Opisthobranch of the Week Data
Phyllodesmium koehleri is considered to be very rare in the waters of Okinawa's main island in as much as I have seen and collected only the above featured animal. It was collected from 130ft and was found crawling on top of strewn coral rubble during a mid-morning SCUBA dive. As of the current date (mid-September, 2008) this is the only individual I've found here. P. koehleri was in the past listed on these pages as Phyllodesmium sp. 1, but with publication of the recent Burghardt, Schrödl & Wägele (2008) paper I've now changed the name.
The following description of both color and external morphology of the living and preserved animals is taken from Burghardt, Schrödl & Wägele, (2008):
Colour and external morphology of living animal:
Body of living animals, including oral tentacles, rhinophores and foot translucent white. Right digestive glandular branch dark brown. Animals elongate, up to approximately 56 mm in length (without cerata), with few short and several very long cerata (longer than rhinophores and oral tentacles), covering whole notum when resting. Smooth oral tentacles somewhat longer than smooth to slightly wrinkled rhinophores, usually directed more laterally. Rhinophores similar in shape to oral tentacles, standing close together. Both rhinophores and oral tentacles tapering. Anterior foot angular. Posterior end of foot tapering to thin line. Papilliform anus prominent and long, dorso-laterally of second cerata pad. Nephroproct not observed.
Up to six cerata arranged in five different clusters on each side. First cluster forming a distinct row on each side, with genital papilla lying beneath right one. Compared to more dorsal cerata, lateral ones smaller and shorter. Cerata spoon-like, flattened with concave and convex side, broadening in upper half. Basal part circular to oval in cross section. Cerata covered with large spiny tubercles, these more elongate along cerata edges. Apex of cerata clubbed and blunt. Cerata never curled. Brownish digestive gland shining through transparent body wall of cerata, giving some specimens a rather brownish colour.
External morphology of preserved animals:
No distinct notal rim present. Foot anteriorly without propodial tentacles, posterior part pointed. Oral tentacles slightly annulated due to preservation. Rhinophores slightly wrinkled, standing close to each other, somewhat longer than oral tentacles. Up to five pads/rows of cerata on each side, lying opposite to each other. First cerata lateral or slightly anterior to rhinophores. Distance between first and second cluster as long as between all other pads. Anal papilla dorsolateral of second ceratal pad. Genital papilla lying beneath first ceratal cluster. Whole epidermis composed of specialized vacuolated cells.
The following taken in part from the discussion of Phyllodesmium koehleri within the above publication (Burghardt, Schrödl & Wägele, 2008):
Phyllodesmium koehleri differs from all other described Phyllodesmium species in its food preferences. This species seems to be specialized on members of the Nephtyidae, probably Paralemnalia or Lemnalia .... The spoon-like spiny cerata of P. koehleri mimic parts of these soft corals and clearly distinguish P. koehleri from all other congeners. In contrast to many other Phyllodesmium species, the cerata are never curled in the upper part. Similar to all non-Xeniidae-feeding Phyllodesmium species described so far, P. koehleri has branches of the digestive gland within the body.
I've posted three additional images of the same animal with a bit more detail than shown above. Also, Bill Rudman has several images of this recently named animal posted on the Sea Slug Forum.
Phyllodesmium koehleri is one of several described and undescribed (or at least unknown by myself) species of Phyllodesmium species known from Okinawan waters. Previously I've featured on these pages the following Phyllodesmium species: