Stuart R. Gelder

Zoogeography of branchiobdellidans (Annelida) and temnocephalidans (Platyhelminthes) ectosymbiotic on freshwater crustaceans, and their reactions to one another in vitro

The zoogeographical distribution of branchiobdellidans (Annelida) and temnocephalidans (Platyhelminthes), ectosymbiotic on freshwater crustaceans, is reviewed and revised. In the areas where the Holarctic branchiobdellidans and Gondwanian temnocephalidans overlap, distributions of species and their respective hosts are reviewed in detail. Specimens of the branchiobdellid, Branchiobdella astaci, and the scutariellid temnocephalidan, Bubalocerus pretneri, were allowed to meet in vitro on the dorsal carapace of a crayfish, Austropotamobius pallipes. This usually resulted in the scutariellid being ingested by a branchiobdellid. Specimens of B. astaci were placed in contact with the host of B. pretneri, Troglocaris sp., a cave-dwelling shrimp and the branchiobdellid immediately moved away from the shrimp.

Phylogenetic relationships of annelids, molluscs, and arthropods evidenced from molecules and morphology.

Annelids and arthropods have long been considered each others closest relatives, as evidenced by similarities in their segmented body plans. An alternative view, more recently advocated by investigators who have examined partial 18S ribosomal RNA data, proposes that annelids, molluscs, and certain other minor phyla with trochophore larva stages share a more recent common ancestor with one another than any do with arthropods. The two hypotheses are mutually exclusive in explaining spiralian relationships. Cladistic analysis of morphological data does not reveal phylogentic relationships among major spiralian taxa but does suggest monophyly for both the annelids and molluscs. Distance and maximum-likelihood analyses of 18S rRNA gene sequences from major spiralian taxa suggest a sister relationship between annelids and molluscs and provide a clear resolution within the major groups of the spiralians. The parsimonious tree based on molecular data, however, indicates a sister relationship of the Annelida and Bivalvia, and an earlier divergence of the Gastropoda than the Annelida-Bivalvia clade. To test further hypotheses on the phylogenetic relationships among annelids, molluscs, and arthropods, and the ingroup relationships within the major spiralian taxa, we combine the molecular and morphological data sets and subject the combined data matrix to parsimony analysis. The resulting tree suggests that the molluscs and annelids form a monophyletic lineage and unites the molluscan taxa to a monophyletic group. Therefore, the result supports the Eutrochozoa hypothesis and the monophyly of molluscs, and indicates early acquisition of segmented body plans in arthropods.

Did the lumbriculids provide the ancestors of the branchiobdellidans, acanthobdellidans and leeches?

Revision of the literature concerning Agriodrilus (Oligochaeta, Lumbriculidae) and Acanthobdella (Acanthobdellida), both supposedly intermediate links in the traditional single line of evolution between lumbriculids, branchiobdellidans, and leeches, supports the alternative hypothesis of an independent origin of most if not all of these groups. Discovery of Phagodrilus, a lumbriculid that is clearly convergent with Agriodrilus in terms of the pharynx, lends further support to this concept. No decision as to the rankings of the various taxa can be made until new material of Acanthobdella is examined and all variable characters are used to determine synapomorphic character states and monophyletic groupings within this complex.

New records and distributions of two North American branchiobdellidan species (Annelida: Clitellata) from introduced signal crayfish, Pacifastacus leniusculus, in Japan

This is the first report of two North American branchiobdellidans, Sathodrilus attenuatus Holt, 1981, and Xironogiton victoriensis Gelder and Hall, 1990, on the signal crayfish, Pacifastacus leniusculus (Dana, 1852) introduced into Japan from the Columbia River system, northwestern North America. Signal crayfish from 12 localities in eastern and northern Hokkaido, Japan, were examined and each supported S. attenuatus. In addition, an individual of this species was found on preserved material from Ishikawa Prefecture, central Honshu. All of these branchiobdellidans reported in Hokkaido most probably came from the original population of signal crayfish introduced into Lake Mashu, Hokkaido, Japan, in 1930. It is suggested that the use of non-pathogenic branchiobdellidans, when present, provides an easy method for tracing the spread of crayfishes around Japan and could also be applied in other countries and continents. Specimens of X. victoriensis were only found on crayfish in a stream at Akashina in Nagano Prefecture, central Honshu, Japan. Although the signal crayfish appears to be displacing the endemic Japanese crayfish, C. japonicus, no native branchiobdellidans were found on any of the introduced signal crayfish examined.

Phylogenetic positions of the aberrant branchiobdellidans and aphanoneurans within the Annelida as derived from 18S ribosomal RNA gene sequences

Different hypotheses have been proposed on the phylogenetic relationships of branchiobdellidans and aphanoneurans among the Annelida based on the anatomical and embryological characters. The 18S ribosomal RNA gene sequences have been analyzed from representatives of the three major taxa of the Annelida plus the branchiobdellidans and aphanoneurans to assess their phylogenetic relationships to each other. In this preliminary study, all of the phylogenetic analyses show the branchiobdellidans as a sister group to the leeches, rather than the oligochaetes. The position of the aphanoneurans is stable as an independent taxon that evolved after the polychaetes branched from the evolutionary stem, but before the ancestral oligochaetes emerged.

