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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. [ABSTRACT FROM AUTHOR]

Here, we review the taxonomy of the Apodida species from the Brazilian coast and oceanic islands. Eleven species are reported, four Chiridotidae (including Chantalia conandae gen. et sp. nov.) and seven Synaptidae (including Yemoja gen. nov.). Chantalia conandae gen. et sp. nov. is a shallow-water species diagnosed by having 12 tentacles, 4–6 Polian vesicles and vase-shaped ciliated funnels along the mesenteries, and by lacking a calcareous ring, sensory cups and ossicles. Based on the morphology of the calcareous ring (dumbbell-shaped plates) and of the tentacles (12, simple), we propose the new genus Yemoja gen. nov. to accommodate Leptosynapta brasiliensis (Yemoja brasiliensis comb. nov.). To date, there are no records of Myriotrochidae in Brazil. In addition to species descriptions and photographs, we provide novel data on the calcareous ring stereom and a discussion about the calcareous ring morphology in Apodida, an identification key for the Brazilian species, a synoptic table with morphological characteristics of the Brazilian genera, and a synoptic table comparing the ossicleless Apodida genera. Finally, we provide the geographic and bathymetric distribution of the Apodida species reported for the South Atlantic and adjacent Southern Ocean. Based on our compendium, the Synaptidae is most diverse in warmer waters, while the Myriotrochidae is most diverse in colder waters. Also, the Atlantic coasts of South America and Africa have a surprisingly low with their adjacent Antarctic waters. We expect that dedicated holothuroid research will greatly increase the diversity of Apodida throughout the South Atlantic Ocean, especially off the continental shelf. [ABSTRACT FROM AUTHOR]

The present study explores rare but taxonomically and geographically widespread cases of anterior body axial bifurcation in adult sea cucumbers (Echinodermata: Holothuroidea). One individual of Holothuria (Halodeima) grisea, a common intertidal species along the Atlantic coast of Brazil, was studied externally and internally. Individuals of Apostichopus californicus from the northeastern Pacific coast of Washington (USA), H. (Mertensiothuria) leucospilota in the Indian Ocean off La Réunion, H. (Panningothuria) forskali from the Atlantic coast of Spain, and Parastichopus tremulus from the northeastern Atlantic off Norway were also reported to display similar anterior body axial bifurcation. In each of these species, the anterior body presented two mouths with their respective crown of tentacles. In vivo observations of H. (Halodeima) grisea showed that the two tentacle crowns and mouths were independently functional. Micro‐computed tomography (μCT) revealed that the anterior region of the body (up to the pharynx) was duplicated. Internally, two aquapharyngeal bulbs were found, each with their own calcareous ring (one with two plates missing), madreporite, and Polian vesicles. The body presented a normal set of five longitudinal muscle bands, some of which bifurcated orally to support more than one calcareous ring plate. This is the first report of such abnormalities in Holothuroidea and hypotheses that may explain such phenomenon are discussed. [ABSTRACT FROM AUTHOR]

Inclusion of fossils can be crucial to address evolutionary questions, because their unique morphology, often drastically modified in recent species, can improve phylogenetic resolution. We performed a cladistic analysis of 45 cassidulids with 98 characters, which resulted in 24 most parsimonious trees. The strict consensus recovers three major cassiduloid clades, and the monophyly of the family Cassidulidae is not supported. Ancillary analyses to determine the sensitivity of the phylogeny to missing data do not result in significantly different topologies. The taxonomic implications of these results, including the description of a new cassiduloid family and the evolution of some morphological features, are discussed. Cassiduloids (as defined here) most probably originated in the Early Cretaceous, and their evolutionary history has been dominated by high levels of homoplasy and a dearth of unique, novel traits. Despite their high diversity during the Palaeogene, there are only seven extant cassiduloid species, and three of these are relicts of lineages dating back to the Eocene. Future studies of the biology of these poorly known species, some of which brood their young, will yield further insights into the evolutionary history of this group. [ABSTRACT FROM AUTHOR]

Thyone pawsoni and Holothuria (Theelothuria) princeps are reported from shallow water of the South Atlantic Ocean. A morphological description of these new records with colour figures and scanning electron microscopy images of their ossicles are provided. With these two new records for the Brazilian Coast, the genus Thyone is now represented by two species and Holothuria by six. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]