Introduction: The knowledge of polychaetes from Oaxaca, Mexico, is represented by 41 families and 241 species, nevertheless, 148 species are considered questionable. The majority of taxonomic studies of polychaetes in Oaxaca have taken placed on estuarine zones or commercial ports, sidelining other marine ecosystems. Objective: To identify the polychaeta-fauna from three different marine ecosystems in Oaxaca, Mexico. Methods: Specimens analyzed came from the Sección de poliquetos de la Colección Científica at the Laboratorio de Sistemática de Invertebrados Marinos, Universidad del Mar. The material deposited in the collection was collected between 2007-2017; additionally, new collect were realized in 2017. For each locality, the family and species richness were estimated using the accumulation function of linear dependence model. Results: One hundred lots and 273 specimens were revised. Seventy-one taxa, belonging to 47 genera and 21 families were identified, only twenty of these taxa are confirmed species (28 %). Chacahua Lagoon had the highest richness and relative abundance with 37 taxa and 149 specimens, Agua Blanca was identified 21 taxa and 92 specimens, and from San Agustín 19 taxa and 32 specimens. Sabellariidae had the highest relative abundance (58 specimens), while Phyllodocidae presented the highest species richness (12 species). Conclusions: This study adds 75 new records of taxa of polychaetes to the coast Oaxaca, which increase the knowledge in this animal group, now represented by 304 species, belonging to 154 genera and 42 families.

Hydroids of the Pacific coast of Mexico have been little studied. For the coast of Oaxaca, only five papers provide information on species of the region, with some records included in those publications being questionable. Seven species, Pennaria disticha, Clytia linearis, Clytia cf. gracilis, Obelia dichotoma, Ventromma halecioides, Dynamena crisioides and Tridentata turbinata, were discovered during the study and are reported herein. Of these species, Pennaria disticha and Tridentata turbinata are new records for the Mexican Pacific coast, and Clytia linearis and Ventromma halecioides are new records for Oaxaca. Geographic ranges of other hydroids, recorded in earlier studies, are expanded.

The family Chrysopetalidae has been poorly studied from the Pacific coast of Mexico compared to other families. Specifically from the southern Mexican Pacific, only two species of the family have been recorded in previous studies, Chrysopetalum occidentale and Paleanotus chrysolepis. In this study 311 specimens were revised, and nine species, belonging to six genera were found. Eight of these species are new records from the southern Mexican Pacific coast: Arichlidon watsonae n. sp., Bhawania cf. goodei, Chrysopetalum elegantoides, C. maculata, Hyalopale sp., Paleaequor psamathe, Paleanotus bellis and P. purpurea. A new species is also described, Arichlidon watsonae n. sp., which is characterized by the curved tips blades of the falcigers and their small and ovoid palps. Additionally, the genera Arichlidon and Hyalopale are recorded by first time from the Tropical Eastern Pacific.

In the material and methods section (page 4), the name of the species for which a neotype is proposed should be read Paleanotus purpurea instead of Bhawatsonia purpurea n. comb. The neotype proposal is related to the speciesgroup name P. purpurea Rioja, 1947, basionym of B. purpurea n. comb., whose type material is lost (ICZN 1999, Art. 72.1.2). In page 33, the synonymy section of Bhawatsonia purpurea n. comb. omitted the basionym of the species (P. purpurea) and subsequent references. In the section of Bhawatsonia purpurea (Rioja, 1947) n. comb. (page 33) the synonymy section is missing. This should be as follows:

The marine annelid family Sigalionidae is little known in the Grand Caribbean Region; there are few records of these worms in the area, and some of the recorded species have uncertain taxonomic status. In this contribution, the subfamily Pelogeniinae was addressed through a faunistic study, aiming to improve the knowledge of Sigalionidae in the region. In order to do this, material deposited in the three following institutions was examined: University of Miami Deep Sea Expeditions; Florida Museum of Natural History, University of Florida, Gainesville; and El Colegio de la Frontera Sur, Chetumal. Eleven species are recognized, including six newly described: Dayipsammolyce paulayi sp. nov., Hartmanipsammolyce pettiboneae sp. nov., Neopsammolyce fragilis sp. nov., Pelogenia brevipalpata sp. nov., P. capitata sp. nov. and P. salazarvallejoi sp. nov. Four other species are confirmed for this region: N. floccifera (Augener, 1906), P. hartmanae Pettibone, 1997, P. kinbergi (Hansen, 1882) and Psammolyce flava Kinberg, 1856; and one is indeterminate: N. aff. floccifera. A standardized terminology of neurochaetae is proposed, along with notes on the notochaetal morphology and elytral structures. For all genera covered in this study, identification keys are also provided.

Chrysopetalids annelids have been little studied in the Tropical Eastern Pacific (TEP), with only 24 species recorded in the region. Most records are from northwestern Mexico and Costa Rica, leaving many sites along the Tropical Pacific coast of America unexplored. Furthermore, there are species recorded and described from the region with problems in their status, including questionable records, modest illustrations or descriptions, and lost type material. This paper aims to improve the knowledge of this family in the TEP. Almost 290 specimens were revised, provided from five scientific collections, covering 51 sites along the TEP and nearby. Two subfamilies: Calamyzinae and Chrysopetalinae, nine genera and 20 species were determined. Of these, ten species have been previously recorded, three are indeterminable and seven are new species: Paleanotus karlyae n. sp., Arichlidon mucropaleum n. sp., Bhawania bastidai n. sp., Chrysopetalum mexicanum n. sp., C. tovarae n. sp. A new genus is proposed, Bhawatsonia n. gen. which includes two new species, B. fusa n. sp. as its type species, B. nenoae n. sp. and, the new combination and neotype of B. purpurea n. comb. An updated and revised checklist of all chrysopetalids species recorded in the region is included, currently composed of 16 genera, 30 species, and four morphospecies.

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