“Eunoa opalina, n. sp. (Pl. X. fig. 5 ; PL XIX. fig. 2).
Habitat.—Trawled at Station 311 (in the Strait of Magellan), January 11, 1876 ; lat. 52° 45' 30" S., long. 73° 46' W. ; depth, 245 fathoms ; bottom temperature 46°∙0, surface temperature 50°∙0 ; blue mud.
The specimens are fragmentary, the longest measuring 25 mm. in length, and with the bristles about 12 mm. in breadth.
In the preparation the scales are milky, but no pigment is elsewhere present.
The head is distinguished by the great prominence of the lateral regions anteriorly, culminating in the widely separated peaks on each side of the tentacle. A pair of rather small transversely ovoid eyes are situated a little in front of the posterior border. Somewhat anterior to these, but yet behind the lateral median prominence, are a much larger round pair, which are barely seen from the dorsum. The tentacle rises abruptly from the large basal segment, and is comparatively short, its filiform tip not reaching the extremity of the palpus. It is pellucid, and shows no appreciable enlargement below the filiform termination. The slender tips of the antennæ extend about half-way along the tentacle. The palpi are quite smooth. The tentacular and dorsal cirri agree with the tentacle in shape, and have likewise a series of clavate sparsely distributed, and as usual longest on the slightly tumid region below the filiform tip. The ventral cirri are tapered nearly from the base to the slender apex, and are quite smooth. There is only an eminence in place of the ventral mamilla.
The scales seem to be fifteen pairs, though neither example is perfect. They are soft, large, milky, as well as slightly translucent, and the dorsum is fully covered by the overlapping organs. Just within the posterior border are a series of soft papillæ arranged at intervals and visible under a lens. The first scale (Pl. XIX. fig. 2) is small and rounded, its soft papillæ are large though few, and all round its border are a series of microscopic clavate processes. Moreover, its anterior region shows minute papillæ scattered over the surface in considerable profusion.
The dorsal division of the foot bears a fascicle of pale yellow bristles, of moderate length, and in all enveloped in pale mud. The tip is smooth, slightly dilated in the middle, and with a peculiar double marking (Pl. VIIIA. fig. 9 shows an average example). The rows of spines are minute. An instance of a regenerated bristle (Pl. VIIIA. fig. 10), apparently after fracture, occurred amongst the others. This is rare, though the inherent recuperative power of these bristles is considerable.
The ventral branch carries pale yellow bristles with peculiarly long curved simple terminations (Pl. VIIIA. fig. 11). Very few forms occur with so decided a curve at the tip. The spinous rows are comparatively small.
An eyeless variety was trawled at Station 299 (between Juan Fernandez and Valparaiso), December 14, 1875 ; lat. 33° 31' S., long. 74° 43' W. ; depth, 2160 fathoms ; bottom temperature 35°∙2, surface temperature 62°∙0 ; sea-bottom, blue mud.
It is of good size, 38 mm. in length, and 15 mm. in breadth inclusive of the bristles. The head is devoid of any trace of eyes, so that it forms another example of the influence of habitat on these important organs. The bristles and other parts correspond with the previous specimens. A developing foot exhibits setigerous lobe, cirrus, dorsal and ventral bristles in miniature, showing that the reproduction of all these parts occurs simultaneously, and that the peculiar characters of the bristles exist independently of size.
The intestinal canal of this example contained a quantity of dark brownish mud, in which were sponge-spicules, vegetable and other organic debris.
The ventral area is well marked, but thin, and the nerves are greatly flattened. The hypoderm externally is apparently diminished, but internally connective tissue and fibres form a protection. The cuticle is quite smooth.”
(McIntosh, 1885)
Eunoe opalina is a scale worm widely distributed in the Southern Ocean at depths of about 200–1400m.[2]
Number of segments 38; elytra 15 pairs. No distinct pigmentation pattern. Prostomium anterior margin comprising a pair of acute anterior projections. Lateral antennae inserted ventrally (beneath Prostomium and median antenna). Notochaetae thinner than neurochaetae. Bidentate neurochaetae absent.[3]
E. oplina is commensal. Its host taxon is a sea cucumber: Bathyplotes bongraini.
Eunoe opalina is a scale worm widely distributed in the Southern Ocean at depths of about 200–1400m.
