Milteliphaster monstrosus, Mah, 2022

Mah, Christopher L., 2022, New Genera, Species and Occurrences of Deep-Sea Asteroidea (Valvatacea, Forcipulatacea, Echinodermata) collected from the North Pacific Ocean by the CAPSTONE Expedition, Zootaxa 5164 (1), pp. 1-75 : 57-60

Milteliphaster monstrosus sp. nov.

FIGURE 19A–F , 20A–B

Etymology: The species epithet, monstrosus is Latin for a “fabulous wonder”, alluding to the very striking appearance of this species.

Diagnosis. Body stellate (R/r=2.56), arms triangular, interradial arcs curved. Abactinal, marginal and actinal intermediate plate surface covered with large, conical pointed spines. Superomarginal plates wide, surface of each plate smooth except for one to four, mostly three, prominent sharp conical spines on raised, rounded bases. Inferomarginals similar in overall shape, but becoming more rectangular distally. Inferomarginals with one to six, mostly four to five sharp, conical spines on raised bases. Furrow spines 6–10 in straight to curved fan with furrow spine number increasing distally along arm. Adjacent to furrow spines are one or two large paddle-shaped pedicellariae with round valves. Subambulacral spines 2 or 3, large in transverse series, each with pointed tips.

Comments. This species was only observed during a dive on Esmerelda Bank in the Marianas ( Figs19A , 20 ). Its entire abactinal surface was covered by a bristling array of pointed conical spines distributed evenly but irregularly over the abactinal surface with two to four identical spines projecting from the superomarginal spines. Papulae project from the abactinal surface between the spines, even on interradial regions. Marginal plates in this species were directed laterally and although wide interradially became elongate along the arms. The extended, strap-like arms, and elongate superomarginals on the arm are consistent with those observed in M. woodmasoni (see re-description by Mah 2018). Although this species was not collected by the NOAA Ship Okeanos Explorer a specimen was discovered in the MNHN collections from the Solomon Islands and is described below as the holotype.

The holotype of Milteliphaster woodmasoni (MNHN-IE-2014-164) and the species herein share the relatively small (and more numerous) polygonal to irregularly-shaped, flat to weakly concave to flat, abactinal plates, flat marginal plate surfaces in conjunction with the prominent pointed spines, the lateral facing marginal plate series, elongate arms displaying upward arm coiling as well as a comparable number of furrow spines (6 to 10). These characters are the basis for identification and placement of this specimen within Miltelphaster.

This species differs from Milteliphaster woodmasoni Alcock based on the shape of the marginals, which are wide interradially versus those in M. woodmasoni , which are elongate interradially. Abactinal spination occurs irregularly throughout the surface in M. monstrosus n. sp. but is present only along carinal series and on the disk in M. woodmasoni . Pedicellariae, which are absent in the type of M. woodmasoni , are present in abundance in M. monstrosus n. sp.

Milteliphaster monstrosus n. sp. also invites comparison with species in the genus Calliaster , such as C. wanganellensis or C. chaos that also possess an abundance of spines on the abactinal surface. As described earlier, other species possess more strongly convex, blockier, and round marginal plates uniformly around the body with none that resemble the smaller, lateral-facing marginal plates in Milteliphaster . The superomarginal plates of these species occupy a greater percentage of the total “r” with M. monstrosus displaying superomarginals with approximately 13% of “r” versus Calliaster wanganellensis (H.E.S. Clark 1982) displaying approximately 17–20% and C. chaos of comparable size displaying approximately 15–20% ( Mah 2018).

Ecological Comments. This species was observed in proximity to what appeared to be thousands of disarticulated spines that are thought to have originated from sea urchins in the genus Caenopedina (Pedinidae) ( Fig. 20B ) that were observed in the surrounding area ( Fig. 20A ) (EX1605L1_IMG_20160508T225233Z_ROVHD_URC_ SPO.jpg). A species of Solaster sp. described herein from images was observed hunched over a subject which is thought to have been prey. These urchins were abundant in the dive region and thousands of disarticulated spines were observed to have accumulated in locations throughout the area. It is unclear if Milteliphaster monstrosus n. sp. was also a predator on these urchins, or if perhaps the spination in M. monstrosus n. sp. is itself a defensive mechanism against predators, such as Solaster , which includes species (e.g. Solaster dawsoni ) documented in North Pacific shallow water settings as voracious predators on sea stars and other echinoderms (Mauzey et al. 1969; Van Veldhuizen & Oakes 1981).

Occurrence: Solomon Islands, Esmerelda Bank, Marianas Islands, 410–446 m. Basalt substrate .

Description. Body stellate (R/r=2.56), arms triangular, tapering and elongate ( Fig. 19A ). Disk thick, interradial arcs curved. Collectively, surface is bristling with homogeneous covering of sharp spines.

