Fibularia, 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 : 39

Fibularia sp.

Figures 27 , 32 , 33

Material studied. Eleven denuded tests: WUSL/EI/158, EI/159, EI/161, EI/164, EI/165, EI/179, EI/180, EI/181, EI/185, EI/186, and EI/187, from Hiriketiya Bay, Sri Lanka.

Description. Shape and size —Test oval, small, 5.3–8.72 mm TL, longer than broad, width 75–84% TL, height 44–50% TL, posterior part of test wider than anterior, test slightly pointed anteriorly and truncated posteriorly; oral side slightly concave.

Apical system —Situated posterior of centre, 53–59% TL from anterior margin; with four circular small gonopores and small hydropores placed in short groove ( Fig. 33 , A).

Ambulacra —Petaloid area 69–76% TL, petaloid width 47–49% TL; petals short, with 5–8 pore pairs in each series of petal III and posterior petals, 3–5 pore pairs in each series of anterior-paired petals; pores small, rounded; petals broad, open distally; pore series slightly diverging; interporiferous zones similar in width to poriferous zones.

Peristome —Moderate in size, length 16–22% TL; rounded pentagonal, width 12–17% TL, situated slightly anterior of centre, 39–43% TL from anterior margin.

Periproct —Small, length 11–12% TL; squarish in outline; slightly elongate, width 8–11% TL; situated closer to peristome than posterior edge, 16–22% TL from posterior margin, four plates on periproctal membrane, no spines on plates.

Observed occurrence in Sri Lanka. Denuded tests only were found on the beach of Hiriketiya Bay, southern coast of Sri Lanka ( Fig. 27 ).

Remarks. This taxon likely represents a new species currently under study by one of us (Rich Mooi). Fibularia sp. can be distinguished from F. cribellum , F. japonica , F. plateia , and F. nutriens in having higher numbers of pore pairs relative to TL. This species is very similar to F. ovulum as both have a relatively high number of pore pairs. However, Fibularia sp. can be consistently distinguished from F. ovulum by its lower test.

Figures

FIGURE 27. Distribution map of Echinocyamus megapetalus, Fibularia ovulum and Fibularia sp. recorded in this study.

FIGURE 32. Fibularia sp. (WUSL/EI/164): A, aboral view; B, oral view; C, lateral view, right side.

FIGURE 33. SEM images showing test characters of Fibularia sp.: A, apical system (WUSL/EI/185); B, internal view of specimen (WUSL/EI/184) showing perignathic girdle; C, internal view of specimen (WUSL/EI/184) showing ambulacra and interambulacra.