Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.

A newly compiled data set of nearly complete sequences of the large subunit of the nuclear ribosome (LSU or 28S) sampled from 31 diverse medusozoans greatly clarifies the phylogenetic history of Cnidaria. These data have substantial power to discern among many of the competing hypotheses of relationship derived from prior work. Moreover, LSU data provide strong support at key nodes that were equivocal based on other molecular markers. Combining LSU sequences with those of the small subunit of the nuclear ribosome (SSU or 18S), we present a detailed working hypothesis of medusozoan relationships and discuss character evolution within this diverse clade. Stauromedusae, comprising the benthic, so-called stalked jellyfish, appears to be the sister group of all other medusozoans, implying that the free-swimming medusa stage, the motor nerve net, and statocysts of ecto-endodermal origin are features derived within Medusozoa. Cubozoans, which have had uncertain phylogenetic affinities since the elucidation of their life cycles, form a clade-named Acraspeda-with the scyphozoan groups Coronatae, Rhizostomeae, and Semaeostomeae. The polyps of both cubozoans and hydrozoans appear to be secondarily simplified. Hydrozoa is comprised by two well-supported clades, Trachylina and Hydroidolina. The position of Limnomedusae within Trachylina indicates that the ancestral hydrozoan had a biphasic life cycle and that the medusa was formed via an entocodon. Recently hypothesized homologies between the entocodon and bilaterian mesoderm are therefore suspect. Laingiomedusae, which has often been viewed as a close ally of the trachyline group Narcomedusae, is instead shown to be unambiguously a member of Hydroidolina. The important model organisms of the Hydra species complex are part of a clade, Aplanulata, with other hydrozoans possessing direct development not involving a ciliated planula stage. Finally, applying phylogenetic mixture models to our data proved to be of little additional value over a more traditional phylogenetic approach involving explicit hypothesis testing and bootstrap analyses under multiple optimality criteria. [18S; 28S; Cubozoa; Hydrozoa; medusa; molecular systematics; polyp; Scyphozoa; Staurozoa.].

MATERIAL AND METHODSFor morphological methods see Schlichen (1996;2004) or Bouillon et al. (2004). Where possible, it was attempted to supplement the species descriptions with 16S DNA sequence information. This allows a much more precise evaluation of the specimens used and will facilitate the work of future re visors. The methods to obtain 16S DNA sequences are described in Schuchert (2005). All new sequences have been submitted to the EMBL database under the accession numbers AM411408-AM411423. Some of the sequences mentioned here have already been used in Schuchert & Reiswig (2006). Phylogenetic analyses were done as described in Schuchert (2005). Additionally, Maximum Likelihood analyses were performed using the program PHYML described by Guindon & Gascuel (2003).

The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Capitata Part 1. -This study reviews all European hydrozoan species belonging to the capitate families Acaulidae, Boreohydridae, Candelabridae, Cladocorynidae, Cladonematidae, Margelopsidae, Pennariidae, Protohydridae, and Tricyclusidae. Updated diagnoses for the families and genera are provided and existing taxonomic problems solved or at least outlined. Candelabrum verrucosum Bonnevie, 1898 is regarded as a valid species and redescribed based on a new record from Greenland. Although Spadix purpurea Gosse, 1853 may be a senior synonym of Candelabrum cocksii (Cocks, 1854), the latter is regarded as the valid name, this because the former name has not been used after 1899, while the latter has been widely used [ICZN article 23.9.1.1]. Likewise, two senior synonyms of Eleutheria claparedii Hartlaub, 1898 are declared as invalid as they have never been used since their original introduction by Haeckel.

Hydroidolina is a group of hydrozoans that includes Anthoathecata, Leptothecata and Siphonophorae. Previous phylogenetic analyses show strong support for Hydroidolina monophyly, but the relationships between and within its subgroups remain uncertain. In an effort to further clarify hydroidolinan relationships, we performed phylogenetic analyses on 97 hydroidolinan taxa, using DNA sequences from partial mitochondrial 16S rDNA, nearly complete nuclear 18S rDNA and nearly complete nuclear 28S rDNA. Our findings are consistent with previous analyses that support monophyly of Siphonophorae and Leptothecata and do not support monophyly of Anthoathecata nor its component subgroups, Filifera and Capitata. Instead, within Anthoathecata, we find support for four separate filiferan clades and two separate capitate clades (Aplanulata and Capitata sensu stricto). Our data however, lack any substantive support for discerning relationships between these eight distinct hydroidolinan clades.