Diadema ascensionis Mortensen, 1909

Gondim, Anne Isabelley, Moura, Rafael Bendayan De, Christoffersen, Martin Lindsey & Dias, Thelma Lúcia Pereira, 2018, Taxonomic guide and historical review of echinoids (Echinodermata: Echinoidea) from northeastern Brazil, Zootaxa 4529 (1), pp. 1-72 : 14-15

Diadema ascensionis Mortensen, 1909

Figure 18 B

Diadema antillarum ascensionis Mortensen, 1909: 279 –281, pl. 48, fig. 2, pl. 54, fig. 4, pl. 61, figs 1–6, pl. 73, figs 14–16.–

Fernandes et al., 2002: 422.– Campos & Moura, 2008: 136 (table), 139.– Lima & Fenandes, 2009: 57–58. Diadema antillarum H.L. Clark, 1925: 279 . Diadema ascensionis Brito, 1962 , 5; 1968: 19–20, pl. 9, fig. 1; 1971: 264–265, fig. 1, pl. 3, figs 4–5.– Tommasi, 1966a: 11.–

Lima-Verde, 1969: 10.– Gondim et al., 2013a: 431–435, figs 1b–d, 1a–h.– Martins et al., 2018: 526, figs 4–5.

Material examined. Pernambuco: 1 spm, Rata Island, Fernando de Noronha, 13.IV.1999, 10 m [MZUSP, without voucher]. Alagoas: 2 spms, Francês Beach, Marechal Deodoro, 20.II.2011 [UFPB/ECH.1910]; 4 spms, Francês Beach, 29.I.1983 [UFPB/ECH.1922]. Bahia: 1 spm, Itapuã Beach, Salvador, 29.XI.2006 [UFBA00151].

Description (modified from Gondim et al. 2013a). Test large, circular, oral region flat. Apical system depressed and hemicyclic. Ocular plates with one or two small tubercles. Genital plates with only one tubercle or

with no tubercles at all. Periproct with small, black anal cone. Ambulacra swollen and narrow. Interambulacra large. Ambulacral plates trigeminate, with one primary tubercle. Interambulacral plates with one or three primary tubercles. Primary spines long, thin, hollow, axial cavities in tips of spines filled with dense, non-reticular tissue. Secondary spines similar to primaries, but smaller. Tubercles perforate and crenulate. Peristome twice as large as periproct.

Pedicellariae. Triphyllous and tridentate pedicellariae distributed all over test surface, being more abundant on the aboral surface. Claviform pedicellariae short and distributed around primary spines. Tridentate pedicellariae with narrow and strongly curved valves. Triphyllous pedicellariae with long stalk and neck. Valves long and narrow, with proximal region narrowest and broadening towards the tip ( Gondim et al. 2013a).

Colour. Specimens are black, with blue lines in the interambulacra and around the apical system (usually appearing completely black). White spots in central zones of naked areas of interambulacrum. Naked test white.

Distribution. Gulf of Mexico, Jamaica, Puerto Rico, Panama, Barbados, and Brazil, including Ascension and St. Helena Islands ( Tommasi 1966a; Coppard & Campbell 2006a). In Brazil from AL, and BA, including Fernando de Noronha, Atol das Rocas, Trindade, and Martin Vaz Islands ( Brito 1968, 1971; Lima-Verde 1969; Fernandes et al. 2002; Martins et al. 2018). From intertidal to 400 m depth ( Tommasi 1966a). In the present study, specimens from Alagoas were collected about 2 m deep.

Remarks. Diadema ascensionis differs from D. antillarum by the strongly curved valves in the tridentate pedicellariae. Since its original description, the taxonomic status of D. ascensionis has been debated, having been considered a synonym or a subspecies of D. antillarum . Presently it is considered a valid species, but molecular data (Lessios 2001; Lessios et al. 2001) conflict with morphology. However, several studies have found differences to support its designation as a distinct species ( Coppard & Campbell 2004, 2006a, 2006b; Gondim et al. 2013a; Rodríguez et al. 2013). Specimens studied herein, from reefs at Francês Beach (Alagoas), had all the characters that permit its distinction from D. antillarum . However, the specimens from this locality were previously identified as D. antillarum . To distinguish these two species correctly, an accurate analysis of the pedicellariae and of the structure of the spines is necessary. We analyzed both adult and young individuals. In distinction to other sea urchins, D. ascensionis has a hemicyclic apical system in all developmental stages, with the possible exception of post-larvae (not observed by us).

Ecological notes. In the coastal reefs of Francês Beach, State of Alagoas, D. ascensionis was found in areas with sandy substrates or among rocks of the reef formations, in zones of clear and well-illuminated water. Both isolated and clusters of individuals were observed, dense populations occurring up to 2 m depth ( Gondim et al., 2013a). Martins et al. (2018) observed a gregarious habit in specimens from Trindade and Martin Vaz Islands, where specimens were usually found in reef crevices during the day and moving around areas with a high percentage of green algae cover.

Figures

FIGURE 18. Some common echinoids from northeastern Brazil in their natural habitat. (A) Eucidaris tribuloides on coral reef; (B) Diadema ascensionis on barrier reef; (C) Echinometra lucunter on rhodolith bed; (D) Lytechinus variegatus near seagrass; (E) Tripneustes ventricosus on coral patch; (F-H) Mellita aff. quinquiesperforata, Leodia sexiesperforata and Encope emarginata, respectively, on muddy bottom of sandy beach near hypersaline mangroves.