Ophioderma peruana, a new species of brittlestar (Echinodermata, Ophiuroidea, Ophiodermatidae) from the Peruvian coast

Abstract Ophioderma peruana sp. n. is a new species of Ophiodermatidae, extending the distribution of the genus Ophioderma to Lobos de Afuera Island, Peru, easily distinguishable from its congeners by its peculiarly fragmented dorsal arm plates. Dense granules, rounded or polygonal cover the disc, the radial shields may be naked or completely covered by granules. A good character for recognizing this species in the field is the dorsal side of the disc which is brown with disc granules lighter cream and brown, the arms are mottled with whitish spots and the ventral part of the disc on the interradial part is brown and the radial part bright yellow.


Introduction
Species of Ophioderma have a distinctive shape and color and are distributed across the Mediterranean Sea, Atlantic Ocean and off the American Pacific coast. The genus Ophioderma has had an interesting taxonomic history since 1840 when Müller & Troschel, described the genus, being the type species Ophioderma longicauda (Bruzelius, 1805) recognized by H.L. Clark in 1915. In the past, the classification of Ophioderma has been unstable, classified as the genus Ophiura, in the 19 th century (e.g. Lyman 1860Lyman , 1882. The first taxonomist to arrange the numerous species under the name Ophioderma was H.L. Clark (1915), A.M. Clark (1976) and Melville (1980), formally separating the previously controversial genus Ophiura from Ophioderma. However, Ziesenhenne (1955) made the latest revision of the genus Ophioderma when 21 species were known (Stöhr et al. 2009). Ophioderma is now well-established and comprises a large, widespread genus of brittlestars. Up to until now, Ophioderma comprises 27 species, 21 of which are distributed in the Atlantic Ocean and six in the Pacific Ocean. Ophioderma can be found in coral reefs, seagrass, coral rubble and under rocks and typically found together with other shallow-water genera, such as Ophiocoma, Ophiothrix, Ophiolepis and Ophiactis. Bathymetric distribution of the genus extends from shallow water to 50 m and is restricted to tropical and temperate seas. The characters used to separate the species are the shape of the disc granules, the disc size, arm length, shape and degree of fragmentation of dorsal arm plates, number of arm spines and color (Stöhr et al. 2009). However, the genus remains poorly studied; for example, it has been recently discovered that the species O. longicauda shows cryptic speciation and represents a species complex (Stöhr et al. 2009, Boissin et al. 2011. As part of a program since 1999 to sample the coast of Peru in order to discover new or previously unreported echinoderm species, different localities have been sampled along the coastline and adjacent islands (from littoral to 30 m depth). At Lobos de Afuera Islands, Lambayeque, Peru (06°55'5"S, 80°42'5"W) a total of 39 echinoderm species have been reported, including six ophiuroids (Ophiactis mirabilis, Ophiothrix spiculata, Ophiocoma aethiops, Ophioderma panamensis and Ophionereis annulata), one of which is described in this paper as a new species of Ophioderma (Hooker et al. 2005).

