Paralacydonia (Polychaeta: Paralacydoniidae) off Rio de Janeiro, Brazil

Abstract

Paralacydoniids are a small group of burrowing polychaetes, with adults reaching ~10 cm in length. The prostomium is subconical, distally bearing two pairs of frontal appendages; the pharynx is eversible and distally papillate and jaws are absent. The parapodia are biramous, except the first segment which is uniramous. Both rami are widely separated, with long, flattened pre- and post-chaetal lobes, interramal cilia and short digitiform dorsal and ventral cirri. The notochaetae are simple, and the neurochaetae are compound spiniger. The posterior end bears a pair of long cirri. A single species, Paralacydonia paradoxa, has been considered valid. Two other named taxa, Paralacydonia weberi and Paralacydonia mortenseni, are usually considered synonyms of P. paradoxa, although a revision has not been undertaken. Paralacydoniids were collected during the Habitats Project–Campos Basin Environmental Heterogeneity coordinated by CENPES/PETROBRAS, of which the first campaign was held in June–July 2008 and the second campaign in January–February 2009. In all, 289 specimens were observed under the light microscope, and some by means of scanning electron microscopy. The paralacydoniids, collected at depths between 380 and 2514 m, were 0.4 to 19 mm in total length, the largest with 74 chaetigers; the size is related to the number of chaetigers.