Opisthobranch of the Week Data
Living specimens of Bulla ampulla are considered to be very rare on the main island of Okinawa as I have collected only six individuals; all six were found over a period of a few hours during an early morning minus spring tide "reef walk" (approx. 01:00am). The specimens were all found within a radius of 5m, crawling on the surface of mixed silty-sand and strewn coral rubble-bottom tidal pools. The six were found together as pairs, but they were neither mating nor were any ova found in the general vicinity of the animals. Remarkably, the shells of this and other closely related Bulla spp. are commonly found on numerous sandy beaches here. These shells are so commonly seen that one would imagine the living animals would be seen far more frequently. I've included an image of some of these Bulla shells, which are without collection data. These shells have been collected from the wrack lines of miscellaneous Okinawan beaches over several years. I've included the image to show the color variation of some of these commonly found shells.
Rudman (2001), in an opinion on the Slug Forum mentions the following:
Species of Bulla are found both in tropical and temperate waters. They are herbivorous but they seem to be quite unrelated to any other herbivorous group or to any other group of opisthobranchs for that matter. They have a strange relatively soft radula, and the gizzard has three * large crushing plates and ancillary spines rather than the grinding plates of the other herbivores such as Haminoea. The Bullidae seem to have evolved separately from a very early stage in the evolutionary history of the opisthobranchs, although some recent hypotheses disagree with this interpretation.
All species of Bulla have very similarly shaped shells and there is clearly some confusion in their taxonomy at present. Unfortunately little difference has been found in the morphology of the radular teeth, or any other part of the anatomy, of the species of the genus that have been investigated.
They appear to be nocturnal, burrowing in soft sediment or hiding under coral slabs during the day.
There has also been a great deal of confusion in the past as to the correct use of the several generic names. Willan (1978) discusses the confusion associated with the generic name of this group of shelled cephalaspids.
* Note: This page previously stated erroneously that Bulla spp. have 4 gizzard plates. Paula Mikkelson (per. comm.) pointed this out to both Bolland & Rudman and the text has been corrected on both this page as well as on the Slug Forum.