Orbiniidae polychaetes ( Polychaeta : Scolecida ) from Coiba Island , eastern Pacific of Panama , with description of a new species

Santa Cruz and El Gambute, two mangrove systems with associated tidal flats, were sampled in Coiba National Park, Coiba Island, Pacific of Panama. At each site, two samplings were done at low, middle and high intertidal levels in February and November of 1997. A new orbiniid species were found: Orbinia oligopapillata n. sp. is characterized by having 15-16 thoracic chaetigers with four or five rows of uncini and up to three papilliform postchaetal processes on neuropodial lobes by the abdominal parapodia bearing flail-tipped neurochaetae, and by the presence on anterior-most abdominal chaetigers of interramal cirri and a low number of subpodial and stomach papillae. A specimen belonging to genus Leitoscoloplos Day, 1977 is described as “Leitoscoloplos sp.”, characterized by the lateral pouches on its abdominal chaetigers, a unique case for the family because these brooding structures have only been previously cited in two species of Scoloplos. Naineris sp. is characterized by the number of its thoracic chaetigers, branchiae, uncini and bilobed abdominal neuropodia with protruding aciculae. Rev. Biol. Trop. 54 (4): 1307-1318. Epub 2006 Dec. 15.

The Orbiniidae (Polychaeta: Scolecida) are burrowing polychaetes that can be found from low tidal to abyssal depths, acting in most cases as nonselective subsurface deposit feeders.The most important review of orbiniid systematics is by Hartman (1957), where all the genera known so far were redefined.Other important contributions to the knowledge of the family have been made by Pettibone (1957), Day (1977), Taylor (1984), Mackie (1987), Solís-Weiss and Fauchald (1989), Blake (1996) and León-González and Rodríguez (1996).However, the systematics of the family is still unclear and in some cases the boundaries between some genera are obscure, causing some close species to have been described within different genera.Blake (2000) performed a brief revision of the family where a new partition in subfamilies is proposed and some genera are erected or re-erected from subgeneric status.

MATERIALS AND METHODS
During 1996 and 1997 a research project aiming to characterize the marine benthic fauna of Coiba National Park was conducted (López et al. 1997, 2002, San Martín et al. 1997, Capa et al. 2001a,b).This park is located off the Pacific coast of Panama, between 7º10'-7º53' N, 81º32'-81º56' W. Several mangrove systems with associated tidal flats occur in Coiba Island, two of which were selected for the present study: Santa Cruz and El Gambute.The first one is located within a cove on the NW coast of the island (7º37'30" N, 81º45'40" W) and, thus, it is under sheltered hydrodynamic conditions.The sediment is quite homogenously fine sand of moderate sorting throughout this large tidal flat and the presence of mangrove-derived tannins is evident from the red-brown color of interstitial water.The second one, much smaller, is located on the NE coast near Coiba Park Biological Station (7º37'25" N, 81º43' W).In this case, the sediment is mainly a poorly sorted mixture of muddy sand and pebbles, although patchy changes in sediment features can be observed.
