Colomastigids ( Amphipoda : Gammaridea : Colomastigidae ) from the Veracruz Coral Reef System , SW Gulf of Mexico , with a description of two new species associated with sponges

Two new species of the genus Colomastix (Amphipoda: Colomastigidae) associated with sponges from the Veracruz Coral Reef System, Mexico, SW Gulf of Mexico, are described. The specimens were collected from the sponges Amphimedon compressa and Desmapsamma anchorata at depths between 3 and 12 m. Colomastix sarae n. sp. and Colomastix escobarae n. sp. are compared to other, very similar species of the genus Colomastix. In addition, we provide ecological and distribution information of sponge-inhabiting Colomastix halichondriae, C. irciniae, and C. tridentata collected from this coral reef system.


INTRODUCTION
The family Colomastigidae Chevreux, 1899 includes small marine amphipods that inhabit from the intertidal zone to bathyal depths.This pattern of bathymetric distribution shows a decrease in the number of species with the depth and distance from the shore increases, as well as an increase in abundance and biodiversity in the coral reef systems of the continental shelves (LeCroy, 1995).Most colomastigids are symbiotic in sponges and cnidarians, with some records including bryozoans, algae, seagrasses, coral-shell rubble and, less frequently, soft bottoms (Bousfield, 1973;Biernbaum, 1981;Mueller, 1992;Alonso de Pina, 1993).
Colomastigid dispersal and speciation mechanisms are poorly known; however, allopatric speciation by vicariance processes has been documented in coral reefs (LeCroy, 1995;Bousfield, 2000Bousfield, , 2001;;Barnard and Karaman, 1991).Therefore, geographical and reproductive isolations occur inside sponges, together with an increase in regional endemism, a wide intra and interspecific morphological variability, and marked sexual dimorphism.In addition, rafting processes and transportation by ship biofoulers have been recognized as important mechanisms in the worldwide geographic distribution pattern (Myers, 1993;Ariyama, 2005).
There are less descriptions of new species of colomastigids than those of other families (e.g.Ampeliscidae, Aoridae, Gammaridae, Leucothoidae), due to their small sizes, from millimeters to a few centimeters, the difficulty in identifying the juvenile, pre-mature, mature and post-mature morphs, the difficult conditions for collecting specimens, and the limited sampling area in coral reef ecosystems (LeCroy, 2004).
This study describes two new species of spongeinhabiting colomastigids from the Veracruz Reef System National Park, southwestern Gulf of Mexico, and provides ecological and distribution information on the members of this family currently collected in this reef system.

MATERIALS AND METHODS
The Veracruz Reef System National Park is located at 19°00.0', 19°16.0'Nand 95°45.0',96°12.0'W,southwestern Gulf of Mexico.In 2007, seven sampling sites (Table 1, Fig. 1) were geopositioned in the bathymetric interval from 3 to 12 m.Sponges were collected manually from each site by scuba divers with a knife, placed in plastic bags underwater and sealed.Once on shore, 5.0 ml of an alcohol/formalin (1:1) solution was added to each sponge to encourage the crustaceans to leave the internal canals.Colomastigids were transferred to glycerin for dissection, illustration, and microstructure analysis under a Motic dissecting microscope at the Crustacean Laboratory, FES-Iztacala, UNAM.Figures were drawn using a camera lucida.The names used for the structures, setae/spines, diagnosis descriptions, and remarks were based on LeCroy (1995LeCroy ( , 2004)).
The type material of the amphipods is deposited in the Colección Nacional de Crustáceos, Instituto de Biología, UNAM, Mexico City.The sponges were deposited and identified in the Colección Nacional del Phylum Porifera Gerardo Green, Instituto de Ciencias del Mar y Limnología, UNAM, Mexico City.Additional material: 2 females (CNCR #25307); data as for holotype.

