Diversity of apostome ciliates, <i>Chromidina</i> spp. (Oligohymenophorea, Opalinopsidae), parasites of cephalopods of the Mediterranean Sea

Abstract – Chromidina spp. are enigmatic apostome ciliates (Oligohymenophorea, Opalinopsidae) that parasitise the

renal and pancreatic appendages of cephalopods. Only four species have been described, among which only three have

been formally named. No DNA sequence has been reported so far. To investigate Chromidina spp. diversity, we

sampled cephalopods in the Mediterranean Sea off Tunis, Tunisia, and identified two distinct Chromidina spp. in

two different host species: Loligo vulgaris and Sepia officinalis. From haematoxylin-stained slides, we described

morphological traits for these parasitic species and compared them to previous descriptions. We also re-described

the morphology of Chromidina elegans (Foettinger, 1881) from Chatton and Lwoff ’s original materials and designated

a neohapantotype and paraneohapantotypes for this species. We describe a new species, Chromidina chattoni

Souidenne, Florent and Grellier n. sp., found in L. vulgaris off Tunisia, and evidence for a probable novel species,

found in S. officinalis off Tunisia, although this latter species presents similarities to some morphological stages

previously described for Chromidina cortezi Hochberg, 1971. We amplified, for the first time, an 18S rDNA marker

for these two Chromidina species. Phylogenetic analysis supports the association of Chromidina within apostome

ciliates. Genetic distance analysis between 18S rDNA sequences of representative apostomes indicates Pseudocollinia

as the most closely related genus to Chromidina.