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The family Centriscidae includes small-sized gregarious fishes that are characterized by a laterally compressed body, head with a long tubular snout and a small terminal mouth (Ehrich, 1986). In the Mediterranean Sea, this family is represented by a single genus, Macroramphosus ZBK . Several authors claim that the genus is monotypic, represented only by M. scolopax , and have defended the synonymization of the two species (D’Ancona, 1933; Ehrich, 1975, 1976, 1986; Fischer et al., 1987). The existence of phenotypically intermediate individuals, and the difficulty in collecting small sized M. scolopax (Linnaeus) specimens has led some authors to consider M. gracilis as a juvenile form of M. scolopax (Assis, 1992). However, the deep-bodied M. scolopax and the slender-bodied M. gracilis have been recognized as two valid species in studies carried out at the Atlantic Ocean; this viewpoint is based on observations of distinct differences in age and growth (Brethes, 1979; Borges, 2000), reproductive biology (Arruda, 1988), morphology (Assis, 1992, 1993) and feeding habits (Matthiessen et al., 2003). Recent investigations on the larval development of specimens of Macroramphosus ZBK from Japan also revealed the occurrence of two distinct species (Kuranaga & Sasaki, 2000; Miyazaki et al., 2004).
Although previous records of M. gracilis are available from various parts of the Mediterranean Sea, there was no agreement among authors on the validity of the species. This paper documents the occurrence of M. gracilis as a valid species in the Mediterranean Sea, and compares the species with M. scolopax . Morphometric characters that distinguishes the two species are also presented.