OKINAWAN
OPISTHOBRANCH OF THE WEEK

Phyllodesmium acanthorhinum Moore & Gosliner, 2014 (21mm)

Opisthobranch of the Week Data

Taxonomy:

Frequency on Okinawa: Collection Data:
[brackets indicate range for all Okinawa-collected specimens of the species]


Species Account:

        This very attractive facelinid, was originally featured on these pages as an unknown Phyllodesmium species (sp. 6) and I'm pleased to say the animal has now been recently described as Phyllodesmium acanthorhinum (Moore & Gosliner 2014). The species is considered to be rare in the waters of Okinawa's main island; I've seen and collected six individuals over a period of more than twenty years of diving in local waters. The above featured animal was collected from the vertical rock wall of a small surge channel near shore. The surge channel was covered with relatively dense growths of several species of Rhodophyta as well as miscellaneous demospongians and encrusting bryozoans.

        The following is from the recent Moore, & Gosliner (2014) publication:

Geographic range

This species is known from the Horseshoe Cliffs, Okinawa, Ryukyu Islands, Japan and Lizard Island, Great Barrier Reef, Australia (Wägele et al., 2006).

Color and external morphology: The living animals are elongate, with edges of the foot extending laterally just beyond the mantle. They range in length from 17 to 28 mm for living animals studied. Preserved specimens examined were 14 mm, 8 mm, and 8 mm. The anterior portion of the foot margin is broad with short, blunt angular foot corners while the posterior end is tapered to a point.

The body of the living animal, including the rhinophores, oral tentacles, and foot is predominantly transparent with opaque white markings on the dorsum. These markings vary and can appear as white specks or as distinct white lines creating a network along the dorsum and head. The anterior margin of the foot is white in some specimens, extending to the angular foot corners. The viscera and gonad are readily visible through the mantle tissue.

The cerata are elongate and cylindrical, with larger cerata near the medial region of the dorsum. The digestive gland is undulating and undivided within the cerata and is cream or yellow colored near the body leading to red, and then yellow at the apex of each ceras. The cerata are primarily transparent, with slight blue coloration near the tips and have a cnidosac without nematocysts. The ceratal arrangement consists of arches and rows, with arches forming in the anterior ceratal groups. The precardiac cerata are grouped into one arch on each side of the body containing 6-7 cerata. The genital aperture is located between the arms of the precardiac arch on the right side of the animal. The renal opening is situated in the interhepatic space, slightly toward the posterior between the precardiac arch and the first postcardiac arch on the right side. The postcardiac cerata are grouped on both sides into arches containing 5-6 cerata in the first two arches, and 4-5 cerata in the third arch. The anal papilla is located within the first postcardiac arch on the right side. The fourth postcardiac group appears as a partial arch in some animals and as a row in others containing 3-4 cerata. One or two additional postcardiac ceratal groups appear as rows containing 2-3 cerata.

The rhinophores are conical in shape and are roughly half as long as the oral tentacles. In addition, there are numerous, yellow-cream-colored tubercles on the entire surface of the rhinophores that lead to a yellow-cream, pointed tip. The oral tentacles are smooth, and taper from the anterior edge of the head to pointed apices. They are transparent or slightly bluish basally, leading to white or yellow-cream tips.

        I've also added an additional page featuring additional images of the above animal as well as images of holotype and paratype specimens of the recently described species.

        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:

Etymology:

Literature Cited:


Page Date: 01 May '15
Page Modification Date: 01 May '15
Digitally manipulated photo
Copyright © 2015 Robert F. Bolland