Nauplii, copepodids and adults of a new mesoparasitic genus and species of Chitonophilidae, Lepetellicola brescianii, are described from the pallial cavity of a deepwater
cocculiniform limpet, Lepetella sierrai, collected in the Bay of Biscay and
Gulf of Cádiz. Re‐examination of the type material of the recently established
Nucellicolidae revealed several important observational errors in the original description,
such as the oversight of the rootlet system in the adult female and misinterpretations
of the tagmosis and antennulary segmentation in the late copepodid. Lamb
et al.’s (1996) criteria used to justify the familial distinctiveness
of the Nucellicolidae are all invalid. The family is relegated to a junior synonym
of the Chitonophilidae on the basis of overwhelming support provided by copepodid
and adult morphology. The impact of heterochrony on the body plan of adults and developmental
stages is discussed. Phylogenetic analysis supports a basal dichotomy dividing the
Chitonophilidae into a mesoparasitic clade, utilizing exclusively polyplacophoran
hosts, and a sisterclade grouping genera associated with chitons, prosobranch gastropods
and cocculiniform limpets. The presence of maxillipeds and postmaxillipedal apodemes
in the adult males of the latter clade is considered as apomorphic rather than plesiomorphic,
being the result of incomplete moulting and correlated with the ventral position
of the genital apertures. Nucellicola is identified as the sistergroup of
the only other endoparasitic genus, Tesonesma, found in the body cavity of chitons. The inferred relationships indicate that host switching has occurred twice in the evolution of the Chitonophilidae.
Examination of the antennulary segmentation and setation patterns of copepodids in Lepetellicola and Nucellicola unequivocally refutes both the current
placement of the Chitonophilidae in the Poecilostomatoida and its alternative assignment
to the Siphonostomatoida. Exclusion from the Poecilostomatoida is reinforced by the
absence of a coxo‐basis in the antenna. The family is placed with the cyclopoids,
providing further evidence for the crown‐group status of the Poecilostomatoida within
the currently paraphyletic Cyclopoida. A critical review of the published reports
of brooding in cocculiniform limpets demonstrated that there is, as yet, no tangible
evidence for this phenomenon in either the Lepetelloidea or Cocculinoidea. ©
2002 The Linnean Society of London, Biological Journal of the Linnean Society,
2002, 75, 187–217.
