Functional morphology of parasitic isopods: understanding morphological adaptations of attachment and feeding structures inNerocilaas a pre-requisite for reconstructing the evolution of Cymothoidae

Abstract

Parasites significantly influence food webs and ecosystems and occur all over the world in almost every animal group. Within crustaceans there are numerous examples of ectoparasites; for example, representatives of the isopod group Cymothoidae. These obligatory parasitic isopods are relatively poorly studied regarding their functional morphology. Here we present new details of the morphological adaptations to parasitism of the cymothoiid ingroup Nerocila with up-to-date imaging methods (macro photography, stereo imaging, fluorescence photography, micro CT, and histology). Central aspects of the study were (1) the morphology of the mouthparts and (2) the attachment on the host, hence the morphology of the thoracopods. The mouthparts (labrum, mandibles, paragnaths, maxillulae, maxillae, maxillipeds) form a distinct mouth cone and are most likely used for true sucking. The mouthparts are tightly “folded” around each other and provide functional rails for the only two moving mouthparts, mandible and maxillula. Both are not moving in an ancestral-type median-lateral movement, but are strongly tilted to move more in a proximal-distal axis. New details concerning the attachment demonstrate that the angular arrangement of the thoracopods is differentiated to impede removal by the host. The increased understanding of morphological adaptation to parasitism of modern forms will be useful in identifying disarticulated (not attached to the host) fossil parasites.

168 million years old “marine lice” and the evolution of parasitism within isopods

“…1f) [59, 66]. Such an arrangement also appears to be present in the fossil specimens studied here (Figs.…”

“…Adults have retained well-developed eyes [85]. The morphology of the mouthparts and thoracopods is strongly modified for a temporary parasitism on fish, comparable to a “marine mosquito”.The ground pattern of the unnamed sister group to Aegidae (including Cymothoidae, Urda, Gnathiidae, Epicaridea, character transition state 4) still includes a mouth cone [59, 66, 73]. Seven thoracopods (II-VIII) are now modified for better attachment to the host with hook-like dactyli [67, 73].…”

Feeding strategies in arthropods from the Rhynie and Windyfield cherts: ecological diversification in an early non-marine biota

“…Similar arrangements have been described in various mandibulate arthropods (e.g. in isopods; [22]). This arrangement allows the mandible a certain forward movement, which could have been used for a type of piercing motion, for example, to feed on fungal hyphae [23 -25].…”

Host-Parasite Interaction between Parasitic Cymothoid Ceratothoa oestroides and Its Host, Farmed European Sea Bass (Dicentrarchus labrax)

“…Another cymothoiid, Nerocila sp. possesses mouthparts that form a distinct mouth cone used for true sucking, which is performed by their tight folding around each other, likewise providing functional rails for the movement of only mandible and maxillula [16]. Authors also recognised that mandible and maxillula seem to be able to cut off small tissue pieces from the host, facilitated by sharp incisor regions and spines of mandibles.…”