Four new species of fan worms ( Polychaeta : Sabellidae ) from worldwide localities

Four new species of soft-bottom sabellid polychaetes are described and illustrated. Branchiomma costaricensis n. sp. is described from 31 m depth off Isla del Coco, Costa Rica; Dialychone arabica n. sp. from 105 m depth in the Arabian Sea; Dialychone blakei n. sp. from 487 m depth off Louisiana in the Gulf of México and Paradialychone harrisae n. sp. from 30 m depth in southern California. Branchiomma costaricensis n. sp. is characterized by having microstylodes with the median pair 1.5 times longer than neighbouring pairs, thoracic uncini with two rows of teeth above the main fang, an unspotted body and large interramal eyespots. Dialychone arabica n. sp. has the anterior peristomial ring lobe exposed beyond the collar and a pre-pygidial depression occupying eight segments. In D. blakei n. sp., the anterior peristomial ring lobe is not exposed beyond the collar, the pre-pygidial depression occupies the last four segments and the posterior segments possess thin elongate, narrowly hooded chaetae. Paradialychone harrisae n. sp. differs from the other species of the genus in having the anterior peristomial ring lobe bilobed and exposed beyond the collar, a rectangular ventral collar shield and paleate chaetae with a long mucro.


INTRODUCTION
Sabellidae Latreille, 1825 is a family of polychaetous annelids commonly known as fan worms, featherduster worms, or sea flowers.Living specimens are easily recognized due to their often colourful crown frequently projecting from the mouth of their tubes.Rioja (1923) divided the sabellids into three subfamilies based primarily on chaetal characters: Sabellinae Latreille, 1825, Myxicolinae Koch in Renier, 1847and Fabriciinae Rioja, 1923. Fitzhugh's (1989) morphology-based cladistic analysis resulted in significant changes to the previous classification of Sabellidae as it demonstrated that only the subfamilies Fabriciinae and Sabellinae could be accepted as monophyletic.The most recent reviews of Fabriciinae bring the number of nominal species to more than 70 (Fitzhugh, 1998(Fitzhugh, , 1999)), while the Sabellinae was emended by Fitzhugh (1991) to include more than 400 nominal species.
Recently, Kupriyanova and Rouse (2008) studied the monophyly of the Sabellidae based on molecular data from three nuclear genes of sabellins and fabricins.Their molecular evidence supports the hypothesis that the Sabellidae does not constitute a monophyletic group as currently formulated since it contains the Serpulidae.Additionally, the Fabriciinae were found to be more closely related to the Serpulidae than to Sabellinae.The authors therefore emphasized that the Fabriciinae must be removed from the Sabellidae and be referred to the Fabriciidae, with the revised Sabellidae being equal to the previous subfamily Sabellinae because its represents the simplest solution with the least disruption to current nomenclature.
Worldwide systematic revisions have been done for the sabellid genera Dialychone Claparède, 1870 andParadialychone Tovar-Hernández, 2008.As a result their taxonomy is better studied and several species have been described within these genera (Tovar-Hernández, 2007;Nishi et al., 2009).The genus Branchiomma Kölliker, 1859 has only partial revisions from the Caribbean Sea (Tovar-Hernández and Knight-Jones, 2006) and the Mediterranean Sea (Licciano and Giangrande, 2008), and phylogenetic analyses have not been performed.
In this contribution four new species of Branchiomma, Dialychone and Paradialychone are described from isolated localities in Costa Rica, the Arabian Sea, southern California and the northern Gulf of México.

MATERIALS AND METHODS
The materials examined are deposited in the Los Angeles County Museum of Natural History, Allan Hancock Foundation (LACM-AHF), the Museum of Comparative Zoology, Harvard University (MCZ) and the Museo de Zoología, Universidad Nacional de Costa Rica (MZUCR).Descriptions are based on holotypes with data in parentheses referring to the paratypes.The methyl green staining for Dialychone and Paradialychone species follows Hofsommer (1913).A Leica MZ75 stereomicroscope and Olympus CH30 optical microscope were used for identification, digital photographs were taken with an attached Canon S5 digital camera, and drawings were made using a camera lucida.Materials were processed and examined after final dehydration in two changes of 100% ethanol at the Laboratorio de Microscopía Electrónica de Barrido (Facultad de Ciencias, Universidad Nacional Autónoma de México).Specimens of Dialychone and Paradialychone were critical-point dried, mounted on stubs and coated with gold (200 Å) before examination with a Cambridge 250 scanning electron microscope (SEM).A specimen of Branchiomma costaricensis n. sp. was critical-point dried and coated with gold (20 Å) at the MCZ by one of us (HD) and examined using a Zeiss EVO 50 Scanning Electron Microscope.In descriptions, data in parenthesis refer to paratypes.Diagnosis.Digitiform microstylodes with the median pair 1.5 times longer than neighbouring pairs; unsegmented radiolar rachis; thoracic uncini with two rows of teeth above the main fang; unspotted body and large interramal eyespots.

