Luís F. Rangel

Morphology, Molecular Data, and Development of Zschokkella mugilis (Myxosporea, Bivalvulida) in a Polychaete Alternate Host, Nereis diversicolor

Abstract The morphology of Zschokkella mugilis Sitjà-Bobadilla and Alvarez-Pellitero, 1993 (Myxosporea, Bivalvulida) in Nereis diversicolor O. F. Müller, 1776 is described for the first time. The molecular data show that the actinospore has 100% similarity to the myxospore of Z. mugilis. Fully mature actinospores are tri-radiate, the spore body has a small process, and the sporoplasm has 2 inner daughter cells. In the polychaete, the spores of the parasite develop in groups of 8 inside pansporocysts. The schizogony phase takes place in the intestinal epithelium, while gametogony and sporogony occur in the coelom of the polychaete. Observations indicate that mature spores are released only during the polychaete reproductive season. Infection was detected only in the winter and spring. In the Aveiro estuary (Portugal), the overall prevalence of infection of the polychaete was 0.5%.

A new actinospore type Unicapsulactinomyxon (Myxozoa), infecting the marine polychaete, Diopatra neapolitana (Polychaeta: Onuphidae) in the Aveiro Estuary (Portugal)

This work reports a new type of actinospore, Unicapsulactinomyxon, which exhibits a unique morphological characteristic in that it has a single and large polar capsule (9·3×4·1 μm) (which possesses a longitudinally-folded polar filament) instead of the 3 polar capsules previously described for actinosporeans. The spore has a binucleated sporoplasm and 3 valves, each of which forms a long process. The spore has a total length of 241·3 μm. This parasite develops in groups of 8 inside pansporocysts in the coelomic cavity of the polychaete host. Molecular investigations on the SSU rDNA show that the new actinospore type is most closely related to Enteromyxum species (81-84% similarity). A survey of actinospore infections of the marine polychaete Diopatra neapolitana in 2007 and 2009, in the Aveiro Estuary (Portugal), showed an annual prevalence of 1·0% and 0·3%, respectively.

Ultrastructure and phylogeny of Ceratomyxa auratae n. sp. (Myxosporea: Ceratomyxidae), a parasite infecting the gilthead seabream Sparus aurata (Teleostei: Sparidae).

A new myxosporean parasite is described from the gall bladder of the gilthead seabream Sparus aurata in a Southern Portuguese fish farm, with basis on light and transmission electron microscopy, as well as in molecular procedures. In the bile, young and mature mono- to disporic plasmodia were elliptical and presented smooth surface membranes. Crescent-shaped myxospores measured 6.7±0.7 (5.3-7.6) μm in length and 27.0±3.0 (19.7-31.2) μm in thickness. The myxospore wall was constituted by two symmetrical valves united along a slightly curved suture line, each presenting a lateral projection with a rounded end. Two equal-sized subspherical polar capsules, measuring 3.6±0.2 (2.9-3.8) μm in length and 3.5±0.3 (2.9-3.8) μm in width, were located at the same level, each displaying a polar filament coiled in 5 turns. Molecular analysis of the SSU rRNA gene confirmed the parasite as a new member of the genus Ceratomyxa, making this the fourth report of Ceratomyxa from the gall bladder of S. aurata in the Iberian Peninsula. This reinforces the assumption that species richness of ceratomyxids in South European sparids is high, but the phylogenetic analysis performed disagrees with the existence of a common ancestor for Ceratomyxa species infecting sparid hosts, as well as their clustering according to geographical location. The main Ceratomyxa clade is not monophyletic due to the inclusion of Palliatus indecorus and Pseudoalatospora kovalevae; a situation that will probably be resolved by the taxonomic revision of these genera.

