Erichsonella Richardson, 1900 is a shallow-water American genus of isopod, inhabiting tropical and warm temperate regions found on algae, mud flats, sea grasses and oyster beds (^{Pirés, 1984}). Erichsonella attenuata (Harger, 1874) vary in colour, from amber to brown and both male and female individuals may have darker spots on the dorsal and ventral areas, with a maximum total length of 18.4 mm; on average adult males are longer than females and are known from the New Jersey, Connecticut, Miami, Florida and Mississippi (^{Pirés, 1984}).

In the Gulf of Mexico, E. attenuata is present along the Texas coast, in the intertidal zone from 0 m to 20 m depth (^{Boström & Mattila, 2005}; ^{Kensley & Schotte, 1989}; ^{Pirés, 1984}). According to the division of the Gulf of Mexico proposed by ^{Felder, Camp, and Tunnell (2009)}, the species is observed in the North-East and North-West regions, delimited in the South by parallel 25° N.

This isopod species has been observed in some sites of the Western Atlantic part of the Gulf of Mexico (^{Kensley, Nelson, & Schotte, 1995}) and it is associated with sea-grass beds (^{Boström & Mattila, 1999}; ^{Darcy & Eggleston, 2005}; ^{Sheridan, 2004}), such as Ruppia maritima, Halodule wrightii and Thalassia testudinum (^{Boström & Mattila, 2005}; ^{Kensley et al., 1995}). In the Indian River Lagoon, Florida, E. attenuata is one of the 3 most common invertebrate species found in H. wrightii beds and it is an important epiphytic grazer. It is also an important food resource for higher trophic levels, occasionally consumed extensively by sea grass-associated fish (^{Ryer & Orth, 1987}).

In this paper, the presence of E. attenuata is reported for the first time in Mexican coasts, in the Tamiahua Lagoon, Veracruz and in the Términos Lagoon, Campeche (Fig. 1). Tamiahua is located in the West-Southwest (WSW) region of the Gulf of Mexico and the Términos Lagoon is located in the South-Southwest (SSW) region (^{Felder et al., 2009}). ^{Schotte, Markham, and Wilson (2009)}, according to regions mentioned by ^{Felder et al. (2009)}, reported E. attenuata in the North-Northeast (NNE) and the East-Northeast (ENE) regions of the Gulf of Mexico.

Figure 1 Map showing Tamiahua and Términos lagoons in Mexican coast in the Southern, Southwestern and East-Northeast regions, respectively, of the Gulf of Mexico. Inset: Erichsonella attenuata (Harger, 1874). (A) Ovigerous female and (B) male. 

In the Tamiahua Lagoon 2,315 individuals of E. attenuata were collected with scoop nets (mesh aperture 1.6 mm) from July 2010 to August 2011, between 21°25′46″-21°28′46″ N and 97°24′22″-97°26′57″ W. These were associated with H. wrightii, which is present on the eastern coasts of America, including Alabama, Florida, Louisiana, Mississippi, and North Carolina (USA), the east coast of Mexico, the West Indies (Cuba, Jamaica, Haiti, Dominican Republic and Puerto Rico), Central America (Belize, Guatemala, Nicaragua), and South America (Venezuela and Brazil) (^{Ferguson, Pawlak, & Wood, 1993}; ^{Haynes, 2000}).

In the Términos Lagoon, E. attenuata individuals were collected with a Seagrove sledge net (mesh aperture 0.8 mm). Only 3 individuals were collected, 1 isopod per month, in December 2012 and in the months of May and July 2013 in the same sampling station (18°30′13″ N, 91°41′58″ W). They were associated with T. testudinum beds, which are present in the Caribbean and the Gulf of Mexico. The northernmost station of T. testudinum is in San Sebastian Inlet, near Cape Kennedy, Florida, in the East, Bermuda Island; while in Central America, it is present in British Honduras, Costa Rica, Panama and Venezuela (^{Hartog, 1970}).

These data suggest that E. attenuata may be widely distributed in the Gulf of Mexico, extending its original distribution from the coasts of Texas, USA to at least the coasts of Campeche, Mexico. The first report was from 26° N and the last is reaching 18° N. Thus, the current distribution of E. attenuata is from the state of Connecticut in the USA, to the state of Campeche in Mexico, covering the North-Western Atlantic coast of Florida and virtually the entire Gulf of Mexico.

The material examined and identified as E. attenuata was 2,318 individuals; 2,315 collected in Tamiahua Lagoon, Veracruz and 3 in Términos Lagoon, Campeche; some individuals were deposited in the Colección Nacional de Crustáceos of the Instituto de Biología, Universidad Nacional Autónoma de México; 258 from Tamiahua Lagoon with catalogue number: CNCR 26120 and from Términos Lagoon, 3 with catalogue numbers: CNCR 28796; CNCR 28797; and CNCR 28798. According to ^{Pirés (1984)}, of the 6 species of the genus, E. attenuata presents the greatest number of primitive characters. In Table 1 we present basic morphological data of the collected material from the 2 sites including number of males and females, range of total length, morphology of the frontal process, pereonites, pleotelson, antenna 1, antenna 2, and uropod.

Special thanks to Ricardo Gaspar and Alan González, undergraduate Biology students of the School of Sciences, Universidad Nacional Autónoma de México for the field work in Tamiahua, and to Hernan Álvarez Guillén and Andrés Reda Deara for their field work in the Términos Lagoon. We also thank Luis and Jorge Luis Díaz, enthusiastic fishermen of the Tamiahua Lagoon, Veracruz; Verónica Aguilar (FC, UNAM) for editing the map, and Dr. Fernando Álvarez, who was in charge of identifying the biological samples.