The Caprellidea ( Crustacea : Peracarida : Amphipoda ) from the Gulf of Mexico with a description of a new species of Paracaprella

A new species of caprellid amphipod of the genus Paracaprella is described and illustrated in detail. All the material reported was collected from coral rubble samples from the Arrecife Tuxpan/Lobos Protected Natural Area, off Veracruz State, Mexico, WSW Gulf of Mexico. The new species is characterized by large eyes; article 2 of peduncle of antenna 2 with a distoventral process; body dorsally setose; large subrectangular projection on the anteroventral margin of pereonite 2; basis of gnathopod 2 elongate and thin with a proximal knob on posterior margin, propodus longer than broad, with a robust grasping spine, and a large and robust tooth distally; and pereopods 5, 6 and 7 with several long plumose setae. The new species increases the numbers of Paracaprella species recorded around the world to 8, and the caprellid species from the Gulf of Mexico to 16. All caprellid amphipod species documented from this gulf inhabit the coastal zone and six in the deep sea. In addition, the number of caprellid species decreases along the bathymetric gradient: 15 species on the littoral zone, 6 on the continental shelf, 5 on the continental slope, and 3 on the abyssal plain.

So far, 401 caprellid species grouped into 88 genera have been recorded worldwide (Ahyong et al. 2011).Caprellid amphipods have been subjected to various controversial phylogenetic analyses (Laubitz 1976, 1993, Takeuchi 1993, Myers and Lowry 2003, Ito et al. 2008, 2011), showing the acquisition of a single body plan with a reduction of the posterior body segments and the thoracic legs.It includes a cylindrical and elongated body, head and pereonite 1 fused, rudimentary coxae, two pairs of gills, oostegites on pereonites 3 and 4, pereopods 3 and 4 absent, reduced or well developed, and a degenerative abdomen and abdominal appendages (Ito et al. 2011).The genus Paracaprella Mayer, 1890 is characterized by a reduction to 2 articles in pereopods 3 and 4, antenna 2 has a 2-articulated flagellum, mandibular palp is reduced to one seta, or when present it has 2 or 3 minute segments, and the abdomen of the male has one pair of appendices and one pair of lobules (McCain 1968, Guerra-García 2003a).
Prior to this study, seven nominal Paracaprella species had been described worldwide.Paracaprella pusilla Mayer, 1890 andP. tenuis Mayer, 1903 are recorded from the Gulf of Mexico as epibiotic organisms associated with hard substrates, seagrasses and macroalgae (McCain 1968, Escobar-Briones and Winfield 2003, Winfield et al. 2006, LeCroy et al. 2009).
During a general research project focused on recording the biodiversity of the amphipod crustaceans associated with the coral reefs of the Veracruz State, Mexico, SW Gulf of Mexico, some specimens of Paracaprella were collected in the Arrecife Tuxpan/Lobos Protected Natural Area, off Veracruz State (WSW Gulf of Mexico), associated with coral rubble Acropora cervicornis (Lamarck 1816).This study describes a new species of Paracaprella and updates the caprellid amphipod checklist from the Gulf of Mexico occurring from the littoral zone to the abyssal plain, and provides the geographic distribution pattern of the genus Paracaprella around the world.

