OKINAWAN
OPISTHOBRANCH OF THE WEEK

Tamanovalva limax Kawaguti & Baba, 1959 (6mm)
Photo by Atsushi Ono

Opisthobranch of the Week Data

Taxonomy:

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


Species Account:

        Currently there is a fair amount of confusion concerning the species placement of Tamanovalva limax. Some workers favor using the fossil generic name Berthelinia (Baba, 1961a, 1961b) but others prefer the use of Tamanovalva. In the Sea Slug Forum, Rudman (2002) mentions the following:

Personally I have difficulty in using the fossil name Berthelinia, as we have no way of determining if the animals that made the fossil shells are really closely related to any living species. The situation is further complicated because it is possible that that Edenttellina typica, which is the earliest name for a living species may be congeneric with Tamanovalva. I don't think there is any purpose in just assuming that all these species are congeneric so my feeling is that we should continue to call this animal Tamanovalva limax until an anatomical review of the living species is conducted. That is why I have continued to use Midorigai and Edenttellina for the Australian species. Without evidence it is no more sensible to say they are the same as it is to say they are different.
I've decided to defer to the opinions of Rudman (2002) in using the generic name Tamanovalva.

        The following generalized description of Tamanovalva limax is taken from Kawaguti & Baba (1959):

        The animal is found on the green alga, Caulerpa okamurai, which grows on the submerged shore rocks where there is a strong current during ebb and flow tides. The whole body of the animal is deep green in colour. Without careful observation, it is difficult to detect the animal so perfectly protected in the native habitat by the shape and colour of the Caulerpa leaves. [sic]
        In an active state, the animal is in the form of an elongated slug; the head, the rhinophores and the foot are extended from the relaxed shell. It creeps using its narrow foot in such a way that the two valves of the shell are held vertically with their umbos at the top, When the animal is stimulated, the head and foot are withdrawn and the shell is tightly closed; the whole appearance of the animal is thus similar to that of the ordinary bivalve.
        The total length of the animal when extended is about 10 mm in the largest specimen.
        The head-part is small, measuring only two or three mm long (one-third of the shell length); the main part (shell and visceral sac) appears too large and heavy to pass smoothly; the foot tapers and is cut short towards the tail. Then, in locomotion, the head-part repeats occasional drawing of the main part of the body to the front. The animal always leaves a mucous thread in its track.
        ... When disturbed, the animal casts a white viscous matter from the hypobranchial gland through the posterior gape of the shell.

        Tamanovalva limax is currently unknown from Okinawa's main Island as of mid-March, 2002. The close proximity of the main island of Okinawa to the Kerama Islands, as well as the similar opisthofauna to that of the Kerama Islands, suggests the possibility that it is also present here on Okinawa proper. The above featured animal is one which was photographed in the waters of Zamami Island, one of a series of islands in the Kerama Islands Group, which are located 30 ~ 40 kilometers west of the Okinawa capitol, Naha. The featured animal was photographed by Atsushi Ono during February of 1999, on a buoy chain in 7m of water. Atsushi's photograph is used here with his kind permission and he considers the species to be rare; Atsushi reports (per. comm.) seeing only four individuals in the Keramas. I've added a second image of an additional specimen of T. limax showing the dorsal aspect of the two valves. This additional image is also furnished by Atsushi.

        Tamanovalva limax is one of three described species of these remarkable little bivalved sacoglossans found in Okinawan waters. The three species are:

  • Berthelinia schlumbergeri
  • Julia exquisita
  • Tamanovalva limax (the above featured animal)
  • Literature Cited:


    Page Date: 18 Mar '02
    Page Modification Date: 18 Mar '02
    Digitally manipulated photo
    Copyright © 2002 Robert F. Bolland