Hippasteria undetermined

Mah, Christopher, Neill, Kate, Eléaume, Marc & Foltz, David, 2014, New species and global revision of Hippasteria (Hippasterinae: Goniasteridae; Asteroidea; Echinodermata), Zoological Journal of the Linnean Society 171 (2), pp. 422-456 : 438-441

HIPPASTERIA MUSCIPULA SP. NOV.

( FIG. 6A–F )

Etymology

This species is named after the large pedicellariae’s resemblance to the Venus flytrap. The species descriptor, muscipula , is Latin for ‘mouse trap’.

Type species

Hippasteria muscipula sp. nov., holotype NIWA 61503 .

Comments

Figure 1 shows little support for affinities between H. muscipula and other Hippasteria species. The Hawaiian paratype possesses large, conical spines and strongly round to quadrate marginals and superficially appears very similar to H. phrygiana but is distinguished by the layer of skin, pedicellariae, and the strongly convex surface of the marginal plates. Spination in H. muscipula is more elongate when compared to that of H. heathi (and related taxa), which has shorter, thicker, and more conical to tubercular spination.

This species is distinctive for the presence of skin covering the body surface, strongly convex abactinal and marginal plates, and large bivalve pedicellariae with prominent interlocking, jagged teeth on each valve covering the abactinal, marginal, and actinal surfaces (only abactinal and actinal in the Hawaiian specimen). These teeth are more prominent on the marginal and abactinal plate pedicellariae than those on the actinal surface, which are wider with lower teeth on each valve.

There is also no bootstrap support for its position in Figure 1 . However, characters present on H. muscipula , specifically the pedicellariae as well as the abactinal and furrow spines, are similar to Evoplosoma , suggesting affinities.

Occurrence

North and South Pacific, Hawaiian Islands, New Zealand, and south of New Caledonia. 425–1500 m.

Description

Disk strongly tumescent, arms thickened. Body shape strongly stellate ( Fig. 6A ). R: r = ∼2.10–2.19. Discrete pulpy membrane covers the abactinal, marginal, and actinal body surfaces. Skeleton rigid and well developed.

Abactinal surface covered by widely and evenly distributed spines, each large (3–4 mm at R = 8.3 cm), conical in shape with a pointed tip, short tubercles and large pedicellariae. Each spine sits on a strongly convex, hemispherical plate ( Fig. 6E ) embedded in the pulpy membrane covering the abactinal surface. Boundaries between plates obscured by membrane. Each plate surrounded by ∼eight to ten papulae arranged in pairs sitting adjacent to each plate. Individual plates strongly convex, round to oval in outline, the larger plates are most abundant and similar in size with fewer, smaller secondary plates present amongst the larger plates. Most smaller, secondary plates present on distal edge in contact with superomarginal plates. Carinal plates and primary circlet indistinct. Distal-most arm plates more strongly convex relative to those on disk. Some plates with no accessories but most with a single, large conical spine although some have a shorter, blunt tubercle (about 1 mm, roughly 25% the length of the larger spines) interspersed amongst larger primary spines. Spine bases on some larger primary spines with small, blunt incipient spines. Spines and plate abundance and morphology homogeneous across abactinal plate surface, no apparent difference in distribution of either between proximal or distal locations on abactinal surface, although some minor secondary plates are present at abactinal and superomarginal contact. Madreporite circular with distinct sulci, flanked by five to seven plates ( Fig. 6E ).

Large, clam-shaped pedicellariae on abactinal surface (∼ 1 cm in length, 2.0 mm in width at R = 8.3 cm) with four to seven pointed teeth present on each valve. These are present irregularly on the abactinal surface and are comparable in size (if not larger) to those plates upon which sit the abactinal spines. Several of these pedicellariae are relatively large and sit above the plane of the abactinal surface.

Marginal plates range in shape from circular to irregularly round/polygonal in outline proximally, becoming more quadrate to rectangular and more regular in shape distally. Marginal plates convex, strong- ly swollen inter-radially, becoming lower distally. All marginal plates, including spines and pedicellariae, covered by smooth tissue. Superomarginals and inferomarginals corresponding 1:1 with minor plate offset distally. Plates quadrate inter-radially, becoming more elongate distally. Superomarginal plates widely spaced inter-radially, with abactinal plate surface present between near-abutting superomarginal plates. Distal superomarginal plates are more closely abutting. Superomarginals 34–46 in each inter-radius (defined as arm-tip to arm-tip), inferomarginals 36–48 per interradius. In the New Zealand and New Caledonia specimens, nearly all inter-radial and proximal marginal plates with a single prominent, large pedicellariae (0.5–0.8 cm in length at R = 14.9 cm) transecting the centre middle of each plate (i.e. for superomarginal plates from abactinal−superomarginal contact to superomarginal−inferomarginal contact) ( Fig. 6C ). The Hawaiian specimen has a large, prominent conical spine similar to those on abactinal plates. Superomarginal central plate surface bare but periphery of plate surface adjacent to inferomarginals with two to eight short, tubercle-like spines. Distal-most plates approximately five to six plates away from terminus in the smaller paratype lack pedicellariae. Each pedicellariae elongate in length, bearing 15–18 short, sharp, interlocking teeth on each valve, which clasp when pedicellariae are closed. Also present on many marginal plates are large conical spines, four to seven, which sit adjacent to the pedicellariae. In the Hawaiian specimen, distal superomarginals bare or with fewer spines and tubercles relative to those inter-radially. Inferomarginals with one to three primary spines, blunt, shorter, and less clearly conical than those on superomarginals. Inferomarginal spines closer in size and shape to short tubercular spines present on plates adjacent to superomarginal plates. Inferomarginal periphery covered by eight to 25 widely spaced, short granules with pointed tips. These granules thick, spine-like, and round to polygonal in cross-section. Inferomarginal plates wider, with partial plate surface facing extending onto actinal surface.

