Phylogenetics and evolution of Capitata (Cnidaria: Hydrozoa), and the systematics of Corynidae

Abstract

Nawrocki, A. M., Schuchert, P. & Cartwright, P. (2010). Phylogenetics and evolution of Capitata (Cnidaria: Hydrozoa), and the systematics of Corynidae.-Zoologica Scripta, 39, 290-304. Generic-and family level classifications in Hydrozoa have been historically problematic due to limited morphological characters for phylogenetic analyses and thus taxonomy, as well as disagreement over the relative importance of polyp vs. medusa characters. Within the recently redefined suborder Capitata (Cnidaria: Hydrozoa: Hydroidolina), which includes 15 families and almost 200 valid species, family level relationships based on morphology alone have proven elusive, and there exist numerous conflicting proposals for the relationships of component species. Relationships within the speciose capitate family Corynidae also remain uncertain, for similar reasons. Here, we combine mitochondrial 16S, and nuclear 18S and 28S sequences from capitate hydrozoans representing 12 of the 15 valid capitate families, to examine family level relationships within Capitata. We further sample densely within Corynidae to investigate the validity of several generic-level classification schemes that rely heavily on the presence ⁄ absence of a medusa, a character that has been questioned for its utility in generic-level classification. We recover largely congruent tree topologies from all three markers, with 28S and the combined dataset providing the most resolution. Our study confirms the monophyly of the redefined Capitata, and provides resolution for family level relationships of most sampled families within the suborder. These analyses reveal Corynidae as paraphyletic and suggest that the limits of the family have been underestimated. Our results contradict all available generic-level classification schemes for Corynidae. As classification schemes for this family have been largely based on reproductive characters such as the presence ⁄ absence of a medusa, our results suggest that these are not valid generic-level characters for the clade. We suggest a new taxonomic structure for the lineage that includes all members of the newly redefined Corynidae, based on molecular and morphological synapomorphies for recovered clades within the group.

Phylogenetic placement of Hydra and relationships within Aplanulata (Cnidaria: Hydrozoa)

“…These are congruent with previous phylogenetic analyses utilizing CO1 or 16S (Collins et al, 2005;Nawrocki et al, 2010;Ortman et al, 2010;Schuchert, 2010), and others utilizing nuclear ribosomal markers Cartwright and Nawrocki, 2010;Collins et al, 2006;Nawrocki et al, 2010). In contrast to 28S, the ribosomal marker 18S does not provide strong support at deep nodes.…”

Additions to the hydroids (Cnidaria, Hydrozoa) of the Bay of Fundy, northeastern North America, with a checklist of species reported from the region

“…Syncoryna lovenii M. Sars, 1846, a species in which mature medusoids usually remain attached to the hydroid (Broch 1916;Hartlaub 1916;Edwards 1978Edwards , 1983Schuchert 2001bSchuchert , 2012, is now assigned to Sarsia Lesson, 1843. Molecular studies support that classification (Collins et al 2005;Nawrocki et al 2010), with S. lovenii being genetically close to S. tubulosa (M. Sars, 1835), type species of Sarsia by monotypy.…”

On the paraphyly of Cytaeididae and placement of Cytaeis within the suborder Filifera (Hydrozoa: Anthoathecata)

“…Molecular phylogenetic studies have significantly clarified the classification and systematics of anthoathecate hydrozoans and defined their major lineages including Aplanulata, Capitata, and four filiferan clades (Collins 2000(Collins , 2002Collins et al 2005Collins et al , 2006Collins et al , 2008Cartwright et al 2008;Cartwright and Nawrocki 2010;Nawrocki et al 2010). Two of the more closely related lineages are Filifera III (Hydractiniidae L. Agassiz, 1862, Stylasteridae Gray, 1847 and Filifera IV (Bougainvilliidae Lütken, 1850, Cytaeididae L. Agassiz, 1862, Oceaniidae Eschscholtz, 1829, Pandeidae Haeckel, 1879, Rathkeidae Russell, 1953 (Cartwright et al 2008: Figs.…”