Microtriches of Tetraphyllidean Metacestodes From Western Mediterranean Striped Dolphins (Stenella coeruleoalba) Celia Agustı ´,* Francisco Javier Aznar, and Juan Antonio Raga Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Valencia, 46071 Valencia, Spain ABSTRACT The tegumental structures of two types of tetraphyllidean plerocercoids and two types of merocer- coids (Phyllobothrium delphini and Monorygma grimal- dii) from Mediterranean striped dolphins, Stenella coeru- leoalba, are described for the first time using scanning electron microscopy. The tegument of all of the specimens was fully covered with microtriches. Four basic types were found: filitriches, blade-like spinitriches of different sizes and shapes, cone-shaped spinitriches (with two parallel small projections of equal length at the apex), and crowned cylindrical spinitriches (with 6 –7 small papillae forming a crown at the apex); the two latter types are newly described. The two types of plerocercoids had a similar morphology and distribution of microtriches; in addition, cilium-like projections appeared interspersed among the microtriches on the apical sucker, accessory suckers, and distal bothridial loculus. Merocercoids exhib- ited a greater variety of tegumental structures, especially on the distal bothridial loculus. Both merocercoid types had regularly spaced papillae or “buttons” on the acces- sory suckers and the distal bothridial loculus that were composed of a central cilium-like projection surrounded by numerous filitriches. However, crowned cylindrical spini- triches were specific to P. delphini and cone-shaped spini- triches were specific to M. grimaldii. Differences in the morphology and distribution of scolex microtriches of adult cestodes have been considered useful for species identification. A previous molecular study has suggested that P. delphini and M. grimaldii are actually different congeneric species. Our study has shown that significant differences in the morphology and distribution of micro- triches occur between these species at the merocercoid stage. J. Morphol. 265:176 –189, 2005. © 2005 Wiley-Liss, Inc. KEY WORDS: Tetraphyllidea; plerocercoid; Phylloboth- rium delphini; Monorygma grimaldii; microtriches; Ceta- cea; tegument; SEM The tegument of both larval and adult cestodes exhibits characteristic structures that appear to be involved in functions such as absorption, attach- ment, protection, and sensory reception (Andersen, 1975; Lumsden, 1975; Thompson et al., 1980; Palm et al., 1998). Among them, microtriches are the hall- mark feature of the tapeworm tegument (Coil, 1991). Recent studies have shown that microthrix patterns in adult forms provide valuable data for the differentiation of species (Caira, 1992; Ruhnke, 1994, 1996; Tyler and Caira, 1999; Caira and Tracy, 2002). However, information on the tegumental structures of tetraphyllidean metacestodes (the ter- minology for the larval cestodes follows Chervy, 2002) is rather scarce. Gabrion and Euzet-Sicard (1979) and Khalil (1995) described the morphology of several tegumental structures on the surface of unidentified tetraphyllidean plerocercoids from Mediterranean teleosts, but did not provide detailed information on the patterns of microthrix distribu- tion. In the most detailed study to date, Caira and Ruhnke (1991) described the microtriches found on the scolex of plerocercoids and adults of the oncho- bothriid Calliobothrium verticillatum and revealed ontogenetic changes in the morphology and distri- bution of microtriches. In the last two centuries, several types of tet- raphyllidean metacestodes have been reported in marine mammals worldwide (Delyamure, 1955; Dai- ley and Brownell, 1972; Dailey, 1985; Bester, 1989; Raga, 1994; Agustı ´ et al., 2005a,b). However, their taxonomic identity still remains unknown. Morpho- logically, four types have been recognized. Two en- cysted forms (merocercoids), i.e., Phyllobothrium delphini and Monorygma grimaldii, occur in the subcutaneous blubber and peritoneum of the abdom- inal cavity, respectively. Two mobile forms (plerocer- coids), tentatively named “small” and “large” (Agustı ´ et al., 2005a), occur in the digestive system: the Contract grant sponsor: the Spanish Government; Contract grant numbers: BOS2002-00878, REN2003-01758 (FEDER); Contract grant sponsor: the Valencian Government; Contract grant number: GV04B- 304; Contract grant sponsor: the Ministerio de Ciencia y Tecnologı ´a of Spain, “Ramo ´n y Cajal” contract (to F.J.A.). *Correspondence to: Celia Agustı ´, Marine Zoology Unit, Cavanilles Institute of Biodiversity and Evolutionary Biology, University of Va- lencia, P.O. Box 22085, 46071 Valencia, Spain. E-mail: celia.agusti@uv.es Published online 15 June 2005 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/jmor.10349 JOURNAL OF MORPHOLOGY 265:176 –189 (2005) © 2005 WILEY-LISS, INC.