Lagenophrys dennisi, a peritrich ciliate, was observed attached to the exoskeleton of the crayfish Cambarellus patzcuarensis in Lake Pátzcuaro, Michoacán, Mexico. Lagenophrys dennisi presents a hemispheroidal, suboval or oval lorica in dorsal view, the distinctive lorica aperture consists of a pair of lips highly arched, unthickened, and smooth. Comparison of morphometric characters of the ciliate with previous records is made. Structures such as a "V"-shaped lorica suture, collar ridges, and myoneme are proposed for species identification. An anterior crescentic thickening on the dorsal surface of the lorica was observed under the scanning electron microscope. Lagenophryids were associated with 11 of 13 body parts with antennules and rostrum showing the highest prevalence. Lagenophrys dennisi was also found attached to submerged glass slides. This study represents the first record of L. dennisi on C. patzcuarensis and the first record of its presence in Mexico.

ABSTRACT. Metacystis truncata, a prostomatid loricate ciliate, was found attached to Thalassia tesudinum, a dominant seagrass of the coral reef lagoons of Veracruz, Mexico. the morphology of the ciliate and its lorica were studied in living and stained specimens and in those prepared for scanning electron microscopy. the lorica is cylindrical (64.6‐115μm) with a well‐developed anterior neck and a sac reinforced by 15‐26 rings. Cell body size is variable (19‐91 μm live), from ovoid to elongate: the terminal protruding vacuole is conspicuous in small and medium‐sized individuals; the macronucleus is terminal in the elongate forms, or located near the mid‐body in the ovoid ones. This marine prostomatid colonizes both natural and artificial substrates such as narrow polyethylene strips placed in an aquarium. the highest density was found in the summer. the present study represents the first description of the lorica of M. truncata and the first record on T. testudinum shoots.

Very few papers deal with the distribution and occurrence of ciliates associated with freshwater crayfish in wild conditions (López-Ochoterena and Ochoa-Gasca, 1971; Matthes and Guhl, 1973; Lahser, 1976). The crayfish distributed in Mexico belong to the subfamilies Cambarinae and Cambarellinae, and attention in regard to their epibionts has only been given to those having commercial importance. Subfamily Cambarinae includes genera such as Cambarus Erichson, Orconectes Cope, and Procambarus Ortmann from which only Procambarus is present in Mexico. The subfamily Cambarellinae is confined to the United States and Mexico. Seventeen species are assigned to genus Cambarellus (Ortmann) Hobbs (Hobbs, 1991). The crayfish Cambarellus patzcuarensis Villalobos constitutes an important link in ecological webs, as it represents a considerable biomass for fish nutrition. No studies have been conducted concerning the occurrence and distribution of Epistylis epibiont species on C. patzcuarensis. The aim of the present paper is to provide morphological data of colonial organization of eight Epistylis species and their occurrence and distribution on C. patzcuarensis exoskeleton.

The goal of the present study was to know the distribution and prevalence of ciliated Protozoa attached to the exoskeleton and gills of the cray sh, Cambarellus patzcuarensis. Samples of cray sh were taken at two sites in Pátzcuaro Lake, Michoacán, Mexico. Fifteen species of ciliated Protozoa (peritrichs) were found attached as epibionts on the cray sh. Their distribution and prevalence on 14 body parts of the basibiont is presented. Community structures were analysed using Jaccard's index and principal component analysis. The results showed that the gills had no similarity with respect to the other body parts as regards peritrich attachment. The pereiopods and the uropods were the body parts with the highest species richness, the gills had the lowest. Cothurnia variabilis is the only species with a high degree of speci city to the body region to which it is attached (gills). Of the 15 species found, only one has been reported exclusively as an epibiont on crustaceans. RESUMENEl objetivo del presente trabajo fue conocer la distribución y frecuencia de especies de protozoarios ciliados adheridos al exoesqueleto y branquias del acocil Cambarellus patzcuarensis. Las muestras de crustáceos fueron recolectadas en dos sitios del lago de Pátzcuaro, Michoacán, Méx-ico. Se presenta la distribución y frecuencia de 15 especies de protozoarios ciliados (peritricos) en 14 regiones del cuerpo del basibionte. La estructura de las comunidades fue analizada utilizando el índice de similitud de Jaccard y el análisis de componentes principales. Los resultados muestran que las branquias no tuvieron ninguna similitud con el resto de las regiones del cuerpo. Los pereiópodos y los urópodos mostraron una alta riqueza especí ca, y las branquias la menor. Cothurnia variabilis fue la única especie con un alto grado de especi cidad respecto a la región del cuerpo donde se adhiere (branquias). De las 15 especies de ciliados, solamente una ha sido registrada exclusivamente como epibionte de crustáceos.

A new epibiontic ciliate of the genus Metacystis is described on the seagrass Thalassia testudinum of the coral reef lagoons of Veracruz, Mexico. The ciliate was studied in living and stained specimens and under the scanning electron microscope. The cell body (10-35 x 10-18 microm in vivo) is transversely annulated (4-6 rings). The somatic ciliature consists of 22-30 longitudinal kineties, and patterned as 5-7 transverse kineties. The circumoral kinety is composed of kinetosomes closely spaced. The macronucleus diameter measures about 3-7 microm. The lorica (18-61 x 11-26 microm) has the posterior end round to conical or irregular with mucoid filaments. This prostomatid colonizes both natural and artificial substrates placed in an aquarium. Metacystis borrori n. sp. is a species that forms part of the ciliate community on Thalassia testudinum with a temperature range of 21-26 degrees C and a salinity of 32-40 per thousand.