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Diseases of Aquatic Organisms

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DAO 55:45-57 (2003)  -  doi:10.3354/dao055045

Characterisation of two novel types of hexactinomyxon spores (Myxozoa) with subsidiary protrusions on their caudal processes

Sascha L. Hallett1, Stephen D. Atkinson1, Heidron Schöl2, Mansour El-Matbouli1,*

1Institute of Zoology, Fish Biology and Fish Diseases, University of Munich, Kaulbachstrasse 37, 80539 Munich, Germany
2Institute of Tropical Medicine and Parasitology, University of Munich, Leopoldstrasse 5, 80539 Munich, Germany
*Corresponding author. \fEmail:

ABSTRACT: Two types of hexactinomyxon spores, Hexactinomyxon type 1 nov. and Hexactinomyxon type 2 nov., are reported from freshwater tubificid oligochaetes, Limnodrilus hoffmeisteri and L. udekemianus. Spores are triradially symmetrical and comprise a spore body, style and 6 caudal processes. The caudal processes arise from the division of each of the 3 valve cells into an equal pair of projections at the base of the style. One of each pair is fused conspicuously to its nearest neighbour for the initial 1/5 to 1/4 of their total length. Distally, each process possesses subsidiary protrusions which are irregularly distributed and irregularly shaped extensions of the valve cell. Scanning electron microscopy of Hexactinomyxon type 2 nov. revealed that these protrusions are a seamless extension of the valve cell wall which branch distally, occasionally laterally, and terminate in a distinct bulbous structure; they also form the terminus of each process. The small subunit ribosomal DNA gene (18S) of both hexactinomyxon types was amplified through a nested PCR, then digested with the restriction enzymes Dde I and Hha I. The resultant cleavage patterns suggested the presence of 2 forms. Subsequent partial sequencing of 18S rDNA confirmed the identification of 2 novel types.

KEY WORDS: Actinosporean · Hexactinomyxon · Myxozoa · 18S rDNA · Oligochaete · SEM

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