GASTROPOD EGG CAPSULES AND THEIR CONTENTS FROM DEEP-SEA HYDROTHERMAL VENT ENVIRONMENTS

Egg capsules from three different prosobranch gastropods were retrieved from the Galapagos Rift and Juan de Fuca Ridge deep-sea hydrothermal vent fields. The morphology of these capsules and their excapsulated embryos and larvae are described and illustrated. Based on their capsule type and the protoconch morphology of their contained larvae, 29 lenticular capsules from the Galapagos Rift could be attributed to a provisionally described neogastropod turrid, Phymorhynchus sp. But 3 inflated, triangular capsules from the Galapagos Rift, and 56 different egg capsules from the Juan de Fuca Ridge, each shaped like an inflated pouch, could not be unambiguously assigned to a member of the known vent gastropod fauna. The mode of development and potential for dispersal is inferred from egg capsule type, the number of embryos per capsule, and protoconch characters comparable to those of confamilial shallow-water gastropods for which the type of development is known. These criteria and a comparison to the known juvenile shell morphology of Phymorhynchus sp., suggest that, after encapsulation, this species develops planktotrophically and is capable of long-range dispersal. Similar evidence suggests that the larvae contained in the inflated triangular capsules from the Galapagos Rift may also develop planktotrophically after hatching; but the larvae in the pouch-like egg capsules from the Juan de Fuca Ridge probably develop non-planktotrophically without a dispersal stage. These developmental patterns are characteristic of shallow-water members of the systematic groups to which these species belong, indicating, as previous studies have shown, that vent gastropods can persist in these patchy, ephemeral environments in the absence of unique adaptations allowing dispersal between active hydrothermal sites.