Zoological Studies

Vol. 38 No. 3, 1999

Morphological and Life History Divergence of the Zoanthid, Sphenopus marsupialis off the Taiwanese Coast

Keryea Soong1,*, Yuh-Saint Shiau1 and Chang-Po Chen2

1Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung, Taiwan 804
2Institute of Zoology, Academia Sinica, Taipei, Taiwan 115

Keryea Soong, Yuh-Saint Shiau and Chang-Po Chen (1999) The morphology and life history of the solitary zoanthid, Sphenopus marsupialis, were studied. Individuals were collected by periodic bottom trawling at about 10-25 m depth at 5 localities along the coast of Taiwan from 1989 to 1995. The sizes (column length) of individuals from 2 southern localities were about twice as great as those from 3 relatively more northern localities. The size of mature specimens was also significantly larger at Linbien (south) than at Chadin (relatively north). The sizes of cnidae occurring on tentacles, actinopharynx, mesenterial filaments, and body columns of the zoanthids were not significantly different between the 2 sites. The seasonal change of oocyte diameters revealed that spawning occurred in August at Linbien, but later at Chadin, between October and November. At Linbien, individuals were strictly gonochoristic, whereas 22% of mature individuals were hermaphroditic at Chadin. Transverse division, the first such case reported in Zoanthidea, occurred in about 7% of more than 8000 examined individuals from the 3 relatively northern localities. In contrast, no evidence of asexual division was observed in more than 500 individuals from the 2 southern localities. Asexual division reduced the size of the organisms to below the normal maturation size. The relative frequencies of dividing individuals were lower between May and October, prior to the presumed spawning, than at any other time of the year. The populations from southern and northern localities are obviously different in their reproductive and life history characteristics, although they cannot be separated by cnidom or septa numbers, which have been traditionally used as taxonomic characteristics. These results suggest that what was considered Sphenopus marsupialis, with worldwide distribution, might actually be comprised of 2 sibling species off the Taiwanese coast.

Key words: Zoanthid, Size, Reproduction, Asexual, Cnida.

*Correspondence: E-mail: keryea@mail.nsysu.edu.tw