Comparative morphology and phylogeny of the family Thompsoniidae (Cirripedia, Rhizocephala, Akentrogonida), with descriptions of three new genera and seven new species

Abstract

Hoeg, J. T. & Lutzen, J. 1993. Comparative morphology and phylogeny of the family Thompsoniidae (Cirripedia, Rhizocephala, Akentrogonida), with descriptions of three new genera and seven new species.-Zool. Scr. 22: 363-386.Akentrogonid rhizocephalans morphologically resembling the genus Thompsonia are revised as a result of examination of new material. The species concerned are all obligatorily colonial and have ovoid or cylindrically shaped externae with a terminal stalk and a much reduced anatomy. A numerical cladistic analysis of all Rhizocephala Akentrogonida using the Hennig86 program leads to a redefinition of the Thompsoniidae H0eg and Rybakov, 1992. Autapomorphies for the Thompsoniidae are primarily the morphology of the attachment to the host and the total absence of a mesentery. The cladistic analysis refutes that the Thompsoniidae should have a plesiomorphic morphology and branch off very low on the rhizocephalan phylogeny. The family now comprises four genera: Pottsia gen. n. (monotypic), Diplothylacus gen. n. with two species, Thompsonia Kossmann with five species. A revived and redefined Thylacoplethus Coutiere includes eight species. The genera are distinguished by the location of the spermatogenic tissue, the site where the eggs are fertilized, the presence or absence of a mantle pore and the way it is formed, the number or absence of oviducts, and the number of cuticular annuli on the stalk. All 16 species, of which six are new to science, are described when necessary, and, if possible, illustrated. A phylogeny for the redefined family is proposed. Thylacoplethus is morphologically closest to the hypothetically ancestral thompsoniid and is likely paraphyletic. The new genus Polysaccus with two species, one of them new to science, and the monotypic genus Pirusaccus Lutzen resemble thompsoniids in externa morphology and in being obligatorily colonial.Thompsonia-like species and their position within the Rhizocephala. Material and methodsThe reproductive bodies (externae) of the following species were examined: Pottsia plesionikae gen. et sp. n.; Thylacoplethus edwardsi Coutikre; T. squillae sp. n.; T. africanus sp. n.; T. magellani sp. n.; T. orientalis sp. n.; Diplothylacus thalamitae gen. et sp. n.; Polysaccus mediterraneus (Caroli), gen. n. and P. japonicus sp. n. Most of the species had been preserved in alcohol, but even if the fixative was formalin ( T . squillae and T. thalamitae), preservation turned out to be poor because of improper penetration. The best results were obtained with fixation in 2% glutaraldehyde (P. japonicus).

Thylacoplethus isaevae sp. nov., a new colonial rhizocephalan (Crustacea: Rhizocephala: Thompsoniidae) parasitic on a north-west Pacific hermit crab Pagurus trigonocheirus

“…Other Akentrogonida, like Duplorbidae, may have more complex spermatogenic bodies with a proper epithelial covering and specialized 'nurse' cells (Rybakov & HÖeg, 1992). Similar spermatogenic bodies with an epithelial envelope, which probably originated from the cells of female externa and 'nurse cells' have been described in a few species of the family Thompsoniidae, namely Thompsonia japonica Ha« fele, 1911 and T. littoralis Lu« tzen & Jespersen, 1990; they might also be present in Thylacoplethus cubensis (Reinhard & Stewart, 1956) (Ha« fele, 1911Reinhard & Stewart, 1956;Yanagimachi & Fujimaki, 1967;Lu« tzen & Jespersen, 1990, 1992HÖeg & Lu« tzen, 1993). Complex spermatogenic bodies have never been observed in any other species of Thompsoniidae.…”

Comparative ultrastructure of the root system in Rhizocephalan barnacles (Crustacea: Cirripedia: Rhizocephala)

“…The Chthamalophilidae are monophyletic and closely related to the Duplorbidae both in the phylogeny of Bocquet-Védrine and Bourdon (1984) and in the numerically cladistic study of Høeg and Lü tzen (1993). It is therefore a more parsimonious solution to consider the bladder-shaped root in Chthamalophilus delagei as an advanced trait.…”

The biology and life cycle of the Rhizocephala (Cirripedia)

“…Therefore it is difficult to propose generalizations concerning host-parasite co-evolution, especially considering that we have only just begun to understand the phylogeny of the Rhizocephala (Hoeg & Liitzen, 1993).…”