The genus Branchiomma ( Polychaeta : Sabellidae ) in the Mediterranean Sea , with the description of B . maerli n . sp .

The genus Branchiomma (Annelida: Polychaeta: Sabellinae) from the Mediterranean Sea is revised based on material collected during several surveys and preserved in the Zoological Laboratory of Lecce University (South Italy). Branchiomma maerli n. sp. is described as a new species and compared with the previously reported B. bombyx, B. lucullanum, B. luctuosum, and B. cf. moebii. Branchiomma maerli n. sp. resembles B. lucullanum, but differs in the shape of the collar and in the length of the dorsal lips. Branchiomma boholensis, reported as the only Mediterranean species with macrostylodes, is not here described because it has not been possible to obtain adequate material. Finally, Branchiomma sp. (similar to B. violaceum, but having the dorsal collar fused to the faecal groove) is not formally described as a new species because there is only one available specimen.


INTRODUCTION
The genus Branchiomma Kölliker, 1858 includes about 30 species mostly distributed in sheltered shallow waters (bays, lagoons and harbours) (Tovar-Hernández and Knight-Jones, 2006).The genus is characterised by the presence of paired stylodes (epithelial flaps) occurring at regular intervals along the outer side of each rounded radiolar rachis (Knight-Jones, 1994).The shape and size of these structures are very important for distinguishing species within the genus.
To facilitate species comparisons, two artificial categories were proposed: group A, including species having the collar fused to the dorsal faecal groove, and group B, including species having the collar with widely separated dorsal margins (Knight-Jones, 1994;Tovar-Hernández and Knight-Jones, 2006).The latter, which contains most of the species, is subdivided into group B1, with macrostylodes on radioles, and group B2, with a length gradation of simple stylodes along the radiole.The species of group B2 may have a thoracic uncinal crest with either numerous or sparse teeth, while the species of group A always have numerous teeth.
Five species are currently known for the Mediterranean Sea: B. bombyx (Dalyell, 1859), the most common; B. lucullanum (Delle Chiaje, 1828), much more abundant in the past; B. luctuosum (Grube, 1870), introduced from the Red Sea (Bianchi, 1983) and at present one of the most abundant species along the Italian coasts; B. moebii Knigth-Jones, 1994, previ-ously identified as B. lucullanum and Branchiomma species A from the Adriatic Sea and the Aegean Sea respectively (Knight-Jones et al., 1991); and B. boholensis (Grube, 1878), a fairly common species in the Indo-West Pacific, recorded by Knight-Jones et al. (1991) from the eastern Mediterranean and previously identified as Dasychone cingulata Grube, 1870 and Dasychone lucullana (Delle Chiaje, 1828).
In this paper the species of the genus Branchiomma from the Mediterranean Sea are revised on the basis of the material collected during several surveys along the Italian coasts since 1989 and preserved in the authors' collection at the Zoological Laboratory of Lecce University (southern Italy).As a result, one new species is described, namely B. maerli, and another is not formally named due to the lack of sufficient available material.

MATERIAL AND METHODS
The holotype of Branchiomma maerli n. sp. is deposited at the Museo Nacional de Ciencias Naturales in Madrid (MNCN).The paratype is preserved in the collection of the Laboratory of Zoology of Lecce (PCZL), along with all the other examined material which comes from ecological studies conducted along the Italian coasts.
The external morphology of the specimens was examined using a stereomicroscope.Detailed observations of structures such as chaetae, uncini and dorsal lips were performed under a light microscope and measured with an ocular micrometer.For all the species, the description of the number of thoracic chaetae and uncini refers to the third chaetiger, while that of the abdomen refers to the middle part of the abdomen.
The photographs were taken with a digital camera (Nikon, Coolpix 990) attached to the stereomicroscope.Drawings were made with the aid of a camera lucida.

TAXONOMIC ACCOUNT
Family Sabellidae Latreille, 1825 Subfamily Sabellinae Latreille, 1825 Genus Branchiomma Kölliker, 1858 Diagnosis.Medium-size sabellid species (except the large B. luctuosum), with numerous radioles.Palmate membrane present, radiolar flanges absent.Stylodes well developed, regularly spaced along the outer side of each rounded radiolar rachis.Radiolar compound eyes paired, distributed along the radiole length.Dorsal lips with radiolar appendages.Ventral lips and parallel lamellae present.Thoracic and abdominal interramal eyespots present.Superior thoracic notochaetae elongate, narrowly hooded.Inferior thoracic notochaete spinelike, fascicles arranged in bundles, with irregular, longitudinal chaetal rows.Abdominal neurochaetal tori as conical lobes, chaetal fascicles arranged in a partial C-shaped configuration formed by outer chaetae geniculate, around a cluster of capillary chaetae.Thoracic uncini avicular with small teeth above the main fang and very short handle.Companion chaetae absent.Abdominal uncini similar to the thoracic ones.

