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Date of Award

1979

Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)

Department

Marine Sciences

First Advisor

Edmund H. Smith

First Committee Member

Steven Obrebski

Second Committee Member

James A. Blake

Third Committee Member

Dwight W. Taylor

Abstract

The morphology of the proboscis--particularly the epiproboscis, the feeding behavior, the function(s) of the epiproboscis, and the functional morphology of the epiproboscis, were studied in Mitra idea Melville and fi. catalinae Dall (Gastropoda: Neogastropoda; Mitridae.

In M. idae, the epiproboscis is an extensible muscular J-shaped rod which curves under the odontophore, and lies parallel to the longitudinal axis of the proboscis. A muscular external sheath encloses that portion of the epiproboscis which lies within the proboscis haemacoel; an invaginated muscular-epithelial internal sheath covers the ventral part of the epiproboscis. The dorsal part of the epiproboscis consists principally of longitudinal muscle; the ventral part of the epiproboscis consists principally of circular muscle surrounding a core of longitudinal muscle. Specialized postural muscles are present along the surface of, and within the circular muscle of, the ventral part of the epiproboscis.

The epiproboscis of M. idae was observed to perform four functions: (1) prey location during attachment of the proboscis to the prey; (2) retrieval of prey viscera; (3) leverage and physical support of the odontophore; and (4) assistance in maintaining a hold on the prey as the proboscis attempts to retract. The anterior displacement of blood along the surface of the epiproboscis serves to protract the organ. The external and internal sheaths displace and contain this blood. The musculature of the epiproboscis provides postural control and assists in retraction of the epiproboscis.

The epiproboscis of M. catal inae was observed to act as a buccal pump to withdraw small volumes of the prey's body fluid, and small numbers of eggs from gravid adults. The anterior displacement of blood within the epiproboscis serves to protract the organ. The external and internal sheaths displace this blood and maintain the cross-sectional form of the epiproboscis, respectively. The musculature of the epiproboscis retracts it. The epiproboscis of M. catalinae is part of a functional unit which includes a pair of peristomial lips and the esophagus. A model was proposed to account for the coordinated actions of each part of this functional unit. These are the first observations of the function and functional morphology of the mitrid epiproboscis.

In M. idae and M. catalinae, the salivary gland ducts connect to the. epiproboscis., and open to the outside of the anterior tip of the epiproboscis as a common lumen. The significance of the presence of the ducts within the epiproboscis remains unclear, but there is no evidence that the ducts carry a toxic or venomous substance.

The behavioral events leading up the prey are similar in both species. of the act and means of attachment of to attachment of the proboscis to Differences exist in the details the proboscis to the prey.

The proboscis morphology of M. idae is representative of other members of the subfamily Mitrinae. The probsocis morphology of M.· catalinae is very different from M. idae with respect to: (l) the peristomial rim; (2) the epiproboscis;-(3) the odontophore; ( 4) the radula; and (5) the esophagus. M. catalinae should probably be placed within the subfamily Cylindromitrinae.

M. idae and M. catalinae feed on supinculids, as do other species of mitrids studied. The observed function of the epiproboscides of these two species, and the essentially homogenous diet of mitrids in general, suggest that the epiproboscis is an adaptation for feeding on softbodied reclusive prey which occupy some form of protective confinement.

A model of the evolution of the epiproboscis is proposed, beginning with a structure analogous to the subradular organ of other gastropods, and ending with the -M. -idae epiproboscis type.

Pages

154

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