A new species of Websterinereis from the Gulf of California and redescription of Websterinereis foli (Fauvel, 1930) (Annelida, Nereididae)

Abstract A new species of Websterinereis Pettibone, 1971, Websterinereis pettiboneae sp. n. is described from La Paz Bay, Gulf of California, Mexico. This species is similar to Websterinereis foli (Fauvel, 1930) in the neuropodial falcigers shape, but can be separated by the tentacular cirri length, notopodial prechaetal lobe shape, and the size of the notopodial dorsal and ventral ligules on posterior parapodia. Websterinereis foli is redescribed based upon type material. Additional observations on the inter-annual density variation of Websterinereis pettiboneae sp. n. during a four-year study are also provided. A key to all species of Websterinereis is included.


Introduction
The family Nereididae de Blainville, 1818 comprises 44 genera which can be separated by a number of characters associated with the eversible pharynx and parapodial structures. Eunereis Malmgren, 1965 andWebsterinereis Pettibone, 1971 are very similar to each other because the pharynx in both has papillae on the oral ring, and there are no paragnaths or papillae on the maxillary ring. These genera can be separated because Eunereis has notopodial homogomph falcigers whereas Websterinereis presents only notopodial homogomph spinigers. Websterinereis was established by Pettibone (1971) and includes four previously described species: W. foli (Fauvel, 1930) from New Caledonia and the Marshall Islands, Pacific Ocean (Reish 1968), W. glauca (Claparède, 1870) from England and along the French Atlantic coast, W. tridentata (Webster, 1879) from the east coast of the United States, and W. punctata (Wesenberg-Lund, 1949) from the Persian Gulf. Most of the records of Websterinereis species are restricted to the type locality; the only species with a wider record is W. glauca. These species can be separated into two groups by the presence of anchylosed chaetae, apparently formed by fusion of the blade to the handle. In W. punctata anchylosed chaetae are bifid and restricted to the supraacicular fascicle of median and posterior neuropodia; in the epitokes of W. glauca there are one or two dark unidentate anchylosed chaetae in a supra-acicular position on the posterior neuropodia. It is noteworthy that in W. tridentata (type species for the genus) and W. foli there are no anchylosed chaetae; W. foli has falcigers with short blades in comparison with those present in W. tridentata, however, a few falcigers of these two species give the appearance of being simple because of blade loss. Of all the described species only W. glauca has reduced notopodial prechaetal lobes present as low ridges, while the other species have larger, more developed lobes, at least in the anterior parapodia.
In this contribution a new species of Websterinereis is described which had previously been confused with W. foli due to the morphological similarity of their compound falcigers. In order to further clarify the taxonomic status of this taxon, a redescription of W. foli is provided based on type material. An additional comment on inter-annual density variation, observed during a four-year study, is given for the new species of Websterinereis.

