WoRMS source details
Arakaki, Y. & Uehara, T. 1999. Morphological comparison of black Echinometra individuals among those in the Indo-West Pacific. Zoological Science Tokyo 16, 551-558.
Arakaki, Y.; Uehara, T.
Morphological comparison of black Echinometra individuals among those in the Indo-West Pacific
Zoological Science Tokyo
It is almost impossible to discriminate each region’s black Echinometra based on appearance, such as the color of spines, milled ring, and skin around the peristome. However, it is possible to divide them into several groups based on such characteristics as the spicules of the gonads and tubefeet, the porepairs, the shape of the sperm, and the pedicellaria. The percentage of spicules of the gonads and tubefeet depends on the region the individuals inhabit. The five pore-pair percentage of Guamanian individuals is very low, and this is significant compared to the individuals of the other regions. The sperm morphology of Guamanian and Hawaiian individuals is significantly more compact than that of Mauritian, Indonesian, Okinawan, and Boninian individuals, while the difference between the Guamanian and Hawaiian individuals is also significant. The tridentate pedicellaria of the Hawaiian individuals are longer than those of the other regions’ individuals, and the difference is significant. The length differences of the ophiocephalous pedicellaria and trifiliate pedicellaria are significant depending on the individuals of the region, and it is possible to discriminate individuals of each region into several groups. Guamanian and Hawaiian individuals are separated into different groups based on all these characteristics, and it is also possible to discriminate these two groups from the other regions’ individuals by several characteristics. Therefore, black Echinometra individuals living in the Indo-West Pacific are divided into three groups, i.e., Mauritian, Indonesian, Okinawan, Boninian individuals; Guamanian individals; and Hawaiian individuals. The number of pore-pairs and morphology of the sperm in the Okinawan Echinometra species complex reflect species level differences, and it is suggested that cross-fertilizations between black Echinometra from Okinawa and Guam as well as Okinawa and Hawaii were not successful. This indicates that the three groupings based on these characteristics reflect a species level difference. In other words, the black Echinometra inhabiting the Indo-West Pacific are a species complex, or a cryptic species composed of at least three species.