Plagiobrissus grandis (Gmelin, 1791)

Figure 17 A–K

Echinus grandis Gmelin, 1791: 3200. Spatangus pectoralis Lamarck, 1816: 29. Eupatagus pectoralis D’Archiac & Haime, 1853: 217. Metalia pectoralis A. Agassiz, 1872: 361. Plagiobrissus pectoralis Pomel, 1883: 30. Eupatagus (Plagiobrissus) grandis Cooke, 1942: 54. Plagiobrissus grandis H.L. Clark, 1917: 207.― Mortensen, 1951: 496 –498, pl. 11–41, 63. figs 13–16.― Tommasi, 1958a: 2, 7,

pl.1, fig. 4; 1959: 602, 603; 1966a: 20, pl. 5b.― Brito, 1962: 6; 1968: 30–31, pl. 15, fig. 1.– Martins et al., 2018: 536, figs

14–15.

Material examined. Alagoas: Photographic record (R.B. Moura, personal observation). Bahia: 1 spm, Busca Vida Beach, Guarajuba, Camaçari, 01.V.1993 [UFBA00522].

Description. Test oval, rounded anteriorly and truncate posteriorly (TL = 103.6 mm; TH = 30.8 mm; TW = 12.3 mm), covered by spines (Fig. 17 A–C). Long and slender spines borne on large primary tubercles occur between petals (Fig. 17A). Apical system ethmolytic. Petaloid large, with long petals. Ambulacrum III slightly depressed. Peripetalous fasciole well-developed. Peristome kidney-shaped, covered by large plates, with small spines (Fig. 17B) and triphyllous pedicellariae. Subanal fasciole well-developed, with anal fascioles stretching aborally on either side of periproct. Spines from oral surface of test expanded at base. Spines of plastron numerous and slenderer than on rest of oral surface. Flat oral surface (Fig. 17B). Periproct small. Narrow amphisternous plastron.

Pedicellariae. Small three-valved pedicellariae without stalk or neck on ambulacra at margins of the plastron. Ophicephalous pedicellariae with long stalk, short neck, and short bottle-shaped valves (Fig. 17F, I). Triphyllous pedicellariae with short valves and large blade (Fig. 17G, H). Tridentate pedicellariae with short stalks and without a neck. Valves narrow, broadened at the base and narrowing toward the tip (Fig. 17J).

Colour. Living specimens are brown. Naked test white.

Distribution. Florida, Gulf of Mexico, Bahamas, Belize, Cuba, Jamaica, Antilles, Panama, Colombia, and Brazil (H.L. Clark 1925; Hendler et al. 1995; del Valle García et al. 2005). In Brazil from AL, BA, SP, and SC, including Trindade Island (ES) (H.L. Clark 1925; Tommasi 1958a; Martins et al. 2018). This is the first record of this species in Alagoas State. From depths of 1 to 210 m, but most common in less than 50 m (Serafy 1979).

Remarks. The genus Plagiobrissus contains three extant species [P. africanus (Verrill, 1871), P. pacificus H.L. Clark, 1940b and P. grandis] (Kroh & Mooi 2016). Plagiobrissus grandis differs from P. africanus, an endemic species from the African coast, by the well-developed labrum, which is composed of two sternal plates of equal size. According to Kier (1975), young individuals of P. grandis can be easily confused with young specimens of Meoma ventricosa (Lamarck, 1816). However, the presence of long, sharp, white spines on the aboral surface of P. grandis readily distinguishes them, as does the more flattened test of the latter. Kier (1975) described detailed morphological variations in the ontogenetic development of P. grandis. In the present study, a single adult was examined that is insufficient to indicate variations.

Ecological notes. Plagiobrissus grandis lives buried in sandy areas where seagrass and algae are sparse or absent (Hendler et al. 1995; del Valle García et al. 2005). Serafy (1979) recorded this species from bottoms formed by shell fragments and quartz sand. According to Kier & Grant (1965), P. grandis is typically found buried at a depth of 50 mm. When buried, P. grandis raises and exposes its long aboral spines, presumably as a defence against predators (Hendler et al. 1995). According to Moore (1956) the gastropods Cassis tuberosa and C. madagascariensis spinella Clench (presently accepted as Cassis madagascariensis Lamarck) are its main predators.