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Ophiuroidea (Echinodermata) from coral reefs in the Mexican Pacific

Abstract There are numerous and important coral reefs in the Mexican Pacific, but scarce studies of brittle stars conducted in these ecosystems. In this regard, this work provides the first annotated checklist of brittle stars associated with coral communities and reefs in the Mexican Pacific and an illustrated key to identify the species. We also provide taxonomic descriptions, spatial and bathymetric distributions and some important remarks of the species. We report a total of 14 species of brittle stars belonging to nine genera and seven families. Ophiocnida hispida in Jalisco, Ophiophragmus papillatus in Guerrero, and Ophiothrix (Ophiothrix) spiculata and Ophiactis simplex in Colima are new distribution records. The record of O. papillatus is remarkable because the species has not been reported since its description in 1940. The brittle stars collected in this study, represent 22.2% of the total species previously reported from the Mexican Pacific. Presently, anthropogenic activities on the coral reefs of the Mexican Pacific have increased, thus the biodiversity of brittle stars in these ecosystems may be threatened.


Introduction
Coral reefs are among the most diverse and complex of all ecosystems and their diversity is comparable to that of the most diverse terrestrial habitats (Reaka-Kudla 1997). Structurally, coral reefs are composed of highly complex three dimensional environments which provide a variety of complex physical structures for the movement, concealment, escape, refuge, reproduction, breeding and feeding of numerous marine animals (Spalding et al. 2001). Coral reef biodiversity is commonly dominated by invertebrates, with the Mollusca, Arthropoda and Echinodermata generally being the most diverse and numerous phyla (Stella et al. 2011).
Echinoderms are conspicuous invertebrates on coral reefs and greatly contribute to the overall ecosystem biomass. Some species play pivotal keystone roles, and changes in their abundance can have large-scale effects on reef community structure and ecosystem functioning (Birkeland 1989, Glynn andEnochs 2011). Amongst the echinoderms, brittle stars are well represented in coral reef ecosystems and most species are associated with various invertebrate hosts or microhabitats (Glynn and Enochs 2011). Some studies reveal that coral reef-associated brittle stars can occur in densities from 20 to 15,000 individuals/m 2 (Chartock 1983, Hendler et al. 1995. Brittle stars feature in the diets of many coral reef fishes. Randall (1967) estimated that brittle stars occurred in the stomachs of 33 Caribbean reef fish, constituting, in some cases, up to 16% of stomach contents. Birkeland (1989) suggests that in virtue of the abundance, biomass and energy flow, it is assumed that brittle stars are influential in coral-reef trophic functioning. For example, Pomory and Lawrence (2001) suggest brittle stars regeneration can contribute from 0.05 to 0.07% of the net primary production on a reef, providing an important biomass flow to higher trophic levels.
Coral reefs of the Pacific coast of Mexico are considered among the most important in the eastern Pacific (Glynn and Ault 2000). Of these, the coral reefs located in the states of Nayarit, Guerrero and Oaxaca are considered the most important and well developed. Reefs of the coast of the states of Jalisco, Colima and Michoacán are numerous eventhough they are small communities and occur in patches (Reyes-Bonilla 2003, Reyes-Bonilla et al. 2013. Mexican Pacific coral reefs are mainly constructed by species of the genera Pocillopora, Porites and Pavona (Reyes-Bonilla 2003). From the Pacific coast of Mexico, there are a large number of studies regarding echinoderms (e.g. Honey-Escandón et al. 2008 and references there in); nevertheless, studies of brittle stars in, or associated with coral reefs in this area are limited , Benítez-Villalobos 2001, Zamorano and Leyte-Morales 2005, 2013, Granja-Fernández and López-Pérez 2011, and most are confined to specific reef localities (e.g. La Entrega, Oaxaca).
Recently it has been suggested that the publication of taxonomic studies and guides of species should be a priority for research and environmental management since they enrich the knowledge of regional biodiversity (Costello et al. 2010), particularly in poorly prospected and potentially megadiverse areas such as the Mexican Pacific. The Tropical Mexican Pacific reefs are among the least prospected, but at the same time are considered among the most important in the Eastern Pacific (Glynn and Ault 2000). Although, the Ophiuroidea inhabiting the coral reefs of the Mexican Pacific have been the subject of research, most of these studies have had an ecological focus, and basic taxonomic baseline data and guides for identification of species are lacking. The aim of the present work is to provide an annotated checklist of brittle stars that inhabit these ecosystems and a key to identify species associated with coral reefs and coral communities.

Methods
This project was part of a larger multidisciplinary and inter-institutional programme on the regarding fauna associated with coral reef zones along the Mexican Pacific. We sampled a total of 59 coral reefs of Mexico located along the coasts of the states of Nayarit (3), Jalisco (6), Colima (4), Michoacán (5), Guerrero (12) and Oaxaca (29), between 2007 and 2012 (Table 1).