Branchiomma bombyx
Remarks.The material collected along the Italian coast corresponds quite well with the description by Rioja (1923), especially in the collar features and in the shape of the stylodes, even if the specimens examined by this author were slightly larger and with longer dorsal lips.The species, the most common within the Mediterranean Sea, is often confused with B. lucullanum from which it can be distinguished by the shape of the shorter stylodes, the lower dorsal and ventral lappets of the collar and the longer dorsal lips.However, the shape of the stylodes is not a satisfactory character in small specimens, which may be better distinguished by the shape and length of the dorsal lips (shorter and blunter in B. lucullanum), as already pointed out by Knight-Jones et al. (1991).
Remarks.The examined material corresponds quite well to the description by Rioja (1923), except for the smaller size and more slender appearance.This species, very common in the past, is now rarer, particularly in the Gulf of Naples where it used to be very abundant and is now absent (authors' pers.obs.).This could be the result of either normal fluctuations of abundance or changes in the environmental conditions during the last 100 years, after Claparède's studies.Another cause of regression could be the introduction, apparently from the Red Sea, of the invasive Branchiomma luctuosum, which became the most abundant species in the Gulf of Naples.
Remarks.Originally described for tropical waters (Grube, 1870), this species represents a possible Lessepsian migrant from the Red Sea.The first finding in the Mediterranean Sea was in the western basin (Tyrrhenian Sea) (Bianchi, 1983), but later it was reported also for the eastern basin (Aegean Sea) (Simboura and Nicolaidou, 2001), and more recently in the eastern Atlantic (Daniel Martin, pers. com.).At present, this species seems to have invaded most of the Italian coast and is considered a pest (Licciano et al., 2002).It is also present on the Brazilian coasts (Nogueira et al., 2006), where it seems to have been introduced recently.For these reasons, B. luctuosum is one of the most investigated sabellid species (Licciano et al., 2002).
Our material agrees with the original description (Grube, 1870) and with that provided by Knight-Jones et al. (1991).However, these authors reported the uncini as having a single row of secondary teeth, contrasting with the 3 rows of our Italian material, and the 2-3 of the Brazilian material examined by Nogueira et al. (2006).In the studied population from Ionian Sea a variable development of stylodes was observed among individuals, some having shorter stylodes than those represented in Figure 3C.Knight-Jones 1994 (Fig. 5)
Description.Small species, 19 mm in body length, up to 15 mm of crown length, with 8 thoracic and about 30 abdominal chaetigers.12-15 pairs of radioles, each with about 20 pairs of digitiform stylodes not covering the small radiolar eyes (Fig. 5C).Collar with a large dorsal gap, (Fig. 5A), higher ventrally with well-developed ventral lappets pointed and not overlapping (Fig. 5B).Dorsal lips enlarged, about 1/3 the length of the branchial crown (Fig. 5A).Superior thoracic notochaetae slender weakly geniculate, 5-6 per fascicle.Inferior thoracic notochaetae spinelike with knee slightly wider than shaft (Fig. 5E), 7 per fascicle.Thoracic uncini avicular, with well-developed breast and very short handle, 38 per Remarks.The description of B. moebii is available in Knight-Jones (1994), who examined material from the Turkish coasts and emended old material from the northern Adriatic Sea and Ligurian Sea previously identified as B. lucullanum.This was probably due to the similarity in the shape of the stylodes, which are digitiform.However, in B. moebii stylodes show a gradation along the radiole, with larger pairs more tongue-shaped towards the bases of dorsal and lateral radioles.Moreover, this species is easily distinguishable from B. lucullanum in having the dorsal margin of the collar not fused to the faecal groove and longer dorsal lips.
The PCZL material differs from B. moebii, especially in the shape and development of stylodes, which are less developed and tongue-shaped dorsally and laterally at the base of the crown than B. moebii, being digitiform and equally developed along the radiole (similarly to B. lucullanum).On the other hand, the dorsal margin of the collar, not fused to the faecal groove, and the length of dorsal lips, differ from B. lucullanum and more closely resemble B. moebii.
Moreover, the PCZL material has a smaller number of thoracic chaetae per fascicle, and ventral collar lappets more prominent than in B. moebii, thus resembling the North Atlantic species B. inconspicuum (Sars, 1862) This species was also discussed by Knight-Jones (1994) as similar to B. moebii.However, the number of radioles, the number of chaetigers and the body size more closely resemble B. moebii than B. inconspicuum.Branchiomma sp.
Remarks.This taxon is very similar to B. violaceum (Schmarda 1861) and to B. natalensis (Kinberg 1867) from South Africa, especially in the shape and development of stylodes and in the number of rows of secondary teeth over the main fang in the thoracic uncini.Both species, however, differ from Branchiomma sp. in having the dorsal collar fused to the faecal groove.Branchiomma infarctum (Krøyer, 1856) also resembles Branchiomma sp. in having the collar margins ventrally separated and in the presence of large tongue-shaped stylodes.However, this species has a northern distribution, ventro-lateral notches in the collar, a thoracic uncinal crest with numerous teeth, and tongue-shaped stylodes developed only at the base of the radiole.A single specimen in bad conditions was available for examination, and this prevented any further systematic inference.A large population seemed to be present at the collecting dates on artificial substrates in a harbour area of southern Italy (Fabio Badalamenti, pers.comm.), allowing us to suggest that it could be another introduced species.However, the original population seems to have disappeared from the collection's site, and further sampling is needed in order to confirm its presence and to clarify its taxonomy.(Grube, 1878) This species, fairly common in the Indo-West Pacific, was reported from the southeastern Mediterranean basin based on material previously identified as Dasychone cingulata and Dasychone lucullana (Knight-Jones et al., 1991) as the only Mediterranean Branchiomma having macrostylodes.The spe-cies was not present in the studied collections, but a good description was provides by Knight-Jones et al. (1991).Description.Holotype a complete specimen, 25 mm in body length, up to 20 mm crown length, with 8 thoracic and 50 abdominal chaetigers.30 pairs of radioles, each with about 10 pairs of small, digitiform stylodes, becoming slightly larger and covering the eyes in the middle part of the radiole (Fig. 7C).Eyes small and compound.Large spots present in the crown and along the body (Figs.7A, B, 4B).Collar fused to the dorsal faecal groove, with dorsal lappets ending at the same height of the lateral col-  lar margin (Fig. 7A).Collar slightly higher ventrally, with poorly developed ventral lappets rounded and overlapped (Fig. 7B).Collar chaetae slender, narrowly hooded, arranged in compact fascicles.Dorsal lips long and tapered, about ½ of the branchial crown (Fig. 7B).Thoracic notochaetae within each fascicle as irregular oblique rows of superior and inferior chaetae, with 20 superior and 18 inferior spinelike chaetae with knee region twice as wide as shaft (Fig. 7D).Thoracic tori abutting ventral shields (Fig. 7B).50 thoracic uncini per torus, avicular, with well-developed breast and short handle.Each uncinus with numerous teeth (7-8 rows in profile) over the main fang (Fig. 7E).15 abdominal chaetae per fascicle, forming compact tufts with the outer geniculate chaetae arranged in C-shaped arcs around a cluster of capillary chaetae.Abdominal uncini avicular, similar to the thoracic ones, 23 per torus.

