Opisthobranch of the Week Data
Trapania gibbera is considered to be very rare in the waters of Okinawa's main island as I have seen and collected only the above singe individual. The animal was found beneath a slab of coral rubble in an area of mixed sand and strewn coral rubble during a daytime SCUBA excursion under high spring tide conditions. Trapania gibbera was in the past listed on these pages as Trapania sp. 1, but with publication of the recent Gosliner & Fahey (2008) paper I've now changed the name. The above image is one of the paratype* specimens (CASIZ** 084868), deposited at California Academy of Sciences.
The following is taken from Gosliner & Fahey (2008):
This species has only been reported from Papua New Guinea, Indonesia and Okinawa.
The living animal ranges from 6-10mm long. The body shape is elongate and convex, without a distinct notal margin. The body is widest in the branchial region and has a dorsal hump in front of the gill. The head is rounded anteriorly and the anterior foot margin is extended into tentacular points. The oral tentacles are long and pointed. The posterior end of the foot is sharply tapered with a somewhat rounded posterior tip. The non-retractile, perfoliate rhinophores are relatively short and stout with 9-10 lamellae. The stalk and the club are the same thickness. The extra-rhinophoral appendages are relatively short and are curved. The gill consists of three bipinnate branches. The extra-branchial appendages are stout and curved, about the same size as the extra-rhinophoral appendages. The body is entirely white, but there is a black line of pigment on the anterior margin of the head. The oral tentacles are reddish brown or orange. The extra-rhinophoral and extra-branchial appendages are white. The rhinophores are translucent white but the edges of the lamellae are reddish brown or orange, the same colour as the oral tentacles. The gill branches have the same reddish-brown or orange colour on the rachis, as do the rhinophore lamellae. The tip of the foot is light blue.
Externally, this species most closely resembles Trapania aurata Rudman, 1987 from Hong Kong and T. vitta sp. nov. All three species have a white body and yellow or orange pigment on the oral tentacles and the rhinophores and/or gill appendages. However, T. gibbera is unique in having a black line along the anterior end of the head, between the oral tentacles and light blue colouration on the tip of the foot. This species also has an elevated hump anterior to the gill that is not present in either T. aurata or T. vitta. In T. aurata the yellow markings are present on the foot, tentacles, extra-rhinophoral and extra-branchial appendages, while in T. gibbera and T. vitta the orange or red markings are limited to the oral tentacles, rhinophores, gill and foot. In T. gibbera the reddish orange markings are present only on the lamellae of the rhinophores and on the rachis of the gill branches. In contrast, T. vitta has these markings at the apices of the rhinophores and on the anterior face of the gill branches.
Members of the group are readily distinguished from other Okinawan nudibranchs by the presence of a pair of thin finger-like processes located near the rhinophores and gills.
* Paratype: See "Type" Dictionary for explanation.
**CASIZ: California Academy of Sciences Department of Invertebrate Zoology
Previously I've featured several members of the genus Trapania on these pages and as of the current date, there are several described species reported from Okinawan waters. The featured animals are as follows:
T. euryeia T. gibbera the above featured animal T. naeva T. squama T. toddi T. vitta