Collections were carried out in a variety of substrata in or adjacent to coral reefs (live and dead stony corals, gorgonians, rock, sand, algae, rhodoliths, and sponges) and at different depths (1-26 m). The sampling was carried out by hand collection while SCUBA diving. Once in the laboratory, the collected ophiuroids were anesthetized using magnesium chloride buffered seawater in order to prevent autotomy. Finally, the specimens were fixed and preserved in 70% ethanol.

Key to the identification of the families, genera and species of brittle stars (Ophiuroidea) from coral reefs of the Mexican Pacific
1a Cluster of dental papillae at the apex of the jaw (Fig. 2F)  Disk covered with spines, stumps ( Fig. 2D) and/or grains (Fig. 3D). Oral papillae absent (Fig. 2F). Arm spines long and erect with a glassy, translucent appearance ( Fig. 2H Disk covered with granules ( Fig 6D). Arms stout (Fig. 6G) Annotated list of the species of brittle stars collected in coral reefs from the Mexican Pacific. In the collected material section, data within parentheses are: 1) number of specimens, 2) substrate, 3) depth, and 4) collection date. In the description of the species, the abbreviation "dd" refers to disk diameter (mm).  Figure 1 A-F Description. Disk rounded (dd = 6 to 7.6 mm) and covered with imbricated scales bearing pointed scattered spines. Radial shields narrow and separated by a row of scales which are larger than those of the disk (Fig. 1D).Ventral interradius with smaller imbricated scales and bearing scattered spines (Fig. 1E). Oral shields diamond shaped, with rounded angles. Adoral shields triangular and not meeting within. Three papillae on each side of the jaw; two outer ones rounded and the innermost one being the largest. The madreporite is evident (Fig. 1F). Dorsal arm plates wider than long, with the corners rounded (Fig. 1B). Ventral arm plates rectangular, wider than long; outer and inner sides slightly curved. Three blunt, cylindrical and short arm spines of nearly equal length. Two small tentacle scales forming a right angle to each other (Fig. 1C). Color of the disk brown (Fig. 1A); the color in the ventral side of the disk is straw-brown (Fig. 1E). Arms straw colored with irregular transversal lines (Fig. 1B). Madreporite with a lighter color (Fig. 1F).
Distribution. From USA (California) to Panama (McClendon 1909, Alvarado et al. 2010. In Mexico, from the Gulf of California (Baja California Sur, Sonora),  (Maluf 1988). In this study, Ophiocnida hispida was collected in coral reefs from Jalisco and Oaxaca at 9.1 m depth.

Remarks.
There are five species of the genus Ophiocnida world-wide (including O. hispida): O. loveni (Ljungman, 1867), O. scabra Lyman, 1879, O. scabriuscula (Lütken, 1859 and O. californica Ziesenhenne, 1940(Stöhr & O'Hara 2013. Ophiocnida hispida and O. californica are the only species reported from the Eastern Pacific; but O. californica is confined to the Gulf of California. Ziesenhenne (1940) reports that both species can be distinguished by the size of the oral shields, with radial shields in contact for half of their length, the divided dorsal arm plates in O. californica, and the arm length which is five times the disk diameter in O. californica and eight to ten in O. hispida. In the present study, O. hispida was found buried exclusively in sand while other species of the genus, O. scabriuscula and O. loveni were reported from seagrass habitats, calcareous algae or under rocks (Hendler et al. 1995, de Barros-Lima andBanja-Fernandes 2009). Ophiocnida hispida is hard to manipulate because it can autotomize both the disk and the arms very easily. Koehler (1907)

Ophiophragmus Lyman, 1865
Ophiophragmus papillatus Ziesenhenne, 1940 http://species-id.net/wiki/Ophiophragmus_papillatus Figure 1 G-L Description. Disk rounded (dd = 1.7 to 2.7 mm). Disk covered with small and imbricated scales. There is a central primary plate surrounded by five separated smaller scales. There are a few blunt papillae in the center of the disk. The disk margin is composed of small and rounded papillae. Radial shields separated proximally by two large scales and distally in contact (Fig. 1J).Ventral side of the disk covered by imbricated and finer scales than those on the dorsal side (Fig. 1K). Oral shields diamond-shaped. Adoral shields meeting within. Three rounded oral papillae on each side of the jaw, apical papillae the largest and thickest. Four teeth (Fig. 1L). Dorsal arm plates rounded, wider than long (Fig. 1H). Ventral arm plates quadrangular with rounded margins, wider than long. Three blunt, thick and small arm spines; upper spine is the most robust. Two small tentacle scales perpendicular to each other (Fig. 1I). Dorsal side of the disk creamy-white. Dorsal arm plates brown with black spots, and with a creamy middle longitudinal line along the arms (Fig. 1G, H). Ventral side uniformly creamy-white (Fig. 1K).
