Leodia sexiesperforata (Leske, 1778)

Figures 13 A–H, 18 G

Echinodiscus sexiesperforatus Leske, 1778: 199.

Mellita sexforis Rathbun, 1879: 144 .

Mellita sexiesperforata Jackson, 1912: 18 .― Tommasi, 1959: 602, 603; 1966b: 241–242.― Magalhães et al., 2005: 63.

Mellita platensis Bernasconi, 1947: 104; 1956: 124–125, pl. 2, figs 5–6.

Mellita (Leodia) sexiesperforata Brito, 1960a: 8, fig. 2–d, fig. 3–b.― Tommasi, 1966a: 25.― Lima-Verde, 1969: 10.― Tommasi et al., 1988a: 5.

Leodia sexiesperforata Brito, 1962: 6; 1968: 28–29, pl. 14, figs 4–5.― Alves & Cerqueira, 2000: 547.― Ventura et al., 2007a: 249.― Gondim et al., 2008: 155 (table).― Manso et al., 2008: 183, figs 5a–c.― Queiroz et al., 2011: 65 –67, figs 1af.― Miranda et al., 2012: 142.– Martins et al., 2018: 534, figs 12–13.

Material examined. Rio Grande do Norte: 3 spms, Ponta do Rio Tubarão, in front of the cliffs of Chico Martins, Diogo Lopes, Macau, 02.II.2011 [UFPB/ECH.1893]; 5 spms, Ponta do Rio Tubarão, in front of the cliffs of Chico Martins, Diogo Lopes, 01.II.2011 [UFPB/ECH.1915]. Paraíba: 1 spm, Baía da Traição Beach, Baía da Traição, 24.XI.2007 [UFPB/ECH.1013]; 1 spm, Baía da Traição Beach, Baía da Traição, 05.V.2008 [UFPB/ECH.1165]; 1 spm, 6°56.139′S 34°49.391′W, Porto Project, Cabedelo, 09.II.2004 [UFPB/ECH.1297]; 1 spm, Ponta de Campina, Cabedelo, 20.XI.1983 [UFPB/ECH.1303]; 1 spm, reefs facing Ponta de Campina, Poço Beach, Cabedelo, 28.II.2010 [UFPB/ECH.1921]. Alagoas: 1 spm, Francês Beach, Marechal Deodoro, 29.I.1983 [UFPB/ECH.1307]. Bahia: 1 spm, Ponta da Coroa Vermelha, Santa Cruz da Cabrália, 14.X.1982 [UFPB/ECH.1302].

Description. Test slightly pentagonal in outline (TL = 84 mm; TW = 79 mm), discoidal, fragile, with slight elevation in centre, ambitus extremely thin and sharp (Fig. 13 A–D). Apical system monobasal (Fig. 13H), four gonopores (Fig. 13H). Petaloid small, occupying only central region of test (Fig. 13C, H). Posterior petals slightly longer than anterior ones (Fig. 13A, C). Six long, slit-like lunules (Fig. 13 A–C), anal lunule shorter than five ambulacral ones (Fig. 13A, C). Aboral primary spines strongly club-shaped, uniformly covering test (Fig. 13A). Miliary spines with sac-like structure on tip, densely scattered among primary spines (Fig. 13G). Lunules with two types of spines, on aboral margin, spines long, flat and slightly curved. Internally, spines are shorter, slenderer than aboral spines, but also slightly curved. Oral surface flat, with locomotory spines long, slender, and slightly curved at base, being largest spines in this region (Fig. 13B). Short and slender spines occur among these spines. Spines on ambitus similar to those around lunules. Peristome circular and central (Fig. 13B, D, E). Periproct small, elongate, close to peristome, slightly indenting basicoronal plate (Fig. 13B, D). Basicoronal plates reduced in size. Ambulacral basicoronal plates almost triangular. Pressure drainage channels and food grooves well-developed (Fig. 13D). Food grooves bifurcating after ambulacral basicoronal plates, surrounding lunules and reaching margin of test (Fig. 13D).

Pedicellariae. Pedicellariae over entire test, more abundant in oral inter and near the lunules, peristome, and periproct. Bidentate pedicellariae with a long neck (of same size or slightly smaller than the stalk) and short head. Valves short, with narrow and slightly curved base, median region enlarged with denticulate margin and two end teeth that cross with the teeth of opposing valve (Fig. 13F).

Colour. From yellow to brown or greenish (Hendler et al. 1995). Naked test white.

Distribution. North Carolina, Bahamas, Florida, Gulf of Mexico, Cuba, Belize, Honduras, Puerto Rico, Costa Rica, Jamaica, Panama, Venezuela, Colombia, Brazil, and Uruguay (Hendler et al. 1995; Alvarado et al. 2008, del Valle García et al. 2008; Francisco & Pauls 2008; Rodríguez-Barreras 2014). In Brazil from CE, RN, PB, PE, AL, BA, RJ, SP, including Trindade Islands (Rathbun 1879; Brito 1962, 1968; Tommasi 1966b; Lima-Verde 1969; Magalhães et al. 2005; Gondim et al. 2008; Manso et al. 2008; Martins et al. 2018). From depths of 0 to 30 m (Francisco & Pauls 2008).

Remarks. The genus Leodia is represented by a single extant species. The status of this genus has been the subject of some dispute (Mooi & Peterson 2000), having been for many years considered to be a synonym or a subgenus of Mellita . Among the features that were used to separate these genera were the process of development and the number of the lunules (Lambert & Thiéry 1921; H.L. Clark 1940a; Mortensen 1948a). However, Durham (1955) pointed out some important differences between Leodia and Mellita that did not rely on lunule number. A series of authors recognized the distinction of these genera (e.g. Durham 1955; Serafy 1979; Mooi 1989; Hendler et al. 1995; Coppard 2016) and phylogenetic studies support this view (Mooi & Peterson 2000; Coppard et al. 2013). Leodia sexiesperforata is distinguished from the species of Mellita by the slightly pentagonal outline of the strongly flattened test, and very narrow lunules. Kier (1963) and Mooi & Peterson (2000) included other characters that are also used for distinguishing L. sexiesperforata from living representatives of Mellita, for example: five ambulacral lunules, posterior lunule not extending far anteriorly between posterior petals, and interambulacral basicoronal plates separated from first interambulacral post-basicoronals by two plates of each adjoining ambulacrum. According to Mooi & Peterson (2000), extant Leodia have aboral primary spines with smooth, very strongly club-shaped tips that are more markedly bent and swollen than those found in any other living mellitid.

Ecological notes. This species lives in sandy areas with little or no vegetation (Hendler et al. 1995). It is usually uncommon along the northeastern littoral, yet some sandy beaches may contain significant population densities of this species, as observed in Macau (State of Rio Grande do Norte) and Lucena (State of Paraíba). In the present study, the species was abundant in hypersaline mangroves (State of Rio Grande do Norte), and co-occurred with M. aff. quinquiesperforata and E. emarginata . In many examined specimens we encountered one or two small crustaceans, possibly of the genus Dissodactylus Smith, 1870, associated with the oral surface of the sand-dollar. We further observed small bivalves living inside one of the lunules. McClintock & Marion (1993) recorded the mollusk gastropod Cassis tuberosa as one of the main predators of L. sexiesperforata in the Bahamas. Goodbody (1960) and Telford & Mooi (1986) summarized data on feeding habits of Leodia.