A report on branchiobdellidans (Annelida: Clitellata) and a taxonomic key to the species in northern Italy, including the first record of Cambarincola mesochoreus on the introduced American red swamp crayfish

Abstract Specimens of Austropotamobius pallipes were found to support Branchiobdella italica, B. parasita, B. astaci, and B. hexodonta, either alone or in a combination, in Piedmont, Liguria, Lombardy, Emilia and Friuli‐Venezia Julia. The American Cambarincola mesochoreus occurs on the introduced Lousiana red swamp crayfish, Procambarus (S.) clarkii, also in Piedmont. A taxonomic key to the species reported in northern Italy is given.

Phylogenetic assessment of the Branchiobdellidae (Annelida, Clitellata) using 18S rDNA, mitochondrial cytochrome c oxidase subunit I and morphological characters

Using 18S rDNA, mitochondrial cytochrome c oxidase subunit I and morphological characters, the Branchiobdellidae (Annelida, Clitellata) were shown to form a monophyletic group distinct from the leeches using two distant ‘oligochaetes’ as outgroups. The study used 20 branchiobdellid species from 14 genera in four subfamilies with these representing each of the taxon’s three distributional regions in the Holarctic realm. No monophyletic groups were found using the gene sequence data that related to either geographical regions or currently recognized subfamilies. However, two monophyletic groups were strongly supported; the two European species of Branchiobdella and the combination of Sathodrilus attenuatus and Xironogiton victoriensis. The latter pair is taxonomically diverse, but sympatric on Signal crayfish, Pacifastacus leniusculus, in California, USA.

TAXONOMIC CONSIDERATIONS AND DISTRIBUTION OF THE BRANCHIOBDELLIDA (ANNELIDA: CLITELLATA) ON THE NORTH AMERICAN CONTINENT

Abstract A brief review of the taxonomic history and integrity of selected North American branchiobdellidans is given to clarify their current status. The zoogeographical distribution of branchiobdellidans on the North American continent is presented based on published reports and information in the Catalog of the National Museum of Natural History, Smithsonian Institution, Washington, DC. These data are tabulated by species with locations referenced to zoogeographical subregions, political units of provinces, states, or countries, and source citations. Distributional anomalies of certain taxa are discussed.

A phylogenetic assessment of the branchiobdellidan family Branchiobdellidae (Annelida, Clitellata) using spermatological and somatic characters

The spermatozoa of six species belonging to the branchiobdellidan family Branchiobdellidae (i.e. Xironogiton victoriensis, Cirrodrilus kawamurai, Ankyrodrilus legaeus, Xironodrilus formosus, Branchiobdella kobayashii, Branchiobdella orientalis) were studied and compared to the other sperma‐tozoa already described in the group. A parsimony analysis was performed on the spermatozoal data of the species examined, as well as on their somatic characters. The results of the two analyses were contrasted and a further parsimony analysis was run on the matrix comprising both sets of characters. The study of sperm ultrastructure confirmed the genera recognized with traditional somatic characters and the monophyly of the branchiobdellidans. Xironodrilus was proved to be the sister species of Ankyrodrilus and its inclusion into the family Branchiobdellidae was supported. Evolutionary hypotheses on intergeneric differences in the family consistent with its biogeography can be suggested by the cladograms: Xironogiton is an early offshoot of branchiobdellidan lineage migrating to North America and probably radiating only in recent times; Branchiobdella kobayashii has a spermatozoon completely different from that of the other species of the genus, thus suggesting a complex story for this widespread taxon with a disjunct distribution.

Molecular phylogeny of North American Branchiobdellida (Annelida: Clitellata)

Branchiobdellidans, or crayfish worms, are ectosymbiotic clitellate annelids associated primarily with freshwater crayfishes. The main objectives of our study were to infer a molecular phylogeny for the North American Branchiobdellida, examine its congruence with morphology-based hypotheses of relationships at the subfamily and genus level, and use our dataset to assess consistency of GenBank-archived branchiobdellidan sequences. We used nucleotide sequence data from two mtDNA genes (COI and 16S rDNA) and three nuclear genes (28S rDNA, 18S rDNA, and ITS1) to estimate phylogenetic relationships among 47 described and one undescribed species of Branchiobdellida. We recovered a monophyletic branchiobdellidan clade with generally short branch lengths, suggesting that a large portion of the taxon has likely undergone a recent and rapid radiation in North America. Results from our phylogenetic analyses indicate that current taxonomic groupings are largely unsupported by the molecular data. All four subfamilies are either paraphyletic or polyphyletic, and only three of seven sampled non-monotypic genera were monophyletic. We found a high rate (49%) of inconsistency in GenBank-archived sequences, over 70% of which can be attributed to field- or laboratory-based error.