Peronella oblonga Mortensen, 1948

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 : 53-57

Peronella oblonga Mortensen, 1948

Figures 45–49

1948a Peronella oblonga Mortensen : p. 71.

1948b Peronella oblonga Mortensen. —Mortensen: p. 299–300; pl. 51: figs. 33, 34.

Material studied. Seven denuded tests: WUSL/EI/38, EI/39, EI/41, EI/48, EI/49, EI/52, and EI/143 from Casuarina Beach, Jaffna.

Description. Shape and size —Test regularly oval in outline, with a pointed to truncated posterior end; small to medium-sized, 18.03–34.57 mm; longer than broad, width 87–90% TL; height 15–20% TL; oral side slightly concave; margin distinctly thickened, with a distinct depression between margin and slightly elevated central part; anterior edge thicker (approximately 14% TL; SD=1), than posterior edge of test (approximately 12% TL; SD=1).

Apical system —Subcentral, 49–50% TL away from anterior margin; with four circular gonopores.

Ambulacra —Petaloid area large, length 55–59% TL, slightly elevated; petals fairly broad (50–55%TL in width), closed distally; petal III slightly longer than others, c. 26% TL (SD=1); anterior paired petals shorter than others, c. 23% TL (SD=1); posterior paired c. 25% TL (SD=1); petal widths and width of interporiferous zones of anterior paired and posterior paired petals similar, c. 13% TL and 8% TL, respectively; outer pore larger than inner pore; pore pairs distinctly conjugate; ridges between consecutive pore pairs carry single, regular series of 6–8 small tubercles; food grooves simple, unbranched, short and inconspicuous, extending 29–39% of corresponding test radius in ambulacrum III.

Interambulacra —Slightly inflated adapically between petals; on oral side, interambulacra forming narrow, straight bands separating broad ambulacra.

Tuberculation —Primary tubercles relatively large, with well-marked, sunken areole; on aboral surface, primary tubercles small and densely distributed among numerous miliary tubercles; on oral surface, primary tubercles larger and sparse relative to those on aboral surface; glassy tubercles larger than primary tubercles; densely distributed near edge of test on both oral and aboral sides; a few small glassy tubercles scattered over oral surface ( Fig. 46 , 47 ).

Peristome —Small, length 8–10% TL; rounded to pentagonal; situated slightly anterior of centre, 43–45% TL away from anterior margin.

Periproct —Small, length 5–6% TL; transverse oval to nearly round in outline; width from 6 to 8% TL; inframarginal, 10–13% TL away from posterior margin; bounded by second and third postbasicoronal interambulacral plates.

Geographic range. Indian Ocean, from Tuticorin Beach, India ( Mortensen 1948b).

Bathymetric range. To date, found only on beach ( Mortensen 1948b).

Observed occurrence in Sri Lanka. No live specimens were found, dead tests only were collected on Casuarina Beach, Jaffna, northern coasts of Sri Lanka ( Fig. 49 ).

Remarks. Based on test characters, the studied material appears closest to P. oblonga as described by Mortensen (1948b). The materials examined show marked variation in glassy tubercle size and distribution on the oral and aboral surfaces. In the largest specimen examined (WUSL/EI/41, TL= 34.57 mm), glassy tubercles are smaller than those in smaller specimens relative to test size ( Fig. 46 ). On the aboral surface close to the edge of the test, glassy tubercles are rare and much less conspicuous compared to the oral side. On the oral surface, small glassy tubercles are dispersed more or less equally even near the peristome but are especially conspicuous near the edge of the test. Glassy tubercle size and distribution are similar to Peronella lesueuri gadiana but P. oblonga is quite distinct from P. l. gadiana by the thicker test margin, and a distinct depression between the margin and slightly elevated central region, small petaloid area, and short petals. In small specimens, glassy tubercles were much more conspicuous than the primary tubercles near the edge of the test, and raised above the primary tubercles, giving the latter a sunken appearance.

There is variation in petal length among the studied specimens. Some specimens (WUSL/EI/38 and EI/48) have equally sized anterior and posterior petals while WUSL/EI/143 has longer posterior petals compared to petal III. WUSL/EI/41 and EI/52 have greater test edge thickness relative to test height. A few specimens (WUSL/EI/50, EI/51, and EI/53) collected from the same locality have an unusually pointed anterior end. In addition, these specimens have a higher test edge thickness and apical system situated 51–52% TL from anterior margin ( Fig. 48 ).

Figures

FIGURE 45. Peronella oblonga (WUSL/EI/49): A, aboral view; B, oral view; C, lateral view.

FIGURE 46. Variation of glassy tubercle distribution on Peronella oblonga: A, B, WUSL/EI/39; C,D, WUSL/EI/41; E, F, WUSL/EI/51.

FIGURE 47. Glassy tubercle distribution on Peronella oblonga (WUSL/EI/48): A, test edge of aboral side; B, test edge of oral side.

FIGURE 48. Variation of test shape of Peronella oblonga: A, B, WUSL/EI/50; C, D, WUSL/EI/51; E, F, WUSL/EI/53.

FIGURE 49. Distribution map of Peronella oblonga recorded in this study.