Diadema antillarum Philippi, 1845

Coppard, Simon Edward & Campbell, Andrew C., 2006, Taxonomic significance of test morphology in the echinoid genera Diadema Gray, 1825 and Echinothrix Peters, 1853 (Echinodermata), Zoosystema 28 (1), pp. 93-112 : 96-97

Diadema antillarum Philippi, 1845

Specimens of D. antillarum examined in this study were collected from Barbados, Gulf of Mexico, Jamaica, North Panama, Puerto Rico and the Virgin Islands. A maximum horizontal test diameter (h.d.) of 105 mm was observed in this species, with a corresponding vertical diameter (v.d.) of 50 mm. A mean horizontal test diameter of 85 mm and a mean vertical diameter of 45 mm were found from 50 specimens measured. Standard deviations (SD ±) in adult test size corresponded to 5.1 mm (h.d.) and 3.7 mm (v.d.).

Test colour in living specimens was typically black, with continuous blue lines of iridophores present down the mid-lines of the interambulacra and around the apical system. Such markings were not as bold as in D. savignyi . White spots on the naked median areas of the interambulacra were clearly visible at night. During the day these marks became smaller and less distinct, to the extent that specimens appeared to be completely black.

The ambulacra measured 25-33% of the width of the interambulacra measured at the ambitus. No differences were found from Mortensen’s (1940) detailed description of the plate arrangements and features of the pore zones.

The apical system was distinctly depressed and hemicyclic ( Fig. 1A ), measuring 18-22% of the test’s horizontal diameter (h.d.) in adults, a somewhat larger percentage in juveniles. The periproct measured 10-14% (h.d.) and had a small black anal cone with no anal ring or other distinct markings.

The genital plates ( Fig. 1A ) typically had between two and four small tubercles along their inner edge. When viewed on the naked test, distinct arch-shaped depressions were present on the genital plates of juvenile specimens. This feature appeared to fade with age. These markings corresponded to the corners of the pentamerous apical ring of iridophores, seen in living specimens.

A clear groove occurred down the mid-line of each interambulacrum. This bisected as it approached the naked median area ( Fig. 2A ). In living specimens this groove contained iridophores, forming clear blue lines, which bisected around the naked white spots, visible at night.

The peristome was black in colour and ranged in size from 45-50% (h.d.).

Figures

FIG. 1. — Drawings of the apical systems, showing species specific characters of the periproct and genital plates: A, Diadema antillarum; B, D. ascensionis; C, D. mexicanum; D, D. palmeri; E, D. paucispinum; F, D. savignyi; G, D. setosum; H, Echinothrix calamaris (brown colour morph); I, E. calamaris (white colour morph); J, E. diadema. Scale bars: 5 mm.

FIG. 2. — A-I, photographs of the median areas of the interambulacra, showing the variation in characters that occur: A, Diadema antillarum; B, D. mexicanum; C, D, D. savignyi; E, D. setosum; F, Echinothrix calamaris (brown colour morph); G, E. calamaris (white colour morph); H, E. diadema; I, D. palmeri; J, D. palmeri (whole specimen). Scale bars: A-I, 5 mm; J, 50 mm.