Phataria unifascialis (Valvatida: Ophidiasteridae) from the Eastern Pacific: Redescription and skeletal morphology

The starfish Phataria unifascialis is widely distributed in the eastern cost of the Pacific Ocean, found on rocky bottoms, at depths between 0 and 50 m. The original description of P. unifascialis made by Gray in 1840 was brief and inaccurate in some important aspects, such as distribution area, plate arrangement and ambulacral spines. Here, we improve the description of P. unifascialis with SEM images and description of its mesodermal skeleton on the basis of a large sample. Rev. Biol. Trop. 65(Suppl. 1): S258-S271. Epub 2017 November 01.

Phataria unifascialis is a well-known starfish that inhabits the rocky bottoms of the Eastern Ocean Pacific shallow waters . The starfish Phataria unifascialis belongs to the family Ophidiasteridae Verrill, 1870, which includes 28 valid genera, mostly shallow water, from tropical and subtropical regions. The species are a conspicuous feature of coral reef fauna. Asexual reproduction by fission occurs in a few species, but fertilization, planktotrophic or lecitothrophic larvae, and bipinnaria and/or brachiolaria stages are more common in the Ophidiasteridae family (Mortensen, 1921). The genus Phataria was proposed by Gray (1840) as a subgenus of the genus Linckia, and later was raised to genus by Sladen (1889). This genus differs from the others of the family Ophidiasteridae by having the papular areas in a longitudinal row or two in the radios, small granules in papular areas and big granules in the abactinal plates. Currently the genus Phataria has only two valid species: P. unifascialis (Gray, 1840) and Phataria mionactis Ziesenhenne, 1942. Morgan and Cowles (1996) studied some aspects of the behaviour, physiology and demography of Phataria unifascialis, were examined to determine whether cool temperature was an important factor limiting this species' distribution in the northern regions of the Gulf of California. Individuals in the population at Bahia de Los Angeles, in the northern gulf, were of larger mean size but were significantly less abundant than at Loreto, a site in the southern gulf. Smaller size classes were also less abundant or missing in the Bahia de Los Angeles population, suggesting limited recruitment. Pyloric caecae and gonads were of similar size at both locations making it unlikely that food limitation or lack of reproductive potential was the limiting factor.
The population at Loreto contained a distinct reproductively-primed subgroup which was not observed at Bahia de Los Angeles. Activity of the species remained relatively constant with temperature down to 17ºC, the winter surface water temperature characteristic of Loreto, but dropped sharply at the 14°C water temperature characteristic of the Bahia de Los Angeles winter. Metabolic rates at these low temperatures were elevated over expected rates even though activity was reduced, suggesting metabolic stress. The species' moderate oxyregulating ability also disappeared at low temperature. Taken together, these data suggest that the low temperatures of the northern gulf may well be an important factor limiting this species' northern distribution in the Gulf (Morgan & Cowles, 1996).
The purpose of the present study is to redescribe the species and its morphology based on several major ossicle types in the ophidiasterid.

MATERIAL AND METHODS
In this work 804 specimens were reviewed and they are deposited at the Colección Nacional de Equinodermos, "Dra. María Elena Caso Muñoz", (CNE, ICML, UNAM) and Los Angeles County Museum, Los Ángeles, California, USA (LACM) ( Table 1). Organisms were observed using both an optic microscope (Olympus ® SZX7) and scanning electron microscope (SEM) imaging (Laboratorio de Microscopía Electrónica de Barrido en el Instituto de Biología (IB), UNAM, Microscope JEOL JSM-6360LV). In order to observe the skeleton of P. unifascialis the skin     was removed with regular household bleach (NaClO), after that the individual skeletal plates were extracted from specimens or parts of them immersed, using regular household bleach, rinsed in tap water, dried, mounted on aluminium stubs and gold-coated (modified from Thuy & Stöhr, 2016). Gray, 1840 Linckia bifascialis Gray, 1840 Linckia unifascialis Gray, 1840Ophidiaster suturalis Müller & Troschel, 1842 Original description (Gray, 1840): Rays trigonal, tapering, back with three rows of flat ossicula; sides with a single abroad band of pores; rather more than three times as long as broad.

Phataria unifascialis (Gray, 1840) (Figs. 1-7) Linckia (Phataria) unifascialis
Emended description: Five rays, tapering, papular areas only in the abactinal surface, the papular areas are in one longitudinal row along the arm, and also have two small rows of papular areas at both sides of the main row. Three longitudinal rows of carinal plates along the arm. Both surfaces are cover by granules, in   the abactinal one there are small granules in the papular areas and bigger ones on the abactinal plates. The actinal surface with smaller, rounded granules with little space between them. The anus is located in the center of the disc; only one rounded madreporite with radial striations. Only one row of ambulacral spines; such spines are wider in the base and tapering (Fig. 1).
Type locality: "Bay of Caracas, West Columbia" (data from holotype label). But there is any locality in the Pacific Ocean with this name.

DISCUSSION
The original description made by Gray (1840) did not include the basic information to indetify P. unifascialis as a separated and independent genus of Ophidiasteridae, instead the specie was included in the genus Linckia (Gray, 1840). Gray's original description can be practically used to describe various genus or species within the family (i.e. Pharia, Phataria, Narcissia, Linckia, etc). The diagnosis presented in this work has the main taxonomical characters to unequivocally can identify the specimens belonging to this species. There are three main contributions in this new emended diagnosis: 1) the papular areas are distributed in one longitudinal row along the arm, and two small rows can reach half or less the main row at both sides of the main longitudinal papular row; 2) there are three longitudinal rows of carinal plates along each arm, and 3) there is only one row of ambulacral spines that are wider in the base and tapering. Currently the genus Phataria has only two valid species: Phataria unifascialis (Gray, 1840) and Phataria mionactis Ziesenhenne, 1942. The specie Phataria mionactis, which has a restricted distribution to the Galapagos Islands, is distinguished by the presence of two continuous rows of papular areas at both sides of the main row (Fig. 8); the carinal plates are in an irregular arrangement, smaller than those in P. unifascialis. The abactinal plates are convex in P. mionactis and flat in P. unifascialis (see Figs. 2 and 8).       The type locality of P. unifascialis was not mentioned by Gray (1840), nevertheless the locality in the holoype label reads: "Bay of Caracas, West Columbia, Venezuela" (Andrew Cabrinovic pers. comm.). Ziesenhenne (1937), mentions that the type locality of the species was "Bay of Caracas, west coast of Colombia". There is no locality in the Colombian Pacific under that name and because the species has a known distribution on the American Pacific Ocean coasts, the type locality is not in Venezuela since this country is located in the Atlantic Ocean. More research is needed to determine the original type locality of P. unifascialis.
The use of plate morphology in Asteroidea identification is higly recommended as presented by Turner and Dearborn (1972). More efforts need to be done in order to use these taxonomic characters, even though type material is so limited and fragile. Whenever material is available, skeletal morphology studies are suggested.

ACKNOWLEDGMENTS
To Maria Berenit Mendoza Garfias (Laboratorio de Microscopía Electrónica y Fotografía de la Biodiversidad, Instituto de Biología, UNAM) for her technical support with the SEM photos. To Andrew Cabrinovic (Aquatic Invertebrates Division, The Natural History Museum, UK) for the information about the holotype.