Multiple species of Phoreiobothrium from the blacktip shark, Carcharhinus limbatus, in the Gulf of Mexico

Abstract

During a survey of the adult tapeworm fauna of sharks from the Gulf of Mexico, the blacktip shark, Carcharhinus limbatus (Müller and Henle, 1839), was found to host cestodes in the genus Phoreiobothrium. Carcharhinus limbatus inhabits the world's tropical and warm temperate waters. As yet, 34 species of cestodes representing the orders Tetraphyllidea, Cathetocephalidea, and Trypanorhyncha have been reported to parasitize the species throughout its range. Little is known about tetraphyllidean diversity in C. limbatus in the Gulf of Mexico; no records exist for Phoreiobothrium from C. limbatus in this region. Between 2005 and 2007, 6 specimens of C. limbatus were collected off Ocean Springs, Mississippi and 14 specimens were collected off Panama City, Florida, and their spiral intestines examined for cestodes. Whole mounts and histological sections of the cestode specimens were prepared for examination with light microscopy; scoleces were prepared for scanning electron microscopy. Overall, C. limbatus was found to host 4 species of Trypanorhyncha and 11 species of Tetraphyllidea. In addition to 1-2 species each in the tetraphyllidean genera Disculiceps, Anthobothrium, and Paraorygmatobothrium, C. limbatus hosted 6 species of Phoreiobothrium. The diversity of Phoreiobothrium species is of special interest: all are new to science and collectively represent an unusually high number of congeners in a single host species. The new species of Phoreiobothrium from C. limbatus can be distinguished from the known species and each other based on characters such as scolex dimensions, number of subloculi, presence or absence of papillae, and distribution of vitellaria. Despite its 11 cosmopolitan distribution, it has been suggested that several distinct populations of C. limbatus exist in the Gulf of Mexico. The complex species assemblage of Phoreiobothrium in C. limbatus in the Gulf of Mexico has the potential to inform us about its population structure of the host.