Abstract.-Cossura chilensis is one of the most abundant polychaete species on soft-bottom benthic communities in central Chile. Nevertheless, it was firstly described by Hartmann-Schröder in 1965 and re-described by Carrasco in 1977; both studies with incomplete specimens. The aim of this research was to made a new description of the species in a detailed way from entire specimens using Scanning Electronic Microscopy. Cossura chilensis has a conical prostomium with a dorsal furrow and its peristomium is short and split by transverse ring. The first chaetiger is uniramous and the following ones are biramous. The branchial filament arises from the anterodorsal part of third chaetiger. Chaetae include short capillaries in the 3 first chaetigers; long capillaries in both rami along the rest of the body and thick capillaries in neuropodia of chaetigers 2-10. In addition, short spine-like chaetae are present from posterior segments. All chaetae are hirsute presenting a dense feather-appearance just by one side of the chaetae. Thoracic segments are short and crowded, while abdominal segments are longer than broad and less crowded. The pygidium is small and round-tip with 3 long cirri around anus. Methyl green staining is intense in prostomium, less intense in peristomium, first two chaetigers and in lateral patches from third chaetiger. The highest mean abundance by field work was 897 ind. m -2 in September 2013 being a dominant species of the soft-bottom Valparaiso bay, central Chile. Key words: Taxonomy, polychaete, annelids, Southeast PacificResumen.-Cossura chilensis es una de las especies más abundantes de poliquetos en las comunidades bentónicas de fondos blandos de Chile central. Sin embargo, fue descrita originalmente por Hartmann-Schröder en 1965 y redescrita por Carrasco en 1977; ambos estudios con ejemplares incompletos. El objetivo de este trabajo fue realizar una nueva descripción de la especie, en detalle y a partir de ejemplares enteros, usando Microscopia Electrónica de Barrido. Cossura chilensis tiene un prostomio cónico con un pliegue dorsal y su peristomio es corto y está divido por un anillo transversal. El primer segmento setígero es unirrámeo mientras que los siguientes son birrámeos. El filamento branquial surge desde la parte anterodorsal del tercer setígero. Los ejemplares presentan setas capilares cortas en los primeros 3 setígeros, setas capilares largas en las dos ramas de la mayor parte del cuerpo y setas capilares gruesas en los neuropodios de los segmentos 2-10. Adicionalmente, están presentes setas cortas con forma de espina en los segmentos posteriores. Todas las setas son hirsutas presentando un aspecto densamente plumoso en un sólo lado de la seta. Los segmentos torácicos son cortos y bien agrupados, mientras que los del abdomen son más largos que anchos y menos agrupados. El pigidio es pequeño y redondeado con 3 cirros largos alrededor del ano. El patrón de tinción con verde metilo muestra una intensa tinción del prostomio, en menor grado del peristomio y los 2 primeros setígeros y l...

In the last decades, the fish Vinciguerria lucetia (Garman) has been of important interest to the fisheries sector; nonetheless, the spawning and nursery zones in the Humboldt Current System (HCS) have not yet been defined. By using a temporal series of 23 oceanographic surveys from austral spring of 1998 to autumn 2004 off northern Chile, the spatial and temporal distribution and abundance of eggs and larvae of V. lucetia were studied. The relationships with environmental conditions (sea surface temperature, water column stratification, salinity, dissolved oxygen) were modeled using generalized additive models (GAMs). Seasonal variations in eggs and larval abundances were recorded, and higher abundances were observed in spring and summer, respectively. The main spawning areas were located at approximately between 40 and 80 nautical miles offshore. The largest abundances of V. lucetia eggs were found during spring 2003; however, larval abundances reached the highest values following the strongest ENSO event 1997–98. GAMs predicted that offshore location, sea surface temperature, and the deepening of the oxygen minimum zone, characteristics of the subtropical waters (22–24°C, >34.9, 3–6 ml/L) drove eggs and larval distributions of V. lucetia in the HCS during 1998–2004, toward areas with scarce food availability for larvae. These results suggest that spawning and larval development of this oceanic species occur in oligotrophic waters as a loophole strategy, in order to reduce predation risk during early life stages.