Taxonomic significance of test morphology in the echinoid genera Diadema Gray, 1825 and Echinothrix Peters, 1853 (Echinodermata) Author Coppard, Simon Edward Author Campbell, Andrew C. School of Biological Sciences, Queen Mary, University of London, Mile End Road, London E 1 4 NS (United Kingdom) simon @ diadema. fsnet. co. uk text Zoosystema 2006 28 1 93 112 journal article 10.5281/zenodo.5401706 1638-9387 5401706 Diadema paucispinum A. Agassiz, 1863 Specimens were collected from Puako Bay, Haunomu Bay, and Kahe Point on the main Hawaiian island of Oahu, as well as from Kahului, in Maui. Specimens were also collected from the islands of Viti Levu and Taveuni in Fiji . Adult specimens had mean test diameters of 70 mm (h.d.) (SD ± 4.4 mm ) by 40 mm (v.d.) (SD ± 3.1 mm ). Maximum test diameters of 82 mm (h.d.) by 48 mm (v.d.) were recorded from 62 specimens . Tests were black with a distinct red tinge in young specimens. Th is colouration was lost with age, becoming jet-black, exhibiting a bluish hue in adults. Th e ambulacra measured 22-26% of the interambulacra at the ambitus and were not as prominent as reported by Agassiz (1863) . The numbers of iridophores were noticeably reduced in this species. No apical ring was observed, while the pattern of iridophores down the mid-lines of the interambulacra were not constant. Typically, iridophores were found among the base of the tubercles on the interambulacra above the ambitus. Mortensen (1940) reported that no white spots were present on the naked median areas of the interambulacra. This was true of specimens during the day. However, at night, light red/brown patches were found in these areas. The test was reported by Mortensen (1940) to be somewhat more flattened than in the other species of the genus. This did not prove to be a consistent or reliable feature. The interambulacra were as Mortensen (1940) described, with fewer interambulacral plates (12-14) than in specimens of the same size in D. savignyi or D. setosum (15-16 plates).This corresponds to the few- er spines found in this species ( D. paucispinum ). The apical system ( Fig. 1E ) measured 20-28% of the test’s horizontal diameter, was hemicyclic with no iridophores present. The periproct measured 11- 15% (h.d.), was uniformly black with a small anal cone and no markings. The genital plates had from two to six small tubercles on their inner edge, but no arch-shaped depressions. This feature was not even found on juveniles in this study. No other distinct markings on the genital plates were found. The peristome was black and measured 40-45% (h.d.).