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The palaemonid shrimp Creaseria morleyi is widely distributed along the northen portion of the Yucatan Peninsula inhabiting submerged cave systems. A High degree of morphological variation is evident in the shape of the carapace and the relative lengths of the first two pereiopods in the larger organisms. In order to find an explanation for these changes in taxonomically important characters, a morphometric analysis was undertaken. Several body parts as well as individual articles of the first and second pereiopods were measured for a total of 24 variables. The equation Y=aXb, was used to calculate the divergence from isometry in relation to caparace length. Males ranged in total length from 31.6 to 49.3 mm and females from 31.8 to 65.6 mm. For males, all regressions considering body variables showed negative allometry, except for gonopod length. For females, the only variable showing positive allometry was carapace width, suggesting that as females increase in size the carapace becomes wider than longer. Regarding the first pereiopod, almost all variables showed negative allometry; males an females did not differ markedly in this respect. For the second pereiopod, males showed negative allometry; however, for females, chela related dimensions exhibited positive allometric growth, consistent with the divering morphology of the larger females. Regressions for males and females were significantly different describing a sexual dimorphism. Graphic representations of the tendencies show that significant changes in the morphology, or in the level of allometry, occur in females at sizes between 46 and 60 mm of total length. Inglés

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