A new species of Paraonis and an annotated checklist of polychaetes from mangroves of the Brazilian Amazon Coast (Annelida, Paraonidae)

Abstract The polychaete fauna from the mangroves of the Amazon Coast in Maranhão state, Brazil, is reported in this study. Fourteen species are listed, namely Alitta succinea (Leuckart, 1847); Arabella (Arabella) iricolor Montagu, 1804; Capitella capitata (Fabricius, 1780) complex; Exogone (Exogone) breviantennata Hartmann-Schröder, 1959; Heteromastus filiformis (Claparède, 1864); Isolda pulchella Müller, 1858; Mediomastus californiensis Hartman, 1944; Namalycastis fauveli Nageswara Rao, 1981; Namalycastis geayi (Gravier, 1901); Namalycastis senegalensis (Saint-Joseph, 1901); Nephtys simoni Perkins, 1980; Paraonis amazonica sp. n.; Sigambra bassi (Hartman, 1945); and Sigambra grubii Müller, 1858. Among them, Namalycastis fauveli and Namalycastis geayi are recorded for the first time in Brazil. Paraonis amazonica sp. n. is a new species for science, characterized by a rounded prostomium, 4–8 pairs of foliaceous branchiae, absent eyes, and two types of modified neurochaetae, acicular and hook-shaped.


Introduction
The two largest rivers that drain South America, the Amazon and the Orinoco, are respectively, the first and third largest rivers in the world in terms of water volume (Degens et al. 1991). The Orinoco and Amazon Rivers are responsible for the discharge of an enormous amount of freshwater and sediment into the ocean, representing nearly 20 % of the total global annual freshwater (Hu et al. 2004;Miloslavich et al. 2011). These rivers have been recognized as zoogeographic barriers to the dispersal of marine fauna between the Caribbean and southwestern Atlantic (Gilbert 1972;Floeter and Gasparini 2000). Accordingly, they influence the Brazilian Northern Coast, also known as the Brazilian Amazon Coast, which extends from the north of the Amapá State to the Gulf of Maranhão and represents 35 % of the entire Brazilian Coast (Silveira 1964;Sousa et al. 2008). This region is characterized by a variety of poorly known estuarine and marine ecosystems with very diverse habitats (Couto et al. 2003).
Most of what is known about the marine biodiversity of the Brazilian Amazon Coast is related to fishing and mangrove habitats Nevertheless, the REVIZEE Program -Living Resources in the Exclusive Economic Zone provided important information regarding the continental shelf and offshore area (Miloslavich et al. 2011). In general, macrobenthos assemblages are one of the least known of Brazil (Amaral and Jablonski 2005;Miloslavich et al. 2011). The lack of studies in this region represents one of the major gaps in the knowledge of the biodiversity of Brazilian polychaetes (see Lana et al. 2009). The main studies concerning polychaetes in this region include ecological research with records in the coast of the states of Maranhão (see Ribeiro and Almeida 2014) and Pará (Rosa-Filho et al. 2006; Morais and Lee 2014) recording a total of 27 species and 24 families.
In this study, polychaetes collected in the mangrove of São Marcos Bay in the Gulf of Maranhão were examined. The current study contributes to increasing the knowledge of polychaetes in the South Atlantic, particularly in the Amazon coastal zone. This is the first taxonomic study with a focus on the polychaete fauna from Maranhão and includes new records and the description of a new species.

Materials and methods
Mangrove specimens from the Gulf of Maranhão were collected between April of 2010 and June of 2012 from two creeks in São Marcos Bay: Buenos Aires at the São Luís (02°35'56"S, 44°21'11.8"W) and Tronco at the Caranguejos Island (02°49'33.6"S, 44°28'51.1"W) (Fig. 1). Along of a 100 m transect, nine sediment samples were taken using a corer (20 cm long and 10 cm diameter) at the intertidal region of each creek. Samples were washed through a 0.5 mm mesh sieve with filtered freshwater in the laboratory; specimens were fixed in 4 % formaldehyde and then transferred to 70 % ethanol for long-term storage.
Polychaetes were identified at the species level using stereo (Olympus SZX-16) and light microscope (Olympus CX31). Specimens were prepared for scanning electron microscopy (SEM) by critical point drying, prior to being mounted on stubs and coated with gold (200 A thick). These specimens were observed and analyzed in the Jeol JSM-6390LV scanning electron microscope of the Museu Nacional/Universidade Federal do Rio de Janeiro (MNRJ). Light microscopy images were taken with a camera attached to a Leica M205A stereo microscope and a Zeiss Axio Scope microscope. Drawings and pictures were processed using Adobe (San Jose, CA, USA) Photoshop CS6.
