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Observations on the Biology of Mudshrimps of the Genus Callianassa (Anomura: Thalassinidea) in Mississippi Sound

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The apparent habitat isolation of the mudshrimps Callianassa islagrande Schmitt and Callianassa jamaicense louisianensis Schmitt (Anomura : Thalassinidea) in Mississippi Sound is a function of species-related differences in ability to burrow and survive in the significantly different substrates of each habitat. C. islagrande is found only in sand bottomed beaches of the offshore barrier islands, whereas C. j. louisianensis is found only in the muddy backwaters of the mainland and Deer Island. Both forms produce deep and extensive permanent or semipermanent burrows in their respective habitat and are probably of some significance in sediment turnover. Laboratory studies show that C. j. louisianensis can only burrow efficiently in mud and cannot burrow or survive in sand unless there is sufficient available mud with which this form constructs its burrow walls. The inability of C. islagrande to tolerate silt limits its ability to burrow and survive in mud. For this reason C. islagrade cannot inhabit the muddy inshore waters. The poor burrowing efficiency of C. j. louisianensis in sand is due to a mechanical inability to handle uncohesive sand grains. The foliaceous third maxillipeds and comparatively larger second and third pereipods of C. islagrande (compared with those of C. j. louisianensis) are adaptations to a sandy habitat, enabling greater burrowing efficiency per unit of effort. Adults and juveniles exhibited the same behavior patterns in aquarium studies. Settling juveniles probably exhibit the same behavior pattern as adults and juveniles.

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