Adult male: unknown
Etymology.The new species is named in honor of Sara LeCroy, a researcher of the Gulf Coast Research Laboratory, U.S.A.
Uropod 1 (Fig. 5C), peduncle 1.2 x rami length, smooth margins, distoventral corner rounded; inner ramus 1.1 x length of outer, smooth margins on both.Uropod 2 (Fig. 5D), peduncle subequal in length to rami; inner ramus 1.2 x length of outer, anteroventral margins slightly serrate.Uropod 3 (Fig. 5E), peduncle slightly shorter and more robust than rami, distal and distoventral margins serrate slightly; outer ramus more robust, ventral margin serrate along two thirds, inner ramus lanceolate and subequal in length to outer, Remarks.Colomastix sarae n. sp. may be recognized and differentiated from all other female species of the Colomastix genus by the following characteristics: rostrum acute; head with lineal margins in dorsal view; antenna 1, peduncle article 1 with 3 robust setae on ventral margin, a small distal notch, 3 spines on dorsomedial margin and 2 robust setae distally; antenna 2, peduncle articles 3-5 with equidistant short robust setae on ventrolateral margin, peduncle article 3 with single distomedial spine and adjacent process, and a robust setae on mediofacial margin; gnathopod 2 without palmar processes; uropod 3, peduncle with distal and distoventral margins serrate slightly, outer ramus more robust, ventral margin serrate along two thirds, inner ramus lanceolate and subequal in length to outer ramus; telson, ovate, distal lobe rounded and tongueshaped, tip rounded.
A Adult male, unknown.

Etymology:
The new species is named in honor of Elva Escobar Briones, a researcher of the Instituto de Ciencias del Mar y Limnología, México.
Remarks.Colomastix escobarae n. sp.can be recognized and differentiated from all other female species of the Colomastix genus by the following characteristics: rostrum strongly acute; head with concave margins in dorsal view; interantennal plate with anteroventral angle projecting further than anterodorsal angle, anterior margin projecting further than rostrum, slightly sinuous; antenna 1, peduncle article 1 with a robust tooth on distoventral margin, 2 dorsomedial spines, and another short distally; antenna 2, peduncle article 3 with dorsal margin bifurcate medially, distomedial process absent, a distomedial long robust seta, and another short robust seta on distal margin; mandible with 7 rakers subequal in length, margins serrate, 5 with differentiated cusps; uropod 1 with 2 distal cusps and minute setae on inner ramus; uropod 3, outer ramus wider and longer than inner, serrate, minute setae on ventral margin, inner ramus naked; telson short, flat dorsally, triangular.

