María Capa

New perspectives on the ecology and evolution of siboglinid tubeworms

Siboglinids are tube-dweling annelids that are important members of deep-sea chemosynthetic communities, which include hydrothermal vents, cold seeps, whale falls and reduced sediments. As adults, they lack a functional digestive system and rely on microbial endosymbionts for their energetic needs. Recent years have seen a revolution in our understanding of these fascinating worms. Molecular systematic methods now place these animals, formerly known as the phyla Pogonophora and Vestimentifera, within the polychaete clade Siboglinidae. Furthermore, an entirely new radiation of siboglinids, Osedax, has just recently been discovered living on whale bones. The unique and intricate evolutionary association of siboglinids with both geology, in the formation of spreading centres and seeps, and biology with the evolution of large whales, offers opportunities for studies of vicariant evolution and the calibration of molecular clocks. Moreover, new advances in our knowledge of siboglinid anatomy coupled with molecular characterization of microbial symbiont communities are revolutionizing our knowledge of host-symbiont relationships in the Metazoa. Despite these advances, considerable debate persists concerning the evolutionary history of siboglinids. Here we review the morphological, molecular, ecological and fossil data in order to address when and how siboglinids evolved. We discuss the role of ecological conditions in the evolution of siboglinids and present possible scenarios of the evolutionary origin of the symbiotic relationships between siboglinids and their endosymbiotic bacteria.

Phylogeny of Sabellidae (Annelida) and relationships with other taxa inferred from morphology and multiple genes

The monophyly of Sabellidae, the phylogenetic relationships of its lineages, and the composition of Sabellida have been debated for many decades. Most studies on sabellid phylogeny have focused on morphological features but little DNA work has been published to date. We performed analyses using maximum‐parsimony methods that included 36 sabellids and members of previously related taxa. We integrated morphological and DNA sequence data to resolve relationships at different hierarchical levels (135 morphological features, fragments of the nuclear ribosomal RNA genes 18S and 28S, and the mitochondrial gene 16S). The results indicate the monophyly of Sabellida, including Sabellidae and Serpulidae. Monophyly of Fabriciinae and Serpulidae is assessed and the two groups are recovered as sister taxa, but with weak support. There is no significant support for the monophyly of Sabellinae. Relationships between members of the Sabellidae are still partially unresolved due to incongruence between partitions and low support for most clades. The evolution and transformation of certain characters within Sabellidae is explored.
© The Willi Hennig Society 2010.

Taxonomic revision and phylogenetic relationships of apomorphic sabellids (Polychaeta) from Australia

Knowledge about the diversity and distribution of Australian coastal sabellids (Polychaeta) is still scarce. Examination of specimens housed in museum collections has increased the number of species recorded in Australia and helped to clarify the relationships among certain taxa of Sabellidae. Australian specimens belonging to a group of genera considered the most derived of the Sabellidae were the subject of this taxonomic revision, resulting in the description of five new species in four genera (Laonome calida, sp. nov.; Perkinsiana anodina, sp. nov.; P. longa, sp. nov.; Potaspina australiensis, sp. nov.; and Pseudopotamilla monoculata, sp. nov.). In addition, this is the first record of Potaspina Hartman, 1969 and Perkinsiana Knight-Jones, 1983 in Australia. A phylogenetic analysis of these and other apomorphic sabellids revealed their evolutionary relationships and supported the monophyly of most genera with the exception of Perkinsiana and Pseudopotamilla Bush, 1905. Some characters not considered in previous cladistic analyses were proven useful in elucidating relationships within Sabellidae. The diagnoses of Perkinsiana, Potaspina and Pseudopotamilla were emended. A dichotomous key is presented for identification of Australian apomorphic sabellids.