Abactinal plates round to weakly polygonal, largely homogenous in size and shape across the disk and arms with some proximal carinal plates wide and 1.5 to twice the length of the adjacent plates. Some smaller, more irregularly shaped secondary plates present, interspersed among the others-but approaching the size of the other abactinal plates. Plates are relatively small with approximately 20–30 counted along the arm base. Nearly all plates with a single, prominent spine, approximately 0.8 to 1.2 cm in length, rising well above the body surface and covering disk and arms, distributed widely and evenly ( Fig. 19A, B, C, D , 20A ). Spines are conical with sharp points, uniform in size and shape across the disk and arms with only proximal carinals showing distinct prominence and these only slightly different from spines elsewhere on the abactinal surface. Each spine articulated with a rounded base. Primary circlet plates and spines with no distinction from other disk and arm spines. Abactinal plates lacking spines, smooth, convex with most bearing a distinct, round tubercle on plate surface or else bare ( Fig. 19B ). Each abactinal plate evenly surrounded by 10 to 40 quadrate granules. Two out of three spined plates with a paddle-like pedicellaria with round, clam-shaped valves bearing smooth edges at base. Pedicellariae also present on unspined plates as the single accessory. Madreporite large, weakly convex with well-developed sulci, flanked by approximately 10 abactinal plates.

Marginal plates forming largely lateral edge along periphery ( Fig. 19B, D ), approximately 66–68 from armtip to armtip. Interradial plates elongate but becoming more quadrate distally. All plates with rounded edges. Marginal plates form approximately 13% of the total distance “r” (0.67/5.3). Superomarginals form rounded angle along dorsolateral edge, surface of each plate smooth except for one to four, mostly three, prominent sharp conical spines on raised, rounded bases. Distalmost superomarginals with two spines but projections on surface very prominent. Inferomarginals similar in overall shape, but becoming more rectangular distally. Inferomarginals with one to six, mostly four to five sharp, conical spines on raised bases. Spines projecting laterally and actinally from separate clusters on inferomarginal surface. Marginal plates with peripheral quadrate-shaped granules, 60 to 150 in direct contact around superomarginal and inferomarginal plates. Intermarginal plates irregularly present. Terminal plates triangular with two short spines.

Actinal plates in three full series in chevron arrangement with one or two partial/irregular series distally adjacent to inferomarginals ( Fig. 19C ). Individual plates quadrate to chevron-shaped with rounder, more polygonal plates at contact with inferomarginal plates. Nearly all actinal plates with sharp, pointed spine identical to those on the abactinal surface. Similarly, a clam-shaped pedicellaria ( Fig. 19C inset) is also present on the base of most actinal spines. Where spines are not present, a shorter nub-like spine is present, or prominence is absent and plate surface is smooth and flat. Actinal plates surrounded by quadrate-like granules, 12–50, in one or two rows around the plate periphery. Where actinal plates not covered by spines or granules, surface is bare and smooth.

Furrow spines 6–10 in straight to curved fan ( Fig. 19E ), with furrow spine number increasing distally along arm. Furrow spines vary among each cluster, some more distal clusters with the abradial furrow spine twice as thick relative to the more homogeneous furrow spines in the same series. More distal furrow clusters completely homogeneous with no enlarged members. Adambulacral plates rectangular in shape. Adjacent to furrow spines are one or two large paddle-shaped pedicellariae with round valves ( Fig. 19E ). Two or three large, three proximally then two distally, pointed sharp subambulacral spines in transverse series with one spine directly adjacent to furrow spines and the pedicellariae on the plate surface. Short distinct smooth surface region on adambulacral plate between furrow and transverse subambulacral spine series.

Oral plates with 13 furrow spines increasing in size, to the 14/15th enlarged, blunt oral spine projecting into mouth ( Fig. 19F ). Oral spine is paired on each half of the oral plate. Both with blunt, round edges on the tips of the spines. quadrate in cross-section. Oral plate surface with four prominent sharp conical spines (i.e. two per plate). Remaining oral plate surface with 20–40 round, flattened granules on plate surface in irregular arrangement.

Color in life is light yellow.

Material Examined. Holotype. IE-2007-1280, Solomon Islands, 8º43’S 161º00’E, 410 m, Coll. Richer & Boiszellar, 16 Sept. 2007, SALOMONBOA 3, N/ O Alis, CP 2798 1 wet spec. 1 set spec. R =13.6 r=5.3

Image Examined

Marianas Bank , Marianas Islands. 15.03003078, 145.2230679, 446 m EX1605 L1_IMG_20160508 T231257 Z_ ROVHD _ ASR _OPH.jpg

Figures

FIGURE 19. Milteliphaster monstrosus n. sp. MNHN IE-2007-1280. A. Abactinal surface. Scale bar=20 mm. B. Abactinal surface close-up showing spines. Scale bar=10.0 mm. C. Actinal view. Scale bar=20 mm. Inset showing pedicellariae, approximately 1.5 mm length. D. Abactinal-lateral surface showing spines on abactinal and superomarginal plates. Scale bar=10.0 mm. E. Furrow spines and adjacent adambulacral spination. Circle shows pedicellariae. Scale bar=10.0 mm. F. Oral region, showing actinal plates, spines on oral plates. Scale bar=10.0 mm.

FIGURE 20. Milteliphaster monstrosus n. sp. in situ. Scale unavailable. A. Observed individual from Marianas Bank, Marianas Islands, 446 m. Note spines to the right. B. Marianas Bank, Marianas Islands 446 m. Caenopedina? urchins present in regions adjacent to M. monstrosus.