The specimens and type material referent to the new species were deposited in the research collection Coleção Científica de Invertebrados Marinhos e Costeiros (NPM) of the Núcleo em Ecologia e Desenvolvimento Sócio-Ambiental de Macaé (NUPEM), Macaé, Brazil, and in the Museo Nacional de Ciencias Naturales (MNCN), Madrid, Spain. Additionally, we elaborated a list of some Brazilian records of the species identified here, taking into account those reported by studies formally published (Suppl. material 1). We designated up to one previous record for each Brazilian state indicated in the species distribution section, plus original description, when applicable. Our criteria to select the studies were, preferably: taxonomic approach, ecological approach providing voucher-specimens, ecological approach without voucher-specimens.
Other abbreviations cited in this study:

BMHN
British Museum (Natural History), London.  Remarks. Arabella (Arabella) iricolor was described to the south coast of Devonshire (UK) as Nereis iricolor (Montagu, 1804). The description of specimens from the Caribbean Sea (Augener 1927) closely resembles specimens in this study, which were identified as this species due to the characteristics: ventralmost chaeta tapering gradually to guards in median and posterior chaetigers, the absence of hooded acicular chaetae, maxilla MxI unidentate and posterior post-chaetal lobe shorter than chaetae. Body surface whitish was observed in small fixed individuals, probably juveniles ( Fig. 2A-C). (Montagu 1804). The species was recorded in ecological studies of the continental shelf, intertidal zone, coral reefs, estuaries, and mangroves (Paiva 1993, Santa-Isabel et al. 2000, but apparently, the material was not deposited in any collection and was not available for comparison. Previous record from Maranhão reports specimens found in mangroves (Oliveira and Mochel 1999). This species has been described with worldwide distribution and is probably a complex of species (Colbath 1989;Zanol and Ruta 2015). Studies on the variation of the symmetry in maxillae and modified ventral chaetae should be conducted to know the polymorphism in species of the genus Arabella (Steiner and Amaral 2009). That would be a challenge to species identification and new descriptions, once Oenonidae species are usually collected in low densities (Zanol 2010, Zanol andRuta 2015).

Order Phyllodocida Family Nephtyidae Grube, 1850 Genus Nephtys Cuvier, 1817
Nephtys simoni Perkins, 1980  Remarks. First record for Maranhão. The specimens present the characters that define Nephtys simoni Perkis, 1980, such as interramal branchiae from the third chaetiger; proboscis with long middorsal and midventral subdistal papilla and 23 conical papilla distal, dorsal cirrus linked to pre-chaetal cirrus, short and finger-like lobes. Individuals that have one pair of eyespots and median reddish pigmentation in the prostomium were reported for juveniles by Perkins (1980). In this study, some specimens presented eyespots, but not the reddish pigmentation pattern. Specimens of N. simoni have been reported in estuarine areas as in the type locality (Perkins 1980) and in Amazon mangroves . In Brazil, the specimens recorded as Nephtys simoni in Paranaguá Bay, Paraná (Lana 1986) are in fact Nephtys californiensis Hartman, 1938 (Rizzo andAmaral 2007).
Distribution. Remarks. This species was described as Nereis succinea (Leuckart 1847), transferred to genus Neanthes (Imajima 1972), and later to Alitta (Bakken and Wilson 2005). The specimens examined in this study share the features of the specimens re-described by Villalobos-Guerrero and Carrera-Parra (2015), such as paragnaths present in all areas of the pharynx, homogomph spinigerous notochaetae, neurochaetae with heterogomph spinigers and homogomph and heterogomph falcigers and the widely expanded notopodial ligule in posterior parapodia. However they are smaller (major individual measuring 3.5 mm of length from the prostomium to the 25 th chaetiger) than those described from the Caribbean Sea (Espinosa et al. 2007) and southern-southeastern Brazil ). On the other hand, specimens from northeastern Brazil measuring less than 5 mm length from the prostomium to the 25 th chaetiger are considered recruits (Sette et al. 2013). Therefore, we suggest all the individuals collected in this study are juveniles. Alitta succinea is widely distributed in the world with records in different environments. This species was recorded in mangroves from the Caribbean Sea (Londoño-Mesa et al. 2002) and Brazil, including a record in Maranhão state (Mochel 1997). This species is reported in environments with different salinity levels and has been considered as a euryhaline species (Sato 2013).