Cryptic diversity, intraspecific phenetic plasticity and recent geographical translocations in Branchiomma (Sabellidae, Annelida)

The importance of identifying biological diversity accurately and efficiently is becoming more evident. It is therefore critical to determine the species boundaries between closely related taxa and to establish diagnostic characters that allow us to define species. This is not an easy task when species exhibit high intraspecific phenotypic plasticity or when distinct evolutionary lineages with an unusually large amount of genetic distinctiveness show no apparent morphological diversity (cryptic species). These phenomena appear to be common in the genus of fan worms Branchiomma (Sabellidae, Annelida), and consequently, taxonomic errors are widespread in the group. Moreover, some Branchiomma species have been unintentionally translocated outside the area where natural range extension is expected, increasing the taxonomic problems. We have performed a range of analytical methods including genetic distances, Bayesian inference, maximum likelihood, maximum parsimony, statistical parsimony analyses and general mixed Yule coalescent model to clarify the taxonomic status and assess the species boundaries of Branchiomma in Australia. This study shows that the traditional diagnostic morphological features are greatly homoplastic. Results also indicate that the diversity of Branchiomma in Australia is higher than previously reported and evidence some cases of high phenetic plasticity (in features previously considered as stable within species), high intraspecific genetic variability, cryptic species and several unexpected cases of translocations.

Establishing species and species boundaries in Sabellastarte Krøyer, 1856 (Annelida: Sabellidae): an integrative approach

Sabellastarte Krøyer, 1856 (Sabellidae), a morphologically homogeneous group distributed in warm and temperate coasts of the Indo-Pacific and Caribbean Sea, is characterized by the presence of a unique combination of features. To date, the genus comprises eight species, but morphological characters traditionally used in diagnostics have shown intra-specific variability, making species boundaries and distributions unclear. The present study constitutes the first attempt to test the monophyly of Sabellastarte and its relationships to other sabellid genera by combining molecular (COI and 16S) and morphological data. Results include placement of a clade containing Stylomma, Sabella, Branchiomma and Bispira as the sister group to Sabellastarte. Phylogenetic analyses and genetic divergence among specimens from several localities around the world indicate the presence of at least six lineages within Sabellastarte. In the context of a discussion of species boundaries and diagnostic features, the distribution of some of those lineages can be explained by the presence of cryptic species and potential introductions.

A taxonomic guide to the fanworms (Sabellidae, Annelida) of Lizard Island, Great Barrier Reef, Australia, including new species and new records.

This comprehensive taxonomic work is the result of the study of fan worms (Sabellidae, Annelida) collected over the last 40 years from around the Lizard Island Archipelago, Great Barrier Reef, Australia. Some species described herein are commonly found in Lizard Island waters but had not previously been formally reported in the literature. Most species appear to be not particularly abundant, and few specimens have been collected despite the sampling effort in the area over this time period. After this study, the overall sabellid diversity of the archipelago has been greatly increased (by more than 650%). Before this revision, only four sabellid species had been recorded for Lizard Island, and in this paper we report 31 species, 13 of which belong to nominal species, six are formally described as new species (Euchone danieloi n. sp., Euchone glennoi n. sp., Jasmineira gustavoi n. sp., Megalomma jubata n. sp., Myxicola nana n. sp., and Paradialychone ambigua n. sp.), and the identity of 12 species is still unknown (those referred as cf. or sp.). Two species are newly recorded in Australia and two in Queensland. The invasive species Branchiomma bairdi is reported for the first time at Lizard Island. The genus Paradialychone is reported for Australia for the first time. Standardised descriptions, general photographs of live and/or preserved specimens and distribution data are provided for all species. New species descriptions are accompanied by detailed illustrations and exhaustive morphological information. A dichotomous key for sabellid identification is also included.

Comparative internal structure of dorsal lips and radiolar appendages in Sabellidae (Polychaeta) and phylogenetic implications.

Fan worms (Sabellidae) possess paired modified prostomial structures at the base of the radiolar crown, dorso‐lateral to the mouth, called dorsal lips. The dorsal lips are involved in the sorting of particles collected by the radiolar crown. The range of variation in the morphology of dorsal lips is extensive, and probably this is not only due to adaptations to different environments and feeding preferences but also due to phylogenetic constraints. In this study, we describe and compare the morphology of dorsal lips in a range of sabellid taxa based on histological cross‐sections of these structures, and compare our data and terminology with those of previous studies. Dorsal lips are maintained erect in most taxa by a modified radiole fused to them known as dorsal radiolar appendage. We suggest that dorsal radiolar appendages with an internal supporting axis (cellular or acellular) and probably also the ventral lips are synapomorphies of the family. J. Morphol., 2011.

Sabellariidae from Lizard Island, Great Barrier Reef, including a new species of Lygdamis and notes on external morphology of the median organ

We document herein the occurrence of three species of Sabellariidae at Lizard Island, Great Barrier Reef, including a new Lygdamis species. Sabellaria lungalla, described from Northern Territory, is reported for Queensland for the first time. The genus Gesaia, represented by a planktonic larva collected in shallow waters of the Archipelago, is a new record for Australia. Lygdamis nasutus n. sp. is characterised by one of the most conspicuous median organ described in the family (cylindrical, distally pigmented and is provided with a flattened, teardrop corona), its paleae morphology (with straight paleae, outer ones with asymmetrical pointed tips and subtle thecal sculpture and inner paleae with blunt tips and smooth surface), three lateral lobes on chaetiger 2, abdominal chaetigers with two type of neurochaetae, and notopodial uncini with 1-4 longitudinal rows of teeth. Comparison of the external morphology of the medial organ and median ridge of several species has been undertaken. Even though its function remains uncertain, the median organ morphology seems species specific and may provide relevant information about the evolutionary history and adaptations of sabellariids.

Sphaerodoridae (Annelida) from Lizard Island, Great Barrier Reef, Australia, including the description of two new species and reproductive notes.

Sphaerodorids are scarce at Lizard Island archipelago and other localities in the Great Barrier Reef, Australia. Intensive collections at a variety of habitats within the Lizard Island archipelago over the last four decades have resulted in a total of just 11 specimens. Nevertheless, they represent two new species and a new record for Lizard Island. Sphaerodoropsis aurantica n. sp. is characterised by nine longitudinal rows of sessile and spherical dorsal macrotubercles, arranged in a single transverse row per segment; parapodia with around 10 spherical papillae; and compound chaetae with thin shafts and long blades. Sphaerodoropsis plurituberculata n. sp. is characterised by more than 12 more or less clearly arranged longitudinal rows of sessile spherical dorsal tubercles (variable in size), in four transverse rows per segment; parapodia lacking papillae; and semi-compound chaetae with distally enlarged shaft and short blades. Ephesiella australiensis is reported for the first time in Lizard Island. Laboratory observations of live specimens of Sphaerodoropsis plurituberculata n. sp., revealed the use of spermatophores by males. These were found attached externally to the body surface of both sexes, indicating pseudo-copulation.

Phylogenetic hypothesis of Sphaerodoridae Malmgren, 1867 (Annelida) and its position within Phyllodocida

Sphaerodoridae is a small, morphologically well‐defined group of annelids, with remarkable spherical tubercles covering their body surface. They have generally been considered as part of Phyllodocida, but there is no consensus about its sister group relationships. Monophyly and internal phylogenetic relationships have never been tested. We present the first phylogenetic analysis of the family, including 33 individuals of 19 species in five genera of Sphaerodoridae, and a wide representation of other Phyllodocida, based on molecular data from nuclear 18S rDNA (2240 bp), mitochondrial 16S rDNA (614 bp), and cytochrome c oxidase subunit I (657 bp). Mitochondrial and nuclear loci were analysed separately and in combination using maximum parsimony, maximum likelihood and Bayesian inference. Results show maximum support for the monophyly of Sphaerodoridae, but sister group relationships remain unclear. The genera Sphaerodoropsis and Sphaerodoridium are found to be paraphyletic. Monophyly of Clavodorum, Ephesiella and Sphaerodorum could not be tested because only one species was included for each of these genera. At least six of the morphotypes included in the study do not fit within current species descriptions, suggesting undescribed species. Finally, the transfer of Sphaerodoropsis minuta back to Sphaerodoridium is proposed.