Knowledge on the sponge fauna from the Mexican Pacific Ocean has increased substantially in recent years (Gómez et al., 2002; Carballo et al., 2003; Carballo et al., 2004a; Carballo and Cruz-Barraza, 2005, 2006, 2008; Cruz-Barraza and Carballo, 2005, 2006, 2008). Most of these modern taxonomic studies have been focused on hadromerids of the sublittoral and littoral rocky areas, which have yielded a total of 40 valid hadromerid species so far. However, an understanding of the species composition, distribution, and biogeographic and ecologic relationships of the Mexican Pacific fauna is not yet possible, until other diverse sponge groups such as poecilosclerids, haplosclerids, etc., are studied as thoroughly as the hadromerids.
This new contribution to the taxonomy of Pacific sponges is focused on Mycale Gray, 1867, which is characterized by having a complex set of morphologic characters that makes their identification straightforward. Mycale has up to eight categories of microscleres, recognized by their distinct shape, a large variety of skeletal arrangements, and the common presence of different size categories in some spicules (Hajdu and Desqueyroux-Faúndez, 1994). It is one of the most diverse sponge genera, with almost 250 species described in the world (Doumenc and Lévi, 1987; Hajdu, 1999; Van Soest, 2010). This suggests a considerable adaptative radiation (Hajdu and Desqueyroux-Faúndez, 1994; Hajdu et al., 1995; Carballo and Hajdu, 1998).
There were several suggestions to split the genus into subgenera. Dendy (1921), and later De Laubenfels (1936a) proposed a subdivision of Mycale by the presence/absence of some specific microsclere categories. This proposal was controversial and finally was abandoned by a subgeneric classification based on the arrangement of the ectosomal skeleton (Topsent, 1924; Van Soest, 1984; Bergquist and Fromont, 1988). Although currently largely accepted, this scheme of classification was shown to be plastic at the species level, for example M. (A.) carmigropila is a species that shows ectosomal skeletal patterns of the subgenus Aegogropila and Carmia (Hajdu and Rützler, 1998), as well as incongruence with the distribution of some microscleres types (see Carballo and Hajdu, 1998). Recently, a preliminary phylogenetic analysis of the genus Mycale using molecular data confirmed that Mycale is a monophyletic group within Poecilosclerida, and the presence of palmate anisochelae is a valid taxonomic character to identify this taxon; however, the study also suggested that the phylogenetic relationships of Mycale sub-genera may have to be reassessed (Loh et al., 2010). Nevertheless, until a molecular phylogenetic classification of Mycale can be established, it is preferable to continue using the current classification scheme based on sub-genera for a genus as diverse as Mycale to avoid unnecessary confusion.
At present, seven species have been described or recorded from the Pacific coast of Mexico but only three of them are valid; Mycale contax Dickinson, 1945, M. cecilia De Laubenfels, 1936 and M. aff. magnirhaphidifera Van Soest, 1984. The aim of this study was to contribute to the knowledge of the order Poecilosclerida from the Eastern Pacific Ocean. Two goals were set for the genus Mycale: first, to review the type material of some species cited in the area, and second, to describe all the material collected.