Diadema antillarum ( Philippi, 1845 )

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 : 13-14

Diadema antillarum ( Philippi, 1845)

Cidaris (Diadema) antillarum Philippi, 1845: 355 –356.

Diadema antillarum A. Agassiz, 1863: 224 .– Brito, 1962: 5.– Tommasi, 1966a: 11, figs 6–12; 1966b: 240; 1972: 24, fig. 45.– Alves & Cerqueira, 2000: 547.– Magalhães et al., 2005: 63.– Oliveira et al., 2010: 10.– Miranda et al., 2012: 142, fig. 4b.

Diadema setosum Rathbun, 1879: 143 .– Brito, 1962: 5 [not Diadema setosum ( Leske, 1778) ].

Material examined. No specimens available for study.

Description (modified from Tommasi 1966a, Coppard & Campbell 2006b, and Rodríguez et al. 2013). Test hemispherical, large, and slightly flattened orally and aborally. Apical system hemicyclic (I, IV and V inserted) and depressed. Ocular plates short and pentagonal, with one or two small tubercles. Genital plates wider than long, slightly triangular, with one to three tubercles along their inner edge. Periproct bearing totally black, small anal cone. Ambulacra narrow and slightly swollen, with two rows of primary tubercles. Primary tubercles of ambulacra much smaller than those of interambulacra. Interambulacra wide, with four series of large primary tubercles. In living specimens, a narrow blue line of iridophores occurs down either side of naked median area of the interambulacra and as a ring around the apical disc (or totally black in some specimens). White spots on naked areas of interambulacra easily distinguished at night. Ambulacral plates trigeminate. Primary spines long (around 5 to 6 times the TD), slender, verticillate and hollow internally, blackish or with alternating white and black stripes (in juveniles). Secondary spines similar to primaries, but smaller. Tubercles perforate and crenulate. Peristomial membrane black and covered with many of triphyllous pedicellariae. Buccal plates without spines.

Pedicellariae. Only tridentate and triphyllous pedicellariae are present. Tridentate pedicellariae occur in two forms, one with broad valves and a long broad neck on a short stalk, and another form with narrow valves, short neck, and a long stalk. Triphyllous pedicellariae with broad valves rounded distally, with two rows of numerous, small peripheral teeth ( Rodríguez et al. 2013).

Colour. According to Tommasi (1966a, 1972), young specimens of D. antillarum have the typical spines with alternating white and black stripes, while adults are whitish, blackish, or greenish. Hendler et al. (1995) further stated that both colour of the test and the spines were typically black, but may have few or many white or gray spines, and some specimens were almost entirely white. In general, black individuals live in clear-water environments, while light-coloured individuals live in less-lighted areas, in turbid waters, rock crevices or deep waters ( Hendler et al. 1995).

Distribution. Bermudas, Gulf of Mexico, Cuba, Puerto Rico, Costa Rica, Panama, Colombia, Venezuela, and Brazil ( Borrero-Pérez et al. 2002; del Valle García et al. 2005; Alvarado 2011). In Brazil, from BA, and RJ, including Trindade and Fernando de Noronha Islands ( Tommasi 1966a; Alves & Cerqueira 2000; del Valle García et al. 2005; Magalhães et al. 2005). From 0 to 400 m, being more common in depths below 50 m ( Hendler et al. 1995).

Remarks. Presently, eight extant and two fossil taxa of Diadema are known, of which only D. antillarum and D. ascensionis are recorded from the Western Atlantic. D. antillarum differs from D. ascensionis by tridentate pedicellariae with straight valves, and six series of primary tubercles on the interambulacra. Diadema antillarum also differs from D. setosum ( Leske, 1778) by not having an orange ring on the anal cone nor genital plates with four or more small tubercles, as in the latter species. Diadema antillarum differs from D. africanum Rodríguez, Hernández, Clemente & Coppard, 2013 by the occurrence of two forms of tridentate pedicellariae, and two to four small tubercles on genital plate. The description of Diadema africanum was based on a population previously identified as D. antillarum-b (see Rodríguez et al. 2013). Considering the close morphological affinity among D. antillarum , D. ascencionis and D. africanum ( Rodríguez et al. 2013) , taxonomical, biological and ecological information about these species must be interpreted with caution. Oliveira (1951) recorded D. setosum and Diadema sp. at Trindade Island and Brito (1962) cited D. setosum for Fernando de Noronha and Bahia. However, Tommasi (1966b) believed that these identifications were incorrect since D. setosum is a typically Indo-Pacific species and its occurrence in these areas is unlikely. Thus, it seems more plausible that the specimens identified by Oliveira and Brito were, in fact, D. antillarum or D. ascensionis . Currently, the records of these latter two species are considered valid for the Brazilian coast. The test of this species is so fine and fragile that it remains intact only for a short time after death ( Kidwell & Baumiller 1990; Greenstein 1989, 1991, 1993).

Ecological notes. This species inhabits reef environments, seagrass beds, mangroves and sandy or rocky bottoms (del Valle García et al. 2005). According to Hendler et al. (1995), the species prefers calm water, actively avoiding heavy wave action. Diadema antillarum is considered omnivorous, feeding preferably on algae ( Weil et al. 2005). However, when foraging high-density habitats, it ingests invertebrates such as zoanthids, sponges and coral tissues ( Randall et al. 1964), thus affecting the recruitment and mortality rates of young coral and other sessile invertebrates ( Sammarco 1980). There are many studies regarding biology and ecology of D. antillarum (e.g. Randall et al. 1964; Lewis 1966; Levitan 1989; Atrill & Kelmo 2007; Blanco et al. 2011; Rodríguez-Barrera et al. 2015).