Echinolampas alexandri de Loriol, 1876

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 : 19-22

Echinolampas alexandri de Loriol, 1876

Figures 13 , 14A, C , 15A , 16

1876 Echinolampas alexandri de Loriol : p. 4; pl. 1: figs. 1–3.

1948a Echinolampas Alexandri de Loriol. —Mortensen: p. 282–286; pl. 2: figs. 20–24; pl. 3: figs. 1–3; pl. 14: figs. 1, 4, 7.

Material studied. Ten denuded tests: WUSL/EI/1, from Mount-Lavinia, WUSL/EI/2 and EI/110, from Negombo 1, WUSL/EI/107 and EI/108, from Baththalangunduwa 1, WUSL/EI/109, from Silavathurai, WUSL/EI/104, EI/ 105 and EI/106, from Kirinda, WUSL/EI/111 from Hambantota, Sri Lanka.

Description. Size and shape —Test moderately large, 44.3–63.0 mm TL; broad, almost circular in outline, TW 90–99% TL; distinctly inflated, TH 58–66% TL; posterior margin rounded to indistinctly pointed.

Apical system —Monobasal with four gonopores; situated anterior of centre 34–39% TL from anterior margin of test.

Ambulacra —Petals with unequal poriferous zones; poriferous zone IIIa of petal III, usually 2–5 pore pairs longer than IIIb; poriferous zones in anterior paired petals of very different length, posterior poriferous zones (IIa, IVb) in each petal 7 to 20 pore pairs longer; difference in posterior paired petals often not as pronounced, posterior poriferous zones (Ia, Vb) in each paired petal 4 to 9 pore pairs shorter than in anterior ones; poriferous zones parallel in anterior and posterior paired petals but converging distally in anterior paired petals; transversely elongated outer pores and circular inner pores in respiratory pore pairs; petal III shortest; posterior paired petals extending c.74%, anterior paired petals 73% and petal III 60 % of corresponding test radius; at their widest point, petals bear 4 to 6 tubercles across interporiferous zone; phyllodes typically consisting of inner series with up to 3 pores per column, outer series with up to 9; phyllodes contain medial double row of up to 10 sphaeridial pits.

Interambulacra —Bourrelets indistinct; oral naked zones absent.

Peristome —Small, oval, transversely elongated; length 9–10% TL and width 12–17% TL; deeply sunken with steep-sided infundibulum; located anterior of centre, approximately 37% TL from anterior margin of test.

Periproct —Inframarginal, slightly larger than peristome, length 8–13% and width 13–19% TL; situated closer to posterior margin, 2–3% TL from posterior margin of test.

Geographic range. Indo-West Pacific, from Islands of West Indian Ocean ( Bell 1909; Mortensen 1948d), Mauritius ( Clark 1925a), Ceylon area ( Clark 1917), Bay of Bengal ( Koehler 1922) and East Indies ( Mortensen 1948a) to Coral Sea ( Miskelly 2002) and South Pacific Islands (Clark 1952).

Bathymetric range. 8–365 m ( Mortensen 1948a).

Observed occurrence in Sri Lanka. This species typically occurs in sandy areas between patch reefs on the western, north-western, and southern coasts of Sri Lanka, at a depth range of 9–28 m ( Fig. 16 ). This species was first reported from Sri Lanka by Clark (1915), but has not been recorded again until the present study.

Remarks. Based on general shape, two groups of Echinolampas could be distinguished in Sri Lanka. The first group is characterized by a more circular outline, elongated outer pores in the petals, parallel poriferous zones in the posterior petals, and indistinct bourrelets ( Fig. 14 , A and C). In the second group, the outline is more ovoid, the outer pores are circular, the posterior petal pore zones converge and the bourrelets are distinct ( Fig. 14 , B and D). In addition, the first group does not have conspicuous oral naked zones ( Fig. 15 , A), while the second group does ( Fig. 15 , B). The first group best matches descriptions of E. alexandri alexandri , being closer to the type material of de Loriol (1876) than to later material from the Siboga Expedition described by Mortensen (1948a) under the name E. alexandri sibogae . In comparison to the syntypes of de Loriol (illustrated in Mortensen 1948a), the present material has a distinctly higher test, but this feature appears to be variable. Mooi (1990: fig. 6b) illustrated a prominent naked median zone in E. alexandri , which is also true for one of the syntypes. This feature, while showing little variation in the present material, seems to display intraspecific variation as well, and can thus only be used in conjunction with the additional characters listed above.

The second group best matches E. ovata , see below.

Figures

FIGURE 13. Echinolampas alexandri (WUSL/EI/1): A, aboral view; B, oral view; C, lateral view.

FIGURE 14. Comparison of pore-pairs (A and B) and peristome (C and D) between Echinolampas alexandri (A and C, WUSL/EI/1) and Echinolampas ovata (B and D, WUSL/EI/3).

FIGURE 15. Comparison of interambulacrum 5 between Echinolampas alexandri (A, WUSL/EI/1) and Echinolampas ovata (B, WUSL/EI/3).

FIGURE 16. Distribution map of Echinolampas alexandri recorded in this study.