Comprehensive Description

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Description

Anseropoda antarctica sp.nov.

 

(Fig. E, 1-1c; Plate X, fig. 3; Plate XII, fig. 1)

 

DIAGNOSIS. Rays 5. R 17 mm., r 10-11 mm., br 12-13 mm. (body distorted).

 

Broadly stellate, the general habit that of a thin-edged Asterina; disk rather arched and oral region sunken; interradial areas thin but restricted in extent. Abactinal surface covered with small, uniform truncate granules, grouped so as to indicate underlying plates; actinal plates with combs of usually 3 spinelets; adambulacral furrow combs with 6-3 webbed, slender, blunt spinelets; subambulacral combs with 5-3 spinelets; marginal oral spinelets 8, basally webbed.

 

DESCRIPTION. The general form is more that of an Asterina than of a typical Ansero­poda owing to the arched disk and concave actinal surface. The small size obviates an extensive development of broad thin actinal interradial areas.

 

The abactinal surface is covered with fairly uniform truncate granuliform spinelets, 0.18–0.22 mm. long, the top of which is subcircular and armed with numerous thornlets. A profile view is shown in fig. 1. The granules, by reason of slightly differentiated spacing, form groups corresponding roughly to underlying plates, most conspicuous in the interradial areas. Larger radial plates carry 12-18 granules; the smaller interradial plates 5 or 6.

 

The abactinal plates are thin, scale-like and strongly imbricated, with a curved external free edge. In the median radial series this edge is directed toward centre of disk. The other plates are arranged in series parallel with the radial, and also in transverse series; and the curved free edge is toward centre of disk and radial line. On the coelomic side the dorsolateral plates each have a conspicuous process which is directed toward the margin of ray and increases in length in successive plates. This process is characteristic of Anseropoda (fig. E, 1a, 1b).

 

Papulae small, "here and there" on centre of disk, and in two radial series, one on either side of carinal plates - about 12 to a series.

 

Madreporite 1 mm. in diameter, situated 4 mm. from centre of disk.

 

Superomarginal plates small, abactinal in position, the margin ray being defined by the outer end of inferomarginals, which form a border outside of the superomarginals nearly as wide as the latter. Superomarginals carry 10-12 granules and the abactinal surface of the inferomarginals about the same number, a trifle smaller in size. There is a distinct groove between the inferomarginals (or the lateral outgrowths of the imbricated plates proper).

 

The actinal plates are in regular oblique transverse series corresponding each to an inferomarginal (and usually to an adambulacral). The grooves, mentioned above, con­tinue to the ambulacral furrow between the regular lines of actinal plates. A few plates near the oral angle carry a central comb of 4 or 5 short sharp thorny spinelets, but usually there are 3 in a slightly curved comb (1-3 in very small specimens, R 5 mm.). Occasionally the spinelets stand in a group, spinelets 0.3-0.37 mm. long.

 

Adambulacral armature: a curved furrow comb of 6 webbed slender spinelets, the laterals much shorter than the 4 central. This number diminishes to 5, 4 and 3 as end of ray is approached. The subambulacrals are on an oblique ridge of the surface at a higher level than the marginals. They are a little shorter, more pointed, and very similar to adjacent actinals. The webbed combs usually start with 5 spines and end with 3. Furrow spines: longest 0.75 mm., shortest laterals, 0.22 mm.

 

Mouth-plates with 8 marginal spinelets, the 16 of an angle basally webbed and decreasing in length laterally from the central pair which are the largest spines on the body. Three or four suborals border the outer half of suture; and usually two somewhat longer ones stand between these and margin.

 

TYPE LOCALITY. St. 170. Off Cape Bowles, Clarence Island, 342 m., 7 specimens.

 

REMARKS. The specimens range in size from R 4.5 mm. to R 17 mm. (type). This is probably a small species since the type does not appear to be immature.

 

The species does not particularly suggest, by its general appearance, an Anseropoda. The abactinal granules constitute an aberrant feature since Anseropoda typically has delicate spinelets. Although the body is thin, its proportions have not reached the bizarre stage of A. placenta and other typical species. The internal processes of the abactinal and actinal plates are proportionately much shorter than in A. placenta and the plates of the midradial region are not obviously stellate. In large species the long internal processes are an essential anatomical contrivance in connection with numerous oblique septa all along the ray. They make possible the survival of a creature which is very thin, broad and delicate. If A. antarctica grows to a large size these processes undoubtedly greatly lengthen.

 

A curious feature of A. antarctica is the presence of hyaline spicules or thornlets on the dorsal, coelomic, surface of the ambulacral plates. They are best developed on the first 2 ambulacrals where they are prominent and occupy nearly the whole length of the plate, especially on the narrow part between ampullae. Further on, they are confined to the lower half of plate. I find a somewhat similar development in the relatively huge six-rayed Anseropoda insignis Fisher of the Hawaiian Islands.

 

There appears to be no described species closely related to this diminutive Anseropoda. The abactinal granulation, alone, is distinctive.”

 

 

(Fisher, 1940: 149-150)

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© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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