Metalia sternalis (Lamarck, 1816)

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 : 75-78

Metalia sternalis (Lamarck, 1816)

Figures 66 , 67

1816 Spatangus sternalis Lamarck : p. 31.

1951 Metalia sternalis (Lamarck) .—Mortensen: p. 535–537; pl. 64: figs. 13, 17, 19, 22.

Material studied. Seven denuded tests: WUSL/EI/70 and EI/71, from Baththalangunduwa 2 and WUSL/EI/122, EI/123, EI/124, EI/125, and EI/126 from Silavathurai, Sri Lanka.

Description. Shape and size —Test large, 60.6–84.5 mm TL; width 89–92% TL; height 55–59% TL; outline of test elliptical to slightly angular in aboral view, with anterior slope more steeply angled forward than the posterior slopes to the periproct; slightly truncated posteriorly; anterior notch deep and broad.

Apical system —Ethmolytic, with four large circular gonopores; posterior paired pores about 1.5 times larger than anterior ones; madreporite expanding beyond posterior oculars; situated anteriorly, 30–37% TL from anterior margin.

Ambulacra —Ambulacrum III narrow and depressed aborally; paired ambulacra distinctly petaloid, deeply sunken towards margin, broad, elongate, somewhat rounded and closed distally; anterior paired petals extend laterally forming an angle of c. 175° from each other, c. 65% of TW; petal III length c. 33% TL (SD=2.3, N=7); interporiferous zone broad, of equal width in each petal; respiratory pores large, pores within one pair about equal in size, connected by deep groove; posterior paired petals 1.25 times longer than anterior ones; adapically posterior paired petals narrow; at about one quarter petal length, inner pore pairs rudimentary; posterior paired petals coalescing, elongate, slightly diverging posteriorly; at about half petal length, two poriferous zones are equal width, up to petal tip.

Interambulacra —Aboral interambulacrum 5 raised, slightly convex to flat; but not keeled, not projecting above periproct; posterior end almost vertically truncated; interambulacra densely packed with perforate crenulate primary tubercles, larger tubercles inside peripetalous fasciole, particularly along petals; adapically no primary tubercles in interambulacrum 5 between posterior paired petals.

Fasciole —Peripetalous fasciole well-developed, closely outlining petals, with indentations between petals; subanal fasciole broad, shield-shaped, wider than long; length 26–29% TL and width 31–39% TL; left and right halves joining at point near posterior edge of plastron; five to six pore pairs inside subanal fasciole on each side; anal branches present, extending aborally to points even with adapical margin of periproct.

Plastron —Narrow, elongate, width 25–31% TL, slightly keeled.

Peristome —Kidney-shaped; very close to anterior edge, 19–27% TL from anterior margin of test; about twice as wide as long; moderately large, length 8–10% TL, width 17–19% TL; labrum narrow and wide.

Periproct —Elongate along anterior-posterior axis; pointed above and below; large, length 15–20% TL and width 8–11% TL.

Geographic range. Indo-West Pacific, from Islands of West Indian Ocean ( Bell 1884), Mauritius ( De Loriol 1883), East Africa & Madagascar ( Mortensen 1948c), Red Sea ( Fourtau 1904), India ( Bell 1888), Bay of Bengal ( Clark 1925a), East Indies (de Meijere 1904), North Australia ( Clark 1925a) to NSW, Australia ( Miskelly 2002), Philippine Islands ( Mortensen 1948e; Mooi & Munguia 2014), China & South Japan ( Döderlein 1885), South Pacific Islands ( Agassiz 1872) and Hawaiian Islands ( Agassiz 1872).

Bathymetric range. Littoral zone to 90 m ( Mortensen 1951).

Observed occurrence in Sri Lanka. Specimens were collected from a sandy bottom with sea grass beds in Silavathurai and Baththalangunduwa, north-western coast of Sri Lanka, at depth range of 10–20 m ( Fig. 67 ). This species was first recorded from Sri Lanka by Clark (1915).

Remarks. M. sternalis can be distinguished from Metalia sp. by having a coalescence between the aboralmost regions of the posterior paired petals.

Figures

FIGURE 66. Denuded test of Metalia sternalis: A, aboral view (WUSL/EI/70); B, oral view (WUSL/EI/70); C, lateral view (WUSL/EI/70); D, posterior (WUSL/EI/72); E, sternal view (WUSL/EI/72).

FIGURE 67. Distribution map of Metalia sternalis recorded in this study.