Colour. Specimens in alcohol yellow. No pigment visible throughout the body. Remarks. First species record for the America. These specimens present some differences from the original description (Nageswara Rao 1981), such as a dorsal surface convex, body less arched mid-anteriorly, longer antennae and tentacular cirri ( Fig. 2A). However, the projection of heterogomph chaetae with an extremely long boss supports this identification for this species (Fig. 2B, C). The differences found are probably because the specimens in this study are juveniles by the smaller size (around 15 mm long, and 80 chaetigers), compared to type material, 21-45 mm long, 134-282 chaetigers, after Glasby (1999). Some Namareneidinae species, as Namalycastis abiuma, can have juveniles with blades longer and up to 80 chaetigers. Namalycastis fauveli is recorded in estuarine beaches and coastal lagoons in the type locality (Nageswara Rao 1981) and in mangroves of this study. (Gravier, 1901)  Diagnosis. Prostomium anterior end smooth or with a shallow cleft. Antennae extending short of the palpophore tip or of the prostomium tip. Two pairs of eyes nearly longitudinally arranged. Dorsal cirri short, similar in length throughout the body. Notochaetae present (Glasby 1999).
Colour. Specimens in alcohol yellow. No pigment visible throughout the body. Remarks. First species record for Brazil. The collected specimens of this study were not complete, but they present the same characters of Namalycastis geayi (Gravier, 1901) based on the anterior end (Fig. 6A). The identification of this species is supported by the presence of only heterogomph spinigers in sub-and supra-preacicular fascicle in the parapodia (Fig. 6B, C). In the original description, N. geayi has been recorded in freshwater environments, muddy river banks, and in coarse sediments (Gravier 1901). This study recorded N. geayi in mangroves and brackish water. Remarks. First record for Maranhão. Complete specimens were not found in this study; however, the features of the anterior body are very similar to the re-description of Glasby (1999). The presence of thick cuticle covering the eyes, supra neuro acicular sesquigomph spinigers in the parapodia of chaetiger 10, with a 1.4 × length of collar or more boss, and distally smooth falciger blades supports the identification of the species. Previous Brazilian records include the Amazon coast, the estuarine beaches of Marajó Island in the mouth of the Amazon River (Glasby 1999), and the delta of the Amazon River (one specimen, ZHM PE405) (Glasby 1999). This species is known to live in brackish water and freshwater environments such as mangroves, creeks, and marshes (Glasby 1999). Remarks. First record for Maranhão. The specimens examined in this study present a long medium antenna reaching up to setiger 5-12; a dorsal hook beginning in the posterior chaetigers supports the identification as Sigambra bassi. The records in the Caribbean and Brazil include estuaries and beaches (Gillet 1986. Remarks. First species record for Maranhão. The presence of notopodial hooks distally curved appearing in setiger 20 and a medium antenna reaching the second chaetiger are characteristics that support the identification of the species based on the original description by Müller (1858) and re-description by Salazar-Vallejo (1990). In this study, the hooks appeared among the segments 6-29, in specimens shorter and with reduced number of chaetigers, the hooks appeared before the chaetiger 20. This type of variability in the hooks position related with the body size and number of chaetigers was also reported by Salazar-Vallejo (1990). No other morphological variation was found. This species is widely recorded in the coast of Brazil, mainly in estuarine environments, including mangroves and coastal lagoons as the type locality (Müller 1858). In the Caribbean, the species was recorded in a coastal lagoon (Liñero-Arana and Díaz-Díaz 2005).  Remarks. First species record for the Brazilian Amazon Coast. The features that confirm these specimens as Exogone (Exogone) breviantennata Hartmann-Schröder, 1959 are median and lateral antennae of similar size, compound spinigers and falcigers with bidentate blades (subdistal tooth larger than distal tooth) and falcigers in the anterior body with 3-4 relatively thick spines. This species is found worldwide in several habitats such as in seagrass in the intertidal zone, rocky shores, algae assemblages, soft bottoms (San Martín and Bone 2001, Paresque et al. 2014), and others. The type material of E. (E.) breviantennata is from a mangrove (Hartmann-Schröder 1959) as in the present study. However, this species has been recorded in several environments and it presents a circumtropical distribution (Núñez et al. 1992). Remarks. The presence of two groups of four branchiae, post-branchial notopodium with sharply curved hooks; twelve or thirteen thoracic segments with pectinate uncini with four to seven teeth support the identification of these specimens as Isolda pulchella Müller, 1858. This species was described in south Brazil and is found along the coast inhabiting estuarine environments, including mangroves and coastal lagoons. The specimens described by Díaz-Díaz and Liñero-Arana (2012) for Caribbean Sea are also similar to the specimens in this study and are recorded in estuaries.