Three transects were selected on each tidal flat and three sampling sites were arranged on each one.The lower one was located close to the low water line and the upper near the high water line, the third site (middle intertidal) was marked mid-way from the two others.Two samplings were carried out in each site, in February and in November of 1997.Each sample consisted of three replicates of 40 x 40 cm square area and 30 cm sediment depth.They were sifted (1 mm gauge mesh) in the field and the obtained material was fixed and preserved in 10 % formalin in seawater.Subsequently, it was separated from the remaining sediment and sorted into the higher taxonomic groups.Further information about the sampling sites and methodology is given in López et al. (2002).In the laboratory, the specimens were examined under a dissecting microscope and a light microscope with interference contrast optics (Nomarsky), both with an incorporated camera lucida.After the study, all specimens were preserved in 70 % ethanol and the types were deposited in the Museo Nacional de Ciencias Naturales de Madrid (MNCN), Spain.For taxonomic descriptions, the character denominations proposed by Blake (2000) are used.Description: Holotype and paratypes are incomplete specimens.Holotype is the largest specimen; 0.8 mm wide at middle thorax, 0.6 mm wide at the beginning of the abdomen; 27 mm long, 81 chaetigers.Body yellowish in alcohol.Prostomium (Fig. 1A, B, 3A) sharp and divided in two regions; anterior one very narrow and small; posterior one clearly wider.Peristomium (Fig. 1A, B) very short and fused to first chaetiger, sharply widening to thorax width; lacking appreciable eyes but bearing lateral nuchal organs (Fig. 1A, 3A) on an anterior position.Mouth (Fig. 1A) ventral and extending to anterior end of first thoracic chaetiger; proboscis partially everted, striated.Thorax (Fig. 1A, B) consisting of the peristomium and 16 chaetigers (15 in some paratypes), slightly flattened in section.Notopodia as short low ridges on first two chaetigers (Fig. 1C); remaining thoracic chaetigers with a digitiform postchaetal lobe increasing in length on posterior thorax (Fig. 1D-F); bearing 13-15 crenulated, slightly curved capillaries.Neuropodia of first chaetiger as low transverse ridges, from chaetiger 2 to 14 (Fig. 1C-E) with a rounded postchaetal lobe bearing a papilliform process; last two thoracic chaetigers (Fig. 1F) similar in shape but bearing three papilliform postchaetal processes and a digitiform prechaetal process (Fig. 3D); with four or five rows of thick, curved uncini, numbering 50 on first chaetiger and increasing in number up to 70; those of anterior chaetigers (Fig. 2A, B, 3C) bearing transversal rows of minute spines and some with a longitudinal median groove; sculpture more indiscernible and median groove more distinct as more posterior the chaetiger (Fig. 2C, 3D); seven to 12 slender crenulated capillaries making a single row posterior to uncini.Abdomen incomplete, cylindrical in section.Anterior parapodial lobes located on sides, posteriorly achieving a more dorsal position.Notopodia with a long, lanceolate postchaetal lobe and a prechaetal lobe of increasing length towards posterior chaetigers (Fig. 2D, E); bearing about 30 crenulated capillaries in anterior abdomen and about 15 in median abdomen, furcated chaetae not seen; prechaetal lobe supported by one or two slightly sigmoid and protruding aciculae.Interramal cirri present on anterior-most abdominal chaetigers (Fig. 2D), progressively becoming less distinct (Fig. 2E) and disappearing.Neuropodia bilobed, with prechaetal lobe longer and supported by a stout, curved acicula (Fig. 2D, E); with about 5-10 crenulated capillaries and 3-7 flail-tipped chaetae (Fig. 2F, G); first two abdominal chaetigers with three piriform, large subpodial papillae (Fig. 2D); subpodial papillae progressively becoming less distinct to make a bilobed subpodial flange on median abdominal chaetigers (Fig. 2E).Stomach papillae only on first three abdominal chaetigers, piriform, numbering only up to eight (Fig. 1A, 3B).Branchiae erected, from chaetiger 10 (11 in some large paratypes); first five pairs (Fig. 1A, B) slender and cirriform or short and papilliform (might be retractile); remaining ones more stout and tapering to a short tip, somewhat longer than postchaetal lobe, bearing two dark glandular ridges but lacking fimbriation (Fig. 1F, 2D, E).

Orbinia
Etymology: The specific name refers to the number of stomach papillae which is much fewer than in other species of the genus.
Remarks: O. oligopapillata n. sp. is characterized by having 15-16 thoracic chaetigers with four or five rows of uncini and up to three papilliform postchaetal processes on neuropodial lobes, abdominal parapodia bearing flail-tipped neurochaetae and lacking furcated notochaetae, branchiae beginning on chaetiger 10 or 11, interramal cirri, and a low number of subpodial and stomach papillae on anteriormost abdominal chaetigers.