MATERIALS AND METHODS
The Tuxpan-Lobos reef system is located on the continental shelf of Veracruz State, Mexico, WSW Gulf of Mexico,at 21°00'55.59" to 21°33'08.47"N and 97°10'30.85" to 97°18'00.23"W(Fig. 1).The reef system includes six reefs grouped into two sectors: Lobos, with the Blanquilla, Medio and Lobos reefs; and Tuxpan, with the Tanhuijo, Enmedio and Tuxpan reefs, all characterized as shelf-type with a maximum depth of 25 m (Chávez et al. 1970).
Samples of coral rubble were collected manually using SCUBA diving at a depth of 16 m.On board, 5.0 ml of an alcohol/formalin (1:1) solution was added to make the crustaceans leave the coral surface, and then the specimens were sieved through a 0.4 mm mesh and conserved in 70% ethanol.Specimens of Paracaprella were examined, dissected and illustrated in detail using a MOTIC SMZ-168 dissecting microscope equipped with a camera lucida.Bucal parts and small appendages were illustrated using a MOTIC BA-210 compound-microscope, also equipped with a camera lucida.Illustrations were completed using the Corel Draw V.12 program.All measurements of type material (holotype and paratype) were made with the Motic Images Plus V.2 program.The names used for the structures, setae/spines, descriptions, remarks, and morphological comparisons were based on McCain (1968), Quitete (1971), Guerra-García (2002, 2004), Diaz et al. (2005) and Guerra-García et al. (2006).The classification system of Myers and Lowry (2003), considering Superfamily Caprelloidea, Family Caprellidae, and Subfamily Caprellinae, was adopted in this study.The type material of the caprellid amphipods is deposited in the Colección Nacional de Crustáceos (CNCR), Instituto de Biología, UNAM, Mexico City.Additional material examined: two males (3.1 mm total length; 2.9 mm total length), two females (2.1 mm total length; 2.0 mm total length) (CNCR#26738); all material was collected from the type locality; June 13, 2011; coll., I. Winfield.
Pereopods (Fig. 5A-E).Pereopods 3 and 4 (Fig. 5A, B) 2-articulated, basal article with a simple seta, distal article with three setae, subapically.Pereopods 5, 6 and 7 (Fig. 5C-E) increasing in length in posterior direction, ventral margins setose with several plumose setae; carpus of pereopod 7 (Fig. 5C) with two distal notches and three robust setae; propodus expanded proximally, first half of palm serrated with three grasping setae, distal half with six short grasping setae, another longer, two small distal knobs; palm of pereopod 6 (Fig. 5D) with two short proximal knobs, each bearing a pair of simple grasping setae; other three robust grasping setae, and a row of five robust setae distally; propodus of pereopod 5 (Fig. 5E) with three small subdistal knobs on dorsal margin.Abdomen (Fig. 5F).Male with a pair of short penes, a pair of uni-articulate appendages and a pair of lateral lobes, each bearing several simple setae and three short processes, marginally.
Paratype female (CNCR#26737).Mature female (Fig. 2B), total length 2.8 mm.Similar to male, except for the following morphological characters: flagellum of antenna 1 6-articulated; oostegites present on pereonites 3 and 4, setose marginally; gnathopod 2 inserted on the anterior half of pereonite 2, basis elongate; subequal to propodus in length; subrectangular projection on anteroventral margin of pereonite 1 minute; abdomen (Fig. 5G) with a pair of lateral lobes, longer than wide; and a single dorsal lobe carrying three simple setae.Etymology.This new species is named in honour of Dr. José Manuel Guerra-García, a renowned carcinologist of the University of Seville, Spain, for his valuable contribution to the study of taxonomy and phylogeny of caprellids worldwide.Remarks.Paracaprella guerragarciai n. sp. is morphologically most similar to Paracaprella digitimanus Quitete, 1971, P. pusilla and P. tenuis; however, males of Paracaprella guerragarciai n. sp.can be easily distinguished from those three Paracaprella species by the following characters: (1) P. guerragarciai n. sp. has eyes large and multi-ommatida, while eyes are minute to small in the other three species; (2) the dorsal margin is setose in P. guerragarciai n. sp., but