Reference: Bio/. Bull. 200: 281-297. (June 2001) Function and Functional Groupings of the Complex Mouth Apparatus of the Squat Lobsters Munida sarsi Huus and M. tenuimana G.O. Sars (Crustacea: Decapoda) A. GARM* AND J. T. H0EG Department of Zoomorpkology, Zoological Institute, University of Copenhagen. Universitetsparken 15, 2100 Copenhagen, Denmark Abstract. Like all other decapods, the anomuran squat lob-sters Munida sarsi and M. tenuimana have a mouth apparatus composed of six pairs of mouthparts plus labrum and para-gnaths (upper and lower lips). To study the functional signif-icance of this complexity, we examined the mouthparts with scanning electron microscopy and also observed their function directly, under laboratory conditions, using macro-video equipment. No differences were found between the two spe-cies. The movement patterns of the mouthparts are described in detail and illustrated as serial drawings. Proceeding from max-illipeds 3 towards the mandibles, the movement pattern gets increasingly stereotypical, with the mandibles performing but a single movement in a medio-lateral plane. From morphology, the mouthparts are subdivided into 20 parts, but from the functional analyses the 20 parts form 8 functional groups: /, transporting mouthparts (maxilliped 2 endopod and maxil-liped 3 endopod); 2, transporting aligning mouthparts (max-illiped 1 basis); 3, sorting-aligning mouthparts (maxilla 1 basis and maxilla 2 basis); 4, current-generating mouthparts (flagella of maxilliped 2 and maxilliped 3 exopods); 5, cutting-crushing mouthparts (incisor and molar processes, labium, and mandibular palp); 6, ingesting mouthparts (maxilla 1 coxa, maxilla 2 coxa, and maxilliped 1 coxa); 7. respiratory nunith-Received 2 February 2000; accepted 12 January 2001. * To whom correspondence should be addressed. E-mail:
[email protected] Abbreviations: Lb. labrum; Inc. incisor process, Mp, molar process; Mdp, mandibular palp: MX I cox, maxilla 1 coxa; Mxl bas. maxilla 1 basis; Mxl endo, maxilla 1 endopod; Mx2 cox. maxilla 2 coxa; Mx2 bas, maxilla 2 basis; Mx2 endo, maxilla 2 endopod; Scapho. scaphognathite; Mxpl cox, maxilliped 1 coxa; Mxpl bas, maxilliped 1 basis; Mxpl endo, maxilliped 1 endopod; Mxpl exo, maxilliped 1 exopod; Mxpl epi, maxilliped 1 epipod; Mxp2 endo, maxilliped 2 endopod; Mxp2 exo. maxilliped 2 exopod; Mxp3 endo, maxil-liped 3 endopod; Mxp3 exo. maxilliped 3 exopod. pans (scaphognathite, maxilliped 1 epipod, and maxilliped 2 and maxilliped 3 exopods); and 8, dorso-ventral mouthparts (maxilla 1 endopod, maxilla 2 endopod, maxilliped 1 endopod, and maxilliped 1 exopod). These groupings apply mostly to the processes of food handling and have little significance with respect to grooming. When comparing our results to the liter-ature on other decapods, we found much resemblance to con-ditions in other anomurans. Introduction One of the most interesting features among crustaceans is their very complex mouth apparatus. The basic limb-pattern for Eucrustacea (the condition in the stem species to all recent Crustacea) was a labrum, paired paragnaths, and two pairs of mouthparts (mandibles and maxillae 1), followed by a large number of more-or-less similar limbs ( Walossek, 1998). Extant members of the Cephalocarida retain this system, but almost all other recent species have at least three pairs of mouthparts, i.e., mandibles (Md), maxillae 1 (Mxl ), and maxillae 2 (Mx2). Further specialization of the mouth apparatus is a very significant event in most crustacean lineages and often involves the specialization of thoracic limbs for food manipulation. This is especially so in the Decapoda, which has the first three pairs of thoracic ap-pendages, the maxillipeds (Mxpl -3). specialized into feed-ing appendages. In many of these decapods, the feeding apparatus is even more advanced since one or more of the pairs of pereiopods, especially if chelate, take part in food manipulation. This complexity has without doubt played an important role in the success of the Decapoda, since it enables the members of the order to feed on such a great diversity of food objects (Schembri, 1982c; Cartes, 1993). 281
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