Echinocyamus bisperforatus Leske 1778

Echinodiscus bisperforatus Leske, 1778

Figures 50, 51A, 52–54

1778 Echinodiscus bisperforatus Leske: p.132–133; pl. 21: figs. A–B.

1948b Echinodiscus bisperforatus Leske. —Mortensen: p. 406–410; pl. 68: figs. 2, 6–8; pl. 71: figs. 6–9, 18.

Apical system —Subcentral, 48–52% TL away from anterior margin, monobasal with four small circular gonopores.

Ambulacra —Well-developed short petals, more or less closed distally; petaloid area broad, mean petaloid length approximately 44% TL (SD=2); mean width approximately 46% TL (SD=2); petal III slightly longer than other petals, c. 24% TL (SD=1); anterior paired petals c. 21% TL (SD=1); posterior paired petals distinctly shorter than others, c. 17% TL (SD=1); petal III and anterior paired petal slightly wider (mean 13% TL) than posterior paired petal (mean 12% TL); pores in pore pairs distinctly conjugated, with sharply delimited furrows that deepen towards outer pore; 12 to 16 primary tubercles on ridges between furrows. Two slit-like lunules in posterior ambulacra; lunule length c. 34% TL and lunule width c. 3% TL; angles between two lunules range from 108° to 117°; adapical end of lunule pointed anteriorly and distal end pointed posteriorly; single pair of plates between lunules and tips of posterior petals (Fig. 53A); food grooves bifurcating close to peristome, with more or less welldeveloped lateral branches encroaching upon interambulacra.

Interambulacra —Anal groove distinct; two plates per column in oral interambulacrum 5; oral interambulacra usually disjunct, but in some cases interambulacrum 2 or 3 (rarely both) are contiguous (Fig. 52).

Tuberculation —Oral ambulacra with much more densely packed, small tubercles than in interambulacra.

Peristome —Round to subpentagonal, small, 3–4% TL in diameter; slightly anterior of test centre, 31–36% TL from anterior margin.

Periproct —Small, 1–3% TL in diameter; close to posterior margin of test, 6–8% TL from posterior edge; opens along suture between 5.a.2/5.b.2 or at junction of 5.a.2/5.b.2/5.a.3 or 5.a.2/5.b.2/5.b.3 of post-basicoronal plates (Fig. 53).

Geographic range. Indian Ocean, from Mauritius (Clark 1923), East Africa & Madagascar (Agassiz 1872), Red Sea (Clark 1925a), Sri Lanka (Bell 1887a), Bay of Bengal (Koehler 1922) to East Indies (Mortensen 1948b).

Bathymetric range. Intertidal zone to 13 m (Koehler 1922).

Observed occurrence in Sri Lanka. Specimens were collected from a muddy bottom at 1–2 m along the north-western coast (Periyapaduwa) and at 1 m along the eastern coast (Kaththankudi) of Sri Lanka (Fig. 54). First recorded in Sri Lanka by Bell (1882).

Remarks. There is high variability in the position of the periproct (Fig. 53). Therefore, this is not a reliable character to distinguish E. bisperforatus from other species in the genus.

The suture between plate 5.a.2 and 5.b.2 is either nearly parallel to the anterior-posterior axis, or distinctly oblique to this axis (close to 45°, see Fig. 55). In the former case, it joins the adradial suture of plate V.b.2 and in the latter case, V.b.3. Otherwise, the studied E. bisperforatus specimens are very similar. This undermines the validity of the genus Paraamphiope recently established solely on this feature by Stara and Sanciu (2014).