|
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
|
