PRONOUNCED HETEROCHELY IN THE GHOST SHRIMP, NEOTRYPAEA-CALIFORNIENSIS(DECAPODA, THALASSINIDEA, CALLIANASSIDAE) - ALLOMETRY, INFERRED FUNCTION AND DEVELOPMENT

To understand their function and ontogeny better, we conducted a morph ometric analysis of claw size and shape variation in the strikingly he terochelous, north-eastern Pacific ghost shrimp, Neotrypaea (formerly Callianassa) californiensis. Master claws approached 25% of total body weight in mature males, but rarely exceeded 10% in females. Minor cla ws were less than 3% of body weight in both sexes. The proportions of right and left master claws did not differ significantly from 50:50. M ales exhibited a greater positive allometry than females in both maste r and minor claw size, though master claws differed more than minor cl aws. Sexual dimorphism was also observed in master but not minor claw shape: compared to females, mature male master claws: a) were proporti onally higher relative to their length; b) exhibited a deeper propodal notch and consequently a larger gape; c) developed a more slender and more distally hooked dactyl; and d) exhibited more well-developed tee th about the periphery of the claw gape. The shape of the conspicuous gape in mature male master claws bore a close resemblance to the cross -section of similar-sized master claws. The shape of this gape, and th e presence of fine teeth about its periphery, strongly suggests that m aster claws function in a highly stereotyped form of grappling during agonistic encounters or perhaps during mating between similar-sized co nspecifics. In addition, a landmark morphometric analysis of relative growth suggested that the pronounced propodal notch develops via local ized deformations near the base of the fixed finger rather than via a more generalized contraction of the ventral manus region. Finally, a p reliminary survey suggests that the distinctive propodal notch, which may be diagnostic of the hypothesized grappling function, has evolved at least twice in the Callianassidae, once in the Callianassinae and o nce in the Callichirinae. Sexual selection may have significantly infl uenced the evolution of these unusual master claws.