Taxonomy and distribution of irregular echinoids (Echinoidea: Irregularia) from Sri Lanka Author Arachchige, Gayashan M. Author Jayakody, Sevvandi Author Mooi, Rich Author Kroh, Andreas text Zootaxa 2019 2019-01-03 4541 1 1 100 journal article 27715 10.11646/zootaxa.4541.1.1 9c3fecf1-4e11-4c79-a908-e0a5abbaf3ca 1175-5326 2617460 B11E734C-218B-418C-84E6-719AB3C58AFF 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. FIGURE 19. Clypeaster humilis (WUSL/EI/14): A, aboral view; B, oral view; C, lateral view. 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. 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. 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) .