MORPHOLOGY OF THE MOUTHPARTS OF LARVAL LOBSTERS,HOMARUS AMERICANUS(DECAPODA: NEPHROPIDAE), WITH SPECIAL EMPHASIS ON THEIR SETAE

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Abstract
A detailed account of the morphology of the mouthparts in larval lobsters (Homarus americanus) and the setae they bear is given. Mouthparts were observed with light- and scanning electron microscopy. The types of setae found on the mouthparts are described and a scheme for their classification, with the distribution of the various setal types is presented. A classification scheme consists of 10 major categories. Detailed descriptions of the mouthparts and the distribution of their setae are presented and major developmental trends are noted. Changes in the mouthparts which occur as lobsters pass through the first 4 stages generally include increases in the size of mouthparts and in the number of setae they bear. Of special interest is the transformation of the comparatively delicate teeth of the 1st stage mandible into the massive molars of the 4th stage. The coordinated development of teeth on the gnathal lobe of the mandible and on the ischium of the 3rd maxilliped emphasizes the coordinated manner in which these appendages function. The development of the mandibles and 3rd maxillipeds enables lobsters to deal successfully with the more substantial food they encounter in the benthic environment, which they usually enter at the 4th or 5th stage. The various functions and possible functions (e.g., chemosensory, tactile and mechanical) of mouthpart setae are discussed in the light of available functional and physiological evidence. The possibility of filter feeding in lobsters, particularly in the constantly-swimming planktonic larval forms, is considered.