Plinthaster dentatus

Plinthaster dentatus (Perrier, 1884)

Figure 21

Pentagonaster dentatus Perrier, 1884: 242–243, pl. 8, fig. 3 (instead of pl. 3, fig. 8 as stated in p. 242).

Plinthaster dentatus — Clark & Downey 1992: 260, pl. 61, figs. D–E; Sumida et al. 2001: 26, fig. 9; Entrambasaguas 2008: 55; Benavides-Serrato et al. 2011: 168; Soaréz 2016: 78; Sandino et al. 2017: S294; Serrano et al. 2017; Borrero-Peìrez et al. 2019: 5; Madeira et al. 2019: 90; Mah 2020b: 232, fig. 14D.

Material examined (1 spec, 20 mm R). BRAZIL. Bahia, Morro de São Paulo (13°42’S; 38°64’W), 801 m, 19.vi.2000, 1 spec, R 20 mm (EQMN 2346).

Comparative material. GRENADA. Off Grenada, 762 m, 28.ii.1879, 1 spec, R 34 mm (MCZ AST 408, lectotype); BRAZIL. Rio de Janeiro, 1227 m, 30.xii.1887, 1 spec, R 15 mm (YPM IZ 9526. EC).

Description (R 20 mm). Body stellate, flat, arms short (Fig. 21A–B); R/r 2.0; 7 SM plates; R/SM# 2.86. Abactinal plates polygonal, flat, bare in center and surrounded by one row of granules (Fig. 21C). Some plates with pedicellariae and crystal bodies (Fig. 21D). Plates irregularly arranged in the center of disc, regularly arranged towards the arms and absent at arm tip. Madreporite large (Fig. 21A, D). Terminal plate large, naked, tapering distally (Fig. 21E). Papulae large, single. Marginal plates block-like, with scattered granules (note that plates in specimen analyzed are abraded), forming an ambitus and surrounded by one row of granules; 14 per interradius. Superomarginal plates naked; three distalmost pairs in contact medially (Fig. 21E). Actinal areas large. Inferomarginal plates similar to superomarginal plates, but with some granules along edge. Actinal plates flat, large, covered with regularly spaced, coarse granules (Fig. 21F). Five blunt adambulacral spines. Two rows of subambulacral spines, smaller than adambulacral spines: first row with 3–4 spines, second row with 3–5 spines per plate (Fig. 21G). Oral plates with nine subprismatic spines (Fig. 21H); spines increasing in size toward mouth. Bivalved pedicellariae on actinal plates, near ambulacral furrow.

Coloration. No record of coloration of in vivo specimens from this region. Halpern (1970b) mentioned that live specimens have an orange abactinal region and creamy actinal. Specimen in ethanol is beige with brown spots.

Distribution. Pacific Ocean: New South Wales, Australia and Kermadec Islands, New Zealand. Eastern Atlantic: Ireland, Bay of Biscay, Spain, Azores, Canary Islands, Morocco, Cape Verde, Liberia, Gulf of Guinea. Western Atlantic: U.S.A. (NC, SC, FL, LA, TX), The Bahamas, Mexico, Cuba, Dominican Republic, Jamaica, Anguilla, Trinidad and Tobago, Honduras, Nicaragua, Panama, Colombia, Venezuela, Uruguay (Clark 1941; Gray et al. 1968; Halpern 1970b; Sibuet 1977; Clark & Downey 1992; Clark & McKnight 2001; Alvarado & Solís-Marín 2013; Soaréz 2016; Sandino et al. 2017; Serrano et al. 2017; Borrero-Peìrez et al. 2019; Madeira et al. 2019; Mah 2020b). BRAZIL: Maranhão, Bahia, Espírito Santo (Halpern 1970b; Ventura et al. 2007; Gondim et al. 2014) and Rio de Janeiro (YPM IZ 9526.EC, not analyzed). Depth. 229–2910 m (Clark & Downey 1992).

Biological notes. Plinthaster dentatus is a deep-water species and its biology is not well studied. This species feeds on foraminifera, crinoid arms, corals, encrusting organisms and geodiid sponges (Halpern 1970a; Mah 2020b).

Lectotype. MCZ 408, by subsequent designation of Halpern (1970b). Perrier (1884) mentioned three specimens in his paper, two from off Cuba (one of them R 14 mm) and one from off Grenada (MCZ 408; about R 34 mm), but we could not locate the specimens from off Cuba.

Type locality. Off Grenada.

Remarks. Plinthaster dentatus is a widely distributed species and the intraspecific variation described is remarkable. Unfortunately, most descriptions do not detail which variation was due to ontogeny. Sumida et al. (2001) provided morphological data on specimens from Ireland ranging from R 1.1 to 7.6 mm and concluded that juveniles of P. dentatus have isometric growth. Next, we compare the specimens described by them with our specimen and the specimens described by Perrier (1884; R 14 mm and 34 mm), Halpern (1970b; R 45 mm), Clark & Downey (1992; R 45 mm) and Mah (2018; R 55–70 mm).

The number of marginal plates per interradius increases from 2–6 in R <3.6 mm, to 10 in R 14 mm (Perrier 1884), to 14 in R 20 mm, to 16 in R 34 mm (lectotype), to up to 20 in R 55–70 mm. Halpern (1970b) and Downey (1973) mentioned that the inferomarginal plates may be smaller and more numerous than the superomarginal plates. The number of superomarginal plates in contact varies from none in R 2.28 mm, to one pair in R 3.6 mm, to three pairs in R 20 mm, reaching five pairs.

The number of spines also increase with growth as following: the number of adambulacral spines increases from 3–4 spines in specimens up to R 7.6 mm, to five spines in R 14–20 mm, to 6–8 spines in R 34–45 mm; the number of subambulacral spines increases from one spine in R <7.6 mm, to 3–4 spines in the first row in R 20 mm, to 4–6 spines in the first row in R 34–45 mm; and the number of oral spines increases from 6–8 per plate in R 1.19 mm, to ten in R 2.27 mm to 18–20 in R 20–45 mm. The number of subambulacral rows varies from one in R <7.6 mm to 2–3 in R 20–45 mm.

Finally, the shape of the body (from pentagonal to stellate; which greatly affects the R/r ratio), the presence and distribution of granules in the marginal plates, the shape of the marginal plates (flat to tumid, thin to thick, round to rectangular), and the number (from none to several), placement (abactinal, actinal or both surfaces) and morphology (number of valves) of pedicellariae show great interspecific variability (Perrier 1884; Halpern 1970b; Clark & Downey 1992; present paper).

Plinthaster dentatus differs from the other species by having 12–20 marginal plates per interradius (vs. 6–8 marginal plates in P. lenaigae and P. untiedtae, and 8–10 in P. ceramoidea) (Mah 2018).