Opisthobranch of the Week Data
For a change, I thought I'd add a non-opisthobranch to the site. I'm adding this as it superficially resembles an opisthobranch, it's actually a ctenophoran, a group to which the comb-jellies belong. The ctenophores, commonly referred to as comb jellies, were previously considered to be cnidarians, because like jelly fish and sea anemones, ctenophores also have nematocysts. Currently they are considered to represent a separate Phylum, the Ctenophora. Most are pelagic animals, spherical in shape, which swim by bands of large beating cilia, arranged in vertical rows, each band being likened to a comb, hence the name "Comb Jelly". The 'jelly' is a reference to jelly fish. Ctenophores catch their prey by everting two groups of stinging and sticky tentacles. There are however a small group of ctenophores [Platyctenida] which have evolved into benthic dwellers. At first glance they appear to be flatworms, in some cases they superficially resemble some opisthobranchs. They are often found on soft corals, like acoel flatworms, and there are only a few described species, but probably many are yet to be recognized. Most are less than 10-15mm long. The above featured animal is larger than this and the two animals (Lyrocteis imperatoris) depicted on the second page are considerably larger.
The above featured animal, Coeloplana sp. 1 is unknown from Okinawa's main island as of late-September, 2013. The above featured animal was photographed but not collected in the waters of Nishihama Beach off Aka Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. It was photographed by Atsushi Ono during August of 2013 in 14m of water on a sandy bottomed environment. Atsushi's photograph is used here with his kind permission. It should be noted that Atsushi considers the species to be rare in the Kerama Islands and he reports seeing approximately five individuals (per. comm.). I've never personally seen this particular ctenophoran in Okinawan waters but I have photographed two fairly large bottom-dwelling ctenophorans, Lyrocteis imperatoris, in 55 and 58m (180 and 190ft) of water. There are images of these shown on an additional page.
In earlier presentations on these pages I've featured a series of opisthobranch-resembling animals, these are seen on the following pages: