Resolving evolutionary relationships in groups that underwent fast radiation in deep time is a problem for molecular phylogeny, as the scant phylogenetic signal that characterises short internal branches is generally swamped by more recent substitutions. We implement an approach, that maps how the support for rival phylogenies changes when analysing subsets of sites with either faster and more ...

Studies examining population structure and genetic diversity of benthic marine invertebrates in the Southern Ocean have emerged in recent years. However, many taxonomic groups remain largely unstudied, echinoderms being one conspicuous example. The brittle star Astrotoma agassizii is distributed widely throughout Antarctica and southern South America. This species is a brooding echinoderm and t...

Feeding arms carrying coelomic extensions of the theca are thought to be unique to crinoids among stemmed echinoderms. However, a new two-armed echinoderm from the earliest Middle Cambrian of Spain displays a highly unexpected morphology. X-ray microtomographic analysis of its arms shows they are polyplated in their proximal part with a dorsal series of uniserial elements enclosing a large coel...

Msx (/msh) family genes encode homeodomain (HD) proteins that control ontogeny in many animal species. We compared the structures of Msx genes from a wide range of Metazoa (Porifera, Cnidaria, Nematoda, Arthropoda, Tardigrada, Platyhelminthes, Mollusca, Brachiopoda, Annelida, Echiura, Echinodermata, Hemichordata, and Chordata) to gain an understanding of the role of these genes in phylogeny. Ex...

Echinoderms are unique in being pentaradiate, having diverged from the ancestral bilaterian body plan more radically than any other animal phylum. This transformation arises during ontogeny, as echinoderm larvae are initially bilateral, then pass through an asymmetric phase, before giving rise to the pentaradiate adult. Many fossil echinoderms are radial and a few are asymmetric, but until now ...

Of the major deuterostome groups, the echinoderms with their multiple forms and complex development are arguably the most mysterious. Although larval echinoderms are bilaterally symmetric, the adult body seems to abandon the larval body plan and to develop independently a new structure with different symmetries. The prevalent pentamer structure, the asymmetry of Lovén's rule and the variable lo...

Description of a new species from Australia, belonging to the subgenus Selenkothuria (Holothuria, Aspidochirotida). A dichotomous key of the thirteen valid species included in the subgenus is also given. The species H. perrieri Thandar, 1977 and H. spinea Cherbonnier, 1988 are considered as non valid.

Although it has been known for many years that certain muscles of echinoderms are responsive to acetylcholine (ACh) (Bacq, 1935, i937> 1939; de Buy 1936; Iriye & Dille, 1940; Sawaya, 1951; Prosser & Judson, 1952; Ambache & Sawaya, 1953; Florey & McLennan, 1959) further studies on the pharmacology of these muscles have mostly been limited in scope. We have recently developed a preparation of the...

Ribosomal RNA (rRNA) genes are probably the most frequently used data source in phylogenetic reconstruction. Individual columns of rRNA alignments are not independent as a consequence of their highly conserved secondary structures. Unless explicitly taken into account, these correlation can distort the phylogenetic signal and/or lead to gross overestimates of tree stability. Maximum likelihood ...