A new species of free-living solitary zoantharian is described from Okinawa, Japan. Sphenopus exilis sp. n. occurs on silty seafloors in Kin Bay and Oura Bay on the east coast of Okinawa-jima Island. Sphenopus exilis sp. n. is easily distinguished from other Sphenopus species by its small polyp size and slender shape, although there were relatively few differences between Sphenopus exilis sp. n. and S. marsupialis in the molecular phylogenetic analyses. Currently, very little is known about the ecology and diversity of Sphenopus species. Thus, reviewing each species carefully via combined morphological and molecular analyses by using newly obtained specimens from type localities is required to clearly understand and distinguish the species within the genus Sphenopus.
Table 1_Re
Cnidae types and sizes in different tissue sections of the holotype of Sphenopus exilis sp. n.
Fig. 2 re2
olyps of Sphenopus exilis sp. n. A. In situ image of S. exilis sp. n., polyp with no black patterns, from the type locality in Kin Bay, Okinawa, Japan on 29 October 2011. B. Polyps of NSMT-Co1576 & NSMT-Co1577 from Kin Bay, Okinawa-jima Island, Japan. The white circle points to the holotype. C. In situ image of NSMT-Co1578 from Oura Bay, Okinawa-jima Island, Japan, on 13 November 2012. Faint black patterns and bands appear on the oral disc and the tentacles. D. Polyps of lot number NSMT-Co1578 showing phenotypic variation with black stripes on the upper part of the polyps. Scale bars: 1 cm.
Fig. 3
Morphological features of Sphenopus exilis sp. n. A. Cross section of holotype NSMT-Co1576 through the actinopharynx showing the mesenterial arrangement and dense sand encrustations. B. Well-developed mesogleal sphincter muscles visible on a hand-cut longitudinal section of the holotype NSMT-Co1576. C. Comparison of polyp shape between S. exilis sp. n. NSMT-Co1577 and S. marsupialis (from Brunei, refer to Reimer et al. 2012).
Fig4
Maximum likelihood tree of nuclear internal transcribed spacer of ribosomal DNA (ITS-rDNA) region for newly obtained sequences from Sphenopus exilis sp. n. in this study along with previously published GenBank sequences of family Sphenopidae. Bootstrap values of ML >60% are shown at respective nodes. Nodes supported by Bayesian posterior probabilities >0.90 are marked with asterisks. Species names’ of sequences obtained from GenBank follow with accession numbers. The subtree shown in b) shows only the clade formed by genus Sphenopus, Palythoa mizigama and P. umbrosa, delineated by the gray square in a).
