NEBALL4 LAGARTENSIS (LEPTOSTRACA) A NEW SPECIES FROM THE YUCATAN PENINSULA, MEXICO BY ELVA ESCOBAR-BRIONES Laboratorio de Ecologia del Bentos, Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autónoma de México, Apartado Postal 70-305, 04510 Mexico City, Mexico and JOSE LUIS VILLALOBOS-HIRIART Collección Carcinológica, Instituto de Biologia, Universidad Nacional Autónoma de México, Apartado Postal 70-153, 04510 Mexico City, Mexico ABSTRACT A new species of Nebalia is described from Ria Lagartos in the Yucatán Peninsula, Mexico, increasing the number of described species in this genus to 13. The species closely resembles a complex of species recognized for the tropical western Atlantic that will need further study. The importance of the shape of the denticles on the dorsal pleonal segments 6 and 7 as a taxonomical character is discussed. RESUMEN Se describe una especie nueva de Nebaliaprocedente de Ría Lagartos, Yucatán, aumentando el número de especies descritas en este género a 13. La especie asemeja notablemente a otras especies que conforman un complejo reconocido para el Atlántico occidental tropical y que requiere de mayor estudio. Se discute la importancia, como caracter taxonómico, de la forma de los dentículos dorsales de los segmentos pleonales 6 y 7. INTRODUCTION The genus Nebalia is the most diversified of the genera included within the family Nebaliidae. It contains 10 described eurybathic species, one subspecies, and two forms recognized as distinct species but yet not formally described (table I). Four of these are confined to the tropical western Atlantic (Wakabara, 1965; Brattegard, 1970). Resemblance among many of the species and the poor taxonomic information available led to confusion and synonymy in earlier years. Systematic arrangements were established for the European species by Dahl (1985) indicating that Nebalia species follow classical zoogeographic distri- bution patterns. Two of the four species occurring in the tropical western Atlantic, have their taxonomic status pending. The present study describes the new species Nebalia lagartensis from the northern Yucatan Peninsula, increasing the number of known species in the tropical western Atlantic to five. 2 TABLE I Geographic distribution and known bathymetric range of the species Nebalia MATERIAL AND METHODS The 33 female specimens were collected with a hand net in shallow areas on bottoms covered with green algae, in the inner portion of the estuary Ria Lagartos in the northern Yucatan State in November 1985. The material was preserved in 10% sea water-formalin, sorted, and transferred to 70% ethyl alcohol for storage and study. Description of the species followed Dahl's (1985) taxonomic model. The individuals captured were designated as o (= ovigerous female) and no (= non-ovigerous female). Total length (T.L.) was measured with a calibrated ocular micrometer in a dissecting microscope and considered the distance along the dorsal midline, from the articulation of the rostrum to the posterior end of the telson. Figures were drawn with the aid of a camera lucida attached to stereoscopic and compound microscopes. Scanning electron microphotographs were taken on a JEOL model JSM-35C, using Kodak Verichrome Pan VP 120 film. RESULTS Nebalia lagartensis new species (figs. 1-5) - Type material. Holotype , I ovigerous female (T.L. 5.7 mm) collected Ria Lagartos, Yucatan Peninsula, northern Yucatan State, Mexico. Dissected on two slides and deposited at IB-UNAM Crustacea Collection under Access. Catalog No. EM-4956. Paratypes, 3 females (T.L. 6.8, 6.9, 6.0 mm) and 26 ovigerous females (T.L. 5.9, 7.6, 6.5, 6.0, 6.2, 7.3, 6.0, 6.6, 7.0, 6.9, 6.7, 6.3, 7.1, 6.2, 6.4, 5.7, 5.5, 3.5, 6.7, 7.2, 5.6, 6.4, 6. I , 7.1, 6.4, 6.7 mm) from the same locality. Material kept at .