Diadema savignyi Michelin, 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 : 100

Diadema savignyi Michelin, 1845

Specimens of D. savignyi were collected from the Amirante Is. ( Seychelles), Eniwetok Atoll ( Marshall Islands), Ryuka Island ( Japan), Nouméa ( New Caledonia), Suva ( Fiji), Rarotonga ( Cook Islands) and Apia ( Samoa). Adult specimens had mean test diameters of 70 mm (h.d.) (SD ± 4.2 mm) by 40 mm (v.d.) (SD ± 2.1 mm). Maximum test diameters of 88 mm (h.d.) by 44 mm (v.d.) were recorded from 200 specimens examined.

The tests of living specimens were typically black and horizontally circular, while the apical system was conspicuously depressed. The ambulacra typically measured 28-30% of the interambulacra measured at the ambitus with pore zones that were only slightly widened towards the peristome.

White lines radiated out from the genital plates down the mid-lines of the interambulacra. In some specimens such lines terminated in white spot markings on the naked, unbleached test ( Fig. 2C ). This was not a consistent feature, with no such marking observed on the naked, unbleached test of specimens examined from Japan ( Fig. 2D ). The naked median areas had small red/brown spot markings during the day, these varied in size between specimens. At night these spot markings increased in size as the chromatophores retracted, revealing the white/cream test.

A bold pattern of iridophores was found on the aboral surface. This took the form of lines rather than spots as found in D. setosum . Lines of iridophores occurred down the mid-lines of the interambulacra. These bisected the naked median continuing to just below the ambitus. Rings of iridophores occurred around the tubercles on the ambulacra. However, this feature was not found on all specimens. A pentamerous ring of iridophores also occurred around the apical system.

The apical system ( Fig. 1F ) was hemicyclic and measured 22-28% of the test’s horizontal diameter. The periproct measured 13-18% (h.d.) and had a small anal cone, with no ring or platelets present. The genital plates ( Fig. 1F ) had clear arch-shaped depressions both in adults and juveniles. Tubercles varied in number from one to three and were typically present on the inner edge of the genital plates. These usually consisted of one larger and two smaller spines.

The peristome was black with a burgundy tinge and measured between 42-50% (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.