title: A study of the mechanisms by which the cercariae of Microphallus primas (Jag, 1909) Stunkard, 1957 penetrate the shore crab, Carcinus maenas (L).
abstract: This study established the mechanisms by which Microphallus primas cercariae penetrate the crab Carcinus maenas in which they form metacercarial cysts. Light and electron microscopy were used to investigate cercarial features and to follow the fate of cercariae released in close proximity to crabs. It was shown that cercariae were carried in respiratory currents into crabs' branchial chambers where each enveloped itself in a transparent penetration cyst on the gill lamellae. When cercariae were present the number of respiratory current reversals performed by crabs increased. Using an 'artificial branchial chamber' it was possible to observe how cercariae attached to crab gills during breaks in current flow that preceded each current reversal. Inside the penetration cysts the now tail-less larvae used their stylets to pierce holes through which they levered themselves into underlying haemolymph channels in the gills. Histochemical tests demonstrated that the penetration cysts were products of glands in the cercariae and that penetration of the crabs was achieved by mechanical means. The importance of crab respiratory current reversals to the success of cercarial penetration is discussed as it represents the exploitation by a parasite of a host behavioural response to an unrelated stimulus.
authors.affiliation: School of Environmental Sciences, University of Ulster at Jordanstown, Shore Road, Newtownabbey, Co. Antrim, BT37 0QB, N. Ireland. DH.Saville@ulster.ac.uk
authors.forename: D H
authors.initials: DH
authors.lastname: Saville
authors.forename: S W B
authors.initials: SW
authors.lastname: Irwin
mesh_terms: D000818:Animals; D003386:Brachyura / Q000469:parasitology*; D005880:Gills / Q000469:parasitology*; D008018:Life Cycle Stages; D008854:Microscopy, Electron; D008855:Microscopy, Electron, Scanning; D014200:Trematoda / Q000254:growth & development / Q000502:physiology* / Q000648:ultrastructure