Family
Description.Body excluding crown 7 mm long (1.5-9), 0.5 mm wide (0.25-0.5).Body pale, lacking pigmentation on the dorsal and ventral surfaces.Large, dark interramal spots along entire body (Figs 1G, 7C), slightly smaller in last posterior segments.Radiolar crown 5 mm long (0.5-6), extending 0.5 to 0.75 times body length, united at base by short web or membrane.Radiolar base with longitudinal bands of diffuse brown spots, below web.Eight pairs of radioles (4-7) with filiform tips (Fig. 1A), with narrow brown bands extending towards pinnular tips, each band occupying the space of three pinnules.Longest pinnules at 0.75 times branchial crown length.Basal stylode unpaired, small, digitiform, 0.25 times rachis width (Figs 1D,2A); seven to eight pairs of small, digitiform microstylodes (Figs 1A-D, 2A-B); median pair 1.5 times as long as adjacent pairs, flanking median area of radiole (Fig. 1B-C).Unsegmented radiolar rachis.Eight pairs of oval compound eyes (4-10) one each side of rachis, ommatidia sub-conical (Fig. 2A-B); those of median and distal region surrounded by accumulation of pigment cells; eyes lacking between last pair of stylodes (Fig. 1A).Dorsal lips of 0.25 times the length of radioles, triangular with distinct longitudinal ridge (mid-rib); ventral lips rounded, 0.25 times the length of dorsal lips; ventral sacs rounded (Fig. 7B).Midline faecal groove deep on first segment forming mounds on each side; collar well separated dorsally (Figs 1F, 7A), lateral collar margins transverse to body axis covering junction between crown and body; ventral lappets (with brown spots) with rounded apices, overlapping medially (Figs 1E, 7B-C).Thorax with five segments (4-7).Thoracic tori extending to sides of brown, trapezoidal ventral shields, latter two times wider than long (Fig. 1E).Collar chaetae slender, narrowly hooded arranged in compact fascicles (Fig. 2G).Thoracic notochaetae arranged within each fascicle in irregular oblique rows of superior and inferior chaetae; superior chaetae slender, hooded, knee region slightly wider than shaft; inferior chaetae with knee up to twice as wide as shaft (Fig. 2C).Avicular uncini with two rows of teeth (seen laterally) occupying 0.5 times main fang length (Fig. 2D-E), with short, curved handle (Fig. 7D).Abdomen with 20 segments (19-44); conical tori smaller than those of thorax.Fascicles of abdominal chaetae forming compact tufts (Fig. 2I), superior chaetae narrowly hooded, arranged in thick C-shaped arc around cluster of capillary chaetae (Fig. 2H-I); number of chaetae per fascicle decreases gradually towards posterior.Abdominal uncini with two rows of teeth and short straight manubrium (Figs 2F, 7E).Bilobed pygidium (Fig. 1H).Tubes unknown.Gametes.One paratype is a simultaneous hermaphrodite, with male and female gametes occurring in the same segments in the anterior abdomen.Sperm with spherical nucleus, rounded cap-like acrosome and a long flagellum.
Etymology.The specific epithet refers to the collecting country, Costa Rica.
Remarks.Branchiomma is a large, widespread, sabellid genus of about 30 species, which are found in sheltered waters such as bays, lagoons and harbours, mainly on floating docks, dock pilings (metal, wood, concrete), floating buoys (metal and PVC) and the hulls of vessels, but also on rocks, coral crevices, sponges and molluscs (Tovar-Hernández and Knight-Jones, 2006).Wide geographical distributions of some sabellid species referred to as cosmopolitan are suspect and detailed study usually finds that more than one species with narrower distributions is involved (Tovar-Hernández and Knight-Jones, 2006;Licciano and Giangrande, 2008).However, at least four species of Branchiomma have been considered as alien (Tovar-Hernández et al., 2009); these include B. luctuosum (Grube, 1870), B. boholense (Grube, 1878), B. curtum (Ehlers, 1901) andB. bairdi (McIntosh, 1885) Other species with thoracic uncini with two rows of teeth above the main fang correspond to Branchiomma cingulatum (Grube, 1870) and Branchiomma sp.(Licciano and Giangrande, 2008).Branchiomma costaricensis n. sp.differ from these in having an unsegmented rachis and short, digitiform stylodes (B.cingulatum has a segmented rachis with filiform stylods and in B. sp. the rachis is unsegmented with long tongue-shaped stylodes).
Six species of Branchiomma are distributed in the tropical American coasts.Among these, B. bairdi and B. conspersum (Ehlers, 1887)  Diagnosis.Anterior peristomial ring lobe entire, exposed beyond the collar; ventral margin of the collar notched; vascular peristomial loops present; short, digitiform radiolar tips; pre-pygidial depression occupying eight segments.
Etymology.The specific name refers to the collecting zone, the Arabian Sea.
Gametes.Paratype female with oocytes in anterior abdomen.

