a pair of yellow hooded bidentate subacicular hooks (Fig. 46, g) appear and take the place of the compound bristles.

The dental formula is 7-9 : 9 + 6-6, and the details of the jaws are shown in the figure (Fig. 46, h). The anterior part of the lower jaws (Fig. 46, i) is calcareous.

REMARKS. There are three known species of this rare abyssal genus, R. agassizi, R. brevibrachiata and R. chuni. The present species is distinguished by the low number of filaments to the gills and the character of its bristles. Fauvel apparently does not accept the genus Rhamphobrachium, for he redescribes (1923, p. 417) the Diopatra brevibrachiata, Ehlers (1875, p. 49), under the generic name Onuphis. Ehlers (1908, p. 78) has himself recognised that this species falls within the genus Rhamphobrachium.”

(Monro, 1930)