Holocephalocotyle monstrosae n. gen. n. sp. (Monogenea, Monocotylidae) from the olfactory rosette of the rabbit fish, Chimaera monstrosa (Holocephali, Chimaeridae) in deep waters off Algeria

Proposal of Troglocephalinae n. subfam. (Monogenea: Monocotylidae) to accommodate existing and two new monocotylids from the gills of rhinopristiform shovelnose rays

Troglocephalinae n. subfam. is proposed for Spinuris Doran, 1953, Neoheterocotyle Hargis, 1955, Anoplocotyloides Young, 1967, Troglocephalus rhinobatidis Young, 1967 (previously incertae sedis), Nonacotyle pristis Ogawa, 1991, Mehracotyle insolita Neifar, Euzet & Ben Hassine, 2002, Scuticotyle cairae n. gen. et sp., and Brancheocotyle imbricata n. gen. et sp. All members of the proposed new subfamily are gill parasites of shovelnose rays of the order Rhinopristiformes. The subfamilies Heterocotylinae Chisholm, Wheeler & Beverley-Burton, 1995, and Dasybatotreminae Bychowsky, 1957, are amended to exclude Spinuris, Nonacotyle, Neoheterocotyle, and Anoplocotyloides and Mehracotyle, respectively. Heterocotylinae includes gill parasites of members of the orders Myliobatiformes and Torpediniformes. Dasybatotreminae includes parasites of the gills and pharyngeal cavity of members of the orders Myliobatiformes and Rajiformes. A revised phylogeny of the Monocotylidae Taschenberg, 1879 is presented and discussed, based on 28S rDNA sequences, including new sequences for Myliocotyle pteromylaei Neifer, Euzet & Ben Hassine, 1999, Heterocotyle tokoloshei Vaughan & Chisholm, 2010, Neoheterocotyle robii Vaughan & Chisholm, 2010, and the two newly proposed species and genera. Additional locality records are also provided for Monocotylidae from off South Africa.

"Something old, something new, something borrowed, and the oioxeny is true": description of Plectanocotyle jeanloujustinei n. sp. (Polyopisthocotylea, Plectanocotylidae) from the MNHN Helminthology collection with novel molecular and morphological data for P. gurnardi (Van Beneden & Hesse, 1863) (sensu stricto) from Sweden

Natural history museums worldwide house billions of apposite specimens, offering the potential for cost-free parasitological datasets. Herein, we provide novel morphological and molecular data (28S and cox1) for the polyopisthocotylean Plectanocotyle gurnardi sensu stricto from the type-host Eutrigla gurnardus from Sweden based on newly collected specimens from the Northeast Atlantic, and specimen from T. Odhner's collections at the Swedish Museum of Natural History (Stockholm, Sweden). The newly generated 28S sequences of P. gurnardi from E. gurnardus from the Northeast Atlantic were identical to those from the Western Mediterranean, and nested in a single clade, suggesting the presence of a single species. A 28S sequences of P. gurnardi sensu stricto from Sweden and those from the U.K. (type locality for P. caudata) were identical; we confirm that P. caudata and P. gurnardi are conspecific and formally synonymize them. A single 28S sequence of Plectanocotyle sp. from Chelidonichthys lastoviza off France differed from P. gurnardi from the Northeast Atlantic by 3-4 % and from P. gurnardi from France by 3%. Plectanocotyle sp. ex C. lastoviza off France is clearly not P. gurnardi, suggesting an oioxenic specificity of P. gurnardi to E gurnardus. Careful re-examination of Plectanocotyle cf. gurnardi from C. lastoviza from the Western Mediterranean from the Helminthology collection of Muséum national d'Histoire naturelle (Paris, France) revealed that it differs from all congeners by morphometry (size of clamps, of terminal lappet and its hamuli and uncinuli, and size of atrial spines). The cox1 divergences between P. cf. gurnardi and P. major, P. lastovizae, and P. gurnardi sensu stricto were 10-11 %, 10-11 % and 8 % respectively, falling within the interspecific variations range. Plectanocotyle from the Mediterranean is described as a new species, P. jeanloujustinei n. sp. We apprise nomenclature problems in Plectanocotyle and consider P. elliptica a species inquirenda.

