Preliminary observations on the mandibles of palaemonoid shrimp (Crustacea: Decapoda: Caridea: Palaemonoidea)

Abstract

The mandibles of caridean shrimps have been widely studied in the taxonomy and functional biology of the group. Within the Palaemonoidea the mandibles reach a high level of structural diversity reflecting the diverse lifestyles within the superfamily. However, the majority of studies have been restricted to light microscopy, with the ultrastructure at finer levels poorly known. This study investigates the mandible of nine species belonging to six of the recognised families of the Palaemonoidea using SEM and analyses the results in a phylogenetic and dietary framework. The results of the study indicate that little phylogenetic information is conveyed by the structure of the mandible, but that its form is influenced by primary food sources of each species. With the exception of Anchistioides antiguensis, all species examined possessed cuticular structures at the distal end of the pars molaris (molar process). Five types of cuticular structures are recognised herein, each with a unique form, but variable in number, placement and arrangement. Each type is presumed to have a different function which is likewise related to diet.

An improbable opportunistic predator: the functional morphology ofPinna nobilis(Bivalvia: Pterioida: Pinnidae)

“…Interestingly, based on similar stable isotope carbon measurements, Kennedy et al (2001) concluded that the commensal pinnotherid Pontonia pinnophylax (Otto, 1821) assimilated similar food to its bivalve host P. nobilis . Further, and based on the form of the mandibles in the palaemonoids examined by Ashelby et al (2015), six types appear to relate to an individual taxon's feeding mode and/or diet. Pontonia pinnophylax has Type A mandibles that are also typical of the largely carnivorous palaemonid Palaemon macrodactylus Rathbun, 1902.…”

Let’s be pals again: major systematic changes in Palaemonidae (Crustacea: Decapoda)

“…5A). In fact, even in Gnathophyllum elegans , the type species of the family Gnathophyllidae, a vestigial incisor is present (see Ashelby, De Grave & Johnson, 2015 , Fig. 5A).…”

Coming out of your shell or crawling back in: multiple interphylum host switching events within a clade of bivalve- and ascidian-associated shrimps (Caridea: Palaemonidae)

“…This is congruent with the host choices of the species in most of the studied genera (supplementary appendix S1), but this does not explain the seemingly difficult switch from one phylum to another. One explanation for these seemingly unexpected host switching events can be found in the internal structures of the host phyla: the studied shrimp species living inside bivalve molluscs are reported as inhabitants of the mantle cavity (e.g., Fransen, 1994), feeding from the mucus and pseudofeces which are built up near the gills (e.g., Kennedy et al, 2001;Ashelby et al, 2015;De Grave et al, 2021). This soft, mucus-producing internal cavity might be morphologically similar to the pharyngeal basket of phlebobranch and stolidobranch solitary ascidians (Horká et al, 2016, for comparison, see Monniot, 1991.…”