Sculpsitechinus Stara & Sanciu, 2014

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 : 67-70

Genus Sculpsitechinus Stara & Sanciu, 2014

1778 Echinodiscus auritus Leske : p. 138

1948b Echinodiscus auritus Leske. —Mortensen: p. 400–403; pl. 56: figs. 2, 3; pl. 57: fig. 7; pl. 71: figs. 1–5, 10–15, 17, 22. 2014 Sculpsitechinus auritus (Leske, 1778) —Stara & Sanciu: p. 348–351; pl. 21: figs. 1–7.

Material studied. Five denuded tests: WUSL/EI/57, from Silavathurai, Mannar; WUSL/EI/59, from Kirinda; WUSL/EI/128, EI/129, and EI/130, from Mandathiv, Jaffna.

Description. Shape and size —Tests large, 62.6–111.7 mm TL; outline of anterior of test rounded, posterior end truncated with two deep, open lunules; greatest width lies about half-way between apex and posterior edge; TW 98–104% TL; test depressed in lateral view, c. 8% TL in height; margin thin and sharp, anterior margin thicker than posterior; oral side flat, food grooves bifurcating, closely following lunules; oral ambulacra with much more densely packed and smaller tubercles than interambulacra.

Apical system —Monobasal, with four small, circular gonopores; subcentral, 44–51% TL from anterior margin. Ambulacra —Petaloid region medium-sized, length 44–47% TL; petals closed; petal III slightly longer (length 24% TL) and broader (10% TL in width) than others; anterior paired petals (mean 20.4% TL) and posterior paired petals (mean 19.8% TL) similar in length, 20% TL and width, c. 9% TL; interporiferous zones of petals small and about equal in width, c. 3% TL; poriferous zones and interporiferous zones about equal in width; pores are elongate anisopores with sharp furrows that deepen towards outer pore; 7–15 primary tubercles on ridges between furrows; food groves bifurcating close to peristome, with well-developed lateral branches encroaching upon interambulacra; 2 to 3 pairs of plates between ambulacral petals and lunules.

Lunules —Open, slit-like; of variable length; width c. 5% TL; angle between lunules 57° to 60°; lunules surrounded by 3–4 plates per column on oral and 4–5 plates per column on aboral side.

Interambulacra —Disjunction of oral interambulacra 1 to 4 variable, sometimes all in contact, in other specimens all are disjunct; interambulacrum 5 always disjunct. Five post-basicoronal plates in oral interambulacrum 5, two in column a and three in column b.

Peristome —Round to subpentagonal, small, diameter 3–4% TL; 44–46% TL from anterior margin.

Periproct —Small, diameter c. 2% TL; situated close to posterior margin of test, 14–19% TL from posterior edge; distance between periproct and peristome 29–35% TL.

Geographic range. Indo-West Pacific, from Mauritius ( De Loriol 1883), East Africa & Madagascar ( Brown 1910a), Red Sea (Agassiz 18841), South East Arabia ( Mortensen 1948c), Persian Gulf ( Mortensen 1940b), India & Pakistan ( Clark 1925a), Sri Lanka ( Clark 1915; Herdman et al. 1904), Bay of Bengal ( Koehler 1922), East Indies (de Meijere 1904), North Australia ( Clark 1938) to Philippine Islands ( Agassiz 1872), China Sea & South Japan ( Mortensen 1948b).

Bathymetric range. Tidal zone to 50 m ( Mortensen 1948b).

Observed occurrence in Sri Lanka. Specimens were collected from sandy and muddy bottoms at three Sri Lankan localities: Mandathiv on the northern coast, Silavathurai on the north-western coast, and Kirinda on the southern coast at 1, 9, and 27 m respectively ( Fig. 61 ). Bathymetric range of this species in Sri Lanka is 1–29 m. This species was first recorded in Sri Lanka by Döderlein (1888).

Remarks. In contrast to Stara & Sanciu’s ( 2014) description, Sri Lankan S. auritus has two pairs of ambulacral plates between the petal tips and lunules. The periproct is close to the posterior margin (mean=16% TL). However, in Stara & Sanciu’s ( 2014) examples, there are four to five pairs of plates between the petal tips and lunules, and the periproct is farther from the posterior margin (mean=21% TL).

Specimen WUSL/EI/58, collected at a depth of 12 m from Palagala reef ( Fig. 1 ) on the western coast of Sri Lanka, differs from the material described above and may represent a different species (or a hybrid). In contrast to typical S. auritus it has 1) a distinct anterior notch, 2) wide interporiferous zones (4–5% TL), and 3) a markedly structured oral side like in fossil Amphiope ( Fig. 60B, D ; in contrast to the rather flattened oral surface of typical S. auritus ). Specimen WUSL/E1/58 is provisionally identified as Sculpsitechinus sp. until more material of Sculpsitechinus from Sri Lanka becomes available and the degree of intraspecific variation of the Sri Lankan population is better understood.

S. auritus can be easily distinguished from other astriclypeids occurring in Sri Lanka ( E. bisperforatus and E. cf. truncatus ) by its open lunules.

Figures

FIGURE 1. Map of collection localities (BT1—Baththalangunduwa 1, BT2—Baththalangunduwa 2, CA—Casuarina Beach, CH—Chaddy Beach, ET—Etalai, HM—Hambantota, HR—Hiriketiya, KL—Kalmunai, KM—Kamburugamuwa, KT—Kattankudy, KI—Kirinda, MN—Mandathiv, MR—Marawila, ML—Mount Lavinia, MU—Mulathiv, NE1—Negombo 1, NE2—Negombo 2, NL—Nilwella, PE—Periyapaduwa, PO—Polhena, SL—Silavathurai, TB—Thennadi Bay, TR—Trincomalee, VL—Velvatithurai; see Appendix 1 for more information).

FIGURE 60. Sculpsitechinus auritus (A and C, WUSL/EI/59) and Sculpsitechinus sp. (B and D, WUSL/EI/58): A–B, aboral and C–D, oral views.

FIGURE 61. Distribution map of Sculpsitechinus auritus recorded in this study.