In the New Zealand and New Caledonia specimens, spines and pedicellariae are largest, most abundant, and most prominent inter-radially, becoming smaller to absent on distal-most marginal plates (at arm upturn). Some individual spines persist on each plate distally where pedicellariae are absent. Smaller, spine-tipped, low granules present at spine/pedicellariae bases near superomarginal/inferomarginal contact. Inferomarginals similar to superomarginals with enlarged, elongate tooth-bearing pedicellariae bearing sharp, interlocking teeth. However, inter-radial inferomarginal pedicellariae valves each flanked by three to 15 spines (becoming granules), each triangular to polygonal in cross-section. Peripheral spines are smallest at each edge, becoming largest near the centre of the pedicellariae. Pedicellariae are most pronounced and inferomarginal spines fewest but most prominent inter-radially, becoming lower and more numerous distally. Pedicellariae are smaller and lower distally. Similar to superomarginal series, pedicellariae are absent from distal-most inferomarginals approximate- ly where arm curve begins its upturn ( Fig. 6F ). Distalmost marginal plates with single granules on plate surface.

Actinal intermediate region large with approximately six to seven well-developed chevrons ( Fig. 6B ). Bestdefined series proximal, adjacent to adambulacral plates, becoming more irregular distally adjacent to inferomarginal contact. Actinal surface covered by smooth skin, identical to that covering abactinal and marginal surfaces. Elongate, bivalve pedicellariae, with each valve bearing eight to 12 interclasping teeth present on nearly every actinal plate ( Fig. 6B ). Pedicellariae largest and most prominent on series adjacent to adambulacral series becoming less prominent distally ( Fig. 6D ). Actinal plates bearing pedicellariae similar to marginals. Each pedicellariae flanked on either side by three to six angular spines, quadrate to triangular in cross-section. Those plates lacking pedicellariae with one to four prominent, blunt, thick spines round to quadrate in cross-section, often in addition to several smaller granules, often quadrate to triangular in cross-section, present on plate surface. Pedicellariae, spines and granules more widely and evenly spaced proximally becoming more densely packed distally adjacent to inferomarginal contact.

Adambulacral plates with thickened, blunt furrow spines, two to four (mostly three) ( Fig. 6D ), triangular to quadrate in cross-section. Approximately every third adambulacral plate with a bivalve pedicellariae immediately behind furrow spines. Valves on these pedicellariae are smooth and lack teeth. In the Hawaiian paratype approximately 50% of adambulacrals with a prominent, large pedicellariae present behind the furrow spines. In these instances, furrow spines are smaller, less evident, and sit below the pedicellariae directed into the tube foot furrow.

In the New Zealand / New Caledonia specimens three to eight (usually six) subambulacral plates, quadrate to triangular in cross-section but in the Hawaiian specimen one to three thick, quadrate to polygonal in crosssection, are present. These become larger distally on adambulacral series. Oral plates with four furrow spines identical to those on adambulacral plates. Oral plate surface smooth but bearing one to five (two to eight in each inter-radius) thick, blunt spines, quadrate to triangular in cross-section. One or two prominent blunt spines project into the mouth from tip of the oral plate. Oral region deeply concave covered by skin, which obscures contact/boundary with matching oral plate and other adjacent actinal plates.

Colour in life is orange-red.

Other notes

The cardiac stomach of the New Caledonia specimen (IE-2007–2362) is extended over the gorgonian Metallogorgia , upon which it was presumably feeding ( Fig. 6B ). Hawaiian Undersea Research Laboratory video shows this species (identified elsewhere as H. imperialis ) feeding on primnoid soft corals.

Material examined

Holotype. NIWA 61503 off New Zealand, 42°49′41.988″S, 179°49′54.12″W to 42°50′35.9″S to 179°50′6″W, 864– 892 m. Coll. Scientific Observer Program, St. TRIP 2626 / 197, 26.vi.2008 (one dry spec. R = 10.3, r = 4.7); paratypes. MNHN IE-2007–2362 . New Caledonia 24°42′S, 170°07′E, 820 m. Coll. N / O Alis, BERYX 2 , 25.x.1991 (one wet spec. R = 14.9, r = 7.1, arms are upturned); CASIZ 157500 . Kona, Hawaii 19°37.3′N, 156°1.9′W, 425–1500 m. Coll. C. Young and S. Arellano 17.xii.2001 (one wet spec. R = 8.3, r = 3.9).

Figures

Figure 1. Evolutionary relationships of sampled Hippasterinae (Goniasteridae) based on 654 aligned nucleotide positions of the cytochrome c oxidase subunit I gene. The phylogenetic tree was inferred using the neighbour-joining method (Saitou & Nei, 1987) in MEGA v. 5.2.1 (Tamura et al., 2011). The bootstrap consensus tree inferred from 500 replicates was drawn to scale, with distances computed using the maximum composite likelihood method (Tamura et al., 2004), in units of numbers of base substitutions per site. Ambiguous positions were removed for each pair of sequences prior to calculating the distance matrix. Terminals were labelled with GenBank accession numbers and (where available) with museum voucher numbers. Bootstrap support values are shown above or below branches when greater than 70%.

Figure 6. Hippasteria muscipula sp. nov. Paratype MNHN IE-2007–2362. Scale bar = 1.0 cm. A, abactinal surface. B, actinal surface. C, marginal plates showing pedicellariae. D, furrow spines, actinal surface, pedicellariae. E, holotype NIWA 61503. Scale bar = 0.5 cm. Close-up of dried specimen, abactinal surface. F, arm-tip showing marginal plates.