Pythonaster atlantidis A.H. Clark 1948

Mah, Christopher L., Mercier, Annie, Hamel, Jean-Francois & Nizinski, Martha, 2012, Range Extensions and Taxonomic Notes on Atlantic Myxasteridae (Velatida; Asteroidea), Zootaxa 3572, pp. 55-62 : 60

Pythonaster atlantidis A.H. Clark 1948

( Fig. 3 A–D)

A.H. Clark 1948: 76; Alton 1966: 688; Clark and Downey 1992: 339; 1906; Clark 1996: 196; Howell et al. 2002: Mah and Hansson 2012.

Description: Arms five, very elongate and gradually tapering (snake-like) with broad arm base, disk small (R:r=5.8 to 7.2) confluent with arm base.

Abactinal surface composed of soft, thin skin, covered by well-spaced clusters of two to ten ensacculate spines ( Fig. 3 A), typically five to seven, each approximately 2–3 mm long rising from a common base on a deeply embedded lenticular plate. Lenticular plates with spine clusters on arms arranged in discrete transverse annular bands that extend from base of arm to arm tip. Spine clusters arranged in regular transverse arm bands alternating with regions of bare skin. Spines more numerous on disk and basal arm region becoming fewer and less abundant distally near the tip resulting in larger gaps between annulations. Papulae, finger-like, present in the skin covering spines and adjoining surface. Interradial sulci, deep, bare regions present between each pair of arms.

Osculum similar in overall structure to those observed in Myxaster ( Fig. 3 A). Opening immediately enclosed by five bare plates, triangular in shape. These plates are each flanked by a large raised palmate plate bearing five to nine widely spaced blunt spines facing distally away from the disk center. Madreporite large (~1.0 cm diameter), irregularly convex, irregularly polygonal in outline with strongly expressed grooves. Small (~1.0 mm tall) mushroom-shaped plates present around madreporite base.

As noted in Myxaster , no clear marginal plate series could be observed, although A.H. Clark (1948: 77) observed vestigal marginals in the holotype. Spine-covered plates present, extend from adambulacral to adambulacral forming a transverse band across the arm ( Fig. 3 B). Similarly, actinal plates are not clearly visible. Actinal surface of specimen essentially an extension of abactinal and lateral surface with regions of bare skin alternating with spine-covered plates. Furrow spines seven or eight (mostly eight), webbed and arranged in a weakly palmate pattern on each adambulacral plate ( Fig. 3 C). A single stout spine present abradially positioned obliquely to furrow spine series.

Oral plates large, paired, thickened elongate, present in each interradius ( Fig. 3 D); each with five oral spines projecting into the mouth (four in type description) and five small lateral spines.

Oral region filled with large, well developed stomach. Poorly preserved, organic, non-sedimentary substance observed in the stomach could not be identified.

Tube feet biserial with much wider tube foot groove present proximally becoming narrower distally. Each tube foot striated with an apparent sucker ( Fig. 3 C).

Distribution: South of Azores (35˚37’N, 30˚15’W), Hudson Canyon, North Atlantic (38˚25’06”N, 70˚52’, 30’W), Porcupine Abyssal Plain, 2976–4877 m (bold designates new occurrence–this paper).

Comments: Other than the slight difference in R:r ratio which may be a function of size and/or the strongly contorted condition of the specimen, the Hudson Canyon specimen described herein is consistent with A.H. Clark’s (1948) original description of a specimen collected from south of the Azores. The Porcupine Seabight specimens indicated in Howell et al. (2002) were not examined.

Material Examined: USNM E18842 Hudson Canyon off the coast of New Jersey. North Atlantic Ocean. 38˚25’06”N, 70˚52’, 30’W, 2976–2995 m. Coll. R/V Chain, WHOI, 5 April 1975 (1 wet spec. R= ~10.1 (arms curled), r=1.4); USNM E7175 South of Azores (west of Gibraltar), mid-Atlantic. 35˚37’N, 30˚15’W, 3200 m, Coll. R/V Atlantis, Aug 16, 1947 (1 wet spec. R=16.5, r=2.8).

Figures

FIGURE 3. Pythonaster atlantidis USNM E 18842. A. Abactinal surface. Scale bar = 1.5 cm B. Annulations on arm. Scale bar = 5.0 mm. C. Actinal surface showing tube foot groove. D. Oral plate. Scale bar = 5.0 mm.