Exploring the macrostructural anatomy of dendrochirotid sea cucumber's (Echinodermata) calcareous rings under micro-computed tomography and its bearing on phylogeny.

Despite descending from heavily calcified ancestors, the holothuroid skeleton is fully internal and composed of microscopic ossicles and a ring of plates bound by connective tissue, the calcareous ring. The calcareous ring exhibits a complex and poorly understood morphology; as a result, establishing unambiguous homology statements about its macrostructure has been challenging and phylogenetic studies have had to simplify this important structure. Here, we provide the first broad comparative study of Dendrochirotida calcareous rings using micro-computed tomography (µCT). A detailed description of the three-dimensional macrostructure of the calcareous ring of 10 sea cucumber species, including rare and type specimens, is presented. The structures observed were highly variable at the subfamily level, especially at the point of tissue attachment. The relationship between the calcareous ring and its associated organs, and their functional morphology are discussed. To aid future phylogenetic studies, we listed 22 characters and performed a preliminary cladistic analysis. The topology obtained supports the idea that the simple, cucumariid ring is ancestral to the mosaic-like phyllophorid ring; however, it did not support the monophyly of the cucumariids. It also did not support the family Sclerodactylidae, which was described based on the ring morphology. Differently from the dermal ossicles, which are highly homoplastic, the general homoplasy index of the calcareous ring characters was relatively low. This result highlights the importance of this structure for phylogenetic inference. Unfortunately, time since collection, rough collection methods and fixation can damage the skeleton, and the calcareous ring is often overlooked in taxonomic descriptions. The data presented here will improve our understanding of holothuroid relationships and facilitate studies on holothuroid functional morphology and biomechanics.

Worms and gills, plates and spines: the evolutionary origins and incredible disparity of deuterostomes revealed by fossils, genes, and development.

Deuterostomes are the major division of animal life which includes sea stars, acorn worms, and humans, among a wide variety of ecologically and morphologically disparate taxa. However, their early evolution is poorly understood, due in part to their disparity, which makes identifying commonalities difficult, as well as their relatively poor early fossil record. Here, we review the available morphological, palaeontological, developmental, and molecular data to establish a framework for exploring the origins of this important and enigmatic group. Recent fossil discoveries strongly support a vermiform ancestor to the group Hemichordata, and a fusiform active swimmer as ancestor to Chordata. The diverse and anatomically bewildering variety of forms among the early echinoderms show evidence of both bilateral and radial symmetry. We consider four characteristics most critical for understanding the form and function of the last common ancestor to Deuterostomia: Hox gene expression patterns, larval morphology, the capacity for biomineralization, and the morphology of the pharyngeal region. We posit a deuterostome last common ancestor with a similar antero-posterior gene regulatory system to that found in modern acorn worms and cephalochordates, a simple planktonic larval form, which was later elaborated in the ambulacrarian lineage, the ability to secrete calcium minerals in a limited fashion, and a pharyngeal respiratory region composed of simple pores. This animal was likely to be motile in adult form, as opposed to the sessile origins that have been historically suggested. Recent debates regarding deuterostome monophyly as well as the wide array of deuterostome-affiliated problematica further suggest the possibility that those features were not only present in the last common ancestor of Deuterostomia, but potentially in the ur-bilaterian. The morphology and development of the early deuterostomes, therefore, underpin some of the most significant questions in the study of metazoan evolution.

Taxonomy of the sea stars (Echinodermata: Asteroidea) from Bahia State, including ontogenetic variation and an illustrated key to the Brazilian species.

Describing ontogenetic morphological change is an important part of integrative taxonomy; still, most taxonomic studies are based only on adult characters. Here, we provide illustrations and a morphological description of the sea stars from Bahia, including ontogenetic and intraspecific variation, and identify taxonomic issues. A total of 293 specimens from different localities along the Bahia State coastline and comparative material from other localities were examined. Eighteen species (11 genera, eight families) of Asteroidea were identified; Astropectinidae was the most representative family. All species identified also occur in subtropical Brazilian waters and most species are from shallow water habitats with soft bottoms. Most observed ontogenetic variation was quantitative in nature, such as the increase in the number of spines in the furrow and of spinelets in the paxillae with specimen growth. Genera that require further taxonomic studies are Astropecten and Othilia, whose specimens are commonly misidentified in local studies. One third of the species from Bahia are currently classified as "Vulnerable" in the Brazilian Red List, but baseline data on the population biology of these species are scarce. An illustrated identification key to the 65 Brazilian sea star species is also provided. This taxonomic study will facilitate the identification of specimens occurring along the Brazilian coast and help scientists and policy makers to establish the conservation status of the Brazilian species.

Synchrotron micro-CT scanning leads to the discovery of a new genus of morphologically conserved echinoid (Echinodermata: Cassiduloida).

Here we use synchrotron radiation-based micro-computed tomography (SRµCT) images of type specimens to confidently place Cassidulus malayanus in a new genus (Kassandrina gen. nov.) that would not have been discovered with traditional techniques, and to describe a new species of Cassidulus (Cassidulus briareus sp. nov.) from Australia and designate a neotype for Cassidulus caribaearum. We also provide remarks describing the taxonomic history of each taxon and a diagnostic table of all living cassidulid species, and extend the known geographic and bathymetric range of C. caribaearum and C. malayanus. Besides rendering novel morphological data, the SRµCT images provide significant insights in the evolution of bourrelets of these cassiduloid echinoids.

Taxonomic review of four western Atlantic dendrochirotids (Holothuroidea) with the description of a new Brazilian cucumariid species and designation of neotypes.

In this paper, we propose the reassignment of three western Atlantic species of the order Dendrochirotida to the family Sclerodactylidae (Euthyonidiella occidentalis comb. nov., Euthyonidiella arenicola comb. nov., and Thandarum manoelina comb. nov.) with a discussion on the classification of the dendrochirotids based on the morphology of the calcareous ring. We also propose the synonymization of Euthyonidiella dentata with Euthyonidiella occidentalis comb. nov., designate a neotype for this species and for Thandarum manoelina, and describe a new species of the genus Cucumaria from Brazil.