Naupliar Development among the Tisbidae (Copepoda: Harpacticidae) with a Phylogenetic Analysis and Naupliar Description of Tisbe thailandensis from Thailand

Ovigerous females of a recently described species Tisbe thailandensis were collected from the seaweed Enteromorpha clathrata on the eastern coast of Thailand and cultured in the laboratory. Six naupliar stages are described, and a key to the identification of the stages is provided. An unweighted analysis of the character matrix yielded a single most parsimonious tree with a length of 27, a consistency index of 0.778, a retention index of 0.786, and a rescaled consistency index of 0.611. There were 15 parsimoniously informative characters. The resulting cladogram, using nauplii from the harpacticoid genus Tachidius (Giesbrecht, 1881) for the outgroup comparison, supports the hypothesis that T. gracilis is the sister taxon of T. cucumariae (both of which belong to the T. gracilis group), and that T. battagliai is the sister taxon of T. holothuriae (both of which belong to the T. holothuriae group), with Tisbe thailandensis adjoining the T. gracilis group on an underived branch. Naupliar comparisons of copepodid morphology provided the greatest number of phylogenetically useful additional characters since copepodids essentially foreshadow the adult condition. Limits of the utility of naupliar characters for phylogenetic inference studies were apparent, as well as their potential and importance for future work in zoological systematics. It was shown that phylogenetic relationships of tisbids are difficult to evaluate on a morphological basis alone, because of the comparatively small morphological differences among them. However, more specific morphological characters can be found, provided studies are detailed enough and different stages of a sufficient number of species are known to allow meaningful comparisons.