Ophidiaster colossus, Mah, 2021

Mah, Christopher L., 2021, The East Pacific / South Pacific Boundary: New taxa and occurrences from Rapa Nui (Easter Island), New Caledonia and adjacent regions, Zootaxa 4980 (3), pp. 401-450 : 432-434

Ophidiaster colossus n. sp.

Figure 13A–E

Etymology. The species epithet is colossus for “large” in reference to this species’ great size.

Diagnosis. Strongly stellate species (R/r=5.2–6.6) with tapering arms, thick body, arms and disk massive, with a continuous granular abactinal cover. Papular pores 10–50, 20–30 on most. Enlarged madreporite. Pedicellariae paddle-like with teeth like projections along edge of each valve sitting in hourglass shaped pit. Two furrow spines per adambulacral plate with one enlarged subambulacral spine for every two furrow spines. R up to 14.7 cm.

Occurrence. New Caledonia, 380–480 m

Taxonomic comments. Ophidiaster colossus n. sp. shares most similarity with other massive deep-sea Ophidiaster -like and some Tamaria species. Among these Ophidiaster spp. , this includes the Atlantic Ophidiaster reyssi Sibuet, 1977 , which occurs at 350 m in the Azores. It shares a general resemblance in that it displays the same massive arm and disk and similar plate shape and abactinal and papular pore arrangement. Subambulacral spines of Ophidiaster reyssi are more circular in shape than those in O. colossus which are more teardrop in outline.

This species also invites comparison with the South Pacific Tamaria giffordensis , which co-occurs with Ophidiaster colossus n. sp. in the New Caledonia region. This latter species differs in the number of papular rows (six versus eight in Ophidiaster colossus n. sp.) but also in pedicellariae shape, with T. giffordensis , bearing forceps-like pedicellariae in alveolar pits versus the more paddle-like pedicellariae in O. colossus n. sp. which sit in hourglassshaped pits. Pedicellariae in T. giffordensis are also highly abundant, occurring on nearly every abactinal plate and adjacent to the adambulacral plates, whereas those in Ophidiaster colossus n. sp. are present only on a minority of plates, occurring irregularly on abactinal papular regions and elsewhere (see description). Granulation is much coarser in Ophidiaster colossus (4 to 8 along a 5.0 mm line) than in T. giffordensis (6 to 10 along a 5.0 mm line). There are fine striations in the actinal granulation in T. giffordensis , absent in O. colossus .

Description. Body strongly stellate (R/r=5.2–6.6), Arms tapering, dome-like to polygonal in cross-section. In largest specimen (R=14.7) arms and disk are massive with heavily developed skeleton. Interradial arcs acute forming narrow “fold” between arms. Surface covered by granulated integument. Skeleton tessellate, papulae in eight distinct serial rows.

Disk strongly convex. Serial papular rows converge on disk forming primary circlet, surrounding anus. Papular serial rows forming more irregular network on disk. Granules coarse and densely spaced, eight to ten along a 1.0 cm line. Papulae 10–50 per region on disk (20–30 on most) with larger specimens displaying, on average higher numbers of papulae in larger papular regions. Anus centrally located, flanked by 14–16 blunt spines, triangular in crosssection surrounded by granules coarser than others on disk. Madreporite large (0.7–1.0 cm diameter in specimens examined) with extensive, well-developed sulci, raised above disk surface. Numerous paddle-shaped pedicellariae (approximately 0.5 mm in length) present on disk and arm surface, residing in hourglass-shaped pits on abactinal surface.

Arms displaying eight, serial papular rows with papulae present in similar numbers (20–30 per papular region, but greater in larger specimens). In the largest specimen examined (R= 14.7 cm) the papular arm series become extremely irregular especially as they continue onto plates on the disk. Abactinal arm plates round, irregular to scalar in shape. Lobate plates with three to four lobes. Granules round to polygonal, dense, present at identical densities with those on disk. Pedicellariae, identical to those on disk present on nearly every papular region on arm and covering over papular regions. Pedicellariae densities heaviest interradially between “folds” of tegument between disk and arms and along actinolateral edge adjacent to actinal plate series.