Remarks. The collection of Ophiophragmus papillatus in La Mina, Oaxaca and Palmitas, Guerrero is remarkable because the species had not been reported since its description by Ziesenhenne in 1940. This study reports a range extension of almost 410 km north of the type locality (Tangolunda, Mexico). We collected three organisms which perfectly match the original description provided by Ziesenhenne (1940). These specimens have a similar disk diameter to the holotype, which is 3.6 mm (Ziesenhenne 1940); the specimen from Palmitas has a disk diameter of 2.7 mm, whereas the specimens from La Mina have disk diameters of 1.7 mm and 2.4 mm. The two smaller specimens presented the color pattern mentioned in the description but the brown color of the dorsal arm plates was less evident than in the largest specimen. Ophiophragmus papillatus was collected in rock and coral. Other members of the genus Ophiophragmus inhabit sand, soft mud, rock, seagrass, mangroves and reefs (Nielsen 1932, Hendler et al. 1995 Figure 2 A-F Description. Disk rounded and bearing spinules (dd = 2.4 to 11 mm). Radial shields completely naked and separated by a line of multifid spinules (Fig. 2D).Ventral side of the disk mostly naked with scattered multifid spinules (Fig. 2E). Oral shields rounded diamond-shape, wider than long. Adoral shields narrowed and slightly separated. Oral papillae lacking. About 35 dental papillae per jaw (Fig. 2F). Dorsal arm plates wider than long, triangular or fan shaped with rounded corners; a spot distally on each arm plate (Fig. 2B). Ventral arm plates quadrangular with rounded corners. Five to seven stout, blunt, rounded, and not serrated arm spines; the two upper ones being the longest. A single, rounded, and very small tentacle scale (Fig. 2C). The color of the dorsal side of the disk is dark indigo-bluish and the ventral side is pale yellow-cream. Spines are bluish ( Fig. 2A). A pale spot may be present distal to the radial shields. Distribution. From California, USA to Oaxaca, Mexico (Lyman 1874, McClendon 1909, Nielsen 1932, Luke 1982. In Mexico, this species is reported from the  (Maluf 1988). In this study, Ophiothrix (Ophiothrix) rudis was collected on coral reefs from Michoacán, Guerrero and Oaxaca, between depths of 1.5 and 13.5 m.
Remarks. Ophiothrix (Ophiothrix) rudis was found living on stony coral, dead coral, rocks, algae and on sponges. Boolotian and Leighton (1966) collected O. (Ophiothrix) rudis from Palos Verdes, California in rocks and coarse sand. Although we made considerable effort to collect brittle stars from sand, we never found this species associated with this substrate. This species is easily distinguished from Ophiothrix (Ophiothrix) spiculata by using the following characteristics of O. Description. Disk circular with interradial protruding (dd = 1.2 to 10.2 mm). Disk totally covered with short multifid spinules and spines. Radial shields nearly touching distally and separated by a row of scales and spinules (Fig. 2J).Ventral side of the disk sparsely covered by small spines and scales (Fig. 2K). Oral shields wider than long and diamond shaped with lateral sides lobate; madreporite evident. Adoral shields triangular, small and in contact. Oral papillae lacking. A dental papillae cluster at the ventral apex of the jaw (Fig. 2L). Dorsal arm plates pentagonal with rounded edges (Fig. 2H). Ventral arm plates wider than long, wider on the distal edge. Up to eight serrated and hyaline arm spines; top-most spine is usually short, second or third are the longest. One small tentacle scale (Fig. 2I). Color of the disk bluish-purple (Fig. 2G). Mouth area whitish-yellow ( Fig. 2
Remarks. Ophiothrix (Ophiothrix) spiculata is one of the most conspicuous and abundant species on the coral reefs of the Mexican Pacific. Numerous authors have reported that this species is very abundant in other areas such as California and Panama (Verrill 1867, McClendon 1909. Austin and Haldfield (1980) reported that densities of O. (Ophiothrix) spiculata reach up to 80 individuals/0.1 m 2 in a siltstone reef off Newport Bay, California. We observed that O. (Ophiothrix) spiculata form massive aggregations; the advantages of which has been reported to be protection from predators, enhanced feeding ability in strong currents and to maximize fertilization during broadcast spawning (Hendler 1991). We found this species in live stony coral, dead coral, rocks, algae, rhodolith and on sponges. According to Maluf (1988), the species can inhabit coral, rocks, sponges, mangroves and sand. As in the same case of O. (Ophiothrix) rudis, we did not find O. (Ophiothrix) spiculata in sand. Besides the most common color pattern described above, we found some specimens completely orange and yellow collected on sponges and, brown in color which was mostly collected on rocks and dead coral. Ophiothrix (Ophiothrix) spiculata is a new record distribution for the state of Colima.