Infraclass Scolecida Family Capitellidae Grube, 1862 Genus Capitella Blainville, 1828
Capitella capitata (Fabricius, 1780), complex Remarks. First record for Maranhão. The specimens examined in this study are similar to the neotype description of Capitella capitata by Blake (2009). C. capitata was considered as a globally distributed species, but allozyme analyses have demonstrated that this species is composed of at least six sibling species (Grassle and Grassle 1976). Additionally, Blake (2009) indicates that C. capitata may be only distributed in Arctic regions, suggesting that the numerous records from lower latitudes are not this species. Nevertheless, the specimens from warmer waters such as in the Caribbean (Amoureux 1985) and Brazil (Pardo et al. 2010) are also similar to the neotype descriptions by Blake (2009). Recently, four new species of Capitella were described from the Capitella capitata complex (Silva et al. 2017). Studies including molecular data must to be conducted on these animals from Maranhão, and the specimens should be re-examined.

Genus Heteromastus Eisig, 1887
Heteromastus filiformis (Claparède, 1864) Remarks. Heteromastus filiformis from São Marcos Bay share the same characters of the specimens described by Day (1967) and Dean (2001) such as thoracic region with 12 segments, the first achaetous; thoracic hooks with long hood and about six denticles above the main tooth; abdominal hooks narrow and three to four denticles above the main tooth, gills in subsequent medial segments. The specimens of H. filiformis examined in this study are very similar to H. similis Southern, 1921. One of the main differences between those species is the presence of gills processes and the shape of neuropodial hooks in H. filiformis. According to Hartman (1947), Heteromastus similis is considered an inhabitant of freshwater areas and H. filiformis is typical of marine environments. Both species have distribution in estuarine environments such as mangroves from Brazil ). In the Caribbean Sea, the records are also in estuarine areas and especially in the muddy intertidal areas of the Caribbean Sea (Gobin 1990). Both species seems to be distributed worldwide, independent of environmental salinity, but descriptions based on fewer characters can be related to several records around the world. Remarks. First record for Maranhão. The specimens examined in this study have triangular prostomium with cylindrical palpodium, in dorsal view; peristomium devoid of setae with a pair of ocelli; 10 chaetigers in thoracic region; only capillaries in chaetigers 1-4; abdominal chaetigers only with hooded hooks defining them as Mediomastus californiensis (Hartman, 1944). In the present study, we found specimens exceeding 100 seg-ments as observed by Warren et al. (1994). Although M. californiensis has been recorded in the Pacific (USA) and Atlantic Ocean (Canada and the USA), Warren et al. (1994) examined specimens from both oceans and did not observe differences among them. This species has been recorded in muddy bottoms of estuarine environments in the Brazilian Amazon Coast (Rosa-Filho et al. 2006) and in the Caribbean Sea (Gobin 1990). Distribution. Only known from the type locality. Diagnosis. Rounded prostomium, clearly wider than longer. Dorsal brownish pigmentation reaching the beginning of the prostomium. Rounded to foliaceous branchiae (4-8 pairs), from the fourth segment. Neurochaetae of two types: acicular chaeta with lateral spine beginning in pre-branchial segments, and hook-shaped chaeta with terminal spines in post-branchial segments.
Description. Complete holotype, 2.68 mm long, 0.17 mm wide (chaetiger 8), and 46 chaetigers. Three complete paratypes with 2.43-2.94 mm long, 0.18-0.20 mm wide and 36-54 chaetigers. Incomplete paratypes up to 4.607 mm long, 0.283 mm wide, and 16-61 chaetigers. Fixed individuals with brown pigmentation that reaches the distal end of the prostomium and extends along the body. Anteriorly flattened body, wider than longer, cylindrical from the 8 th chaetiger and in all middle body region (Fig. 12A, B). Branchial region dorsoventrally flattened. Rounded prostomium, wider than longer (Fig. 12B, D). Absence of antenna, palpode, ciliated bands and eyes in the prostomium (Fig. 12A, B). The anterior segments are short, wider than longer. Long and biannulate segments in the post-branchial region. One pair of nuchal organs located on the posterior edge of the prostomium (Fig. 13A). Notopodial postchaetal lobes absent in the pre-branchial region, the first notopodial post-chaetal lobe appear in the fifth branchial chaetiger. Notopodial post-chaetal cirrifom lobes, longer from the middle and posterior regions. Branchiae from chaetiger 4, rounded to foliaceous, flat, short, 4-8 pairs, first and last pairs are shorter (Fig. 12D). Notopodial capillary chaetae throughout the body. Curved capillary chaetae in the neuropodium and notopodium of the pre-branchial and branchial segments (Fig. 13B). Capillary neurochaetae progressively thinner, longer, and straight in the post-branchial segments. Capillary notochaetae of the posterior segments thicker than those anterior and median segments. Pre-branchial and branchial segments with 3-5 chaetae capil-laries in the notopodium and 2-5 in the neuropodium. Post-branchial segments with 1-2 chaetae capillary in the notopodium, absent in the neuropodium. First acicular neuropodial chaetae with a lateral spine in chaetiger 2-8, and 2-3 chaetae in the branchial segments (Figs 13B, 14A). Neuropodium in the post-branchial middle segments and posterior end segments with one acicular chaeta with a lateral spine (Figs 13B, C, 14A-C). Hook-shaped neurochaetae with terminal spine beginning in postbranchial chaetigers, 1-2 chaetae. Neuropodium in the post-branchial middle chaetigers with 2-4 hook-shaped chaetae with a terminal spine. Neuropodium in posterior chaetigers with two hook-shaped chaetae with a terminal spine (Figs 13B, C, 14B, C). Pygidium rounded with two anal lobes and three anal cirri: two dorsolateral and one medium-ventral (Figs 12C, 14D).  Colour. Specimens in alcohol show brownish pigment spots all over the body, two pairs of reddish brown lateral spots in the pygidial lobes of some specimens.
