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Diseases of Aquatic Organisms

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DAO 135:175-191 (2019)  -  DOI:

New actinosporean description prompts union of the raabeia and echinactinomyxon collective groups (Cnidaria, Myxozoa)

Sónia Rocha1,2,*, Ângela Alves2, Pedro Fernandes2, Carlos Antunes1,3, Carlos Azevedo1,2, Graça Casal4

1Laboratory of Animal Pathology, Interdisciplinary Centre of Marine and Environmental Research (CIIMAR), University of Porto, Terminal de Cruzeiros de Leixões, Av. General Norton de Matos s/n, 4450-208 Matosinhos, Portugal
2Laboratory of Cell Biology, Institute of Biomedical Sciences Abel Salazar (ICBAS), University of Porto, Rua Jorge Viterbo Ferreira no. 228, 4050-313 Porto, Portugal
3Aquamuseu do Rio Minho, Parque do Castelinho, 4920-290 Vila Nova de Cerveira, Portugal
4University Institute of Health Sciences & Institute of Research and Advanced Training in Health Sciences and Technologies, CESPU, Rua Central da Gandra no. 1317, 4585-116 Gandra, Portugal
*Corresponding author:

ABSTRACT: We describe, morphologically and molecularly, a new actinosporean from the intestinal epithelium of the freshwater oligochaete Ilyodrilus templetoni in the upper estuary of the River Minho, Northern Portugal. Mature actinospores resembled both echinactinomyxon and raabeia types, emphasizing the previously known lack of a clear boundary between these 2 collective groups. Historically, raabeia and echinactinomyxon types have been differentiated solely based on the shape of the valvular processes being curved or straight, respectively. Our observations, however, show that this morphological character is too variable for distinguishing between these 2 collective groups, since the actinospores of the raabeia described here displayed valvular processes that could either be straight, downward or upward curved. Several similar cases can be found in the available literature. Considering this overlap in actinospore morphology, we propose that echinactinomyxon be deemed invalid and its types be included in raabeia, as the latter constitutes the older of the 2 groups. Known echinactinomyxon types, however, should not be renamed as raabeia, as this would create unnecessary confusion. Accordingly, a more comprehensive definition of the raabeia collective group is provided. Phylogenetic analyses revealed polyphyletic clustering of raabeia/echinactinomyxon types among members of the myxosporean suborders Variisporina and Platysporina, reiterating the lack of agreement between actinosporean morphotypes and myxosporean genera. The new type described here specifically clusters within the Paramyxidium clade, alongside other SSU rDNA sequences of raabeia, echinactinomyxon, aurantiactinomyxon and synactinomyxon. Considering that most Paramyxidium spp. parasitize Anguilla anguilla (Linnaeus, 1758), future myxozoan surveys in the River Minho should include this species.

KEY WORDS: Myxosporea · Actinospore · Freshwater oligochaete · Ilyodrilus templetoni · SSU rDNA gene · Transmission electron microscopy · Portugal · River Minho

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Cite this article as: Rocha S, Alves  Fernandes P, Antunes C, Azevedo C, Casal G (2019) New actinosporean description prompts union of the raabeia and echinactinomyxon collective groups (Cnidaria, Myxozoa). Dis Aquat Org 135:175-191.

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