The Phylum Echinodermata contains near 7000 living species divided into five Classes. Throughout the years, much has been discovered about them. Besides traditional studies on their ecology, morphology and taxonomy, recent studies are emphasizing new subjects such as medicinal uses, paleoenvironmental indicators and even craftwork. In this study it is presented the occurrence of the Echinodermata species from the Bahia State (Brazil), which are represented by a total of seventy one living species and six fossils. Among the living species, eight belong to the Asteroidea Class, forty to the Ophiuroidea, thirteen to the Echinoidea, seven to the Holoturoidea and three to the Crinoidea. Even though the Bahia State has the longest coastal line, in the whole country, its diversity represent only 21 % of the currently registered Echinodermal fauna of Brazil.

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A large number multitentaculate cirratulids have been described worldwide but most are only known through the original descriptions. Type material, voucher and recently collected specimens from Brazil were revisited in order to reveal their true identity and confirm the records of widely distributed species in this region. Six species are described, three of which are new, Cirriformia capixabensis sp. nov., Cirriformia chicoi sp. nov. and Timarete ceciliae sp. nov. COI and 16S sequences were obtained and used for inter-specific comparisons. Timarete caribous is reported from several localities along the Brazilian coast and a new synonym, Cirratulus melanacanthus, is proposed. The species Timarete oculata, originally described from Brazil and lumped into the Timarete filigera species complex, is herein revalidated and redescribed. The occurrence of the species Timarete filigera and Cirriformia tentaculata is not confirmed from the Brazilian coast. Descriptions, illustrations and a key to genera and species are provided.

Thirteen cirratulid species from the Hawaiian, Mariana and Marshall Islands are described. Nine species are new to science: Aphelochaeta arizonae sp. nov., Aphelochaeta honouliuli sp. nov., Caulleriella cordiformia sp. nov., Chaetozone michellae sp. nov., Chaetozone ronaldi sp. nov., Monticellina anterobranchiata sp. nov., Monticellina hanaumaensis sp. nov., and Tharyx tumulosa sp. nov., from Oahu, Hawaii and Aphelochaeta saipanensis sp. nov., from Saipan in the Mariana Islands. Dodecaceria fewkesi and Monticellina nr. cryptica are newly recorded from the Hawaiian Islands. Dodecaceria laddi is widely distributed in the western Pacific and material collected from the Hawaiian, Mariana and Marshall islands is described. We provide SEM photographs for all species in addition to line drawings and methyl green staining pattern photographs for the new species.

Polychaete assemblages are of special interest when studying dynamic environments such as estuaries because of their high plasticity in life strategies to cope with environmental variability. We tested the hypothesis that polychaete feeding guilds would be more related to environmental characteristics than to taxonomic composition. Polychaetes were sampled on two different occasions along three tropical estuarine systems in north-eastern Brazil. Different polychaete taxa replaced one another along the entire salinity gradient and the overall pattern from high- to low-salinity regions was from high species and feeding-guild diversities to dominance by a single species or a feeding group. We suggest that the relationships between structure and function of polychaete assemblages might provide a measure of the resilience of estuarine conditions; estuaries with a high redundancy in the trophic role of polychaetes might recover faster from disturbance and retain more natural ecological functions than those estuaries with low or no redundancy, because more species would have the capacity to expand their niches to compensate for the loss of neighbouring species. Integrative approaches allying species composition to their trophic role need to be thoroughly investigated to help understand such complex temporal and spatial organisation of benthic assemblages in estuaries.