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 Jacksonaster sp. 2 Figures 39 , 40B , 41 Material studied. Two denuded tests: WUSL/EI/25, EI/29 from Silavathurai, northern coast of Sri Lanka . FIGURE 39. Jacksonaster sp. 2 (A–C, WUSL/EI/25; D, E, WUSL/EI/29): A, D, aboral view; B, E, oral view; C, lateral view. FIGURE 40. Comparison of apical system and petaloid area of Jacksonaster sp. 1 (A, WUSL/EI/26) and Jacksonaster sp. 2 (B, WUSL/EI/29). Description. Shape and size —Test elliptical to rounded; medium-sized, 32.1 mm and 43.0 mm TL, longer than broad, width 87% and 89% TL; greatest width coinciding with anterior paired petals; TH 18% TL; oral side flat; edge thick, anterior edge thickness approximately 12% TL, posterior edge slightly thinner than anterior edge of test. Apical system —Subcentral, 49% and 50% TL from anterior margin of test; with five circular gonopores; hydropores in sinuous groove. Ambulacra —Petaloid area large, 73% and 77% TL, slightly elevated; petals narrow, closed distally; outer pore of each pair more elongate than inner pore; pores conjugate, but conjugating furrows inconspicuous; anterior unpaired petal slightly longer than others, 35% and 38% TL; anterior paired petals shortest, 31% and 32% TL; posterior paired petals slightly shorter than petal III 34 % and 35% TL; all petal widths similar, approximately 12% TL; width of poriferous zone IIIa 128% and 103% of interporiferous zone at 2/3 of the petal length; food grooves simple, unbranched, reaching up to 64% and 71% of corresponding test radius of ambulacrum III. Interambulacra —On oral side, interambulacra narrow, forming straight bands separating broad ambulacra. Tuberculation —Aboral primary tubercles small and densely distributed among numerous miliary tubercles; on oral surface, primary tubercles larger and sparse relative to those on aboral surface. Peristome —Small, length approximately 7% TL, width approximately 9% TL; rounded to pentagonal; situated slightly anterior of centre, 46% and 48% TL from anterior margin of test. Periproct —Small, length 5% and 7% TL; transversely elongate; width 6% and 8% TL; lying on oral surface 13% and 14% TL from posterior margin of test. Observed occurrence in Sri Lanka . Denuded tests were collected from Silavathurai, northern coast of Sri Lanka at 28 m ( Fig. 41 ). Remarks. The two specimens of Jacksonaster sp. 2 were collected from a different locality to Jacksonaster sp. 1. They can be distinguished from Jacksonaster sp. 1 in having a more elliptical, rounded test outline, thicker test margin, relatively larger petaloid area, relatively closed petals, wider interporiferous zones ( Fig. 40B ) and the periproct situated further from the posterior margin. Using the key of Clark and Rowe (1971) , these specimens resemble Jacksonaster depressum . However, as stated in Mortensen (1948b) , the posterior end of Jacksonaster depressum is usually “reenteringly curved” (indented). This feature was not observed in Jacksonaster sp. 2. These specimens are similar in outline to Laganum joubini , but L. joubini has a more anterior periproct and more anterior apical system. Jacksonaster in Sri Lanka requires further examination and revision, perhaps through future molecular analyses.