Gametes. Unknown.
Methyl green staining.Collar with two triangular glandular areas dorsally (Fig. 7Q), these extend laterally towards the ventral side (Fig. 7P), where only the ventral shield of the collar is stained (Fig. 6A).Sparse glands are distributed along the entire body.Pygidium deeply coloured (Fig. 7A).
Etymology.This species is named in honour of Leslie Harris (Los Angeles County Museum of Natural History) in recognition of her important contributions to the knowledge of polychaetes from California, as well as her continuous support to the Mexican col-leagues to facilitate the research in the country for this group of invertebrates.
Dialychone arabica n. sp.differs from D. usticensis in having the ventral margin of the collar notched (unnotched in D. usticensis); vascular peristomial loops (absent in D. usticen-sis); short, digitiform radiolar tips (long and filiform in D. usticensis); and with the longest pinnules 0.75 times the branchial crown length (equal in size along the entire radiole in D. usticencis).Dialychone arabica n. sp.differ from D. blakei n. sp. in having a pygidium with a triangular posterior margin (rounded in D. blakei n. sp.); a triangular anterior peristomial ring lobe (bilobed in D. blakei n. sp.), short radiolar tips (very long in D. blakei n. sp.) and a posterior pre-pygidial depression occupying eight segments (four segments in D. blakei n. sp.).
. In order to recognize possible new introductions of alien Branchiomma species in Costa Rica, a comparison of these species and B. costaricensis n. sp. is provided: Branchiomma luctuosum, B. curtum and B. costaricensis n. sp.share the presence of microstylodes but B. luctuosum differ from the other two species in having the radiolar rachis segmented (not segmented in B. curtum and B. costaricensis n. sp.).Branchiomma costaricensis n. sp.resembles B. curtum, in that both species are small; however, B. costaricensis n. sp. has thoracic uncini with main fang surmounted by two rows of teeth (three in B. curtum), large interramal spots (small in B. curtum) and short and medium sized stylods (only short in B. curtum).Branchiomma boholense and B. bairdi have macrostylodes, while in B. costaricensis n. sp.there are only microstylodes.Branchiomma costaricensis n. sp., and B. boholense have thoracic uncini with two rows of teeth above the main fang, but B. costaricensis n. sp. has digitiform stylodes (digitiform and flattened, tongue-shaped in B. boholense).
have short, medium, long and extra-long stylodes in the same radiole; B. coheni Tovar-Hernández and Knight-Jones, 2006 has short, medium and long stylodes; B. illifei Tovar-Hernández and Knight-Jones, 2006 has medium and long stylodes; B. curtum has only short stylodes and B. nigromaculatum (Baird, 1865) and B. costaricensis n. sp.have short and medium stylodes.Branchiomma costaricensis n. sp.differ from B. nigromaculatum in possessing thoracic uncini with the main fang surmounted by two rows of teeth (one in B. nigromaculatum) and an unsegmented radiolar rachis (segmented in B. nigromaculatum).Species of Branchiomma can lose body spot patterns due to sloughing after imperfect fixation and preservation.Holotype and paratypes examined here have unspotted bodies although further collections are needed to document live coloration.