Ophiothela Verrill, 1867
Ophiothela mirabilis Verrill, 1867 http://species-id.net/wiki/Ophiothela_mirabilis Figure 3 A-F Description. Disk lobulated (dd = 1.3 to 4.3 mm) and totally covered by large, rounded and scattered grains of different sizes. Disk mostly covered by large radial shields which are in contact and covered by grains (Fig. 3D). The ventral side of the disk is covered by skin (Fig. 3E). Oral and adoral shields appear to be fused, forming a continuous ring; covered by skin. Oral papillae lacking. A cluster of rounded dental papillae; about 10-18 (Fig. 3F). Six rolled up arms. Dorsal arm plates concealed and covered by numerous rounded grains, there are naked spaces between plates (Fig. 3B). Ventral arm plates with rounded edges, separated by the lateral arm plates and covered with skin (Fig. 3C). Lateral arm plates well developed. Six arm spines provided with well-developed hooks at the tip; the third spine is the longest. Tentacle scales lacking. Color purplish-rosaceous; dorsal side of the disk mostly rosaceous with purplish arms (Fig. 3A), ventral side uniformly rosaceous (Fig. 3E).
Remarks. Ophiothela mirabilis was collected in gorgonians and sponges, but was more numerous and conspicuous in the former. We observed that O. mirabilis had a great variety of colors (purple rosaceous, creamy, burgundy and yellow) which were correlated with the color of the gorgonians upon which the brittle stars were collected. This color matching between Ophiothela and gorgonians also has been reported by Clark AM (1976a). Ophiothela mirabilis is always attached to the gorgonians rolling up their arms and with the help of their hooked spines of the arms. Specimens were found in three forms: specimens with six well-developed arms, with six arms, of which three were not well-developed or with only three arms. This is correlated with asexual reproduction by fission where the disk splits in two parts and each split disk regenerates the missing part (Clark AM 1976a, Hendler et al. 2012. Ophiothela mirabilis has recently been found in emergent populations in the Atlantic and the Caribbean, where it may alter the appearance and ecology of the areas due to the high densities of the species (Hendler et al. 2012). Description. Disk rounded (dd = 1.1 to 5 mm) and covered by large imbricated scales and short scattered spines over and at the edge of disk. Radial shields large, triangular and joining distally (Fig. 3J). Ventral interradius with scales and scattered spines (Fig.  3K). Oral shields diamond shaped with rounded edges. Adoral shields small and not meeting proximally. Two flattened oral papillae in each side of the jaw (Fig. 3L). Five or six arms. Dorsal arm plates wider than long with rounded edges (Fig. 3H). Ventral arm plates quadrangular with rounded edges. Five to six short, rugose and spinulose arm spines. Single, rounded, lanceolated tentacle scale (Fig. 3I). Color of the disk olive greenish-brown, with darker radial shields (Fig. 3G). Ventral side cream (Fig. 3K).

Distribution.
Cosmopolitan. Indo-Pacific, Eastern Pacific and both sides of the Atlantic. In the Eastern Pacific, the species has been recorded in the Hawaiian Islands, Mexico, Costa Rica, Panama, Colombia, Galapagos Islands and Peru (Clark HL 1915, Nielsen 1932, Maluf 1988, Hendler et al. 1995, Alvarado and Fernández 2005, Neira and Cantera 2005. In Mexico from the Gulf of California, on the Pacific side of Baja California and Baja California Sur, Nayarit, Marías Islands, Jalisco, Colima, Revillagigedo Islands, Michoacán, Guerrero and Oaxaca (Brusca 1980. Commonly found in shallow water up to 518 m (Hendler et al. 1995). In this study, Ophiactis savignyi was collected on coral reefs from Nayarit, Jalisco, Colima, Michoacán, Guerrero and Oaxaca; between 2.3 to 26 m depth.
Remarks. This small species is one of the most abundant on the coral reefs from the Mexican Pacific. Emson and Wilkie (1984) suggested that the sexual and asexual reproduction is important for the abundance and distribution of Ophiactis savignyi; small populations of this fissiparous brittle star may be increased by sexual reproduction. We found the species attached to live stony coral, dead coral, rock, algae, rhodoliths and sponges. Hendler et al. (1995) mentioned that this species is commonly found in all reef zones and substrata reported in this study, chiefly in sponges and algae. Ophiactis savignyi is a well-studied species; there are numerous works about its reproduction (e.g. Emson and Wilkie 1984, Hendler 1991, Chao and Tsai 1995, McGovern 2002, feeding (e.g. Boffi 1972, Emson andMladenov 1992) and habitat (e.g. Boffi 1972, Sloan 1982, Hendler and Littman 1986, Neves et al. 2007). Other authors (Hendler et al. 1995, Pomory 2007 have reported that O. savignyi can have three oral papillae on each side of the mouth; most of the collected individuals in this study presented two oral papillae, with a few specimens presenting three. Short spines at the edge of the disk. Radial shields small and widely separated by scales (Fig. 4D). Ventral side of the disk with spines and small imbricated scales (Fig.  4E). Oral shields oval, with a large madreporite shield evident. Adoral shields large about as wide as the oral shields, meeting within. One large oral papillae at each side of the jaw (Fig. 4F). Five arms. Dorsal arm plates wider than long with rounded edges (Fig. 4B). Ventral arm plates quadrangular with rounded edges. Lateral arm plates prominent. Four to five rounded and blunt arm spines, the lowest one shortest. A single, large and oval tentacle scale (Fig. 4C). Color of the dorsal side brown (Fig. 4A). Ventral side yellowish-cream, some ventral arm plates with darker bands (Fig. 4C, E).
