First description of the lorica of Metacystis truncata and its occurrence on Thalassia testudinum

Metacystis truncata, a prostomatid loricate ciliate, was found attached to Thalassia testudinum, 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 (64.6-115 mu m) with a well-developed anterior neck and a sac reinforced by 15-26 rings. Cell body size is variable (19-91 mu m 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 midbody 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.