A new species of Nicon Kinberg, 1866 (Polychaeta, Nereididae) from Ecuador, Eastern Pacific, with a key to all known species of the genus

Abstract A new species of Nicon Kinberg, 1866 from the east Pacific coast of Ecuador is described. The new species is characterized by a long, thin dorsal ligule on median and posterior parapodia and infracicular sesquigomph falcigers in the neuropodia. A key to all species of Nicon is provided.


introduction
Ecuador possesses a great variety of coastal environments resulting in a high diversity of marine species; however, taxonomic studies on marine invertebrates are few, especially in the case of the polychaetes. In Ecuador (excluding the Galapagos), only 29 families, 53 genera and 75 species of polychaetes have been recorded. Hartman (1939) was the first to report on the polychaetes from Ecuador and described four new species and ten new records from Puna and Santa Clara Islands (Guayas Province). Later, Cruz et al. (1980) provided four new records from benthic samples collected on the Estero Salado, Guayaquil Gulf. In the same Gulf, 29 species of polychaetes were identified by Villamar (1983). Villamar (1989) later reported marine species at Canal del Morro and Jambeli in the Guayaquil Gulf. Villamar and Cruz (2007) reported three taxa for Ecuador from the intertidal zone of Monteverde (Guayas Province). A new species of Australonuphis, used as fishing bait, was described by de León-González et al. (2008) in Santa Elena Bay (Guayas Province). In northern Ecuador very little is known about the polychaete fauna and only one ecological study has been carried out by Villamar (2006) in the intertidal zones of Manabi and Esmeraldas Provinces. In that paper he reported 27 species, of which 14 constituted new records for Ecuador. More recently, Trovant et al. (2012) reported 12 new species records in the Bunche and Cabo San Francisco intertidal sandy beaches of northern Ecuador (Esmeraldas Province).
The importance of the family Nereididae is manifested by their high diversity and abundance in all marine substrates, occurring in all oceans from the supralittoral to the abyssal zone. This family includes 44 genera and approximately 460 valid species (de León-González, 2009). Nicon is one of the least species rich genera of Nereididae. The genus was first described by Kinberg, (1866) for six species, N. pictus, N. tahitianus, N. maculata, N. eugeniae, N. loxechini and N. virgini, none of which were figured. In this paper, a new species of Nicon is described. It is characterized by having an elongate notopodial dorsal ligule, resembling a long cirrus on median and posterior parapodia, as well by the presence of sesquigomph falcigers in the neuropodia.

Material and methods
Samples were collected in March 2009 (dry season) in the intertidal zone of two sandy beaches located in the Esmeraldas Province, northern Ecuador (Fig. 1). Bunche beach (0°37'55"N, 80°02'14"W) is a protected area characterized as a low energy beach, with soft sloping banks and very fine particle sand, and Cabo San Francisco beach (0°39'11"N, 80°04'10"W) is characterized as a high energy environment, subjected to frequent and severe storms, with high slopes. Fresh-water discharges affect both beaches. Sediment samples were sieved through a 1mm mesh. Specimens were fixed in 10% formalin and later preserved in 70% ethanol. Terminology of parapodial structures was taken from Bakken and Wilson (2005). Type material has been deposited in the Natural History Museum of Los Angeles County, Allan Hancock Foundation Polychaete Collection (LACM-AHF), and the Polychaetological Collection of the Universidad Autónoma de Nuevo León (UANL).  Kinberg, 1866. Diagnosis. Prostomium pyriform to subpyriform, with two pairs of eyespots, paired frontal antennae and biarticulate palps. Four pairs of tentacular cirri with distinct cirrophores, smooth or articulated. Parapodia of first two chaetigers subbiramous, notopodium represented by a single ligule with dorsal cirri at its base. Subsequent notopodia with dorsal and ventral ligules with or without a small notopodial prechaetal lobe decreasing in far posterior parapodia. Neuropodia with superior and inferior prechaetal lobes, digitiform or conical postchaetal lobe present or absent along body, and a ventral ligule which can be reduced in posterior parapodia; ventral cirri short, tapered. All notochaetae homogomph spinigers; neurochaetae homogomph, heterogomph or sesquigomph falcigers, may be accompanied by homogomph and heterogomph spinigers, and simple chaetae. Pygidium with paired anal cirri. Pharynx with paired mandibles, without paragnaths or papillae. Remarks. This generic diagnosis was modified from Pettibone (1971), Wu and Sun (1979) and Hutchings and Reid (1990). Some important characteristics were not included by Pettibone (1971) because at that time she recognized N. maculata as the only member of the genus. Later on, Wu and Sun (1979) and Hutchings and Reid (1990) expanded the genus diagnosis including characters of recently described species such as N. japonicus Imajima, 1972, N. yaguinae Fauchald, 1972, N. sinica Wu & Sun, 1979and N. rotunda Hutchings & Reid, 1990. Some new characters included in the present diagnosis are the presence-absence of a notopodial prechaetal lobe, and the occurrence of neuropodial sesquigomph falcigers. Description. Holotype incomplete posteriorly, with 85 chaetigers, 19mm long, 1.4mm wide. Prostomium pyriform, with frontal cleft extending to middle of prostomium. Two pairs of eyespots in trapezoidal arrangement, anterior pair slightly larger, with lenses. Pair of small cirriform antennae extending slightly beyond palps. Palps biarticulate, globose, with subspherical palpostyles. Peristomium longer than next segment, with four pairs of short tentacular cirri, longest reaching chaetiger two (Figs 2A, 3A). Pharynx lacking papillae or paragnaths, armed with pair of toothed mandibles (Fig. 3B). Anterior notopodia with short cirriform dorsal cirri, subtriangular dorsal ligule, and subulate notopodial ventral ligule. Small triangular prechaetal lobe, restricted to limited number of anterior chaetigers, reducing in size posteriorly, last present about chaetigers 28-30. Anterior neuropodia with superior and inferior lobe, subulate ventral ligule, ventral cirrus with inflated base (Fig. 2B, 3C), postchaetal neuropodial lobe subulate, present in first 18 chaetigers, not visible in anterior view. Median and posterior notopodia with dorsal ligule long cirrus-like; prechaetal lobe absent, notopodial ventral ligule triangular, decreasing in size in posterior chaetigers. Median and posterior neuropodia with superior and inferior lobes poorly defined, neuropodial postchaetal lobe absent, neuropodial ventral ligule subulate, decreasing in size in posterior chaetigers until disappearing completely, ventral cirri cirriform, shorter than dorsal one (Figs 2C-D, 3D-E). All notochaetae homogomph spinigers, with long, thin blades. Anterior supracicular neurochaetae 6 long-bladed homogomph spinigers superiorly; 6 short-bladed heterogomph spinigers inferiorly. Anterior infracicular chaetae homogomph spinigers with long blade, and sesquigomph falcigers with anterior part ending in a blunt tooth (Fig. 2 E). Median and posterior supracicular neurochaetae with long-bladed homogomph spinigers. Infracicular neurochaetae with a few homogomph spinigers superiorly, and sesquigomph falcigers inferiorly, anterior end sharper (Figs 2F-G, 3F). Pygidium lacking in holotype, with terminal anus and two thin lateral cirri on others specimens.