Distribution. USA (California), Mexico, Nicaragua, Costa Rica, Panama, Galapagos Islands and Peru (Nielsen 1932, Maluf 1988, Alvarado et al. 2010, Tirado et al. 2012. Remarks. We collected Ophiactis simplex in the same substrata as Ophiactis savignyi (stony coral, dead coral, rocks, algae, rhodoliths and sponges). The results suggest that live stony coral is the preferred substrate for both species. Moreover, despite that both species inhabit sponges, O. savignyi was more numerous in this substrate than O. simplex. According to Lyman (1865), it is probable that larger organisms of O. simplex have five arms, while the smaller individuals have six. In this study, we only found five armed individuals of different sizes . Notwithstanding that both species of  Description. Disk rounded (dd = 2.8 to 14.3 mm) and covered by small and imbricating scales. Central primary plate evident. Radial shields small, triangular and surrounded by large disk scales (Fig. 4J). Ventral interradius covered by imbricating scales, which are smaller than dorsal scales. Bursal slits large and with small genital papillae (Fig. 4K). Oral shields diamond-shape, longer than wide. The madreporite is evident. Adoral shields lanceolate, not meeting within. Four rounded and spaced oral papillae on each side of jaw. Single enlarged, triangular papillae found distally (Fig. 4L). Dorsal arm plates longer than wide. Accessory dorsal arm plates well developed (Fig. 4H). Ventral arm plates slightly longer than wide. Three arm spines with blunt tips. A single, flat and oval tentacle scale completely covering each tentacle pore (Fig. 4I). Disk light brown with closely spaced brown-purplish rounded spots. Arms with dark dorsal plates every fourth or fifth plate (Fig. 4G).
Remarks. Adult specimens of Ophionereis annulata were found buried in sand, while specimens found in live stony corals were juveniles. Maluf (1988) reports O. annulata inhabiting rock, algae and sponge in the Central Eastern Pacific, along with the substrata recorded in this study. This species is the only one in the Mexican Pacific having an association with a scale-worm (Malmgrenia cf. variegata); this association was found in localities from Jalisco, Guerrero and Oaxaca, Mexico (Granja-Fernández et al. 2013). This species is most closely related to Ophionereis reticulata (Say, 1825) from the east coast of America; although there are morphological characteristics that distinguish both species (Clark AM 1953). In the studied area, the color pattern of O. annulata displayed two variations: 1) the most common was of a creamy-yellowish-colored disk with brown spots or reticulations, while the arms were creamy and purplish but every fourth-fifth joint possessed a green-darker band; 2) the coloration of the disk was similar to the above but with smaller reticulations, the arms green in color with olive-green darker bands and blotches; the darker bands every fourth-fifth joint and, occupying one or two arm plates. These color patterns have been reported by different authors in other areas of the Eastern Pacific (Verrill 1867, Nielsen 1932, Ziesenhenne 1940, Caso 1951.

Family Ophiocomidae Ljungman, 1867 Ophiocoma L. Agassiz, 1835
Ophiocoma aethiops Lütken, 1859 http://species-id.net/wiki/Ophiocoma_aethiops Figure 5 A-F Description. Disk rounded (dd = 1.1 to 29.4 mm) and totally covered by fine granulation. The granulation covers the base of arms and the radial shields (Fig. 5D). The ventral side of the disc covered with scattered grains (Fig. 5E). Oral shields large, oblong; longer than wide. Adoral shields small, triangular and not meeting within. Cluster of rounded dental papillae on apex of jaw. Four oral papillae on each side of the jaw, the outer papillae being the largest. Four to five teeth (Fig. 5F). Dorsal arm plates wider than long, hexagonal shape (Fig. 5B). Ventral arm plates quadrangular with circular edges. Reduced lateral arm plates. Arm spines rounded, stout and slightly flattened. Arm spines, three and four, alternating. Two tentacle scales (Fig. 5C). Dorsal side dark brown-black in color. Disk with a brown large spot (Fig. 5A). Ventral arm plates and jaw with lighter dark color (Fig. 5K).