Morphological and molecular characterization of Encotyllabe vallei Monticelli, 1907 (Monopisthocotylea, Monogenea) from the gilthead seabream Sparus aurata Linnaeus (Teleostei, Sparidae) from the southwestern Mediterranean and notes on host specificity of the genus Encotyllabe Diesing, 1850

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.

Truly a hyperparasite, or simply an epibiont on a parasite? The case of Cyclocotyla bellones (Monogenea, Diclidophoridae)

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.

PERUANOCOTYLE PELAGICA N. SP. (MONOGENEA: MONOCOTYLIDAE), PARASITE OF THE PACIFIC COWNOSE RAY RHINOPTERA STEINDACHNERI EVERMANN AND JENKINS, 1891 (BATOIDEA: RHINOPTERIDAE) FROM THE SOUTHERN MEXICAN PACIFIC OCEAN

Peruanocotyle pelagica n. sp. is described based on specimens collected from the wall of the pharyngeal cavity of the Pacific cownose ray Rhinoptera steindachneri offshore Oaxaca and Guerrero, Mexico. The new species is distinguished from Peruanocotyle chisholmae by its anchors, which include a slender guard that curves towards the tip of the blade and which lack an accessory piece, morphological differences of the seminal vesicle, the lack of a male copulatory organ accessory piece and a greater number of spines, and an unsclerotized vagina. Molecular data of Peruanocotyle pelagica were generated to place the phylogenetic position of the genus within Monocotylidae.

ON THAUMATOCOTYLE SCOTT, 1904 (MONOGENOIDEA: MONOCOTYLIDAE) AND THAUMATOCOTYLE PSEUDODASYBATIS HARGIS, 1955 WITH DESCRIPTIONS OF ITS PUTATIVE SIBLING SPECIES THAUMATOCOTYLE ADELPHA N. SP. AND THAUMATOCOTYLE CASIGNETA N. SP. PARASITIZING THE OLFACTORY ORGANS OF PELAGIC EAGLE RAYS (MYLIOBATIFORMES: AETOBATIDAE) IN THE PACIFIC OCEAN

An emended diagnosis of ThaumatocotyleScott, 1904 (Monogenoidea: Monocotylidae) and a list of its species are provided. Merizocotyle urolophiChisholm and Whittington, 1999, Merizocotyle macrostrobusChisholm and Whittington, 2012, Merizocotyle papillaeChisholm and Whittington, 2012, and Merizocotyle rhadinopeosChisholm and Whittington, 2012 are transferred to Thaumatocotyle as new combinations. Thaumatocotyle pseudodasybatisHargis, 1955 is redescribed and is currently restricted to Thaumatocotyle-like helminths parasitizing the olfactory organs of the white-spotted eagle ray Aetobatus narinari (Euphrasen, 1790) (Myliobatiformes: Aetobatidae) in the western Atlantic Ocean. Two new species are described that infect the olfactory organs of pelagic eagle rays: Thaumatocotyle adelpha n. sp. from the ocellated eagle ray Aetobatus ocellatus (Kuhl, 1823) in the central and western Pacific Ocean and Thaumatocotyle casigneta n. sp. from the Pacific eagle ray Aetobatus laticeps Gill, 1865 from the eastern Pacific Ocean off the western coast of Mexico. Based on comparative morphology, T. pseudodasybatis, T. adelpha, and T. casigneta appear to form a subgroup of species that developed secondarily within the genus.

