Amage sculpta Ehlers 1908

“Amage sculpta Ehlers. (Pl. III, figs. 94-99.)

Ehlers, 1908, p. 141, pl. XX, figs. 1-9 ; Hessle, 1917, p. 121.

Although the form of the body of the two individuals at my disposal differs considerably from the figures given by Ehlers, yet I think that this is a matter of preservation. There is evidence that the specimen figured by him is much contracted; for instance, the shortness of the segments, the very marked excess in size of the thorax over the abdomen, the relative shortness of the latter region, the fact that the prostomium is almost completely concealed by the following segments and the apparently distorted arrangement of the gill-bases, all seem to be explicable as a result of contraction.

There are, it is true, one or two other slight differences; for example, Ehlers found that the parapodia extend right to the posterior end of the body, and that the anus bears on its margin two low cones : whereas in the specimens before me there is a pair of very long anal cirri, and the anus is carried at the end of a short region consisting of six segments without neuropods, which suggests that his specimen had been injured at this end.

It will, therefore, be advisable to give a description of an extended individual so far as this differs from Ehlers' account. The worm, which had been removed from its tube before preservation, measured 23 mm. in length, with the greatest diameter of 3^.75 mm. at about the 5th-12th segments, where its height is 3^.25 mm. Thence the body tapers forwards and backwards, to 3 mm. at the anterior end and 2^.75 at the commencement of the abdomen. The last segment of the body is 2 mm. in diameter. Thus the worm has the shape usual in the family; the tapering posteriorly is quite gradual and the difference in size between thorax and abdomen is much less than in Ehlers' type.

The colour is reddish-brown, iridescent : and the bristles are bronze coloured.

The length of the thorax (with head) is 12 mm. and of the abdomen 11 mm. The body contains 31 segments, of which 16 constitute the thorax. The hinder end of the body is somewhat dilated to form a thin-walled cup-shaped depression, from the edge of which arise two long filamentous cirri, which are as long as the last five chaetigerous segments, and there also appears to be a circle of minute cirri or papillae round the anus.

The prostomium is quadrate with rounded corners ; it slopes, as usual, downwards and forwards so that its anterior margin nearly touches the lower lip. On its upper face a raised rectangular area is marked out by a wide posterior groove and a pair of lateral furrows, which cut the anterior margin so as to divide it into a larger median and a pair of smaller lateral lobes. The regions outside the furrows both basal and lateral are swollen.

A small group of pigment spots lies at the angle formed by the junction of the lateral with the transverse basal furrow.

The tips of a few tentacles issue from between the prostomium and the lower lip.

The buccal segment is narrow dorsally but, as usual, widens out to form a thick ventral lip, which is furrowed lengthwise. This segment dorsally overlaps the base of the prostomium, whose full extent is only seen when viewed from the front or by pressing back the buccal and branchial segments.

The second or branchial segment presents in the median dorsal region a large quadrate shield or plate which is longitudinally furrowed and lined and occupying the space between the right and left couple of anterior gills projects over the buccal segment and the base of the prostomium.

On either side of this platform a pair of gills arise, beyond the outer one of which is a small parapodium with a small bunch of short bristles ; below this the anterior margin of the segment is notched, and shows a low papilla (? nephridiopore). The lateral and ventral portions of the segment are glandular, forming a prominent ridge round the base of the preceding segment.

The third segment is biannulate dorsally and carries on each side a second pair of gills, of which one is situated just behind the interval between the anterior pair, and the second is immediately behind this. The posterior gill is the longest of the four and reaches back as far as the 10th notopod. Hence, instead of the four gills on each side forming, as Ehlers interprets, an oblique line, they form a clump, in which the anterior two are transversely and the posterior longitudinally placed.

Thus ^­0₀⁰ .

⁰

In one of the two specimens, which was still within its tube, all eight gills are present ; in the other, three are in position on the left side, and only one remains on the right.

Of the fifteen notopods, the anterior three borne by the 2nd, 3rd, and 4th segments are small, after which they become larger and project as short cylinders, and the bristles are longer and more numerous.

In the abdominal region, after the cessation of the bristle-bearing notopods, there is above the neuropod of each segment a small cylindrical papilla, without chaetae, which is no doubt a vestigial representative of a notopod. It is absent only in the last six segments of the body, which are also without neuropods.

The neuropods commence on the 5th segment below the 4th notopod; the first three are longer than the rest, and the first is the longest. At the 15th segment the torus is only half the height of the first, while in the abdomen they are still further reduced in length.

The notopodial bristles are of two lengths, but all are alike in form; straight, with finely striated narrow wings, of which one is about twice the width of the other. There is a small rounded knob or lip behind the bundle.

The uncini are uniserial and as many as 70 occur on the 13th neuropod, and about 24 in the posterior tori. The form of the uncini seems to differ slightly from that described by Ehlers, for I find, below the first or anterior denticles, a short pointed process apparently part of the manubrium, which he does not figure, and at the other end a fifth denticle, which is not always apparent or may be duplicated. As in other members of the family these denticles form more than one row. I find generally the formula 1-22-3-4-5 (5). Ehlers gives the formula 1-2-3·3-4, which, moreover, does not agree with his figure which shows 1-2-2-3-4. But, as Fauvel has pointed out, the exact number and disposition of these denticles are liable to variation.

The tube is of grey mud with abundant sponge spicules embedded and foreign bodies adherent. This tube measures 35 mm. by 4 mm. at its upper end. The con­tained worm is 15 mm. in length.

Locality.—Ross Sea, opposite Granite Harbour, Station 340, depth 160 fathoms.

Distribution.—Bouvet Island (Ehlers); Graham's Land (Hessle).”

(Benham, 1927)