Diadema setosum (Leske, 1778)

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 : 100-101

Diadema setosum (Leske, 1778)

Specimens of D. setosum were collected from Port Louis ( Mauritius), Sulawesi Is. ( Indonesia), Nouméa ( New Caledonia), Luzon ( Philippines), Lizard Is. ( Australia) and Suva ( Fiji). Adult specimens were found to have mean test diameters of 70 mm (h.d.) (SD ± 3.7 mm) by 40 mm (v.d.) (SD ± 2.9 mm). Maximum test diameters of 84 mm (h.d.) by 48 mm (v.d.) were recorded from 200 specimens examined.

Tests were black with a green tinge occasionally seen on large adult specimens. This was particularly apparent on specimens from Fiji. The typical shape of the test was horizontally circular, with the apical system conspicuously depressed. The ambulacra typically measured 24-30% of the interambulacra measured at the ambitus.

The naked median areas had white spots seen both day and night. These white spots were also visible on the naked test ( Fig. 2E ) in conjunction with white lines continuing from the spot marking along the mid-lines of the interambulacra to the genital plates. A bold pattern of blue iridophores occurred in this species. These have been described as “spots” by many authors ( Sarasin & Sarasin 1887; Agassiz & Clark 1908; Clark 1921; Mortensen 1940). The pattern of iridophores occurred as a series of “spots” down the mid-lines of the interambulacra. These bisected the naked median areas continuing down just below the ambitus. Lines of blue “spots” also occurred as two series down the ambulacra in some specimens. A single blue “spot” was also present on each genital plate, including above the madreporite.

The apical system ( Fig. 1G ) was hemicyclic and measured 22-28% of the test’s horizontal diameter. The periproct measured 12-20% (h.d.) and had a small black anal cone with a distinct orange anal ring, unique to the species. No platelets were present in the membrane. The genital plates had from three to five tubercles present along their inner edge, with green/blue spot markings when viewed on the denuded test ( Fig. 1G ). These represented the location of the blue iridophores observed in living specimens.

The peristome was grey in colour and measured 40-50% (h.d.).

Figures

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.

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.