REDESCRIPTION OF CATHARIOTREMA SELACHII (MACCALLUM, 1916) JOHNSTON AND TIEGS, 1922 (MONOGENOIDEA: MONOCOTYLIDAE), EMENDATION OF MONOTYPIC CATHARIOTREMA JOHNSTON AND TIEGS, 1922, AND PROPOSAL OF CATHARIOTREMATINAE N. SUBFAM. BASED ON MORPHOLOGICAL AND NUCLEOTIDE EVIDENCE

We herein redescribe the enigmatic Cathariotrema selachii (MacCallum, 1916) Johnston and Tiegs, 1922 based on the holotype, paratypes, and newly collected specimens infecting the olfactory organ of 5 shark species from the Gulf of Mexico (all new host records): scalloped hammerhead shark, Sphyrna lewini (Griffith and Smith, 1834) (Carcharhiniformes: Sphyrnidae); great hammerhead shark, Sphyrna mokarran (Rüppell, 1837); blacktip shark, Carcharhinus limbatus (Müller and Henle, 1839) (Carcharhiniformes: Carcharhinidae); spinner shark, Carcharhinus brevipinna (Müller and Henle, 1839); and Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson, 1836) (Carcharhinidae). These specimens were morphologically indistinguishable from each other and from MacCallum's holotype and paratypes. Those sequenced had identical first internal transcribed spacer (ITS1) and large subunit ribosomal DNA (28S) nucleotide sequences. As such, C. selachii infects sharks of 2 orders (Carcharhiniformes, Lamniformes) and 3 families (Carcharhinidae, Sphyrnidae, Lamnidae) in the Northwestern Atlantic Ocean (type locality) and Gulf of Mexico (new records herein). This report is the first of new specimens of C. selachii in the Atlantic Ocean Basin in 95 yr and corrects long-standing error cascades and ambiguities concerning the morphology and systematic placement of C. selachii. Considering morphology and nucleotide-based phylogenetic evidence (28S, Bayesian analysis), we herein emend monotypic CathariotremaJohnston and Tiegs, 1922 and propose Cathariotrematinae Bullard n. subfam. for it and 4 other genera (all formerly assigned to Merizocotylinae Johnston and Tiegs, 1922). These genera comprise species infecting only the nose of sharks (monotypic Cathariotrema, SqualotremaKearn and Green, 1983 and SeptitremaKheddam, Chisholm, and Tazerouti, 2020 plus 3 species of TriloculotremaKearn, 1993) and nose of a chimaera (monotypic HolocephalocotyleDerouiche, Neifar, Gey, Justine, and Tazerouti, 2019). Cathariotrematinae differs from Merizocotylinae by having a 3-part attachment organ and by lacking open loculi that symmetrically encircle a cluster of >2 loculi in the center of the haptor. Monophyletic Cathariotrematinae (with sequences representing species of Cathariotrema, Triloculotrema, and Holocephalocotyle only) was sister to monophyletic Merizocotylinae, which together were sister to monophyletic Calicotylinae Monticelli, 1903. These subfamilies comprise a monophyletic group of monocotylids that have a double vagina and infect extrabranchial, enclosed niches (urogenital system, body cavity, olfactory chamber/nose) on their shark, ray, and chimaera hosts (all other monocotylids have a single vagina and infect the gill or body surfaces of rays only). Monocotylinae Taschenberg, 1879 and Decacotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 were recovered as monophyletic. Heterocotylinae Chisholm, Wheeler, and Beverley-Burton, 1995 remained paraphyletic. We accept ParacalicotyleSzidat, 1970.

Triple barcoding for a hyperparasite, its parasitic host, and the host itself: a study of Cyclocotyla bellones (Monogenea) on Ceratothoa parallela (Isopoda) on Boops boops (Teleostei)

Cyclocotyla bellones Otto, 1823 (Diclidophoridae) is a monogenean characterised by an exceptional way of life. It is a hyperparasite that attaches itself to the dorsal face of isopods, themselves parasites in the buccal cavity of fishes. In this study, Cy. bellones was found on Ceratothoa parallela (Otto, 1828), a cymothoid isopod parasite of the sparid fish Boops boops off Algeria in the Mediterranean Sea. We provide, for the first time, molecular barcoding information of a hyperparasitic monogenean, the parasitic crustacean host, and the fish host, with COI sequences.

