Armaster chondros, Mah, 2023

Mah, Christopher L., 2023, New Goniasteridae and in situ observations significant to deep-sea coral predation, Memoirs of Museum Victoria 83, pp. 1-35 : 3-5

Armaster chondros nov. gen. nov. sp.

urn:lsid:zoobank.org:act:B120E152-22CE-4AC3-8AE5-

A 01042932 CC5

Figure 1a–f

Etymology. The genus is derived from the Latin arma for “armed” or “weapons”, alluding to the prominent spines present on the marginal plate series. The species epithet chondros is Greek for “grain”, alluding to the granules present on the abactinal surface.

Diagnosis. Body stellate, arms elongate, triangular, interradial arcs weakly curved. Abactinal surface with continuous layer of granules covering surfaces, obscuring plate boundaries. Most abactinal arm plates do not show the abrupt enlarged size as they do in Atheraster o r Circeaster , although exceptionally plates 1–3 are smooth and 2–3 times the size of adjacent plates. Most superomarginals with a large single spine or strongly arched central area where spine has been broken, spination more weakly expressed distally. Inferomarginals with granulation on surface interradially but not along plates more distally. Oral surface covered by granules similar to those on aboral, marginals; pedicellariae, 6–7 per interradius, paddle-shaped, valves broad. Furrow spines, 3 to 5, most with a single large subambulacral spine and a paddle-shaped pedicellariae.

Comments. Armaster n. gen. shows arm plates consistent in size with those on disk and similar to those of Lydiaster but differing in the presence of prominent conical spines on superomarginal and inferomarginal plates, much in the way that Atheraster displays marginal plate spines relative to Circeaster . Armaster is further distinguished from other circeasterines by a dense granular cover on the abactinal plate surface that completely covers the plates and obscures boundaries between them.

Arm shape, marginal plate spination, surficial granulation and pedicellariae in Armaster resembles those in the hippasterine Evoplosoma , suggesting that the Hippasterinae and the Circeasterinae share characteristics.

Occurrence . Huon Seamount, Tasman Sea , 900 m.

Description. Body stout, stellate (R/r=3.0). Arms tapering, elongate, triangular tips pointed.Interradial arcs weakly curved.

Abactinals abutted, ranging in shape from quadrate to irregularly polygonal, larger proximally becoming smaller and more homogeneous distally adjacent to superomarginal contact. Abactinals covered by coarse, round granules, 8–15 per plate, 2–3 along a 1.0 mm line. Granular cover obscuring plate boundaries; granules round to polygonal. Plates extend onto arms for at least 70% of arm distance; superomarginals abutted, 4–6 (mostly five), adjacent to the terminus. Granules present on abactinal plates on arms and disk. Most arm plates similar to those on disk; only one to three larger plates smooth and devoid of granulation. Surface with no enlarged spines or tubercles. Papulae tentacular, extended from pores, relatively abundant on radial regions on disk and proximally on arms, becoming absent midway to distally along arms. Madreporite pentagonal, flanked by five plates. No pedicellariae observed.

Marginal plates, 18–20, in each interradius from arm tip to arm tip; each plate with 14–30 peripheral granules, 6–10 per side. Each superomarginal with either a single, prominent cone-shaped spine or a strongly arched central surface where the spine is absent, central surface strongly arched; alternatively, plate surface low rounded and with 1–6 granules. Distalmost superomarginal plates with or without prominent spines. Inferomarginal plates spineless, proximal plates with large granules, 15–30 covering plate surface with enlarged tubercular granules present centrally on plate. These granules present interradially, with inferomarginals on arms lacking accessories on plate surface. No pedicellariae observed on either series.

Actinal surface composed of 2–3 full series with most elongate actinal plates extending to base of arm. Individual plates quadrate to irregular, surface covered by coarse granules, 4–15, widely spaced, variably round to polygonal. Exceptionally 4–7 large tubercular granules in each interradius. Large paddle-shaped pedicellariae present, 6–8 in actinal interradial region, primarily adjacent to adambulacral plates.

Furrow spines quadrate, 3–5, tips thick, blunt; series weakly palmate to straight. One paddle-shaped pedicellaria adjacent to each furrow spine series; one enlarged blunt spine, approximately twice the thickness of furrow spines. Subambulacral spines more elongate and prominent distally, thickness approaching 2–3 times that of the furrow spines. Remaining cover on adambulacral plates composed of 4–8 widely spaced ground granules.

Oral plate form identical to adambulacral, a single enlarged spine projecting into the mouth, 9–10 furrow spines. Remainder of oral plate surface with 8–10 hemispherical granules, 4–5 present along the edge of the central diastema, with the remainder on the oral plate surface adjacent to the actinal plate contact.

Material examined. Holotype. NMV F240317 , Huon seamounts, Tasman Sea, Australia. 44.2771° S, 147.266° E, 900 m, coll. R / V Southern Surveyor. 1 wet spec, R =4.9, r=1.6.