The spatial distribution and abundance of the seven most abundant species of echinoderms (Diadema mexicanum, Centrostephanus coronatus, Eucidaris thouarsii, Isostichopus fuscus, Pharia pyramidatus, Phataria unifascialis and Acanthaster ellisii) were evaluated in coral communities of Isla Isabel National Park (Mexico). Biological (corals and other benthic groups) and physical (rocks and boulders) structural elements of the habitat were evaluated to determine their relationship to these species. Our results show that species composition and abundance varied among sampling sites and between seasons. Also were obtained significant differences in the echinoderm assemblage among sites across seasons. Similar results were detected for the environmental variables related to benthic habitat structure. D. mexicanum, P. unifascialis, E. thouarsii and C. coronatus were the main contributors to the species abundance and distribution in Isla Isabel. Most echinoderm species were positively related to the coverage of different coral species, algae and various types of benthic organisms as well as to physical benthic variables. These outcomes suggest that the spatial distribution and abundance of these echinoderms are explained by the habitat structure, which should be used to design conservation and management strategies for coral communities

The taxonomic composition of 160 species of bivalves and gastropods recorded in the Gulf of Tehuantepec is presented with information on their habitat and distribution along 10 different localities of the shoreline and 42 stations of the continental shelf. The species were on sandy and rocky beaches, coastal lagoons, estuaries, mangroves, rocky breakwaters of ports, and shallow subtidal areas (14–47 m depth). A total of 78 bivalve species and 82 gastropod species were recorded. Most of these were associated with sandy and rocky beaches and breakwaters of ports. The estuaries host 30 species and the coastal lagoons only two. In the shallow subtidal there were 18 gastropod species and 40 bivalve species representing 36.3% of all. This study adds 24 bivalve species and 29 gastropod species not recorded in previous studies for a total count of 213 species (102 bivalves and 111 gastropods) for Gulf of Tehuantepec.

Cuarenta especies de equinodermos fueron recolectadas en las zonas intermareal y submareal somero de14 sitios de bahía Chamela. Destacan 7 nuevos registros para la costa de Jalisco. Los análisis de escalonamientomultidimensional no métrico y el índice de similitud de Jaccard permitieron identificar grupos y entidades aisladas deacuerdo a la contribución y frecuencia de las especies de 4 clases de equinodermos en los sitios de la bahía y en otraslocalidades del Pacífico tropical mexicano (PTM). La mayor similitud se presentó con las localidades del golfo deCalifornia. Los índices de distinción taxonómica promedio (Δ+) y su variación (Λ+) fueron utilizados para analizar ladiversidad de equinodermos en los niveles de especie, género, familia, orden y clase para cada sitio de la bahía y paradistintas localidades del PTM de acuerdo al número de jerarquías taxonómicas de alto orden y la variabilidad en sudiversidad taxonómica. La riqueza de especies de Chamela representa el 20% de la diversidad total de equinodermosde las zonas intermareal y submareal somero del PTM, lo que indica su importancia en la contribución a la diversidadtaxonómica de la región.

Background The islands and islets of Bahia de Chamela, in the Eastern Tropical Pacific, were declared as the first marine sanctuary in Mexico and has been protected since 2002. Their marine biodiversity has been documented in a series of papers in the last decade, but only three species of polychaete worms have been reported. New information Sixteen species of sedentary polychaete worms belonging to the families Maldanidae, Oweniidae, Sabellariidae, Sabellidae and Serpulidae are reported to the Bahia de Chamela Islands Sanctuary, 15 of these species constituting the first records in the area. lsocirrus tropicus (Monro, 1928) (Monro 1928) and Notaulax californica (Treadwell, 1906) (Treadwell 1906) constitute new records to Mexico; Idanthyrsus mexicanus Kirtley, 1904 (Kirtley 1994) is first recorded since its description and one species of bamboo worm (Maldanidae) is described as new to science. The new species belongs to the genus Clymenura Verril, 1900 (Verrill 1900) and its characterised by the presence of a glandular shield on chaetiger 8; a cephalic plaque oval with smooth margins and a rounded palpode; nuchal organs straight, parallel, almost full length of plaque; manubriavicular uncini present from chaetiger 1 with 3-4 teeth above the main fang without hairs or bristles; two pre-anal achaetous segments with tori; an anal funnel with alternating triangular cirri, being the longest that are located mid-ventrally.