Because of these features, it belongs to a distinct group of species characterized by the presence of subpodial papillae on first abdominal chaetigers, by a low number of stomach papillae on each segment and, in most cases, by having flail-tipped chaetae.Since in these species the number of stomach papillae is so clearly below the typical in the genus, they have been referred either to Scoloplos or to Orbinia.However, according to Blake (2000) all the species bearing stomach papillae and lacking modified spines on thoracic notopodia should be assigned to Orbinia and the type material of the species referred to Scoloplos should be carefully examined in order to evaluate the transfer of these species to Orbinia.This is far beyond the scope of the present work and these species are referred to by the name most widely used in the literature.
Orbinia hartmanae Day, 1977, from Australia (Day 1977), is the most similar species, with 12-21 thoracic chaetigers, branchiae from chaetiger eight, four rows of thoracic uncini, a similar number of postchaetal processes on thoracic neuropodia and of stomach papillae on first abdominal chaetigers, and flail-tipped chaetae.However, this species lacks a prechaetal process on thoracic neuropodia and interramal cirrus on abdominal chaetigers.Moreover, although the number of stomach papillae is also low, they occur in more chaetigers (last two in thorax and first six in abdomen).Day, 1934 from Southern Africa and Australia (Day 1967(Day , 1977)), is a second species that also bears flail-tipped chaetae and a few subpodial and stomach papillae on first abdominal chaetigers, as well as thoracic neuropodia with four rows of uncini and one or two postchaetal processes, but it possesses 18-24 thoracic chaetigers, branchiae from chaetiger six onwards, and furcated notopodial chaetae on abdomen.

Scoloplos (Leodamas) johnstonei
Orbinia riseri (Pettibone, 1957), from western Atlantic (Pettibone 1957, 1963, Day 1973, Taylor 1984), is similar to the new species in having branchiae that begin on chaetiger 8-10, thoracic neuropodia with four rows of uncini and 2-3 postchaetal processes, interramal cirri on abdominal neuropodia, and a low number of stomach papillae.On the other hand, it can be distinguished by lacking flail-tipped chaetae and by bearing many more chaetigers with stomach papillae (last six in thorax, first five in abdomen) and with interramal cirri (70 first abdominal chaetigers).
Remarks: The studied specimen of Leitoscoloplos sp.most likely belongs to an undescribed species but due to the variability of characters in the family a formal description based on a single specimen would be necessarily incomplete.It is characterized by having a large number of thoracic chaetigers ( 22), by possessing inconspicuous parapodial lobes in both rami of thorax, by having anterior abdominal lobes with interramal cirri and three subpodial papillae and by bearing branchiae from chaetiger 23.However, the most notorious characteristic of the specimen is the presence of lateral pouches on abdominal chaetigers.In the family Orbiniidae, this feature is present only in Scoloplos marsupialis Southern, 1921 and S. tumidus Mackie, 1991(Mackie 1991), but the material from Coiba can readily be distinguished from them by the absence of neuropodial uncini on thorax.Although Day (1967) recorded juvenile specimens of S. marsupialis that lacked neuropodial uncini, the size of our specimen (too large to be a juvenile) prevents confusion.
Within genus Leitoscoloplos, the specimen can be placed in the last of the five groups stated by Mackie (1987).It is composed of species with numerous thoracic chaetigers and bearing interramal cirri and subpodial papillae: L. robustus (Verrill, 1873), L. fragilis (Verrill, 1873), L. panamensis (Monro, 1933) and L. obovatus Mackie, 1987.Apart of the lack of pouches, L. panamensis, from Pacific coast of Panama, and L. obovatus, from western Atlantic, further differ from Leitoscoloplos sp. in the shape of thoracic neuropodial lobes (mammiform in L. panamensis and triangular in L. obovatus, clearly projecting in the two species) as well as in the branchiae, which first occur on a more anterior chaetiger (11 in L. obovatus, nine in L. panamensis); also L. robustus, from Eastern Pacific, differs in having mammiform neuropodial lobes in thorax, albeit the first pair of branchiae appears on a quite posterior chaetiger (chaetiger 20-22).L. fragilis, from Western Atlantic, is the most similar species, having inconspicuous thoracic neuropodial lobes, but it has somewhat shorter thorax (up to 16 thoracic chaetiger according to Mackie 1987) and only two subpodial papillae on anterior abdomen.
Description: Incomplete specimen.Medium sized specimen; 13.5 mm long for 57 chaetigers; 2.5 mm wide at middle thorax, 1.2 mm wide at first abdominal chaetigers.Body yellowish in alcohol with slightly dark dorsal bands on thorax; thoracic transversal ciliary rows not seen.Prostomium (Fig. 5A) broadly rounded and spatulate, without appreciable eyes or nuchal organs.Proboscis (Fig. 5A) partially everted, broad and irregularly lobed.Thorax (Fig. 5A) consisting of the peristomium and 40 chaetigers; dorso-ventrally flattened, rectangular in section, and distinctly expanded.Transition to abdomen is gradual between chaetigers 31 and 40.All thoracic parapodia biramous; first one similar to the remainder but smaller.Thoracic notopodia bearing a cirriform postchaetal lobe supported by a straight acicula and with a knob-like expansion near base (Fig. 5B, F); with 15-30 crenulated capillaries.Thoracic neuropodia (Fig. 5B, F) simple ridges, with a rounded postchaetal lobe bearing a distinct dorsal papilla from chaetiger four; with 5-6 rows of setae, numbering about 130 as a whole, all rows but one composed of geniculate capillaries (Fig. 5C, E), longer in the most posterior row; the row before the last consisting of about 15 heavy uncini grading from dorsal pointed spines to ventral blunted setae with distally open hoods (Fig. 5D); uncini and shafts of geniculate capillaries both bearing transversal ridges.Transition thoracic neuropodia bearing only geniculate capillaries (about 80) and spine-shaped uncini (about seven).Abdomen incomplete, near-cylindrical in section with flattened dorsum.Abdominal parapodia without interramal cirri.Notopodia (Fig. 5I) directed obliquely, with long postchaetal lobe bearing a cirriform dorsal process; bearing about 10 crenulated capillaries and 2-3 furcated chaetae (Fig. 5G), distal tines unequally long, shaft with rows of minute spines on the side of the shorter tine.Neuropodia (Fig. 5I) bilobed with prechaetal lobe shorter, supported by a protruding, sigmoid, distally rounded acicula (Fig. 5H); first abdominal neuropodia bearing a slender subpodial cirrus that gradually shortens until disappearing; about 10 crenulated capillaries, slightly thicker than notopodial ones.Branchiae from chaetiger 6 (Fig. 5A); bearing two dark glandular ridges but no fimbriation, compressed and tapering to a slender tip that lacks glandular material; first thoracic pair small, progressively increasing in length (Fig. 5F); abdominal branchiae (Fig. 5I) longer, darker and with proportionately longer tips.
The two most similar species of the genus have been reported from the Gulf of Mexico and nearby regions.Naineris setosa (Verrill, 1900) and N. bicornis Hartman, 1951 closely resemble the specimen of Coiba in their general body form, very similar branchiae that start on chaetiger 6, thoracic neuropodia with dorsally located postchaetal papillae and bilobed abdominal neuropodia with protruding aciculae.However, N. setosa is unique within the genus in lacking any kind of uncini (Hartman 1951, Solis-Weiss andFauchald 1989).Naineris bicornis is the most similar species, and the only differences are the bifid prostomium, the distinct fimbriation of branchiae and a slightly larger number of thoracic chaetigers, about 50, of which 10 form the transition region (Hartman 1951, Taylor 1984).

ACKNOWLEDGMENTS
The present work was performed within the framework of a research project financially supported by AECI (Agencia Española de Cooperación Internacional) and developed with the invaluable help of Panamanian INRENARE.The authors express their gratitude to the staff of Coiba National Park, especially to Narciso Bastida, Luis Jiménez, Cesar Pecchio and Iván Tuñón, who guided us all over the island coasts.Also our colleagues in the project staff (María Capa, Francisco García, Antonio Laborda and Elisa Roldán) are to be gratefully acknowledged for their inestimable collaboration, both in the field and in the laboratory tasks.