Derogenes varicus (Müller, 1784) is widely reported as a trematode with exceptionally low host specificity and a wide, bipolar distribution. However, several recent studies have suggested that D. varicus represents a species complex and based on molecular evidence, four genetic lineages (labeled as “DV1–4”) have been designated within the D. varicus species complex. This possibility requires improved (ideally molecular) characterisation of specimens from the type-host (Salmo salar) and type-locality (off Denmark). During examination of trematode parasites of fish from Scandinavian and Arctic waters (Sweden and Norway), we found specimens of D. varicus in the stomach of Merlangius merlangus off the coast of Sweden, and in Gadus morhua off the coast of Sweden and Norway; we compared them to D. varicus from the type-host, the Atlantic salmon Salmo salar from Norway, to verify their conspecificity. Newly generated sequences (28S rDNA, ITS2 and cox1) of Scandinavian and Arctic specimens consistent with D. varicus all formed a single clade, DV1. 28S sequences of D. varicus from S. salar from Norway, i.e., close to the Danish type locality, clustered within the DV1 clade along with sequences of D. varicus from various hosts including Limanda limanda, G. morhua and Myoxocephalus scorpius from the White Sea and the Barents Sea (Russia), without any host-related structuring. We thus consider that the lineage DV1 represents D. varicus sensu stricto. Additionally, specimens from M. merlangus had a similar morphology and anatomy to those of D. varicus from L. limanda, G. morhua and M. scorpius from T. Odhner’s collection, supporting the presence of a single species in the DV1 lineage designated herein as D. varicus sensu stricto. We redescribe D. varicus sensu stricto, add new morphological characters and provide morphometric data. We infer that D. varicus types DV2–4 all relate to separate species. We also revise type-specimens of Derogenes minor Looss, 1901 from the A. Looss collection in the Swedish Museum of Natural History and provide redescriptions of it and of the type-species of the genus, Derogenes ruber Lühe, 1900. In light of their morphological distinctiveness relative to D. varicus sensu stricto, we reinstate D. parvus Szidat, 1950 and D. fuhrmanni Mola, 1912.
Axine belones Abildgaard, 1794 is a polyopisthocotylean monogenean, parasite of belonid fishes, and there are few accounts with morphological and morphometrical data. Here, we redescribe A. belones based on newly collected specimens from its type-host, the garfish Belone belone (Linnaeus, 1760) collected off Algeria, Western Mediterranean, a new locality for this species. Several anatomical and morphological features (genital apertures and clamps sclerites) are described and illustrated. We provide morpho-anatomical and morphometrical data, along with detailed illustrations of A. belones, and we discuss the host specificity of A. belones. Notes on hosts and localities of this species and other congeners are presented, and host specificity patterns of A. belones revealed stenoxenic specificity to Belonidae Bonaparte, 1835, whilst the genus Axine Abildgaard, 1794 seems to be restricted to fishes of the order Beloniformes. Our attempt to investigate morphometric variations between Mediterranean and oceanic specimens revealed that the two populations differed by the number of testes, body length, and clamp dimensions. However, the limited number of measured organs in the various accounts precluded any distinction between the populations. Molecular data for both Mediterranean and oceanic specimens are needed to determine the existence of cryptic species.
Cyclocotyla bellones Otto, 1823 (Monogenea, Diclidophoridae) is one of the few monogenean species reported as hyperparasitic: the worms dwell on cymothoid isopods, themselves parasites of the buccal cavity of fishes. We present here observations based on newly collected monogenean specimens from Ceratothoa parallela (Otto, 1828), an isopod parasite of Boops boops off Algeria and also investigated its diet to address whether Cy. bellones is indeed a hyperparasite, i.e., whether it feeds on the isopod. We also compared the body shape of various monogeneans belonging to the same family as Cy. bellones, the Diclidophoridae, including Choricotyle cf. chrysophryi Van Beneden & Hesse, 1863, collected from Pagellus acarne off Algeria. No morphological character of the anterior organs suggested any special adaptation in Cy. bellones to the perforation of the crustacean cuticle. The wall of the oesophagus and of the intestine of Cy. bellones was lined with a dark pigment similar to what is usually observed in haematophagous polyopisthocotyleans, and which is derived from ingested fish blood. We noticed that an anterior elongate stem exists only in diclidophorids dwelling on parasitic isopods and never in those attached to the gills. We hypothesize that the anterior stem of the body of Cy. bellones is an anatomical adaptation for the monogenean to feed on the fish while dwelling on the isopod. We thus consider that Cy. bellones is an epibiont of the parasitic crustacean, as it uses it merely as an attachment substrate, and is not a true hyperparasite
Capsalids are monopisthocotylean monogenean parasites found on the skin and gills of fish. Capsalines (subfamily Capsalinae) are large-sized capsalids, parasitic on highly prized gamefish, and species of Tristoma parasitise only the gills of swordfish (Xiphias gladius). We obtained specimens of Tristoma integrum Diesing, 1850 from swordfish collected off Algeria in the Mediterranean Sea. Here, we describe the specimens, including the key systematics characters of dorsolateral body sclerites. One specimen was used for a next generation sequencing analysis but a part of it, including the sclerites, was mounted on a permanent slide, drawn, and deposited in a curated collection. We characterised the complete mitogenome, the ribosomal cluster (including 18S and 28S) and additional genes such as Elongation factor 1 alpha (EF1α) and Histone 3. We also retrieved molecular information from the host tissue present in the gut of the monogenean and provide the sequence of the complete rRNA cluster of the host, X. gladius. The mitogenome of T. integrum is 13 968 bp in length and codes for 12 protein, 2 rRNA and 22 tRNA. Phylogenies of capsalids were generated from 28S sequences and concatenated mitochondrial protein-coding genes, respectively. In the 28S phylogeny, most subfamilies based on morphology were not found to be monophyletic, but the Capsalinae were monophyletic. In both phylogenies, the closest member to Tristoma spp. was a member of the Capsaloides. In an Appendix, we report the complex nomenclatural history of Tristoma Cuvier, 1817 and its species.