Actinal region broad. Three to four series of actinal plates present on individuals with R<9.0 cm versus the large individual (R= 14.7 cm) showing up to eight series present. On that largest specimen, the number of plates decreases as one progresses more distally along the arm gradually declining to a single series about halfway along the arm. Granules on actinal surface coarser than those on other surfaces, with three to six present along a 1.0 mm line. Granules disk broader still with only two or three present along a 1.0 mm line. Large paddle shaped spines present in moderate abundance on actinal regions, similar in appearance to subambulacrals, approximately one per plate, but up to 20 per interradial region on some individuals (on MNHN IE-2013-6655). Paddle-shaped pedicellariae, similar to those on other surfaces but larger 0.7 mm with four to five teeth per valve, present in regular series along plate series adjacent to adambulacral plates. When present, pedicellariae most abundant proximally on actinal surface disappearing along about 60% of arm length. Pedicellariae sit in corresponding, but deep grooves on the actinal surface with hourglass-like shape. Pedicellariae largest proximally becoming smaller in size along arm. Pedicellariae presence and frequency variable among individuals. The largest individual (R=14.7) shows much fewer pedicellariae present than other smaller individuals (e.g., MNHN IE-2013-6655). Furrow spines, blunt, quadrate in shape with round to angular edges, two per adambulacral plate, quadrate in cross-section. Furrow spines variably offset along series with some showing furrow spines as longer and shorter but with some furrow spines displaying identical height. Approximately one subambulacral present for every two furrow spines.

Adambulacral granulation/spination set away from furrow and subambulacral spines by distinct space, approximately three to five spines/granules present. Pedicellariae paddle-like with wide valves (length=~1.0–2.0 mm) each with rough edges.

Oral plate region weakly convex, rising standing above actinal surface. Furrow spines on oral plate number identically with those on adambulacral plates. Two blunt but pointed spines, quadrate to polygonal in cross-section projecting from oral plate into mouth. Oral plate surface covered by large, coarse granules and three to four paddlelike spines identical to those on other actinal plate regions.

Based on examination of differently sized specimens, smaller (R<8.0) individuals appear to show more conventional ophidiasterid appearance with more cylindrical arms and flattened disk. Larger individuals (R> 9.0) show more convex and irregular disk shape with thicker arms and more strongly expressed deformation on proximal arm regions.

Material examined. Holotype: MNHN IE-2013-4683 . New Caledonia, 24° 55′S, 168° 22′E, 505–514 m. Coll. NORFOLK 2 , CP 2082, 28 Oct. 2003. 1 wet spec. R =14.7, r=2.8.

Paratypes: MNHN IE-2013-6655 . South New Caledonia, banc Jumeau Ouest, 23º43.2′S, 168º16.2′E, 379– 391 m. Coll. Richer, IRD aboard N/ O Alis, campagne LITHIST, St. CP 16. 12 Aug. 1999. 1 dry spec. R =9.5, r=1.8. MNHN IE-2013-6656 (ex EcAh 4998). Norfolk Ridge , New Caledonia. 23º44′S, 168º17′E, 383– 394 m. Coll. Lozouet et al. aboard NORFOLK 1 St. CP 1706. 25 June 2001. 1 wet spec. R =9.9, r=1.5. MNHN IE-2013-6657 (EcAs 12417). South New Caledonia, 23º03′S, 166º59′E, 464– 480 m. Coll. Richer et al. aboard N/ O Alis, campagne HALIPRO 1, CP 877. 31 March 1994. 1 dry spec. R =7.8, r=1.1. MNHN IE-2013-6658 (ex EcAh 5107). New Caledonia, 22º51′S, 167º13′E, 445– 460 m. Coll. C. Vadon aboard N/O Alis, campagne, MUSORSTOM 4 DW 229, 30 Sept. 1985. 1 wet spec. R =7.7, r=1.6. MNHN IE-2013-6806 (EcAs 12417). Stylaster Bank , South New Caledonia, 23º37′S, 167º41′E, 447 m. Coll., LITHIST CP 3, Richer IRD, aboard N/O Alis, 1 dry spec., R =6.7, r=1.0. MNHN IE-2013-9192 . New Caledonia, 22°45′S, 167°4′E to 22°46′S, 167°5′E, 275– 291 m. Coll. KANACONO DW 4729, 20 Aug. 2016, 1 wet spec. R =9.6, r=1.7. MNHN IE-2013-9508 . New Caledonia, 22°45′S, 167°4′E to 22°46′S, 167°5′E, 275– 291 m. Coll. KANACONO, DW 4729, 2 wet specs. R =3.5, r=0.5; R =3.4, r=0.5 .

Figures

FIGURE 13. Ophidiaster colossus n. sp. Holotype MNHN IE-2013-4683 (New Caledonia): A. Abactinal view. Scale bar equals 3.0 cm. B. Abactinal close-up. Scale bar equals 1.0 cm. C. Actinal view with furrow spines in inset. Scale bar equals 3.0 cm, inset scale bar equals 1.0 cm. D. Lateral view. Scale bar equals 1.0 cm. E. Close-up actinal view. Scale bar equals 1.5 cm.