The Teuthoid Radula as a taxonomic criterion, with specific reference to the families Architeuthidae and Ommastrephidae (Cephalopoda: Coleoidea)

Aldrich, Margueritte Luise Marks (1969) The Teuthoid Radula as a taxonomic criterion, with specific reference to the families Architeuthidae and Ommastrephidae (Cephalopoda: Coleoidea). Masters thesis, Memorial University of Newfoundland.

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Abstract

A study of the radular morphology of Cephalopoda was undertaken to determine the feasibility of its use as a taxonomic character. -- A search of the literature for illustrations of radular teeth of as many species as possible was made. Using available original material studies were also carried out using preparations of additional species. Where possible, comparisons were made based on both original preparations and information from the literature. In all, a total of 92 species representing 22 families were considered and are illustrated herein. -- A comparison of the illustrations and radular ribbon preparations of these specimens indicated morphological differences of such a degree as to facilitate separation even to the species level. -- The illustrations and radular ribbon preparations of members of the Family Architeuthidae show that both historical records and current specimens from Newfoundland waters exhibit similarities in the configuration of their radular teeth. There are, however, sufficient differences in the morphology of the teeth of individual specimens to cast serious doubt upon the designation of all five specimens as Architeuthis dux. Other families, genera, and indeed species within genera, can be separated on the basis of their radulae. Since this is true, the situation in the Architeuthidae becomes increasingly difficult to interpret on the basis of their radulae and on the limited amount of material available. -- The members of the Family Ommastrephidae show definite familial similarities in their radular teeth. The recorded differences in the morphology of these teeth, however, facilitate their separation into genera, but subspecies of the genus Illex cannot be so separated. The three subspecies can be separated on the basis of radular morphometry. Also, the radular apparatus of Illex illecebrosus coindetii is apparently to be added to the list of characters exhibiting sexual dimorphism in that form. -- The evidence cannot support the view that the cephalopod radula is without function. As suggested by Bidder and others, the radula functions in teuthoid forms as an aid in swallowing. Such usage causes a wearing-away of the cusps of the teeth and occasional loss of teeth, necessitating their continual replacement at the most posterior, or growing, portion of the radular ribbon. -- Because of the above described phenomenon, only teeth from certain rows (those retained within the radular sac) are of such a uniform configuration as to warrant their use in taxonomy.

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