Materials and methods
Samples were taken by SCUBA in the intertidal zone at Lobos de Afuera Island, Lambayeque, Peru ( Fig. 1) due to its complexity and it's southernmost limit for many echinoderm species (Hooker et al. 2005). After collection, specimens were placed inside plastic bags with seawater for transportation. The animals were then relaxed in a solution of 4% magnesium chloride and seawater. After labeling, fixation of the specimens was done with 70% ethyl alcohol. Some specimens were dried and photographed in the laboratory under a SZ-ST Olympus dissecting microscope. Holotype and paratypes have been preserved in alcohol and dried, respectively. The specimens are deposited at the Colección Nacional de Equinodermos "M. Elena Caso M." of the Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de Mexico (UNAM-ICML) and in the Laboratorio de Biología Marina, Facultad de Ciencias y Filosofía, Universidad Peruana Caytano Heredia, Lima, Peru (CZA). Abbreviations used in this paper are: DD: disc diameter, AL: arm length; AW: arm width.
Only 13 specimens of the new species of Ophioderma were collected on different localities along the Pacific coast, but they are sufficiently distinctive and unique to establish a new species.
Diagnosis. (modified from Müller and Troschel 1840) The dorsal and ventral surfaces of the disc are covered by granules. Sometimes these granules cover the radial and adoral shields. Oral papillae are broader than long, rectangular or conical in shape. There are three to five teeth. The oral shields are oval, pentagonal or triangular in shape. Each interradial space has four genital slits; the first two are on the distal side of the oral shield and the second are parallel to the arms and near the disc edge. The arms are cylindrical proximally and conical distally. The dorsal arm plates are broader than long and can be fragmented. The lateral arm plates are semi-lunar in outline and have six to thirteen arm spines that are large, rectangular or conical in shape. There are two tentacle scales per segment.
Remarks. There are six known species of the genus reported for the eastern and southern Pacific in addition to the new species described here. Diagnosis. Disc pentagonal, elevated and covered with dense granules that are somewhat rounded or polygonal, but more or less dispersed. The radial shields can be completely covered by the granules or scarcely covered. The dorsal arm plates are fragmented; in addition there are some smaller and tiny fragments that resembles granules of the dorsal disc, only visible on the proximal plates (not evident in all the arm segments). Nine or ten flattened and elongated oral papillae. Granules also cover the adoral shields. Ten arm spines, the ventral is the largest, reaching the next tentacle scale.
Disc. Disc pentagonal, broad and flat, covered by granules; the dorsal granules are closely packed and have the same size on the middle and periphery of the disc, these granules are rounded and polygonal. The radial shields are almost fully covered by granules with only a small section exposed; the size is 3.81 mm and fit 9.5 times the disc diameter; the disc scales are small and imbricated, oval shape with polygonal borders, the interradial scales are smaller than the radial ones. Jaws with seven to nine oral papillae; the two distal ones are stout and longer than broad. The oral papillae have rounded edges and are almost of the same size and shape. The oral shields are broader than long, triangular in shape with convex proximal sides and are surrounded by granules that are slightly larger than those on the interradial disc surface. The adoral shields are rectangular and covered by larger and taller granules than those on the dorsal disc, which are contiguous. Four genital slits on each interradii; the two proximal ones are touching the oral shield and are located between the distal part of the oral shields and the first lateral arm plate; the two distal genital slits are placed between the fifth and and the sixth arm segment and close to the periphery of the disc.
Arms. The basal portion of the arm is 7.6 mm broad and the arm length is 120.6 mm. The dorsal arm plates occupy less than ¼ of the arm, are 4.6 times wider than long and rectangular, fragmented in six pieces that differ in shape; there are some granules on the proximal portion and sparcely distributed on the distal portion. The lateral arm plates have a half-circle shape, and occupy a sub-ventral position; with ten arm spines conical, large and slightly flattened with a rounded tip, half segment length decreasing slightly in size dorsally. The ventral-most arm spine is the longest and widest, almost the size of the segment. The ventral arm plates are contiguous, broader than long, the proximal plates are elongated in comparison to the distal plates. Two tentacle scales on each side of the ventral plate; the adradial tentacle scale is oval in shape, twice as long as wide and the abradial tentacle scale triangular in shape, with the straight side touching the ventral arm plate (Fig. 3).
Color. Specimen preserved in alcohol. The dorsal side of the disc is light brown and the arms are darker brown, the dorsal arm plates of each segment are ornamented with a double row of tiny, whitish, rounded spots; the spines are brown except the two ventral ones that are cream color, like the ventral side of the arms; the jaws are white; the ventral side of the disc in the proximal part is white and the distal part is slightly darker; the oral shields are mottled. Dry specimens, have the dorsal side of the disc pale brown, the arms are brown with black and white spots; the tentacle feet are yellowish. Live specimens in the field could be identified by this color pattern: the dorsal side of the disc is brown with the disc granules lighter cream and brown; the arms are mottled with whitish spots; the ventral disc interradii are brown and arms under the disc are bright yellow.
Paratype variations. On the smallest specimen (14 mm DD; 35 mm AL; 4 mm AW) the radial shields are completely naked with white spots (same color pattern as the dorsal arm plates), oval and surrounded by the disc granules by the disc granules, scarcely covered (in specimens with 40-42 mm DD) or completely naked (in specimens with14-35 mm DD). On certain segments of the arm, the dorsal arm plates are not as fragmented, with only two or three pieces. The presence of granules along the arm is not evident as in the holotype. In some specimens (22-31 mm DD) the radial shields are also completely naked. The oral shields are twice as wide as long, proximally elongated but the shape may vary in specimens. In two specimens (30 mm; 42 mm DD) the radial shields are naked and/or covered by granules. The radial shields are completely covered by granules and dorsal arm plates are fragmented in only a single specimen (35 mm DD) (Fig. 4). Therefore, as the animal grows, the radial shields become more covered in granules and the dorsal arm plates are fragment further.
Etymology. Named after the type locality.

Remarks.
The new species is distinguishable by its thick and rounded granules on the disc, the number of fragments of the dorsal arm plates, which can be more than six with other smaller fragments. The distal border of the dorsal arm plates, from the base to the middle part of the arm, supports some granules similar to those on the dorsal part of the disc.
Ophioderma peruana sp. n. is the third record of a species of Ophioderma for the Tropical Peruvian Eastern Pacific. It is the second Ophioderma species reported from Lobos de Afuera Island, Quebrada Verde, El Ñuro and Hooker Reefs. The Peruvian sea is considered one of the most productive in the world because of an intense upwelling system off most of its coastline (Hooker et al. 2013). It is important to continue the research in this area, because besides being the southern limit of distribution of Panamic fauna, the remote Lobos de Afuera Islands could be an area of endemism, due to less frequent dispersal from the mainland (Hooker et al. 2005). Koehler, 1895, andO. tongana Lütken, 1872, have been described from the Indo-west Pacific. With the exception of the mistaken identification of O. tongana from Simon's Bay, South Africa (see Mortensen 1933;A.M. Clark andRowe 1971, A.M. Clark andCourtman-Stock 1976), these two species have not been reported in over 100 years since they were first described. Their validity is therefore doubtful and their identification within the genus Ophioderma must be considered suspect.