Jacksonaster Lambert in Lambert & Thiery 1914
Creators: name: Arachchige, Gayashan M.
name: Jayakody, Sevvandi
name: Mooi, Rich
name: Kroh, Andreas
Publisher: name: Zenodo
Year: 2019
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Echinoidea
Clypeasteroida
Laganidae
Jacksonaster

description: 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).
description: Published as part of Arachchige, Gayashan M., Jayakody, Sevvandi, Mooi, Rich & Kroh, Andreas, 2019, Taxonomy and distribution of irregular echinoids (Echinoidea: Irregularia) from Sri Lanka, pp. 1-100 in Zootaxa 4541 (1) on pages 44-45, DOI: 10.11646/zootaxa.4541.1.1, http://zenodo.org/record/2617460