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 : 448-450

HIPPASTERIA TIBURONI SP. NOV.

( FIG. 9A–E )

Etymology

This species is named for the Monterey Bay Aquarium Research Institute’s retired Remotely Operated Vehicle ( ROV) (1996–2008) the Tiburon, which was used to collect the type specimen .

Type species

Hippasteria tiburoni sp. nov., holotype USNM 1208019 .

Comments

This species is supported as part of the H. heathi clade and shares several characters with H. heathi , including identical abactinal and actinal spination and pedicellariae types (in large specimens). Hippasteria tiburoni differs in that a pronounced thickened skin is present on the abactinal and actinal surfaces, and unlike H. heathi , large, prominent pedicellariae are absent from the marginal plates. Spination pattern in H. tiburoni is also different with larger, primary spines limited primarily to primary circlet and radial series. Large, primary spines are more widespread on H. heathi .

The holotype was observed feeding on an isidid (‘bamboo’) coral.

Occurrence

Pioneer Seamount, North Pacific Ocean, 998–1297 m. Description

Body stellate, arms triangular, disk broad (R: r = 2.0) ( Fig. 9A ). Smaller specimen less stellate (R: r = 1.63).

Abactinal surface tumescent, minor folds present interradially. Discrete epidermis present over abactinal surface plates, especially visible around papular pores. Individual plates round to polygonal, slightly convex. Plates especially round and larger on central and radial areas with smaller more irregular shaped plates distally adjacent to superomarginal series. Approximately four to five plates (two large radial plates, two to three smaller plates on distal edges) present across arm base. Large (about 1–1.5 mm length), conical spines, one or two (mostly one) irregularly present on most abactinal plates, especially inter-radially ( Fig. 9A, C ). Carinal series with one to two (mostly one) large spines per plate. Other plates covered by smaller granular spinelets, less than half to a quarter of the length of primary spines, densely covering abactinal plates. Smaller spines on abactinal plates present on base surrounding larger spines on larger plates. Large pedicellariae (∼2.0 mm in length) with elongate rectangular valves (teeth absent), present irregularly on surface ( Fig. 9C ). In the smaller specimen, pedicellariae valves are more elongate (and tong-like in shape) with more pronounced jagged, interlocking edges. Short spines, four to eight, present on plates surrounding large pedicellariae. Papulae prominent, emerging through pores with distinct epidermis around edges. Papulae distributed over complete (radial and interradial) abactinal surface.

Marginal plates, 20 (counted from arm-tip to armtip), form strongly expressed peripheral border, occupying slightly over half (∼57%) of distal arm width ( Fig. 9A ). Only ten superomarginals (arm-tip to armtip) in the smaller (R = 1.3) specimen. Marginal plates swollen and strongly tumescent. Other than spination and associated accessories, plate surfaces are smooth and bare. Superomarginal and inferomarginals slightly offset but with more correspondence between plates distally. Superomarginal plates with zero to five large conical spines (1–2.0 mm in length) located centrally on plate surface ( Fig. 9C ). Smaller specimen with single spine on most plates. Other than spines, plate surfaces on marginal plates are bare. Peripheral granules pointed, 20–30, on marginal plates but only on three sides, absent on the side in contact with abactinal surface. Smaller, secondary granules with spiny tips, four to six, on lower surface of superomarginal plates adjacent to inferomarginal surface. Inferomarginals with spiny granules, 20–40, largely identical to those on superomarginals but slightly larger, with more pointed tips and present on all four inferomarginal sides. Inferomarginal plate surface also with zero to five large (up to 3.0 mm length), conical spines, comparable in length to those on superomarginals. Smaller specimen with mostly one larger and one to several smaller spines present. Spines largest, most abundant inter-radially, becoming few to absent distally. Fasciolar grooves shallow. Pedicellariae not observed on marginals. Terminal plate large, round to polygonal, about 2.0 mm in diameter. Terminal plate in smaller specimen large, triangular in shape and approximately twice the size of adjacent superomarginal plate.

Actinal surface composed of approximately three chevron-like series ( Fig. 9B ). Individual plates polygonal with shallow fasciolar grooves. Surface covered by epidermis. One complete series adjacent to the adambulacral plates with two more irregular series distally adjacent to inferomarginal series. Actinal surface ornamentation composed of large conical spines, shorter spines and bivalve pedicellariae similar to those on abactinal surface ( Fig. 9B, D, E ). Pedicellariae from 1.0 to 3.0 mm in length. Actinal plate adjacent to adambulacral series with both pedicellariae and spines present irregularly. Actinal plates with pedicellariae also with smaller spines flanking each valve. Actinal plates adjacent to inferomarginals covered by angular granules and pointed granules ( Fig. 9E ).

Furrow spines two or three; elongate (1–2 mm in length) primarily two proximally, becoming three distally projecting outward ( Fig. 9D, E ). Smaller individual with two furrow spines, including one shorter, smaller spine and one longer, larger spine. Larger specimens with two similar length/shaped furrow spines. When a proximal furrow spine is present, it is shorter than the other two. Spines slender, round to oval in cross-section. Single subambulacral spine on each adambulacral plate, similar in length and thickness to furrow spines. Spinelets and angular granules, three to five, present on adambulacral plate surfaces around base of subambulacral spine and on surface adjacent to actinal intermediate region. Accessory granules and spinelets on smaller individual much smaller, low in aspect. Oral plates with flattened to rounded spines, five to six. Longest spines directed into mouth region. Oral plate surface with five or six spade-shaped spiny granules with matching pairs on either plate. Another seven to eight angular granules, similar in size to those matching on either plate.

Material examined

USNM 1208019 holotype , North Pacific Ocean , Pioneer Seamount 37°23′40.77N, 123°26′1.23W, 1297 m, coll. D. Clague with Remotely Operated Vehicle ( ROV) Tiburon MBARI T892 - A2 (one wet spec. R = 2.6, r = 1.3) . USNM 1208020 paratype Pioneer Seamount , North Pacific Ocean. 37°23′23.61N, 123°25′22.6W, 998 m. Coll. D. Clague, with ROV Tiburon , MBARI T892 - A13 (one wet spec. R = 1.3, r = 0.8).

Figures

Figure 9. Hippasteria tiburoni sp. nov. USNM 1208019. Scale bar = 0.5 cm for all unless specified otherwise. A, abactinal surface. B, actinal surface. C, marginal plate series. D, oral view showing mouth region with spines and other accessories. Scale bar = 3.0 mm. E, actinolateral view showing marginal plates, actinal and furrow spines.