Jacksonaster, Lambert in Lambert & Thiery, 1914

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 : 44-45

Jacksonaster sp. 1

Figures 36–38 , 40A

Material studied. Seven denuded tests: WUSL/EI/23, EI/26, EI/27, EI/140, EI/141, and EI/142 from Thennadi Bay, and WUSL/EI/27 from Chaddy Beach, Jaffna, Sri Lanka.

Description. Shape and size —Test pentagonal, posterior end gently indented; medium-sized, 30.0– 47.2 mm TL, slightly longer than broad, width 88–93% TL, larger specimens more elongate than smaller specimens; greatest width at end of anterior paired petals; height 15–17% of TL; oral side flat; edge thin, 7–10% TL, posterior edge slightly thinner than anterior edge.

Apical system —Subcentral, approximately 52% TL from anterior margin of test; with five circular gonopores; hydropores in sinuous groove.

Ambulacra —Petaloid area large, 67–71% TL, slightly elevated; petals narrow, slightly open distally; pore series straight; pores elongate anisopores; outer pores of pore pairs greatly elongated transversely relative to inner pores; pores conjugate, but connecting furrows shallow; petal III slightly longer than others, approximately 35% TL (SD=2); anterior paired petals shortest, approximately 31% TL (SD=1); posterior paired petals slightly shorter than petal III, approximately 33% TL (SD=2); all petal widths similar, approximately 12% TL; width of poriferous zone IIIa 75–89% of interporiferous zone width at 2/3 of the petal length; food grooves simple, unbranched, lying along each oral perradius, up to 62–70% of corresponding test radius in ambulacrum III.

Interambulacra —Oral interambulacra narrow, forming straight bands separating broad ambulacra.

Tuberculation —Primary tubercles small and densely distributed among numerous miliary tubercles on aboral side; on oral surface, primary tubercles larger and sparse relative to those on aboral surface; primary tubercles of oral interambulacra close to peristome slightly larger than those of oral ambulacra; smallest primary tubercles near food grooves.

Peristome —Small, length 6–8% TL, rounded to pentagonal, width 5–8% TL; situated slightly anterior of centre, 45–48% TL from anterior margin of test.

Periproct —Small, length 5% TL, transversely elongate to rounded, width 6–7% TL; lying 11–12% TL from posterior margin of test.

Observed occurrence in Sri Lanka. Specimens were collected on the beach at Chaddy Beach , Jaffna , northern coast and Thennadi Bay, eastern coast of Sri Lanka. This species was also observed in Mount Lavinia (at 30 m) and Negombo 1 (at 27 m), western coast and at Mulathiv (at 10 m), northern coast of Sri Lanka ( Fig. 38 ).

Remarks. Considering the characters pointed out by Mortensen (1948b), these specimens best match Jacksonaster depressum tenue (Mortensen, 1948) . The latter subspecies has a thinner test and margin, and narrower petals with straighter pore series than usually found in J. depressum from other parts of its range.

Jacksonaster sp. 1 can be distinguished from Jacksonaster sp. 2 by having a much thinner test, thinner test margin, and slightly open petals with straight pore series. In addition, Jacksonaster sp. 1 has narrower poriferous zones than Jacksonaster sp. 2, being approximately 81% of the width of the interporiferous zone in the former and 116% in the latter ( Fig. 40A ).

Figures

FIGURE 36. Jacksonaster sp. 1 (WUSL/EI/23): A, aboral view; B, oral view; C, lateral view.

FIGURE 37. Jacksonaster sp. 1 (WUSL/EI/26), oral and aboral tuberculation: A, aboral side; B, oral side.

FIGURE 38. Distribution map of Jacksonaster sp. 1 recorded in this study.

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).