Splanchnotrophid systematics: a case of polyphyly and taxonomic myopia

The Splanchnotrophidae is a small family of bizarre poecilostomatoid copepo ds which utilize marine opisthobranch gastropods, including nudibranchs and pteropods, as hosts. Species have traditionally been placed in this family primarily on the basis of host affiliation, largely neglecting the fundame ntal differences in morphology and paying virtually no attention to the con cept of homology. Morphological analysis based on detailed re-examination o f types and newly obtained material from existing museum collections reveal ed that the Splanchnotrophidae comprises genera drawn from three different families in addition to one non-copepodan taxon. The family Splanchnotrophi dae is redefined to include only Splanchnotrophus Hancock and Norman, 1863, Ismaila Bergh, 1867, Lomanoticola Scott and Scott, 1895, and two new monot ypic genera. All splanchnotrophids are endoparasites of nudibranch and saco glossan opisthobranchs and show a vast size disparity between the sexes cau sed by hypermorphosis in the female. The genus Splanchnotrophus is restrict ed here to the European species and assumes a boreo-mediterranean distribut ion. It is redefined on the basis of redescriptions given for S. gracilis N orman and Hancock, 1863, and S. angulatus Hecht, 1893. The Western Australi an species S. elysiae Jensen, 1990, and S. sacculatus O'Donoghue, 1924, are re-examined and placed in two new genera, Arthurius and Ceratosomicola, re spectively. Re-examination of the mouthparts provided unambiguous evidence justifying formal placement of Briarella Bergh, 1876, in the Philoblennidae , a family thus far known only as ectoparasites from prosobranch gastropods in the Far East. The inadequately described genus Chondrocarpus Bassett-Sm ith, 1903, is provisionally placed as genus incertae sedis in this family. A new family Micrallectidae is proposed to accommodate Micrallecto Stock, 1 971. The genus Nannallecto Stock, 1973, is regarded as a junior subjective synonym of the latter because the generic distinction was largely based on two glaring observational errors: the absence of maxillae in M. uncinata St ock, 1971, caused by imperfect removal of the parasite from the host, and t he presence of a chelate leg 2 in N. fusii Stock, 1973, which in reality is a feature of the developing nauplii visible through the body wall of the b rooding female. Previous interpretations of the mouthparts in Micrallecto w ere essentially unsound. Micrallectids are ectoparasites of gymnosome ptero pods and display a unique, extremely abbreviated life cycle, involving leci thotrophic nauplii and highly paedomorphic ovoviviparous adults that attain sexual maturity at the metanaupliar stage. Inspection of pteropod collecti ons in the Natural History Museum led to the discovery of the first male sp ecimen providing conclusive evidence for the proposal of a new family. The Micrallectidae is placed in the Poecilostomatoida on the basis of antennary armature, mandibular palp morphology and mating posture. The genus Megalle cto Gotto, 1986, is based on a head fragment of a hyperiid amphipod that wa s erroneously interpreted upside down and back to front. Its type species M . thirioti Gotto, 1986, is identified as a junior subjective synonym of Phr osina semilunata Risso, 1822, a widely distributed and very abundant hyperi id in the Atlantic.