Published online by Cambridge University Press: 06 April 2009
1. Recent studies by Gerichter have demonstrated that I have erred in referring the skrjabingylin lungworms to the family Trichostrongylidae.
2. On the basis of his data and a re-evaluation of my theories of metastrongylid evolution it is suggested that the Skrjabingylinae (except Dictyocaulus) are close to the Filaroidinae and that quite possibly the position of the vulva in the former is the consequence of a secondary shift from opening just anterior to the anus to opening in the mid-region of the body; the ‘trichostrongylid’ configuration of the ovejectoral apparatus would thus be convergent.
3. The genus Dictyocaulus is removed from the Skrjabingylinae and left in a subfamily Dictyocaulinae in the family Metastrongylidae, although its trichostrongylid affinities are very suggestive. If trichostrongylid, this genus is considered to exhibit convergence with the metastrongylids and not to represent an evolutionary link between the two families.
4. The nature of metastrongylid life cycles is discussed, and the compatibility of known data with the evolutionary scheme proposed for the family is pointed out. It is evident that in metastrongylids symbiotizing marine littoral and pelagic hosts (Pinnipedia and Odontoceti) larval development must rely upon new intermediate host groups if the basic pattern has been retained from ancestors in terrestrial hosts.
5. The possible importance of histological studies and of investigations on chromosome number and structure for a further understanding of the evolution of the suborder Strongylina is pointed out.
6. A revised scheme for the evolution of the Metastrongylidae is presented as Fig. 1. The family Metastrongylidae now includes six subfamilies: Metastrongylinae, Filaroidinae, Skrjabingylinae, Pseudaliinae, Protostrongylinae, and Dictyocaulinae. The basic premises previously expressed (Dougherty, 1949b) on the evolution of the family are retained in the amended scheme.