Remarks. Ophiocoma aethiops is the largest brittle star on coral reefs from the Mexican Pacific. It is associated with live and dead stony coral, rocks, algae and rhodoliths. Juvenile organisms inhabit all the above mentioned substrata, meanwhile adults inhabit the interstitial spaces of live and dead stony corals and rocks. We observed that it is common to find juveniles attached to the dorsal side of the arms and disk of adults; an observation that has been previously recorded by Hendler et al. (1999) for Panama. Ophiocoma aethiops is a gonochoric species without sexual dimorphism (Benítez-Villalobos et al. 2012). On the Estacahuite reef of Oaxaca, females of O. aethiops spawn from May to November, while male spawning occurs throughout the year, whereas the spawning of O. aethiops in Panama occurs during November and December (Hendler 1979, Benítez-Villalobos et al. 2012. Besides the color pattern mentioned in the description of the species, we noted that some specimens can have a large white patch on the dorsal side of the disk, whereas the whole body of other specimens are black-brownish. Description. Disk rounded (dd = 1.3 to 25.2 mm), covered by elongated grains. Radial shields totally covered by grains as well as the base of the arms (Fig. 5J). Ventral side of the disk covered with similar grains, but less numerous (Fig. 5K). Oral shields round. Adoral shields small and not meeting within. Four to five oral papillae on each side of the jaw, being the outer one lager. Cluster of rounded dental papillae on apex of jaw. Three of four teeth (Fig. 5L). Dorsal arm plates oval heart-shaped, wider than long (Fig. 5H). Ventral arm plates quadrangular with circular edges, wider than long (Fig.  5I). Reduced lateral arm plates. Five to seven long, stout, blunt arm spines. On first two to four joints, two lanceolated tentacle scales occur, and only one for remainder of the arm (Fig. 5K). Disk brown in color; dorsal arm plates light brown in color, some plates banded (Fig. 5G). Ventral arm plates with a brown longitudinal stripe along the arm (Fig. 5I).

Family Ophiodermatidae Ljungman, 1867 Ophioderma Müller & Troschel, 1840
Ophioderma panamensis Lütken, 1859 http://species-id.net/wiki/Ophioderma_panamensis Figure 6 A-F Description. Disk pentagonal (dd = 4.7 to 18.1 mm); dorsal and ventral side covered by fine, closely and rounded granulation. Radial shields naked, small and oval (Fig.  6D, E). Oral shields large and oval; wider than long. Adoral shields covered by granules. The madreporite is evident. Eight to ten oral papillae on each side of the jaw (Fig. 6F). Dorsal arm plates overlapping and rectangular with rounded edges; wider than long (Fig. 6B). Ventral arm plates oval and slightly overlapping; wider than long. Reduced lateral arm plates. Ten to 11 short and blunt arm spines; all spines are closely equal in size except the lowest which is longer. Two lanceolated tentacle scales (Fig. 6C). Four bursal slits per interradius (Fig. 6E). Disk brownish (Fig. 6A,D). Dorsal arm plates brown with dark and light bands (Fig. 6B).
Distribution. USA (California), Mexico, El Salvador, Nicaragua, Costa Rica, Panama, Peru, Colombia and Galapagos Islands (Clark HL 1940, Hooker et al. 2005, Neira and Cantera 2005, Alvarado et al. 2010. In Mexico, from the Gulf of California (Baja California Sur, Sonora, Sinaloa), on the Pacific side of Baja California and Baja California Sur, Jalisco, Revillagigedo Islands, Guerrero and Oaxaca , Granja-Fernández and López-Pérez 2011. From intertidal to 40 m depth (Austin and Hadfield 1980). In this study, Ophioderma panamensis was collected on coral reefs from Guerrero and Oaxaca, 4.9 to 9.1 m depth.
Remarks. Ophioderma panamensis was collected under rocks and on sand. Maluf (1988) reported that this species may inhabit rocks, corals and algae. Adults and juveniles were found cohabiting together. Juveniles curled their arms over the dorsal side of the disk which is white in most individuals. This behavior camouflages juveniles on the white sand under the rocks. There are studies that report a wide variety of color patterns in O. panamensis (Ives 1889, Nielsen 1932, Ziesenhenne 1955) but, we only found two variations in body colors: brown or grey. In addition, some specimens had white spots on the disk and all specimens presented bands on the dorsal side of the arms. Although some authors report a high incidence of subdivided dorsal arm plates (Ives 1889, Nielsen 1932, Ziesenhenne 1955, we found only a few specimens with  Ophioderma teres (Lyman, 1860) http://species-id.net/wiki/Ophioderma_teres Figure 6 G-L Description. Disk pentagonal (dd = 5.3 to 12.2 mm). Dorsal and ventral sides of the disk covered by fine and rounded granulation. Radial shields naked and oval (Fig. 6J, K). Oral shields heart-shaped, small and with three rounded lobes. Adoral shields covered by granulation. Madreporite evident. Eight to nine oral papillae on each side of the jaw (Fig. 6L). Dorsal arm plates wider than long and divided in several irregular pieces (two to four) (Fig. 6H). Ventral arm plates quadrangular and rounded. Reduced lateral arm plates. Six to seven short arm spines, all spines are closely equal in size, except the lowest which is longer. Two tentacle scales (Fig. 6I). Four bursal slits per interradius (Fig. 6K). Dorsal side uniformly chocolate-brown in color, with irregular black rings on the disk (Fig. 6G, J). Ventral side yellowish-cream in color (Fig. 6K).
