On the fourth Diadema species (Diadema-sp) from Japan.

Seinen Chow,Yoshikazu Kajigaya,Hiroaki Kurogi,Setuo Kiyomoto,Atsushi Nanami,Takuro Shibuno,Kentaro Niwa,Sebastian D Fugmann

doi:10.1371/journal.pone.0102376

Seinen Chow, Yoshikazu Kajigaya + Show 6 more

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https://doi.org/10.1371/journal.pone.0102376

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Abstract

Four long-spined sea urchin species in the genus Diadema are known to occur around the Japanese Archipelago. Three species (D. savignyi, D. setosum, and D. paucispinum) are widely distributed in the Indo-Pacific Ocean. The fourth species was detected by DNA analysis among samples originally collected as D. savignyi or D. setosum in Japan and the Marshall Islands and tentatively designated as Diadema -sp, remaining an undescribed species. We analyzed nucleotide sequences of the cytochrome oxidase I (COI) gene in the “D. savignyi-like” samples, and found all 17 individuals collected in the mainland of Japan (Sagami Bay and Kyushu) to be Diadema-sp, but all nine in the Ryukyu Archipelago (Okinawa and Ishigaki Islands) to be D. savignyi, with large nucleotide sequence difference between them (11.0%±1.7 SE). Diadema-sp and D. savignyi shared Y-shaped blue lines of iridophores along the interambulacrals, but individuals of Diadema-sp typically exhibited a conspicuous white streak at the fork of the Y-shaped blue iridophore lines, while this feature was absent in D. savignyi. Also, the central axis of the Y-shaped blue lines of iridophores was approximately twice as long as the V-component in D. savignyi whereas it was of similar length in Diadema-sp. Two parallel lines were observed to constitute the central axis of the Y-shaped blue lines in both species, but these were considerably narrower in Diadema-sp. Despite marked morphological and genetic differences, it appears that Diadema-sp has been mis-identified as D. savignyi for more than half a century.

Highlights

Long-spined sea urchins in the genus Diadema Gray, 1825 are widespread species found in tropical and sub-tropical regions [1,2]
Using mtDNA analysis, the fourth species of Diadema was found among samples collected from Japanese and Marshall Island samples initially identified as D. savignyi or D. setosum and tentatively designated as Diadema-sp [3]
The species of the genus Diadema sampled in the present study were not endangered in Japan and verbal permits for collecting Diadema species were obtained from the above organizations

Summary

Introduction

Long-spined sea urchins in the genus Diadema Gray, 1825 are widespread species found in tropical and sub-tropical regions [1,2]. Four Diadema species are reported from the southern part of the Japanese Archipelago [3]. D. savignyi (Audouin, 1829) and D. setosum (Leske, 1778) are the most abundant and well known, both having the widest geographic range in the Indo-Pacific Ocean of any species in the genus. 1864, and the species is suspected to inhabit other parts of the tropical Indo-Pacific [1], and has been observed in Japanese waters [3]. Using mtDNA analysis, the fourth species of Diadema was found among samples collected from Japanese and Marshall Island samples initially identified as D. savignyi or D. setosum and tentatively designated as Diadema-sp [3]. Since first being reported in 2001 Diadema-sp has received almost no attention from researchers [3]

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