Description of new types of sphaeractinomyxon actinospores (Myxozoa: Myxosporea) from marine tubificid oligochaetes, with a discussion on the validity of the tetraspora and the endocapsa as actinospore collective group names

Abstract

Ten new types of sphaeractinomyxon actinospores are morphologically and molecularly described from the coelomic cavity of two marine oligochaete hosts, Hrabě, 1967 and Tubificoides pseudogaster (Dahl, 1960), from Aveiro 2 estuary, Portugal. The smallest sphaeractinomyxon type measured 17 µm (length) × 19 µm (width) × 19 µm (apical diameter), whereas the largest type measured 61 µm × 76 µm × 80 µm. While considering the ten types of sphaeractinomyxon, it was found that the number of spores developing inside pansporocysts varied between one, two, four and eight. The total prevalence of infection was of 19% for the two host species, with a maximum recorded for spring and summer (25-26%). While considering each type of sphaeractinomyxon individually, it was found that the prevalence values ranged between 0.3 and 1.7%. All described sphaeractinomyxons were most similar to mugilids infecting Myxobolus species. Limnodriloides agnesThe validity of the tetraspora and endocapsa collective group names is discussed.

Characterisation of sphaeractinomyxon types (Cnidaria: Myxozoa) from marine and freshwater oligochaetes in a Portuguese estuary, with the demise of the endocapsa collective group

“…R e m a r k s : The SSU rDNA sequences obtained for this type in three infected host specimens were ~2,010 bp long. They were identical with the sequence available for Sphaeractinomyxon type 10 of Rangel et al (2016) from its original description in the coelomic cavity of the same host, T. pseudogaster, in the Aveiro estuary, Portugal. Significant morphometric variation was not recorded in relation to the original description of this type, nor to its report from T. insularis in the Alvor estuary, near the Algarve Atlantic coast (see Rangel et al 2016, Rocha et al 2019a.…”

“…In this study, actinosporean infection by members of the sphaeractinomyxon collective group was found in the coelomic cavity of both freshwater and marine oligochaetes inhabiting the Minho River estuary. Four new types are described here, whereas two others were identified as being Sphaeractinomyxon types 8 and 10 of Rangel et al (2016). These two latter types were originally described from specimens of Tubificoides pseudogaster collected from the Aveiro estuary (Portugal) (Rangel et al 2016), about 180 km south from our sampling location in the Minho River.…”

“…In the years that followed, Sphaeractinomyxon types 1 and 2 of Hallett et al (1997), Sphaeractinomyxon ersei Hallett, OʼDonoghue et Lester, 1998 and Sphaeractinomyxon leptocapsula Hallett, Erséus et Lester, 1999 were described from marine oligochaetes in Hong Kong and Australia (Hallett et al 1998, but only S. ersei had its SSU rRNA gene sequenced. More recently, 13 sphaeractinomyxon types were morphologically and molecularly described from marine oligochaetes in two Portuguese estuaries (Rangel et al 2016, Rocha et al 2019a. Overall, the implementation of molecular methodologies to the study of sphaeractinomyxon types has revealed a higher biodiversity than expected based on morphology-based criteria.…”

“…Overall, the implementation of molecular methodologies to the study of sphaeractinomyxon types has revealed a higher biodiversity than expected based on morphology-based criteria. In fact, Rangel et al (2016) showed that actinospore measurements overlap between different types of this collective group, so that the usage of molecular tools is indispensable for the description of new types. Phylogenetic analyses of the SSU rRNA gene further disclosed a possible involvement of the sphaeractinomyxon collective group in the life cycle of mugiliform-infecting myxobolids (Rocha et al 2019a), which remains to be proved by either molecular inference or experimental transmission studies.…”

“…In turn, endocapsa was erected to encompass actinospores that differed from sphaeractinomyxon only in the presence of valvular swellings that do not change when in contact with water . The validity of this collective group was questioned in recent studies (Rangel et al 2016, Rocha et al 2019a. Nonetheless, it remained valid and currently comprises four types: Endocapsa rosulata Hallett, Erséus et Lester, 1999 andEndocapsa stepheni Hallett, Erséus et Lester, 1999 from the marine oligochaete Heterodrilus cf.…”