Meeting Abstract
S8.9 Wednesday, Jan. 6 Phylogeny, evolution, and systematics of the stalked jellyfishes (Cnidaria, Staurozoa) COLLINS, Allen G.; National Systematics Lab of NOAA’s Fisheries Service collinsa@si.edu
An early divergence within Medusozoa gave rise to the class Staurozoa. A relatively species poor group, there are approximately 50 species of benthic, stalked jellyfishes distributed in two orders. Many species are cryptic in their habitats — most being found in near shore, temperate to polar waters on macroalgae — and rarely encountered. As part of the Cnidarian Tree of Life project, a collaborative team has been working on conducting the most comprehensive phylogenetic analysis of the group possible. Our sampling includes 21 species representing four of the five families and 10 of the 13 genera. From these we have derived sequence data from five markers: nuclear 18S, 28S, and ITS1-2, and mitochondrial 16S and COI. Analyses of these data yield results with very little conflict resulting from marker or optimality-criterion choice. A claustrum vertically dividing the gastric cavities of some species appears to have evolved more than once, so the traditional orders defined by the presence/absence of this feature, Cleistocarpida and Eleutherocarpida, should be abandoned. Instead, it appears that an early divergence within Staurozoa separated those species with (the plesiomorphic condition) and without four septal muscles in the peduncle. Early diverging lineages within Staurozoa tend to have ephemeral primary tentacles that disappear during ontogeny. Those species with primary tentacles retained as adults appear to form a grade that has given rise to a clade characterized by the presence of rhopalioids or anchors. Some straightforward nomenclatural changes can bring the taxonomy of Staurozoa more closely in line with our phylogenetic results. We also calculate within and between species divergences with available data and conclude that mitochondrial 16S would make the most suitable “barcode” marker for the group.
