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ABSTRACT Morphological trends or clines in a variety of morphometric, meristic, and two-state characters are described and analysed for the caridean shrimp genus Heptacarpus. One objective of this study was to determine the evolutionary polarity (ancestral to derived) in these various morphoclines. Evidence from functional morphology and out-group comparison strongly support the hypothesis that a high epipod (epipod-setobranch complex) number is primitive in Heptacarpus and related genera and that a lower number represents the derived or advanced condition (epipod loss). The evolutionary polarity in epipod number is used to hypothesize the direction of evolution in morphoclines that are significantly correlated with epipod number. Using this criterion, Heptacarpus species with high epipod number, a short high caparace, short and high abdominal segments, a short rostrum, large first chelae, a high number of antennular spinules, and a branchiostegal setal fringe are considered primitive with respect to these characters. Heptacarpus species which are farthest from the hypothesized ancestral form show a reduced epipod number, a slender or elongate carapace shape, elongate abdominal segments, a proportionately long rostrum, small first chelae, a reduced number of antennular spinules, and no branchiostegal setal fringe. Species groups are formed on the basis of morphological similarity from the 16 Heptacarpus species examined in detail. An index of affinity, based on 17 characters, was calculated for all possible pairs of species. A group is formed by species which show a significant morphological similarity (index of affinity greater than 0.5) to all other members of the group. The phylogenetic validity of species groups formed by this phenetic method was tested by examining the concordance in epipod number among members of a particular group. Evidence is given that epipod number is an indicator of phylogenetic relationships.

Affiliations: 1: Department of Biology, University of Puerto Rico, Rio Piedras, Puerto Rico 00931.


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