Ortholinea auratae n. sp. (Myxozoa, Ortholineidae) infecting the urinary bladder of the gilthead seabream Sparus aurata (Teleostei, Sparidae), in a Portuguese fish farm

A new myxosporean species, Ortholinea auratae n. sp., is described from the gilthead seabream, Sparus aurata Linnaeus, 1758 (Teleostei, Sparidae) from a fish farm in Algarve, Portugal. Plasmodia and spores were found in the urinary bladder and, less frequently, in the posterior kidney. Plasmodia were polymorphic, presenting an irregular cellular membrane due to the presence of several peripheral projections, which in turn were covered by a glycocalyx-like sheet. Mature spores were subspherical in valvular view and ellipsoidal in sutural view, measuring 9.0 ± 0.3 (8.2–10.1) μm in length, 8.3 ± 0.4 (7.5–9.1) μm in width, and 7.2 ± 0.5 (6.3–8.4) μm in thickness. The two valves comprising the spores displayed an intricate pattern of surface ridges and were also enveloped by a glycocalyx-like sheet. Two subspherical polar capsules, 3.2 ± 0.1 (2.9–3.6) μm long and 2.7 ± 0.1 (2.4–2.9) μm wide, were located at the anterior pole and displayed divergent orientation. The polar filament coiled in three to four turns. The comprehensive analysis of the parasite’s ultrastructural observations and molecular data for the small subunit (SSU) ribosomal DNA (rDNA) gene identify O. auratae n. sp. as a new species, clustering together with other myxosporeans infecting the excretory system to form a subclade of the main freshwater clade.

Ultrastructural Aspects of Ellipsomyxa mugilis (Myxozoa: Ceratomyxidae) Spores and Developmental Stages In Nereis diversicolor (Polychaeta: Nereidae)

Abstract: The ultrastructure of the spores and developmental stages of Ellipsomyxa mugilis in Nereis diversicolor were studied by transmission electron microscopy. The ultrastructure features and the developmental stages show many similarities with the general pattern described for other actinospores. However, several new features are definitely worth noting. For example, tetranucleated cells precede the formation of the initial pansporocyst, which preserves the 2 original enveloping cells until the end of sporogony. In the initial stages of sporogony, the future sporoplasm cell acquires the first secondary cell by an engulfment process. In the final stage of sporogony, spores are formed by a sporoplasm with 2 secondary cells and 1 somatic nucleus, and the polar capsule has a polar filament with a helicoidal arrangement possessing 7–8 coils.

Morphological description and phylogeny of Ceratomyxa scorpaeni n. sp. (Myxosporea: Ceratomyxidae) infecting the gallbladder of Scorpaena porcus (L.) (Scorpaeniformes: Scorpaenidae) from the bay of Bizerte in Tunisia

A new marine myxosporean species Ceratomyxa scorpaeni n. sp. is described using morphological characteristics and small subunit ribosomal DNA (rDNA) sequence data. The parasite was found infecting the gallbladder of Scorpaena porcus Linnaeus, 1758 collected from the Bay of Bizerte. Mature plasmodia were disporous free floating in the bile. Spores were transversely elongated and crescent-shaped with unequal shell valves and measured 7.6 ± 0.2 (7.2–8.0) μm in length and 32.8 ± 0.3 (21.6–44.0) μm in thickness. Two sub-spherical polar capsules equal in size, situated at the same level and measured 3.0 ± 0.2 (3.0–3.2) μm in length and 2.4 ± 0.3 (2.3–3.3) μm in width. The infection with C. scorpaeni n. sp. was prevalent throughout the year with a maximum prevalence of infection during spring and summer. Molecular analysis of the SSU rRNA gene confirmed the parasite as a new member of the genus Ceratomyxa and showed close relationship with the species of Ceratomyxa infecting the gallbladders of Sparidae from the Mediterranean Sea. This is the first report of Ceratomyxa species from the gallbladder of S. porcus in Tunisian coastal waters.

Tetractinomyxon stages genetically consistent with Sphaerospora dicentrarchi (Myxozoa: Sphaerosporidae) found in Capitella sp. (Polychaeta: Capitellidae) suggest potential role of marine polychaetes in parasite's life cycle.

