Comprehensive DescriptionRead full entry
“Phyllocomus crocea, Grube (Pl. XLVII. fig. 11 ; Pl. XXVIA. fig. 25 ; Pl. XXX VIIA. fig. 6).
Phyllocomus crocea, Grube, Monatsber. d. k. preuss. Akad. d. Wiss. Berlin, August 1877, p. 543.
Habitat.—Dredged at Station 151 (off Heard Island), February 7, 1874 ; lat. 52° 59' S., long. 73° 33' E. ; depth, 75 fathoms ; surface temperature, 36°·2 ; sea-bottom, volcanic mud.
A fragment of the anterior region of a comparatively large form, the greatest diameter, which is immediately behind the head, being 4 mm., and the length about 10 mm. Grube's specimen was larger and more complete, measuring 83 mm. in length by 7 mm. in breadth.
The snout is flattened and broadly spathulate anteriorly, the margin being somewhat rectangular. A shallow groove occurs in the middle line, with a slight elevation on each side. Just where the fold of the buccal segment runs forward to meet the margin of the flattened region of the snout a well-marked slit occurs on each side, and may be connected with a sensory, or, as Grube says, a secretory function. No tentacles are present in the species, and this is exceptional in the family. The next segment bears dorsally the marks of four branchial processes on each side, the two inner occurring in a transverse line, while the two outer are placed in a line running obliquely outward and forward from the foregoing. In the centre of the bases of these organs are certain small chitinous masses of an elongate-ovoid shape, resembling undeveloped spines. No trace of paleolæ is visible. Grube describes the branchiæ as broadly lanceolate, the posterior with long tapering tips, which extend considerably beyond the frontal margin.
There are fifteen pairs of bristle-bundles on each side, and their structure agrees with that usually met with in the family, viz., each possesses a stoutish shaft, with a well-marked terminal wing. The shorter series in each tuft is also stout and furnished with wings. The bristle-papillæ are less prominent than the larger hook-pads beneath, so that both are seen from the dorsum.
The hooks (Pl. XXVIA. fig. 25) possess five well-defined teeth, the middle being that most developed. The inferior fang has beneath it a small micro, so that there is a double curve between it and the terminal process. The body of the hook is marked by hold transverse lines which pass into the bases of the three middle teeth.
The greyish mud in the alimentary canal is very rich in Diatoms, and there are also a few Radiolarians and other organisms.
A glance at the body-wall (Pl. XXXVIIA. fig. 6) in section shows that the type differs from that of any other member of the group. The cuticular and hypodermic coats are thin, except on the lateral processes, where a considerable depth of hypoderm exists. The circular muscular layer is feebly developed all round. The longitudinal dorsal form two powerful sausage-shaped masses which have a deep symphysis in the middle line and a firm internal boundary. The ventral, again, are reniform, since the outer edge is reflected inward. A wide hiatus occurs between these muscles, the inner edges of which are bounded by the powerful oblique passing to their insertions in the circular coat outside the nerve-area. The latter lies external to the circular coat, and a round neural canal lies in the median line toward the upper border. Two capacious and much folded hollow organs lie over the area below the alimentary canal, and plaited masses occur superiorly above the latter. The ventral blood-vessel runs in the middle line below the alimentary canal. The latter is firm and brownish, the external coat consisting of a chitinous layer, on which the somewhat compact glandular tissue rests. The glands form close parallel rows, so that when viewed from the inner surface the aspect is characteristic. The granular masses and folded organs in the upper region of the perivisceral cavity are probably connected with the reproductive apparatus.
The form of the snout in this species somewhat approaches the Sabellides angustifolia1 of Grube, from the Philippines, but which Marenzeller has placed under Amphicteis, and extended its distribution to Japan. Both this and the Amphicteis philippinarum of Grube have a spathulate snout.
Grube's example was procured between the Crozets and Kerguelen. The number of the anterior segments in his example was seventeen, and the posterior forty-five.”