A new species of Fauveliopsidae (Annelida) from the North Sea

Abstract A new species of the genus Laubieriopsis Petersen, 2000 is described based on 28 specimens collected in the north-east part of the North Sea. It is characterized by fixed number of chaetigers (22), paired genital papillae, bidentate neurochaeta of chaetigers 1–4, the absence of acicular chaetae on chaetigers 5–21 and, on the last chaetiger, one acicular and three capillary chaetae enlarged and directed backward. The present study brings the number of known species of Laubieriopsis to five and the number of Northeast Atlantic species of this genus to two.


Introduction
The Fauveliopsidae are a small (about 20 species) family of detritus-feeding polychaetes. They are small benthic animals, mainly found on deep bottoms down to 6000 m (Levenstein 1970), although a few species can be found above 100 m deep (Katz-mann and Laubier 1974, Riser 1987, Núñez et al. 1997. Members of the family are either free-living or inhabit dead shells of scaphopods, gastropods or foraminiferans (Blake andPetersen 2000, Petersen 2000).
The family Fauveliopsidae was erected by Hartman (1971) and initially consisted of one genus, Fauveliopsis McIntosh, 1922;later Petersen (2000) divided this genus into two -Fauveliopsis and Laubieriopsis Petersen, 2000. Fauveliopsidae are usually grouped together with Flabelligeridae, based on the presence of a retractable anterior region of the body, but differ from Flabelligeridae by the lack of a cephalic cage, retractile oral branchiae and palps. The presence of an interramal papilla is the characteristic feature for the family, though Fauchald and Rouse (1997) considered it to be the same as the interramal papillae of Flabelligeridae and thus found no evidence for monophyly of the family. Genital papilla (single or paired) could be another characteristic feature for the family Fauveliopsidae (Petersen 2000).
The internal morphology and ultrastructure of fauveliopsids have been poorly studied. Riser (1987) described some features for Laubieriopsis arenicola Riser, 1987, L. brevis (Hartman, 1965 and Fauveliopsis glabra (Hartman, 1960). Purschke (2011) gave a detailed description of the anterior end of Fauveliopsis cf. adriatica, its brain and sensory structures. Thiel et al. (2011) described some anatomical features of Fauveliopsis confusa Thiel, Purschke and Böggemann, 2011. Common characters of all the studied species are a thick cuticle, a brain with four posterior lobes, longitudinal muscles forming four muscle bands, strong prostomium protractors, muscular dissepiments, two ventral mesenteries, and epidermal glands associated with parapodia.
Zhadan and Atroshchenko (2010) described the inner organization of Laubieriopsis sp. They examined the morphology of the body wall, introvert, and body cavities as well as the digestive, reproductive, and nervous systems. In the present work we formally describe this species.

Material and methods
Specimens of Laubieriopsis sp. were collected in the North Sea (60°34'N, 03°41'E; 03°26'E, 60°54'N) (Fig. 1) by the company Akvaplan-niva in May 1998 (collector Andrey Sikorski). All specimens were fixed in a 4% formaldehyde seawater solution and later transferred to 70% ethanol. The material is stored in the Zoological Museum of M.V. Lomonosov Moscow State University (ZMMU).
Twenty-one specimens were examined under a stereomicroscope after dehydration in a glycerin series. Additional data were obtained using scanning electron microscopy: seven specimens were critical point-dried after dehydration in an ethanol series and acetone, and then coated with gold prior to examination with a Scanning Electron Microscope HITACHI S-405 A and Camscan-S2.

Genus Laubieriopsis Petersen, 2000
http://species-id.net/wiki/Laubieriopsis Diagnosis. Body cylindrical, weakly divided into two regions by segment shape and type of chaetae. Fixed number of segments. Cuticle smooth, without papillae or papillae minute and inconspicuous. Chaetae include capillaries and acicular types, some might be bidentate. Interramal papillae small, mostly sessile. Last segment similar in size to preceding ones, often bilobed, pygidium retracted inside it.    Diagnosis. Adult specimens with 22 chaetigers. First four chaetigers with sigmoidal acicular chaetae, neurochaetae often bidentate. Chaetigers 5-21 without acicular chaetae, with one thin capillary chaeta and one very small and thin additional chaeta in each ramus. Chaetiger 22 with one thick acicular notochaetae and three capillary neurochaetae. Two weltlike genital papillae present at posterior edge of segment 8.
Ventral nerve cord visible by transparency. Ganglia longitudinally elongated and indistinctly separated from each other.
Pygidium retracted within last chaetiger, anus terminal. Boundary between distal part of last segment and pygidium indistinct. Inverted part (distal to chaetae) with a number of conical papillae, which are larger than in rest of body (Fig. 2E, 3C, 4B).
Sperm cells hardly visible through body wall, but observed in SEM in body cavity of dissected specimen. They have rounded heads about 3 μm in diameter, an acrosome with elongated distal part and free flagellum at least 10 μm long (Fig. 4G, H).
Etymology. The species name refers to its type locality. Distribution. Northeast part of the North Sea. Ecology. Inhabits muddy sediments with small admixture (0.8 -7.7 %) of fine and medium sand, in depth of 300-350 m.
Discussion. L. norvegica sp. n. differs from all previously described species of the family Fauveliopsidae by the highly reduced chaetal bunds in median and posterior parapodia. Whereas all fauveliopsid species have one, rarely two acicular spines in each parapodial ramus, noto-and neuropodia of chaetigers 5-21 in L. norvegica sp. n bear one fine, slender capillary and one even smaller chaeta which may be absent.
Species of the genus Laubieriopsis are characterized by a fixed number of chaetigers; previously described species have 16, 21 and 25 chaetigers (Petersen 2000). L. norvegica sp.n. is most similar to L. cabiochi (Amoureux, 1982) in the number of chaetigers (22 and 21, respectively) but it has significant differences. Laubieriopsis norvegica have paired genital papillae while in L. cabiochi the genital papilla is unpaired. Paired genital papillae were observed in some other species of the genus, for example L. arenicola. Parapodia of the last chaetiger in L. norvegica differ from the other parapodia, bearing one thick acicular chaeta and three capillary chaetae. Enlarged and backward-directed chaetae of the terminal chaetiger -"pygidial cage" -were described also for other Laubieriopsis species (L. brevis, L. arenicola) (Riser 1987, Petersen 2000. Laubieriopsis arenicola differs from L. norvegica by having 25 thoracic chaetigers and in the location of genital papillae on chaetiger 7. Our study confirms Petersen's (2000) statement on characters useful for distinguishing species in the genus Laubieriopsis: number of chaetigers, number of anterior chaetigers with acicular chaetae, presence of bidentate anterior neurochaetae, enlarged and directed backward chaetae of the last chaetiger, and paired/unpaired genital papilla. Interestingly, one of 28 specimens studied here has 23 instead 22 thoracic chaetigers and another one has an unpaired genital papilla. As intraspecific variability was noted for all characters (present work, Petersen 2000), description of new as well as redescription of existing taxa should be based on examination of several specimens and the whole complex of characters.
There was only one species of the genus Laubieriopsis previously known from the Northeast Atlantic, L. cabiochi. The present study increases the number of known species of Laubieriopsis to five and the number of Northeast Atlantic species of this genus to two.