Purpose: Derogenes ruber Lühe, 1900, the type-species of the genus Derogenes Lühe, 1900, is a poorly known derogenid digenean. The original description of this species was not illustrated and aspects of the morphology of the parasite from the type-host remain scarce. Available records of this species were brief and/or lacked illustrations and were based on morphology alone. Additionally, molecular data for Derogenes spp. are warranted to untangle species complexes as they provide a better assessment of interspecifc genetic divergence.
Methods: Derogenes ruber is redescribed based on newly collected specimens from the gall bladder of its type-host Chelidonichthys lastoviza (Bonnaterre, 1788) collected in the Western Mediterranean of the Algerian coast during 2017–2019 and molecular data are provided using a partial fragment of the nuclear 28S ribosomal RNA gene (28S rRNA), the internal transcribed spacer 2 (ITS2) and a fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene.
Results: We herein provide a detailed illustrated redescription and morphometric data of D. ruber from its type-host C. lastoviza. We report a new geographical record (of Algeria) for it. Derogenes ruber is also genetically characterised for the frst time. Species/lineages of Derogenes were recovered in fve strongly supported reciprocally monophyletic clades: (i) D. ruber from C. lastoviza of Algeria; (ii) D. lacustris from Galaxias maculatus (Jenyns) of Argentina; (iii) Lineage “D. varicus DV1” (D. varicus sensu stricto) from fsh hosts in the White and Barents seas and the North Sea; (iv) Lineage “D. varicus DV2” from mollusc hosts in the White Sea; and (v) Lineage “D. varicus DV3” from Eumicrotremus fedorovi Mandrytsa. in the Pacifc Ocean. Hence, comparison of the newly generated sequences with other available data for Derogenes species supports the distinction of D. ruber confrming its taxonomic status and helping assess interspecifc variation. Comparison of D. ruber with the closely related species Derogenes latus revealed overlaps in morphometric data and the validity of the latter species is questioned. Conclusion The combination of morphological and molecular data provided for D. ruber provides a frm foundation for further investigations of Derogenes spp. Although we do describe herein material of D. ruber from the type-host, given that the occurrence of a single Derogenes species in various hosts has been challenged by molecular data, and both D. lacustris and D. varicus sensu stricto had been genetically proven to occur in various hosts, D. ruber and D. latus may be indeed synonymous. Additional sequencing efort on Derogenes spp. will strengthen systematic comparative studies and evolutionary relationships within the Derogenidae in general.
Incomplete original descriptions, the unavailability or poor conditions of specimens and the lack of detailed redescriptions have caused the validity of several species of the genus Encotyllabe Diesing, 1850 to be questioned. To date, seven of the recognized species were described upon one or two specimens, hindering study of intraspecific variations. This was made worse by considering few morphoanatomical differences sufficient to erect new species. Among Encotyllabe spp. occurring in Mediterranean waters, E. vallei was first described from the gilt-head bream Sparus aurata (Sparidae) off Italy. Although beautifully illustrated for a paper from that century, morphometric data for E. vallei from the type-host S. aurata remain unavailable. Previous records of E. vallei provided either morphometrical or molecular data, and its validity was questioned. We provide a redescription of E. vallei based on newly collected specimens from the S. aurata from the southwestern Mediterranean (off Algeria) using integrative taxonomy. Analysis of cox1 sequences of E. vallei from S. aurata, compared to sequences from other sparid hosts, mainly Pagellus bogaraveo, revealed a divergence not exceeding 2%, suggesting a stenoxenic specificity for this monogenean. Given that P. bogaraveo is the type-host for Encotyllabe pagelli, we were tempted to suggest a synonymy between E. vallei and E. pagelli. We refrained from doing so because E. pagelli was first described from the Atlantic coast off Brest, France. Morphological data for Encotyllabe from P. bogaraveo are warranted assessing the host specificity of E. vallei and whether there might be a species complex within individual sparid fish species.