Unicauda magna sp.n. (Protozoa: Myxozoa): a new myxozoan from the fin tissues of the fathead minnow, Pimephales promelas Rafinesque

Abstract. Unicauda magna sp.n. (Protozoa: Myxozoa) was found in hatchery-raised fathead minnows, Pimephales promelas (Cyprinidae) from Pennsylvania. A large number of whitish-coloured cysts were located in the tissues of the pectoral, pelvic and caudal fins of infected fish. Spore dimensions (in μm) based on 30 measurements (10 spores/cyst) included the following: total length, 109.6 (75–170); spore body length, 15.5 (14–17); spore body thickness, 12.1 (10–13); spore body width, 13.2 (12–14.5); tail length, 94.1 (60–154); polar capsule lengths, 8.6 (7.5–9.5); polar capsule width 4.1 (3.0–5.0); sutural ridge width, about 1. The tail and body of the spores differed in colour when stained with each of three dyes. They are, therefore, composed of different material.