Known life cycles of myxosporean parasites have two hosts, but very few life cycles have been disclosed, especially in the marine environment. Sphaerospora dicentrarchi Sitjà-Bobadilla and Álvarez-Pellitero, 1992 is a systemic parasite from the European seabass, Dicentrarchus labrax (Linnaeus, 1758), a highly valuable commercial fish. It affects its health, leading to aquaculture production losses. During 2013 and 2014, an actinospore survey was conducted in a total of 5942 annelids collected from a fish farm in Algarve and from the Aveiro Estuary, in Portugal. A new tetractinomyxon actinospore was found in a capitellid polychaete, belonging to the genera Capitella collected at the fish farm. The tetractinomyxons were pyriform measuring 11·1 ± 0·7 µm in length and 7·2 ± 0·4 µm in width, and presented three rounded polar capsules measuring 2·4 ± 0·3 µm in diameter. The molecular analysis of the 18S rRNA gene sequences from the tetractinomyxons revealed a similarity of 100% with the DNA sequences deposited in the GenBank from S. dicentrarchi myxospores collected from the European seabass and the spotted seabass in the same fish farm and 99·9% similarity with the DNA sequence obtained from the myxospores found infecting the European seabass in the Aveiro Estuary. Therefore, the new tetractinomyxons are inferred to represent the actinospore phase of the S. dicentrarchi life cycle.

Syndesmis aethopharynx Westervelt & Kozloff, 1990 (Rhabdocoela: Umagillidae): a revisitation supported by scanning electron microscopy and molecular analyses

Species of Syndesmis Francois, 1886 are rhabdocoel platyhelminths typically found in echinoids. Our knowledge of this group is based on old and insufficient studies, generally representing light microscopy-based species descriptions. Syndesmis aethopharynx Westervelt & Kozloff, 1990 is an understudied endosymbiont of Paracentrotus lividus (Lamarck), which is likely to have been confused with the type-species, i.e. Syndesmis echinorum François, 1886, in the literature. In this work, S. aethopharynx is revisited based on new data on surface morphology and phylogeny and basic ecological data are provided. Scanning electron microscopy analysis revealed that the whole ventral region of the worm is equipped with cilia, which supports the assumption that the unciliated epidermal area reported for some species of umagillids, likewise endosymbiotic in echinoderms, is an apomorphy. Following the results of the molecular phylogenetic analysis, species of Syndesmis are closely-related to symbionts of other echinoderms, i.e. holothurians, and like them, may have evolved from some free-living or symbiotic Provorticidae ancestor. Syndesmis spp. may stand for a key group in studying the evolution of feeding strategies in rhabdocoels, as their phylogenetic position is between intestinal and coelomic symbionts, and since both the digestive tube and perivisceral fluid were recorded as sites of infection. The infection levels were low, likely reflecting the aggregated distribution of the host and the fragile nature of the symbiont.

Synopsis of the species of the genus Myxobilatus Davis, 1944 (Myxozoa: Myxosporea: Myxobilatidae)

A synopsis of the species of Myxobilatus Davis, 1944 (Myxozoa: Myxosporea: Myxobilatidae) is presented. Thirty-nine nominal species are included. The major characteristics and an illustration are given for each species based on the original records.

Syndesmis François, 1886 (Rhabdocoela: Umagillidae): a revisitation, with a synopsis and an identification key to species, and new molecular evidence for ascertaining the phylogeny of the group

Syndesmis François, 1886 is a genus of umagillid turbellarians comprising species which are typically endosymbionts of echinoids, i.e. sea urchins. This group is likely key in addressing the issue of transition between a free-living and a parasitic mode of life in the Platyhelminthes. Accordingly, its phylogeny should be considered for detailed analysis, namely by addressing molecular evidence for its different species. At the present time, a revisitation of Syndesmis is required and fully justified by the following lines of argument: (i) the body of knowledge on Syndesmis is large, but the information is scattered through many different works in the literature; (ii) for about 60 years, it was a common practice to assign the umagillids isolated from sea urchins as a single species, i.e. the type-species, Syndesmis echinorum François, 1886, which was later split into several species on morphological grounds; and (iii) the type-species - for which no molecular information is available - was redescribed and new species were described in recent years but the generic diagnosis of Syndesmis was not emended accordingly. The present state of art additionally justifies the necessity of (i) an updated synopsis of species and (ii) an identification key to the 26 species described from different hosts and geographical locations. All these aspects define the aims of the present study. It is proposed that S. antillarum is attributed to Stunkard & Corliss (1951) and not to Powers (1936).