Metalia, Gray, 1855

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 : 78-83

Metalia sp.

Figures 68–71

Material studied. Four denuded tests: WUSL/EI/85 and EI/86, from Kamburugamuwa and WUSL/EI/138 and EI/ 139 from Negombo 1, Sri Lanka; one complete specimen, WUSL/EI/85 and three broken specimens.

Description. Shape and size —Test large, robust 121.0– 144.3 mm TL; width 89–92% TL; height approximately 50% TL; test oval in outline when viewed aborally; no ambital notch in ambulacrum III.

Apical system —Ethmolytic, with four large circular gonopores; madreporite expanding beyond posterior oculars; length 4–5% TL; situated anteriorly, 40–43% TL away from anterior margin.

Ambulacra —Ambulacrum III narrow and flush with test, with pore pairs not differentiated to support respiratory tube feet; paired ambulacra distinctly petaloid; petals deeply sunken towards ambitus, straight; each anterior paired petal extending 92–96% of corresponding test radius; anterior paired petals forming angle of 135–145°; anterior and posterior paired petals about equal, length 39–42% TL, width 5–6% TL; angle between anterior paired petals slightly larger than angle between posterior paired petals; interporiferous zones narrow, of equal width, c. 1% TL; pores large, about equal in size, connected by deep groove; adorally well-developed phyllodes occur, featuring 17–18 pores in the anterior paired ambulacra, 8 in posterior paired ambulacra, and 10–11 in ambulacrum III.

Tuberculation —Aboral surface densely packed with primary tubercles; larger tubercles inside peripetalous fasciole, bordering ambulacrum III and scattered over posterior interambulacra, usually arranged in short, oblique bands; primary tubercles on oral side larger than aboral ones; primary tubercles in plastron much smaller than those of oral interambulacra 1, 2, 3 and 4.

Fasciole —Peripetalous fasciole well-developed, closely outlining petals; fasciole strongly indented between petals; subanal fasciole shield-shaped, wider than long; length 16–18% TL, width 22–27% TL; tapering to one point at posterior edge of plastron; upper part shallowly indented; usually four pore pairs enclosed on each side of subanal fasciole; anal branches extending aborally to points even with midpoint of periproct.

Plastron —Narrow, elongate, width 19–20% TL, slightly keeled.

Peristome —Kidney-shaped; situated anteriorly, c. 21% TL from anterior margin of test; about twice as wide as long; moderately large, length c. 6% TL, width c. 14% TL; from labrum pointed and overhanging peristome.

Periproct —Vertically elongate; pointed aborally and orally; large, length 10–11% TL, width 5–7% TL; region just oral to periproct concave.

Observed occurrence in Sri Lanka. Specimens were collected at 20–25 m from sand patches between patch reefs in Kamburugamuwa, southern coast, and from 27–28 m at Negombo, western coast of Sri Lanka ( Fig. 71 ).

Remarks. As noted by one of us (R. Mooi, unpublished and Askin & Mooi 2017), these specimens differ from the 10 known, extant congeners, M. angustus de Ridder, 1984 , M. dicrana H.L. Clark, 1917 , M. kermadecensis Baker & Rowe, 1990 , M. latissima H.L. Clark, 1925 , M. nobilis Verrill, 1867 , M. persica ( Mortensen, 1940) , M. robillardi (de Loriol, 1876) , M. spatagus (Linnaeus, 1758) , M. sternalis (Lamarck, 1816) , and M. townsendi ( Bell, 1904) .

The new species lacks a notch in ambulacrum III, a condition that strongly differs from that in the following species: M. angustus , M. kermadecensis , M. latissima , M. persica , and M. robillardi . The lack of coalescence between the aboralmost regions of the posterior paired petals is very different from the situation seen in M. sternalis . M. townsendi differs in having a subcentral position of the apical system, and much lower anterior end of the test.

Forms that lack the anterior notch, lack the coalescence, and have the apical system at least somewhat anterior, as in the new species, include M. dicrana , M. nobilis , and M. spatagus .

M. nobilis , the only Metalia known from the Americas, has small petals relative to its congeners. In addition, the periproct in Metalia n. sp. is directed downwards and is not fully visible from the aboral side. This is not only unlike M. nobilis , it is not like M. spatagus either, which has a more vertical posterior region with at least part of the periproct visible in aboral view. This is also true for M. dicrana , which is distinguished from all other Metalia by its peculiar double point along the sternum just adoral to the subanal fasciole (Mooi, unpubl. data). Therefore, the specimens are very unlike M. dicrana .

The Sri Lankan specimens of this new form have a very distinctive, concave region below the periproct which has not been noted in other Metalia species ( Fig. 70 ), although it does occur to some degree in some of the species (Mooi, unpubl. data). As discovered by Askin & Mooi (2017) using molecular techniques, it would appear that this is a new species. It was depicted by van Noordenburg (2008), but remains unnamed pending further work on the abundant material at the California Academy of Sciences and the Natural History Museum, Vienna .

Variation in the path of the peripetalous fasciole was noted in collected specimens. WUSL/IE/E85 shows shallow aborally-curved segments in interambulacrum 4, and one sharply defined indentation in interambulacrum 1 ( Fig. 68 , A).

Figures

FIGURE 68. Metalia sp. (WUSL/EI/85): A, aboral view; B, oral view; C, lateral view; D, anterior view; E, posterior view.

FIGURE 69. Metalia sp. (WUSL/EI/138), aboral view.

FIGURE 70. Metalia sp. (WUSL/EI/85): A, sternal view; B, subanal fasciole view.

FIGURE 71. Distribution map of Metalia sp. recorded in this study.