Distribution. Mexico, El Salvador, Nicaragua, Costa Rica, Panama, Ecuador, Colombia and Galapagos Islands (Ziesenhenne 1955, Neira and Cantera 2005, Alvarado et al. 2010. In Mexico, from the Gulf of California (Baja California Sur, Sonora, Sinaloa), in the Pacific side of Baja California and Baja California Sur, Nayarit, Jalisco, Guerrero and Oaxaca . From intertidal to 46 m depth (Maluf 1988). In this study, Ophioderma teres was collected on coral reefs from Guerrero and Oaxaca; 9.1 to 10.7 m depth.
Remarks. All the collected material of Ophioderma teres corresponded to juvenile specimens according to the juvenile species description by Lyman (1860). Adults are distinguished from juveniles by having grain-covered radial shields, a large number of subdivided dorsal plates in the arms (up to five), nine arm spines, and body uniformly dark-brown in color (Lyman 1860, Ziesenhenne 1955. Many juvenile specimens have been collected in the Gulf of California, Pacific side of Mexico, Panama, Ecuador and Galapagos Islands (Lyman 1860, Caso 1951, Ziesenhenne 1955 (Lyman 1860, Verrill 1867, Nielsen 1932, Clark HL 1940, Ziesenhenne 1955 Figure 7 A-F Description. Disk pentagonal (dd = 8 to 16 mm). Radial shields covered by granulation (Fig. 7D). Dorsal and ventral side of the disk covered by fine, closely and rounded granulation (Fig. 7E). Oral shields large, heart-shaped and with three rounded lobes. Madreporite evident. Adoral shields not covered by granules, small and triangular. Eight to nine oral papillae on each side of the jaw, the outer one being the largest. Four teeth (Fig. 7F). Dorsal arm plates wider than long, rectangular with rounded edges (Fig. 7B). Ventral arm plates quadrangular and rounded. Ten to 11 short and blunt arm spines; all spines closely equal in size, except the lowest which is longer and thicker. Two tentacle scales, inner one larger and lanceolated. Four bursal slits per interradius (Fig. 7C). Dorsal side of the disk brown in color with some white marks (Fig. 7A, D); ventral side creamy but brown at margin (Fig. 7E). Dorsal arm plates brown with every five-seven plates with transversal and white bands. Ventral side creamy; the distal side of the ventral arm plates darker (Fig. 7E).
Distribution. In this study, Ophioderma sp.1 was collected on coral reefs from Guerrero and Oaxaca, from 6.4 and 26 m depth.
Remarks. Ophioderma sp. 1 is a new species currently being described (pers. comm. FA Solís-Marín, UNAM, 2013). At first sight Ophioderma sp. 1 resembles Ophioderma variegata Lütken, 1856; however some significant different morphological character- istics were noted: 1) the oral shields of Ophioderma sp. 1 are heart-shaped, meanwhile in O. variegata are oval; 2) small adoral shields in Ophioderma sp. 1 but large in O. variegata; 3) Ophioderma sp. 1 has ten to 11 very short and blunt arm spines (occupying almost the half of the lateral arm plates) equal in size except the lowest arm spine that is longer and thicker, whilst O. variegata has seven-eight large arm spines equal in size and as long as the lateral arm plates; 4) all the collected individuals of Ophioderma sp. 1 displayed the color pattern mentioned in the species description section (brown in the dorsal side and creamy in the ventral side of the body), while O. variegata usually presents bright colors as pink, red, green and yellow (Verrill 1867, Koehler 1914, Caso 1951. Ophioderma sp. 1 can be easily distinguished from O. panamensis and O. teres by its naked adoral shields. Ophioderma sp. 1 was collected under rocks. Description. Disk rounded (dd = 4 to 10 mm). Disk covered by large scales, surrounded by smaller scales of different sizes and shapes. There is a primary central scale surrounded by five oval scales. Radial shields triangular and distally separated by a row of scales; with a furrow that parallels the margin (Fig. 7J). The ventral interradial area is covered by scales smaller in comparison to the dorsal side (Fig. 7K). Oral shields pentagonal, longer than wide. Madreporite evident. Adoral shields large, triangular, not in contact. Four oral papillae at each side of the jaw; the outer one being the largest (Fig. 7K). Dorsal arm plates wider than long. Accessory dorsal arm plates restricted to the first arm segments (Fig. 7H).Ventral arm plates with distal margin rounded, wider than long. Four to five short and conical arm spines. Two tentacle scales closely equal in size (Fig. 7I). Dorsal side light brown in color; dorsal arm plates with darker transvers bands (Fig. 7G). Ventral side uniformly creamy-white in color (Fig. 7K).