Among the five valid species of Paraonis, P. fulgens, P. paucibranchiata, and P. strelzovi also have the first pair of branchiae in the fourth chaetiger as seen in P. amazonica sp. n. However, P. fulgens has more than 25 pairs of branchiae and the first post-chaetal lobe starts in the third chaetiger, whereas P. amazonica sp. n. has 4-8 pairs of branchiae and first postchaetal lobe in the 9 th chaetiger. In addition, P. fulgens (about 120 chaetigers in total) seems to be longer than P. amazonica sp. n. (up to 54 chaetigers in complete individuals). However, longer animals could be found, since incomplete individuals of P. amazonica sp. n. showed up to 61 chaetigers. Only four pairs of branchiae are described in P. paucibranchiata and P. strelzovi whereas P. amazonica sp. n. has 4-8 pairs of branchiae. Moreover, P. paucibranchiata differs from P. amazonica sp. n. by the presence of eyes and longer and straighter branchiae. The other two species mainly differ on the first chaetiger with branchiae and post-chaetal lobe. Paraonis pygoenigmatica has approximately 20 pairs of branchiae that begin in the sixth chaetiger, joined to the first dorsal lobes. In P. pycnobranchiata, the branchiae (about 19) are present from chaetiger 6-25. P. amazonica sp. n. and P. pycnobranchiata have the same pigmentation pattern consisting in small pigment spots scattered along the body. Species of Paraonis are usually reported in marine, inshore and continental shelf environments (Glasby and Wilson 2003). There are some exceptions, such as P. fulgens, recorded in the intertidal zone from Caribbean Sea (Helguera et al. 2011), P. strelzovi in mangroves from Australia (Hartmann-Schröder 1980), and P. pygoenigmatica recorded in estuarine areas from Brazil (Barros et al. 2001). Paraonis amazonica sp. n. is the first record of a Paraonis species found in muddy bottoms in mangrove vegetated areas.

Conclusion
In total, 14 species belonging to eight families and eleven genera were identified in São Marcos Bay, Maranhão, Brazilian Amazon Coast. Two of them were first recorded to Brazilian Coast (N. fauveli, N. geayi) and one new species was described (P. amazonica sp. n.). Two other species are new records for the Brazilian Amazon Coast (E. (E.) breviantennata and S. bassi), and five species are new records for the Maranhão Coast (C. capitata complex, M. californiensis, N. senegalensis, N. simoni, and S. grubii).
This study expands the occurrence of N. geayi to the Brazilian Amazon Coast (in estuarine muddy sediments) because the type specimens of N. geayi were collected in freshwater and muddy bottoms in the Ouanary Stream in French Guiana (Gravier 1901). In addition, a new species of Paraonis is described in Amazon mangroves, although Paraonidae is a family commonly found and highly diversified in deep-sea environments (Aguirrezabalaga and Gil 2009). We encourage further studies on this genus because many species need improved descriptions, given that some features lack information in the original descriptions.
In summary, this checklist increases the number of recorded species in the Brazilian Amazon Coast. Further studies targeting sampling beyond mangroves and soft bottoms, including deep sea, seagrasses, and algal mats, can lead to the discovery of higher diversity of annelids in the Brazilian Amazon Coast. We assume that other new species can be found in this region or described from the worldwide species reported here, since they probably correspond to species complexes.