Branchiomma maerli
Etymology.The specific name refers to the habitat of the species, the mäerl, unusual for the genus.
Remarks.The new species belongs to group A together with B. bombyx, B. violaceum, B. pseudoviolaceum Augener, 1922 and B. natalensis, but can be distinguished by the shape and development of stylodes, which are digitiform and not foliaceous.This makes B. maerli n. sp.more similar to B. lucullanum, even though the former has shorter stylodes, a larger size and a higher number of radioles, lower dorsal and ventral collar lappets, a collar with ventro-lateral notches, and longer dorsal lips, which are even longer than those of B. bombyx (Table 1).
Branchiomma maerli n. sp.can also be clearly distinguished from the remaining Mediterranean species of Branchiomma (Table 1), and a very peculiar feature is also the pigmentation of the body (Fig. 3A).A similar pattern is only present in an extra-Mediterranean species, Branchiomma nigromaculatum (Baird, 1865), and, although less evident, in B. luctuosum (Fig. 3B).
Finally, the new species differs from the other known Mediterranean species, which are characteristically shallow-water species, in that it has only been found on mäerl bottoms.The peculiar habitat where the species has been collected must be stressed.The mäerl is a typical biocoenosis, whose bathimetric distribution in the Mediterranean ranges from 20 m deep in the Gulf of Cadiz to about 180 m deep in the eastern basin (Bellan-Santini et al., 1994).

Table 1 .
-Comparative analysis of the main taxonomic characters of Branchiomma species from the Mediterranean Sea.The indication "shortlong" in the column "stylode size" indicates the presence of different sizes along the radiole (gradation) or the presence of macrostylodes.