Malacosaccus coatsi Topsent 1910

Malacosaccus coatsi Topsent, 1910

(Figs. 1 B, 2 & 3, Table 1)

Material examined: SMF 10702, ANDEEP III, R.V. 'Polarstern' stn PS67/102-11, Weddell Sea, Antarctica, 0 6 Mar. 2005, 65°35.40'–35.51'S, 36°29.00'–28.83'W, 4794–4797 m; ANDEEP III, SMF 10521, SMF 10703, SMF 10704, R.V. 'Polarstern', stn PS67/121-7, Weddell Sea, Antarctica, 14 Mar. 2005, 63°34.92'–34.65'S, 50°41.97'–41.68'W, 2616–2617 m.

Description: Specimens were collected from two trawl stations, a single large nearly intact cup torn from the missing stalk (Fig. 2 A) from the first station and another specimen with stalk and root intact but with upper cup slightly damaged (Fig. 1 B) and two smaller fragments from the second station. The first specimen is 91 mm tall, 102 mm in diameter with a wall up to 25 mm in thickness. The second specimen is a stalked cup, total height 495 mm, upper cup width 234 mm, stalk 258 mm long by 41 mm diameter, root ball 152 mm diameter. The external surfaces of the upper body of both specimens are heavily mud-laden and woolly in appearance; the atrial surfaces are penetrated by apertures of exhalant canals, 1–8 mm in diameter (Fig. 2 A).

Megascleres of both specimens are were found to be essentially identical; only those of the first specimen (station 102-11) were examined in detail (measurements given in Table 1). Dermalia and atrialia are pinular hexactins (Figs. 2 B, 3A) with scale-like, distal-pointed spines on the long, smoothly tapered, inflated pinular ray. All other rays are smooth and cylindrical, with rounded or parabolic tips. Principalia are very large hexactins (Fig. 3 B) and pentactins (Fig. 3 C), about equal in abundance. Their rays are smooth and cylindrical, terminating in rounded or slightly parabolic tips. Large triactins and stauractins are additionally present in the stalk of specimen 2; their rays are similar in form to the principalia of the body. No diactine megascleres are present and the only spines occurring are on the pinular ray of dermalia and atrialia.

Microscleres of both specimens include floricomes, discohexasters, and onychohexasters, but the two specimens differ in oxyhexasters, these being very abundant in the specimen from station 102-11, and absent in the specimen from station 121-7. Measurements of the former are given in Table 1. The relatively large oxyhexasters (Figs. 2 C, 3F) have six short primary rays, each bearing 2–4 straight terminal rays which are smooth in LM and seen to bear sparse, very small spines in SEM. The moderately abundant floricomes (Figs 2 C, 3E & F) have six short primary rays, each of which bear 2–9 s-shaped terminals ending in typical eccentric heads bearing 4–8 short claws. Primary rays are sparsely spined in SEM and terminal rays are densely covered in small recurved spines which are evident in LM. Discohexasters (Figs. 2 E, 3F) are floricoidal in form and often more slender, with six short primary rays each bearing 3–8 s-shaped terminal rays ending in complete discs with 4–8 marginal spines. They are ornamented like the true floricomes. Onychohexasters (Figs. 2 F, 3F) are floricoid in form and very slender; they are difficult to find and often broken. Each of the six short primary rays carries 2–5 s-shaped terminal rays ending in a tuft of 3–5 perpendicular claws. Recurved spines are sparse on the primary rays and dense on the secondary rays. Rare µm).

abnormal variants include spiroxyhexasters (Fig. 3 G) and bizarre crab-like oxyasters. No evidence of graphiocomes was found in either specimen. One spherical discohexaster (not figured), 58 µm in diameter, with about 10 straight terminal rays on each primary ray was found in the first specimen; it is considered likely to be foreign in origin.

Remarks: The ANDEEP III specimens are clearly assignable to Topsent's Malacosaccus coatsi in their possession of both pentactin and hexactin principalia and range of floricoidal microscleres. Although Topsent did not designate the discohexasters with tufts of spines at terminal ray ends as onychohexasters, he correctly described and figured them in his 1913 description. These specimens differ from M. pedunculatus Topsent, 1910, originally collected at the same location as M. coatsi, in their larger dermalia pinule rays, their possession of pentactin principalia and lack of spheric discohexasters. As M. coatsi is presently understood, oxyhexasters seem to be a variable spicule which is not correlated to geography but may be related to depth. They are present in low numbers in the original type specimen (2579 m, 16º34'W), absent in the EASIZ fragments (1540 m, 21º24'W) reported by Janussen et al. (2004), and absent in the western ANDEEP III specimen (2616 m, 50º41'W) but abundant in the eastern, deeper water specimen (4794 m, 36º33'W). Future collected material may help reveal the pattern of oxyhexaster production in various portions of the M. coatsi population.