Taxonomic studies involving only adult forms of organisms may not necessarily provide complete information about differentiation of species or about the evolutionary relationships between species grouped in higher taxa. The taxonomic importance of embryonic or larval morphology has been limited only by the lack of detailed comparative morphological work on development. Fretter (1967) has shown that larval shell characteristics are reliable for taxonomic identification of some British prosobranchs. Ostergaard (1950) proposed using the structure of egg masses, larval shell type and developmental characteristics to confirm adult taxonomic position. In recent literature reviews of the larval biology of opisthobranch, it has become apparent that a considerable amount of plasticity occurs with respect to patterns for development. Often, closely related species have radically different developmental types. Even different populations of a single species may exhibit different development. Often the ecology of the adults of closely related species is also different. However, it is not possible to make meaningful correlations between the biology of the adults and the larvae unless additional ecological and developmental information is available. There is a clear need for studies of larval development and the ways in which larval characteristics and embryology are correlated with adult biology in marine organisms. Aspects of the larval development and adult ecology of Phyllaplysia taylori Dall, are reported in this study.

Beetles of the genus Mordellistena Costa are submitted to a morphometric analysis as a more feasible method of identification and as a foundation for the construction of a phylogeny. In the past, species groups were based on questionable morphological characters and a morphological analysis is an attempt, through numerical methods, to eliminate such doubts. Thirty external characters were chosen for measurement in a preliminary statistical analysis of four well defined species groups. These results were submitted to a discriminant analysis which reduced the number of significant characters to 14. Over 500 specimens were then measured for these characters and the results were then submitted to a cluster analysis. The results of the analysis illuminated several relationships among the genus. The analysis found 14 major groups (five or more members), 25 minor groups (4 or fewer members), and 102 odd specimens not assigned to any group. The major groups, two of the minor groups, and the 102 odd specimens are discussed in detail. The accomplishments of the study included an expansion of the list of species of Mordellistena for Arizona, the discovery of several previously undescribed species, a more confident method of identification, and the foundation of a phylogeny for the genus. Shortcomings of the study were the failure to construct species specific groups and failure to group 102 specimens. Both successes and failures of the study are discussed in detail and explanations are offered. The major successes of the study were the formation of a basis for a complete revision of the genus Mordellistena and the foundation of a phylogeny for the group.