Echinothrix calamaris (Pallas, 1774)

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 : 101-102

Echinothrix calamaris (Pallas, 1774)

Specimens were collected from Ryuka Is. ( Japan), Red Sea ( Egypt), Mariana Is. ( Guam), Ignoitijala ( Maldives), Luzon ( Philippines), Dravuni Is., Taveuni Is., Yanuca Is., Suva ( Fiji), and Nouméa ( New Caledonia).

This species is reported to have the broadest range of colour morphs of any species in the family Diadematidae (H. L. Clark 1925) . The most commonly found colour morphs throughout the Indo-Pacific were the white (interambulacral spines) and brown (test and ambulacral spines) and the completely brown colour morph. These were commonly found together throughout the Pacific, and were therefore closely studied in this investigation.

Test diameters varied significantly between colour morphs. Adult specimens of the white colour morph had a mean horizontal test diameter of 108 mm (SD ± 8.2 mm) and a mean vertical diameter of 45 mm (SD ± 5.4 mm). Adults of the brown colour morph typically grew to a significantly larger size, with mean test diameters of 120 mm (h.d.) (SD ± 8.7 mm) and 60 mm (v.d.) (SD ± 5.5 mm). Mortensen (1940) reported that the largest recorded specimen of E. calamaris measured 130 mm (h.d.) from the old collection of the “Royal Museum”, Copenhagen. The largest specimen recorded in this study, from 200 specimens of each colour morph measured 143 mm (h.d.) by 68mm (v.d.) and was of the brown colour variety. In comparison, the largest white colour morph only measured 119 mm (h.d.) by 52 mm (v.d.).

The ambulacra in both colour morphs measured 24-28% of the interambulacra measured at the ambitus and widened distinctly towards the periproct, narrowing beneath the ambitus then widening towards the peristome. Many authors including Clark & Rowe (1971) have differentiated this species from Echinothrix diadema by the ambulacra which are distinctly raised aborally in E. calamaris . This feature was, however, not constant, and as Mortensen (1940) reported, “considerable variation occurs in the elevation aborally of the ambulacra”. Such variation was most apparent between colour morphs. The test of the white colour morphs was typically more flattened aborally, while the ambulacra were less distinctly raised and the interambulacra less correspondingly sunken. The brown colour morph had clearly raised ambulacra and interambulacra that were sunken aborally. This differentiation appeared to increase with age.

Large, naked median areas occurred down the mid-line of the interambulacra ( Fig. 2F, G ) as green or blue bands in living specimens. Green bands could also be seen on the denuded test of the white colour morph. This feature was, however, less noticeable on the naked test of the brown colour morph. The interambulacra was green on the naked test, in contrast to the white ambulacra. This was more apparent on the white colour morph.

The apical systems measured 23-28% of the test’s horizontal diameter in the brown colour morph ( Fig. 1H ) and 25-30% in the white colour morph ( Fig. 1I ). Both were monocyclic and conspicuously depressed. The periproct measured 14-20% (h.d.) in the brown colour morph and 16-20% in the white colour morph. In living specimens both colour morphs had a large, swollen anal cone with small white platelets present in the membrane. Mortensen (1940) reported that one particular specimen from Hawaii had spines on the periproct; this feature was never seen in this study.

The genital plates ( Fig. 1H, I ) had tubercles present along their inner edge. When viewed on the naked test, the genital plates typically had a green tinge, particularly in the white colour morph. The gonopores were relatively small (smaller than in E. diadema ) with no other distinguishing features. The brown colour morph typically had a slightly smaller apical system than the white colour morph, with more elongated genital plates.

The peristome was large and typically measured 42-50% (h.d.) in the brown colour morph and 40-48% in the white colour morph. Mortensen (1940) reported that spines may be present on the buccal plates. However, these were never seen in this investigation, even in very large specimens.

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.