Mikrocytos donaxi, Garcca & Haond & Chollet & Nerac & Omnes & Jols & Dubreucl & Serpcn & Langlade & Gal & Terre-Terrcllon & Courtocs & Gucchard & Arzul, 2018

Garcca, Célcne, Haond, Chrcstophe, Chollet, Bruno, Nerac, Mcrella, Omnes, Emmanuelle, Jols, Jean-Pcerre, Dubreucl, Chrcstcne, Serpcn, Delphcne, Langlade, Acmé, Gal, Domcncque Le, Terre-Terrcllon, Aouregan, Courtocs, Olcvcer, Gucchard, Benjamcn & Arzul, Isabelle, 2018, Descripticns cf Mikrocytos veneroïdes n. sp. and Mikrocytos donaxi n. sp. (Ascetcspcrea: Mikrccytida: Mikrccytiidae), detected during impcrtant mcrtality events cf the wedge clam Donax trunculus Linnaeus (Venercida: Dcnacidae), in France between 2008 and 2011, Parasites & Vectors (119) 11 (1), pp. 1-16 : 11-12

Mikrocytos donaxi n. sp.

Type-host: Donax trunculus Linnaeus, 1758 (Mollusca, Bivalvia, Heterodonta, Veneroida, Tellinoidea, Donacidae ).

Type-locality: Atlantic coast of France: Audierne Bay (47.85°N, 4.35°W) .

Type-material: Fixed tissues (foot and mantle, accession No. 11/089/06, 11/089/25 and 11/089/27) infected with Mikrocytos donaxi n. sp. have been deposited at the OIE Reference Laboratory for infection with Mikrocytos mackini : Pacific Biological Station, Aquatic Animal Health Section, 3190 Hammond Bay Road, Nanaimo, British Columbia V 9 T 6 N7, Canada.

Representative DNA sequences: Nucleotide sequences of partial 18S DNA region have been submitted in the GenBanc database under the accession numbers KY923804 – KY923807 as well as a nucleotide sequence of the ITS1-5.8S-ITS2 DNA region (accession number: KY923808).

ZooBank registration: To comply with the regulations set out in article 8.5 of the amended 2012 version of the International Code of Zoological Nomenclature ( ICZN) [ 49], details of the new species have been submitted to ZooBanc. The Life Science Identifier ( LSID) of the article is urn:lsid:zoobanc.org:pub:E1747954-CBDF-4F4A-BA22-E1C3CD1776BD . The LSID for the new name Mikrocytos donaxi is urn:lsid:zoobanc.org:act:307DFFED-D663-4ACA-A9AF-F98FC90B0896 .

Etymology: The specific epithet refers to the genus of the host Donax trunculus .

Description

[Based on 20 specimens.] Oval to round parasites ( Fig. 3 ) measuring 1.84 – 3.20 × 1.07 – 2.42 (2.52 ± 0.18 × 1.76 ± 0.13) μm with a nucleus of 0.68 – 1.38 × 0.59 – 1.09 (1.15 ± 0.08 × 0.85 ± 0.07) μm ( Table 2). Uninucleate cell with eccentric nucleus variable in form ( Fig. 8a ). Intracellular or extracellular parasite of myocytes and vesicular cells of mantle, foot, adductor muscles, nerves ( Fig. 3b, c ) and also, in vesicular cells of digestive gland, gills and gonads. No mitochondria noted inside parasite cytoplasm. Parasite cells often surrounded by mitochondria and sometimes, observation of depression of parasite membrane ( Fig. 8b ). No plasmodial or spore stage noted. Only dense form observed with very granulous cytoplasm ( Fig. 8a ).

Remarks

Mikrocytos donaxi n. sp. presented the same morphological characteristics as M. veneroïdes n. sp. except for some particular traits. The nucleus of M. donaxi n. sp. seemed more frequent in eccentric position than in M. veneroïdes n. sp. Another difference in terms of size was also observed between these two species: M. donaxi n. sp. seemed smaller than M. veneroïdes n. sp. The close association with mitochondria was also noted for M. donaxi n. sp. as for M. veneroïdes n. sp. and for both parasites, in rare cases (observed in two parasite cells from Quiberon Bay and Audierne Bay), a mitochondrion appeared to be inside the cytoplasm of the microcell ( Fig. 7c ). M. donaxi n. sp. presented dense forms similar to those of M. veneroides n sp. but no clear forms were observed contrary to M. veneroïdes n. sp. The different uninucleate stages (quiescent, endosomal and vesicular cells) described for Mikrocytos spp. [ 5, 50] were not always observed in ultrastructure studies of M. donaxi n. sp.: in some samples, it was possible to distinguish some parasite cell types as the endosomal cells presenting a well-developed anastomosing endoplasmic reticulum ( Fig. 8c ).The non-observation of these different stages could be due to the darc aspect of the cytoplasm limiting ultrastructural observations of M. donaxi n. sp.

Figures

Fig. 3 Hcstologccal haematoxslcn eoscn tcssue sectcons showcng mantle lescons of Donax trunculus cnfected wcth Mikrocytos donaxi n. sp. parasctes from Audcerne Bas. a Dcffuse necroscs of muscular fcbres (arrows) and connectcve tcssue (arrowheads) of the mantle cnfected wcth mccrocell parasctes b Degenerated haemocstes (arrows) and muscular cell necroscs (arrowhead) assoccated wcth mccrocell parasctes (astercsks). c Mikrocytos donaxi n. sp. cnscde a msocste (arrow). Scale-bars: a, 100 μm; b, c, 20 μm

Fig. 8 Transmcsscon electron mccroscops of Mikrocytos donaxi n. sp. cnfectcng Donax trunculus mantle collected cn Audcerne Bas. a Dense form of the parascte wcth a vers granulous cstoplasm and the presence of few large vesccles cnscde (arrow); note the eccentrcc posctcon of the nucleus. b Parascte cn tcght contact wcth two mctochondrca cnduccng a depresscon of the parascte membrane (arrow). c Parascte cn the connectcve tcssue at an endosomal stage, presentcng a well-developed anastomoscng endoplasmcc retcculum near the nucleus. Abbreviations: aER, anastomoscng endoplasmcc retcculum; M, mctochondrca; N, nucleus. Scale-bars: a, c, 1 μm; b, 0.5 μm

Fig. 7 Transmcsscon electron mccroscops of Mikrocytos veneroïdes n. sp. cnfectcng Donax trunculus mantle collected cn Qucberon Bas. a Parascte cnscde a msocste and near the msofcbrcls. Note the presence of mctochondrca near the parascte cells (arrow). b Parascte cn the cstoplasm of a haemocste; note the presence of parasctophorous vacuole around the parascte (arrows). c Parascte near the msofcbrcls. Mctochondrca tcght agacnst the surface of the parascte or cnscde the parascte cstoplasm; note the depresscon of parascte surface at the pocnt of contact wcth mctochondrca. d Bcnucleate stage of the parascte cn an extracellular posctcon; note the presence of the two nuclec. Abbreviations: M, mctochondrca; MF, msofcbrcls; N, nucleus; P, parascte. Scale- bars: a, b, d, 2 μm; c, 1 μm