Clypeaster humilis (Leske, 1778)

Arachchige, Gayashan M., Jayakody, Sevvandi, Mooi, Rich & Kroh, Andreas, 2019, Taxonomy and distribution of irregular echinoids (Echinoidea: Irregularia) from Sri Lanka, Zootaxa 4541 (1), pp. 1-100 : 26-30

Clypeaster humilis (Leske, 1778)

Figures 19–21

1778 Echinanthus humilis Leske : p. 185–189; pl. 17: fig. A; pl. 18: fig. B; pl. 19: figs. A–D. 1948b Clypeaster (Stolonoclypus) humilis (Leske) .—Mortensen: p. 88–94; pl. 17: fig. 1; pl. 28: figs. 1–4; pl. 29: figs. 1–3, 5–8; pl. 30: fig. 1; pl. 40: figs. 2, 3; pl. 47: figs. 3, 8, 11, 15–18.

Material studied. Six denuded specimens: WUSL/EI/10, from Marawila, WUSL/EI/13, from Mount Lavinia, and WUSL/EI/11, EI/12, EI/14 and EI/15 from Negombo, Sri Lanka.

Description. Shape and size —Test pentagonal, large, 70.5–96.9 mm TL, distinctly longer than broad, width 87–93% TL, greatest width at anterior paired petals, more prominently demonstrated in larger specimens; TH 16–21% TL; in larger specimens, all interambulacra (except interambulacrum 5) usually conspicuously indented at test margin; in smaller specimens, posterior end more rounded and all other interambulacra only slightly indented or with regular ovoid outline; oral side more or less flat to slightly concave, particularly near peristome; infundibulum shallow, 6–8% TL in depth.

Apical system —Monobasal, situated closer to centre of aboral surface, 50–53% TL (mean=52% TL, SD=1.2) away from anterior margin; a circular gonopore in each interambulacrum adjacent to madreporic plate; ocular pores small and indistinct.

Ambulacra —Petaloid small, 53–56% TL (mean=55% TL, SD=1.0), considerably elevated; petals more or less broad, elongate ovoid in shape, closed distally; except in petal III, which is slightly open distally in some specimens; opening 1–4% TL; petal III length 27–30% TL (mean 29% TL) and is distinctly longer than other petals; anterior paired petals length range from 23 to 26% TL (mean 25% TL) and are shorter than other petals; posterior paired petals length 27–28% TL (mean 27% TL). Shape of inner pore of each pore pair circular, outer pore elongate, length about twice diameter of inner pore; interporiferous zones conspicuously elevated, bearing 9–16 primary tubercles across widest part of petals; furrow connecting pores of each pore pair deep and sharply delimited; 3–7 primary tubercles on ridges between furrows; ambulacral furrows of oral side simple unbranched and prominent.

Interambulacra —Slightly inflated adapically between petals; densely packed with primary tubercles; all interambulacra on oral surface disjunct and more or less flat.

Tuberculation —Primary tubercles perforate, areoles sunken; miliary tubercles more or less densely and evenly distributed among primary tubercles; density and size (mean size=0.23% TL, N=5) of primary tubercles on aboral surface almost homogenous, primary tubercles on oral surface slightly larger (mean=0.30% TL, N=5), density increasing towards edge of test.

Peristome —Small, 5–8% TL (mean length=6% TL, mean width=7% TL); slightly wider than long, located slightly anterior of centre, c. 48% TL away from anterior margin.

Periproct —Small, 3–6% TL; slightly oval, transversely elongated (mean width=5% TL), situated close to posterior edge, c. 3% TL from posterior margin.

Internal buttressing —Marginal buttressing well-developed and reinforced by dense internal pillar system, best developed close to margin.

Geographic range. Indo-West Pacific, from East Africa & Madagascar ( Brown 1910a; Clark 1923), Red Sea ( Koehler 1922), South East Arabia ( Clark 1925a; Mortensen 1948c), Persian Gulf ( Mortensen 1940), Sri Lanka ( Clark 1915; Herdman et al. 1904), North Australia ( Clark 1946) and East Indies (de Meijere 1904) to Philippine Islands ( Mortensen 1948e; Mooi & Munguia 2014) and South Pacific Islands ( Agassiz 1872).

Bathymetric range. 0–216 m ( Mortensen 1948b).

Observed occurrence in Sri Lanka. Sandy bottoms on the western, and north-western coasts of Sri Lanka at depths of 25–30 m ( Fig. 21 ); first recorded in Sri Lanka by Agassiz (1872). Bathymetric range in Sri Lanka is 15–30 m.

Remarks. An open petal III was observed in each examined specimen with the degree of opening being extremely variable. In addition, specimens with a highly elevated petaloid area have more open anterior petals. This is consistent with similar observations by Mortensen (1948a: 91).

Figures

FIGURE 19. Clypeaster humilis (WUSL/EI/14): A, aboral view; B, oral view; C, lateral view.

FIGURE 20. Details of test features of Clypeaster humilis: A, apical system (WUSL/EI/14); B, oral side, peristome, periproct and interambulacrum 5 (WUSL/EI/14); C, internal buttressing (WUSL/EI/21).

FIGURE 21. Distribution map of Clypeaster humilis recorded in this study.