Character evolution in light of phylogenetic analysis and taxonomic revision of the zooxanthellate sea anemone families Thalassianthidae and Aliciidae

Abstract

Aliciidae and Thalassianthidae look similar because they possess both morphological features of branched outgrowths and spherical defensive structures, and their identification can be confused because of their similarity. These sea anemones are involved in a symbiosis with zooxanthellae (intracellular photosynthetic algae), which is implicated in the evolution of these morphological structures to increase surface area available for zooxanthellae and to provide protection against predation. Both families have been classified in Endomyaria; the phylogenetic relationships within this group are poorly known. I analyzed mitochondrial and nuclear sequences to hypothesize phylogenetic relationships between and within Aliciidae and Thalassianthidae. I recovered Thalassianthidae as monophyletic and nested in a well-supported clade containing some members of Stichodactylidae, within the larger Endomyaria clade. Monophyly of Aliciidae was not recovered, but all members were affiliated with the larger Metrididoidea clade, and closely related with Boloceroididae. Sea anemones in a symbiotic relationship with crabs of the genus Lybiahave been identified as Triactis producta, which I confirmed with molecular data. The similarity between Aliciidae and Thalassianthidae is a case of convergence, supported by both molecular and morphological data. The branched outgrowths and spherical defensive structures in Thalassianthidae are of the oral disc, while in Aliciidae they are projections of the column. To understand the diversity of species possessing branched outgrowths and spherical structures, I did a morphological revision of both Aliciidae and Thalassianthidae. From the seven nominal genera and 16 nominal species of Aliciidae, I found four genera and nine species to be valid. From the five nominal genera and 11 nominal species of Thalassianthidae, I found two genera and seven species to be valid. Each family, genus, and species has been redescribed.