The troglomorphic adaptations of Namanereidinae (Annelida, Nereididae) revisited, including a redescription of Namanereis cavernicola (Solís-Weiss & Espinasa, 1991), and a new Caribbean species of Namanereis Chamberlin, 1919

Most species belonging to Namanereis Chamberlin, 1919 live in freshwater and subterranean waters, even in water bodies several meters above sea level. A new species belonging to the stygobiont Namanereis group is described here; it shares the common morphological characters of absence of eyes and pigmentation, bifid jaws, elongation of chaetae and cirri, which have been recently regarded as troglomorphies. Because these features are used in evaluations of phylogenetic affinity in Namanereis, a review of these features was made for all known namanereidins, and it was extended to include species in Namalycastis Hartman, 1959. It is shown that elongation of tentacular and dorsal cirri, or elongation of upper sub-acicular falcigers in pre- or post-acicular fascicles, are not exclusive or restricted to species living in subterranean habitats or to Namanereis, because these features are also present in several Namalycastis species. However, the presence of bifid jaws, and the absence of eyes are exclusively found in namanereidins living in subterranean habitats. A hypothetical evolutionary derivation of bifid jaws is proposed, based upon observations of jaw morphology of several species. These exclusive troglomorphic characters (bifid jaws, eyeless) are regarded as convergent features to aphotic environments, and they should be discouraged as indicators of common ancestry. The new species, herein described as Namanereis christopheri sp. n., was collected in a cave 435 m above sea level in Saint Vincent, Caribbean Sea. The species resembles N. cavernicola but it differs because it has shorter tentacular cirri, margin of prostomium entire, rounded neuropodial lobes and broader dorsal cirri throughout body. A key to identify all known Namanereis species is included.