Methods
Specimens of the new species were collected during a long-term study of coral reef recuperation following a tanker vessel grounding in San Lorenzo Channel, La Paz Bay, in the south-western Gulf of California, Mexico. In 2001 thirty concrete and rock, artificial-reef structures were deployed on the bottom of the grounding site. Later, live fragments of the coral Pocillopora spp. were attached over the artificial reef surfaces. From 2004 to 2009 a seasonal monitoring survey was carried out aimed at evaluating the structural and ecological recovery of the restored site (Balart et al. 2010). It included samplings of rocky benthic infauna in ten of the artificial reef structures as a proxy for benthic reef community recovery. An area of 0.20 × 0.20 m on a lateral wall in each structure was sampled (0.04 m 2 ; total sampled area by survey 0.4 m 2 ). This area was fragmented with chisel and hammer and the fragments transferred to polyethylene bags in situ. Sorting and taxonomic analysis of formalin-fixed worm material was performed in the Laboratory of Biosystematics (UANL). All identified specimens were deposited in the Polychaete Collection of the Universidad Autónoma de Nuevo León (UANL). Paratypes were deposited in the Los Angeles County Museum, USA. Terminology of parapodial structures used in this work was taken from the proposed by Bakken and Wilson (2005), elaborated on the basis of previous proposals used by several authors including Hylleberg et al (1986), Hutchings and Reid (1990) and Wilson et al. (2003).
The mean density (individual per m 2 ) of the ten artificial reef structures sampled per survey was used to evaluate the variation in abundance of the new species of Websterinereis throughout the study period. Relationships between density data and environmental variables were also analyzed.
Diagnosis. Prostomium sub-pyriform to pentagonal, one pair of frontal antennae, a pair of globose biarticulate palps, and two pairs of eyes of different shape. Peristomium with four pairs of short tentacular cirri. Pharynx with pair of jaws. Maxillary ring unarmed, oral ring with papillae on areas VI and VII-VIII. First two parapodia uniramous, remainder biramous. Notopodium represented by dorsal cirri with dorsal and median ligulae, notopodial prechaetal lobe present on anterior parapodia. Neuropodium with superior and inferior lobe forming prechaetal area; postchaetal lobe subulate to triangular, ventral ligule generally subulate. Ventral cirri short. Notochaetae homogomph spinigers; neurochaetae homogomph and heterogomph spinigers and heterogomph falcigers, those in posterior parapodia with short to long blades; anchylosed chaetae may be present. Pygidium with pair of anal cirri.  Description. Holotype complete with restricted blackish pigmentation (Fig. 1A); prostomium with anteriorly truncate, extended dark area, leaving pale mid-dorsal thin band, not reaching anterior prostomial margin; palpophores with some pigmentation over external, subdistal surfaces; tentacular segment with continuous dorsal transverse wide band, reduced to progressively thinner bands along anterior and posterior segmental margins.
Pharynx with brown jaws, each with six teeth. Maxillary ring lacking paragnaths or papillae; oral ring with subconical papillae in area VI, and five globose papillae in line along areas VII-VIII.
Pygidium with terminal anus and two anal cirri. Epitokous female. Best preserved specimen with 64 chaetigers, 9 mm long and 0.5 mm wide (excluding parapodia). Prostomium pentagonal, wider than longer, with frontal median dorsal groove. Antennae minute, shorter than anterior end of palpi. Two pairs of eyes in trapezoidal arrangement, anterior pair enlarged, oval in shape, posterior pair rounded in shape. Biarticulate palps globose, each with spherical palpostyle. Tentacular ring with four pairs of tentacular cirri, posterodorsal pair extending back to anterior margin of sixth chaetiger (Fig. 2 A). Pharynx equal to non-epitokous specimens.
Pygidium similar to those of atokous specimens. Etymology. Specific name is in honor of Marian H. Pettibone for her great work on increasing the knowledge of polychaetes.
Remarks. Websterinereis pettiboneae sp. n. resembles W. foli in the shape of the compound falcigers, although there is greater variation in the shape of compound falcigers in W. foli. These species differ in the following features: W. pettiboneae has longer tentacular cirri reaching chaetiger 3, notopodial prechaetal lobes are triangular, and notopodial dorsal and ventral ligule are progressively smaller in posterior parapodia. In W. foli the longest tentacular cirri reaches chaetiger one, with a thin, cirriform prechaetal notopodial lobe inserted at the base of the notopodial ventral ligule, and the dorsal and ventral ligule increasing slightly in posterior parapodia.
Distribution. Websterinereis pettiboneae sp. n. is known only from Canal de San Lorenzo, La Paz Bay, Gulf of California, Mexico.
Pigmentation blackish; prostomium with longitudinal narrow band throughout its length, leaving thin pale mid-dorsal line, pale subtriangular area around the anterior eyes, and pale semicircular area around posterior eyes; palpophores pale; tentacular segment with solid blackish dorsal pigmentation, laterally pale, reduced to wide dorsal longitudinal band on first chaetiger.
Prostomium subpentagonal, longer than wide, with slight depression along anterior half. Two pairs of black eyes, distal ones reniform larger than proximal ones which are rounded and show lenses. Antennae tapered, not reaching tips of palpostyles; palps globose, palpostyles conical; both antennae and palps directed ventrally as result of an artifact of fxation. One apodous anterior segment, shorter than first chaetiger. Tentacular cirri short, tapered, longest pair reaching chaetiger one (Fig. 4 A-B).
Pharynx with single jaw (left one lost), thin, with seven well-developed teeth. Maxillary ring without paragnaths or papillae; oral ring with triangular papillae on area VI, area V lacking papillae, areas VII-VIII, with seven rounded papillae.
Remarks. After reviewing the holotype of W. foli some differences were noted from the description by Pettibone (1971). In her description of W. foli Pettibone combined her observations of the holotype of Leptonereis foli Fauvel, 1930 and the holotype and paratypes of Ceratocephala corallicola Reish, 1968. This explains why her description begins with the measurements of a specimen that does not match the holotypes of either species, as 20 mm long and up to 112 chaetigers. Since Pettibone (1971) mixed morphological features of these two species originally described from very distant localities we have restricted our redescription of W. foli to only the specimen that Fauvel (1930)