Systematics
Type locality. Bunche beach, Esmeraldas Province, Ecuador Distribution. This species is only known from Bunche and Cabo San Francisco beaches, Esmeraldas Province, Ecuador.
Discussion. Of the six species originally included in the genus Nicon by Kinberg (1866) two have been transferred to other genera (N. eugeniae, currently Nereis eugeniae from Strait of Magellan and N. loxochini, currently Platynereis magalhensis from Strait of Magellan) and three species are considered indeterminable due to their incomplete descriptions and the poor condition of the available syntypes (N. maculata from La Plata, Argentina, N. pictus from Brazil, N. tahitianus from Tahiti, and N. virgini from Strait of Magellan) (Pettibone, 1971). Of these species, only N. maculata is considered valid at the present time. No type species was designated by Kinberg. Hartman (1949) designated N. pictus as the type species, even though she did not provide a diagnosis or figures. Pettibone (1971) later revised the genus and designated N. maculata as the type species. Currently this genus consists of ten species: N. maculata Kinberg, 1866 from La Plata, Argentina, N. moniloceras (Hartman, 1940) from Catalina Island, USA, N. aestuarensis Knox, 1951from New Zealand, N. polaris Hartman, 1967 from the Antarctic peninsula, N. abyssalis Hartman, 1967  from the Antarctic peninsula, N. japonicus Imajima, 1972from Japan, N. yaquinae Fauchald, 1977 from off the Oregon coast, USA, N. sinica Wu & Sun, 1979from the Yellow Sea, N. rotunda Hutchings & Reid, 1990from Australia, and N. pettibonae de León-González & Salazar-Vallejo, 2003 from the Loyalty Islands, New Caledonia. Pettibone (1971) also considered that N. abyssalis and N. polaris had doubtful generic affinities with Nicon; however, we believe that N. abyssalis possesses the generic characters of Nicon and therefore should be included in the genus. Nicon polaris was described based on an epitoke; however, the possession of an expanded elytra-shaped dorsal cirrus in the chaetiger 7 makes it doubtful that it belongs to Nicon; a similar structure is found in Kainonereis, currently a genus in inquirenda described from an epitokous stage by Chamberlin (1919).
Species of Nicon may be separated into two groups based on the presence or absence of notopodial prechaetal lobes. Those species with a notopodial prechaetal lobe are: N. aestuarensis, N. japonicus, N. polaris, N. rotunda, and N. sinica; while N. abyssalis, N. maculata, N. moniloceras, N. pettibonae and N. yaquinae lack a superior notopodial lobe. Some important characteristics of Nicon species are listed in Table 1.
Nicon orensanzi sp. n. is a member of the first group but differs in its long, thin notopodial dorsal ligule in median and posterior parapodia. N. orensanzi sp. n. and N. pettibonae are the only species in the genus with neuropodial infracicular sesquigomph falcigers in all parapodia. These two species differ in the shape of their sesquigomph falcigers, the presence of heterogomph falcigers, and a reduced dorsal ligule in the posterior parapodia of N. pettibonae.  (CSIC, Spain) and carried out at the Universidad Central del Ecuador. We thank to Santiago Tineo for their help in fieldwork. Authors would also like to thank two anonymous reviewers and Chris Glasby whose comments and suggestions were much appreciated and very helpful in improving the manuscript.