Colomastix tridentata
Distribution.Isla Verde coral reef, southwestern Gulf of Mexico.Previous records: Texas, west coast Florida, Florida Keys, Yucatan (Mexico), Caribbean Sea (Gran Cayman Island, Tobago Island, Turks and Caicos Islands, and Georgia and North Carolina (LeCroy, 2004).DISCUSSION LeCroy (1995) published the first extensive study of the family Colomastigidae collected in the northeastern and northwestern Gulf of Mexico, in which she analyzed a variety of taxonomic, biological and ecological topics.This paper included, up to the year 1994, 32 colomastigid species grouped into two genera: Colomastix with 28 species and Yulumara with four.In addition to nine species already described, Ariyama (2005), Ren (2006) Currently, this gulf is the ocean basin with the greatest species richness of the genus Colomastix (13 spp), as 28.3% of the species found worldwide inhabit this area.It is followed by Madagascar with eight species (equivalent to 17.4% of the total) (Ledoyer, 1982), the Sea of Japan with seven species (15.2%) (Bulycheva, 1955;Ariyama, 2005), the Great Barrier Reef with six species (13%) (LeCroy, 2009), New Zealand (Hurley, 1954), Hawaii (Barnard, 1970), New England (Bousfield, 1973) and the China Sea (Ren, 2006) with two species each (4.3% respectively), and the Weddell Sea, Antarctic Peninsula, with one species (2.2%) (Lörz, 2001).This relative difference in the number of colomastigid species could be attributed to several factors: differences in collection effort, the area covered by sampling, the number and structural complexity of the sponges, and the recruitment and dispersion mechanisms in each ocean basin.
Different mechanisms have been documented to explain the dispersion of colomastigid amphipods in the marine environment: Barnard (1976) proposed transportation on rafting materials, that is, attached hosts such as sponges and ascidians; Myers (1993) associated rafting processes with dispersion at a megascale; and Ariyama (2005) considered transportation in ship fouling as the main factor in the distributiondispersion process.In this study, two facts suggest that the dispersion and recruitment of colomastigid amphipods in the Veracruz Coral Reef System is mainly associated with the international ships towards the port of Veracruz, both as biofoulers and as organisms in ballast water.Sampling carried out in this coral reef system has confirmed the presence of C. halinchondriae and C. irciniae as macrofoulers on the hulls and in the ballast water, as well as C. irciniae and C. tridentata as macrofoulers on submerged artificial panels in the northern area of the reef system (Winfield et al. unpublished data).
These changes in the distribution pattern of the Colomastix from the Veracruz Coral Reef System are probably the result of differences in the architectonic complexity, the species richness and relative abundance of sponges, and the impact of maritime traffic, all of which are greater in the northern sector than the southern area.Gómez (2002Gómez ( , 2007) ) documented 46 species of sponges in the Veracruz Coral Reef System, of which 31 species occur in the northern sector; in addition, there is an increase in the complexity of the reef structure in this sector.
Of the nine sponges (Demospongiae) analyzed in this study (Table 3), five included at least one species of Colomastix (55.5%), with a co-occurrence of 20% (C.ircinia, C. tridentata versus Aplysina fistularis) (Table 3).This may be an underestimation of the real percentage of occurrence and co-occurrence in this environment, considering the species richness and wide distribution of the recorded sponges, as well as the consistency in the patterns of co-occurrence reported for the genus Colomastix (>30%) (LeCroy, 1995;Ariyama, 2005).
Host-generalist and host-specific associations have been documented for different species of isopods and amphipods in accordance with the number of host species that they inhabit, and have been explained considering the processes of intraspecific competition and reproductive biology (Thiel, 1999).Based on criteria established by LeCroy (1995), two patterns of distribution-occurrence for the Colomastix and sponge species were observed in this study.The first includes C. halichondriae, C. tridentata, C. sarae n. sp. and C. escobarae n. sp. with a greater degree of host specificity, and the second pattern relates to C. irciniae, which showed a generalized distribution in several species of reef sponges (Table 4).
This study provides seven new records of reef sponge species as hosts of the genus Colomastix (Table 4).In addition, we believe that the diversity of the genus Colomastix is poorly known in many regions, including the Gulf of México, and more extensive sampling programs in the Veracruz Coral Reef System itself would probably yield additional species.

Table 1 .
-Geographic locations and depths of sampling stations from the Veracruz Coral Reef System National Park during June, August and October, 2007.Geographic distribution of coral reefs in the Veracruz Coral Reef System National Park, southwestern Gulf of Mexico.The boundaries and the collection localities are included.
Station (Reefs) Interval depth (m) Position (N) Position (W) morphological comparison of the Colomastix species (female) from the Gulf of Mexico showed that Colomastix sarae n. sp. and C. irciniae are closely related due to the following characteristics: rostrum acute, head with concave slightly margins in dorsal view (lineal in C. sarae); interantennal plate, anterodorsal and anter- , and LeCroy (2009) described eight more colomastigid species from Japan, China, and the Great Barrier Reef.By the year 2009, a total of 44 species of Colomastix and five of Yulumara had been recognized.With the descriptions of Colomastix sarae n. sp. and Colomastix escobarae n. sp., the genus Colomastix now has 46 nominal species worldwide (Table 2).Of these, C. camura, C. tridentata, C. cornuticauda, C. irciniae, C. heardi, C. bousfieldi, C. falcirama, C. denticornis, C. gibbosa, C. halichondriae, C. janiceae, C. sarae n. sp. and C. escobarae n. sp.inhabit coral reefs and soft bottoms of the Gulf of Mexico.

Table 3 .
-Occurrence and abundance of Colomastix species among examined sponges at the Veracruz Coral Reef System National Park.