The ultrastructure of the parasite—host interface of three tetraphyllidean tapeworms of the elasmobranchRaja naevus

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Abstract
Ultrastructural examination of the parasite-host interface of three tetraphyllidean cestodes ofRaja naevus(sectioned attached to the intestine) indicates that while the strobilar tegument of each closely follows the typical cestode pattern that of the bothridia has several modifications probably associated with attachment. Microtriches similar to those of the strobilum are absent, although small spines onEcheneibothriumsp. andPhyllobothrium pirieiand wart-like structures onAcanthobothrium quadripartitumbothridia are considered to represent the osmiophilic tips of specialized microtriches. The bothridia of the three species have no apparent function in the absorption of food but evidence suggests that the apical pad of the myzorhynchus ofEcheneibothriumis specialized for the uptake of nutrients directly from the submucosa of the host intestine to which it is applied. Attachment and sensory roles by the myzorhynchus are also indicated.EcheneibothriumandP. pirieibothridia severely damage the host mucosal surface, while those ofA. quadripartitumdo little harm. This difference is probably associated with the size, mobility and mode of attachment of the cestodes. There are indications that the bothridia ofEcheneibothriumupset the metabolism of mucosal cells in the attachment region. The tips of the strobilar microtriches ofA. quadripartitumare shown to function in the attachment of the strobilum to the host mucosa, and in the protection of the microthrix proximal surfaces by a filtering action.