Distribution. Mexico, Costa Rica and Panama (Clark HL 1940, Verrill 1867, Alvarado et al. 2010. In Mexico, from the Gulf of California (Sinaloa), Nayarit, Jalisco, Guerrero and Oaxaca (Caso 1951, Solís-Marín et al. andLópez-Pérez 2011). The numerical discrepancy of species among studies may be due to the larger number of reef systems visited (59) and the systematic sampling of independent substrata of the present study. Regarding the substrata, we collected on live and dead stony corals, gorgonians, rock, sand, algae, rhodoliths, and sponges, whereas previous studies focused only on coral, rock and/or sand , Benítez-Villalobos 2001, Zamorano and Leyte-Morales 2005, Ríos-Jara et al. 2008, 2013. In addition, this study was focused exclusively on collecting brittle stars rather than all echinoderms.
All the collected brittle stars have an Eastern Pacific biogeographic affinity except Ophiactis savignyi which is considered cosmopolitan (Hendler et al. 1995). The most conspicuous species were members of the genera Ophiocoma (O. aethiops and O. alexandri), Ophiactis (O. savignyi and O. simplex) and the brittle star Ophiothrix (Ophiothrix) spiculata. Ophiocomidae, Ophiotrichidae and Ophiactidae are the most specious families in tropical shallow waters as well as on coral reefs world-wide (i.e. Caribbean, Barbados, Mexico, Seychelles) (Taylor 1968, Clark AM 1976b, Lewis and Bray 1983, Hendler et al 1995, Benítez-Villalobos 2001). On the contrary, the brittle stars Ophiocnida hispida, Ophiophragmus papillatus and Ophioderma sp. 1 were rare or least common in the study area.
Four out of the 14 collected species represent new distribution records for the Mexican Pacific: Ophiocnida hispida is a new record for Jalisco, Ophiophragmus papillatus for Guerrero, and Ophiothrix (Ophiothrix) spiculata, and Ophiactis simplex are new for Colima. As previously mentioned, the collection of O. papillatus specimens is notable given that the holotype is the only known specimen of the species (Ziesenhenne 1940). Clearly, O. papillatus is a rare species in the study area; as we only found three specimens during 70 field collecting trips. All O. papillatus collected were juvenile and we recommend carrying out further directed samplings trips in order to find the substrata where adults occur or inhabit. Regarding Ophioderma sp. 1, the species is morphologically similar to O. variegata but differences are enough to grant species status to the former.
Finally, our results suggest that species of the same genus tend to use and or inhabit the same substrata. For example, members of the genus Ophiocoma were only collected on live and dead stony coral, rocks, algae and rhodoliths. Ophiactis and Ophiothrix were recorded in live and dead stony coral, rocks, algae, rhodoliths and sponges, while Ophioderma were only found on rocks and in sand. Along the Mexican Pacific, all these substrata exist in areas other than coral reefs, making the identification key provided here an important potential tool for use in non-reef areas. It is also evident that corals are an important key habitat for juvenile and adult brittle stars of several genera and species in the Tropical Mexican Pacific. Studies suggest that coral reefs could provide refuge from predation, for reproduction and feeding for both brittle stars and other invertebrates Littman 1986, Spalding et al. 2001). Recently, corals and coral reefs in the Mexican Pacific have experienced a progressive increase in disturbance associated with anthropogenic activities (fisheries, aquaculture, agriculture, industrial development, tourism and recreation, harbor construction and maintenance, urban development, garbage presence, habitat destruction and wastewater discharges) (Reyes-Bonilla 2003, Ortiz-Lozano et al. 2005, and subsequent loss in coral cover , with few signs of this deterioration slowing in the near future. The loss of coral reef-building species can reduce the three dimensional structure and functional integrity of the reef (Álvarez-Filip et al. 2013) affecting different brittle stars activities (e.g. reproduction, refuge), while eutrophication due to anthropogenic activities can increase the dominance and biomass of some species (e.g. suspension feeders) and reduce other (Duinevald et al. 1987). Consequently, the future for brittle stars in the Mexican Pacific may be threatened if coral substrata are further reduced or degraded.