smooth in the other three species; (3) anteroventral projection on pereonite 2 is large and subquadrate in P. guerragarciai n. sp., but small to large and subtriangular to sharp-pointed in the other three species; (4) gnathopod 2 with a very large robust tooth on proximal quadrate projection and dactylus with inner margin serrate in P. guerragarciai n. sp., but with a short robust tooth and smooth inner margin in the other three species; and (5) several long plumose setae are present on pereopods 5-7 in P. guerragarciai n. sp., but setae are longer and simpler in the other three species.The main differences are summarized in Table 1.
The global geographic distribution of the genus Paracaprella is mostly from 40°N to 20°S, corresponding to temperate, subtropical and tropical seas (Fig. 6).Based on this geographic pattern, five species (P.alata, P. digitimanus, P. pusilla, P. tenuis and P. guerragarciai n. sp.) are recorded from the western Atlantic coasts, in contrast with the shallow waters of the Indian Ocean and the western Pacific (the latter including the Sea of China, the Sea of Japan and the eastern coast of Australia), with four species each (Fig. 6); only Paracaprella alata and P. pusilla are distributed worldwide, even at higher latitudes, with the exception of polar zones.Ros and Guerra-García (2012) reported P. pusilla as tropical caprellid amphipod with most of the records from the Gulf of Mexico and the Caribbean Sea.So far, 16 species of caprellids (including Paracaprella guerragarciai n. sp.) belonging to eight genera have been documented from the Gulf of Mexico: Caprella Lamarck, 1801 (5 species), Paracaprella (3 species), Deutella Mayer, 1890 (3 species), Hemiaegina Mayer, 1890, Hemiproto McCain, 1968, Metaprotella Mayer, 1890, Phtisica Slabber, 1769and Pseudaeginella Mayer, 1890 (1 species each) (McCain 1968, Escobar-Briones and Winfield 2003, Guerra-García 2003b, Winfield et al. 2006, 2007, Winfield and Escobar-Briones 2008, LeCroy et al. 2009) (Table 2).All caprellid amphipod species from the Gulf of Mexico inhabit the coastal zone (0-200 m depth), and six species in the deep sea (201-3800 m depth) (Table 2).The number of species decreases along the bathymetric gradient, with the greatest number (15 species) on the littoral fringe (0-20 m depth), six species on the continental shelf (21-200 m depth), five on the continental slope (201-2000 m depth), and three on the abyssal plain (2001-3800 m depth); only Caprella equilibra Say, 1818 inhabits depths from 1 to 3800 m (Table 2).The species Caprella penantis Leach 1814, Deutella incerta (Mayer, 1903), Hemiaegina minuta Mayer, 1890 and Paracaprella pusilla are distributed table 2. -Number of caprellid species from the Gulf of Mexico.Depth, habitat and geographic sectors in the Gulf of Mexico (see Fig. 1) are included.Information based on McCain 1968, Escobar-Briones and Winfield 2003, Guerra-García 2003a, Winfield et al. 2006, 2007, Winfield and Escobar-Briones 2008, LeCroy et al. 2009 1890, 1903;McCain 1967, 1968, Arimoto 1980, Guerra-García 2002, 2003b, Díaz et al. 2005, Guerra-García et al. 2006, 2010, Winfield et al. 2006, 2007, Winfield and Escobar-Briones 2008, Ortiz et al. 2009, Ros and Guerra-García 2012.throughout the four sectors of the Gulf of Mexico (Table 2).The northeastern and southwestern sectors have been studied intensively with the greatest number of benthic caprellid species (seven each), in comparison with the less studied southeastern (four species) and northwestern (three species) sectors (Table 2).Summarizing, the numbers of caprellid amphipods known to inhabit the shallow waters and deep sea in the Gulf of Mexico will increase with further sampling, especially from soft bottoms, hard substrates, algal mats, seagrasses, sponges, hydroids, bryozoans, and shell debris, on oceanographic cruises to be carried out in the coming years in this Large Marine Ecosystem.

Fig. 1 .
Fig. 1. -Map of the Gulf of Mexico showing the four sectors and the sampling locality.

table 1 .
-Main morphological differences between males of Paracaprella guerragarciai n. sp. and the three closely related species P. digitimanus, P. pusilla and P. tenuis.