Redescription of Flexophora ophidii Prost & Euzet, 1962 (Monogenea: Diclidophoridae) from Ophidion barbatum (Ophidiidae) off the Algerian coast, Mediterranean Sea

The diclidophorid Flexophora ophidii Prost & Euzet, 1962, the type- and only species of the genus Flexophora Prost & Euzet, 1962, has never been redescribed neither reported since its original description. The latest lacked a diagnosis of the genus that remains unavailable to date. Flexophora ophidii is redescribed and illustrated based on examination of new material from the type-host Ophidion barbatum L. (Ophidiiformes: Ophidiidae) collected off the Algerian coast (new geographical record), southern Mediterranean. A diagnosis of the genus is provided.

No vagina, one vagina, or multiple vaginae? An integrative study of Pseudaxine trachuri (Monogenea, Gastrocotylidae) leads to a better understanding of the systematics of Pseudaxine and related genera

The presence/absence and number of vaginae is a major characteristic for the systematics of the Monogenea. Three gastrocotylid genera share similar morphology and anatomy but are distinguished by this character: Pseudaxine Parona & Perugia, 1890 has no vagina, Allogastrocotyle Nasir & Fuentes Zambrano, 1983 has two vaginae, and Pseudaxinoides Lebedev, 1968 has multiple vaginae. In the course of a study of Pseudaxine trachuri Parona & Perugia 1890, we found specimens with structures resembling "multiple vaginae"; we compared them with specimens without vaginae in terms of both morphology and molecular characterisitics (COI barcode), and found that they belonged to the same species. We also investigated the male copulatory organ (MCO) of this species, the accuracy of the original description of which is known to be a matter of debate. We found that the genital atrium is armed with 12 hooks arranged as a single circle and a central hollow stylet which is probably involved in traumatic insemination. We redescribed Pseudaxine trachuri based on newly collected specimens from off the coast of Algeria and Museum specimens from off France. Specimens from the type-host, Trachurus trachurus, were found to be similar, for both molecular sequences and morphology, to those found on Boops boops. We can therefore confirm, for the first time with molecular evidence, that B. boops is a host of this parasite. We consider that Pseudaxinoides was erected on the basis of an erroneous interpretation of structures which are not vaginae and, consequently, propose the transfer of most of its species to Pseudaxine, as P. australis (Lebedev, 1968) n. comb., P. bychowskyi (Lebedev, 1977) n. comb., P. caballeroi (Lebedev, 1977) n. comb., P. cariacoensis (Nasir & Fuentes-Zambrano, 1983) n. comb., and P. vietnamensis (Lebedev, Parukhin & Roitman, 1970) n. comb. We also propose Allogastrocotyle dillonhargisorum nom. nov. for Pseudaxine bivaginalis Dillon & Hargis, 1965 to avoid a secondary homonymy.

Redescription and molecular characterisation of Allogastrocotyle bivaginalis Nasir & Fuentes Zambrano, 1983 (Monogenea: Gastrocotylidae) from Trachurus picturatus (Bowdich) (Perciformes: Carangidae) off the Algerian coast, Mediterranean Sea

Allogastrocotyle bivaginalis Nasir & Fuentes Zambrano, 1983, the sole species of Allogastrocotyle Nasir & Fuentes Zambrano, 1983, was described from Trachurus lathami Nichols off Venezuela and never recorded since. We found monogeneans on Trachurus picturatus (Bowdich) (Carangidae) off the Algerian coast, Mediterranean Sea, which had the characteristics of the genus, including, especially, paired vaginae. We compared them to the single available specimen of A. bivaginalis, the holotype. Unfortunately, this holotype does not show clamp structure and soft internal anatomy. Our specimens were similar to A. bivaginalis in most characteristics such as body shape, vaginal openings, and number of testes, clamps and hooks in genital atrium. We detected minor differences in clamp structure but could not ascertain if these were the result of incomplete observations in the original description of real morphological differences. The host fish of our specimens were barcoded (cox1) confirming their specific identity. A phylogenetic analysis of cox1 sequences showed that our sequences of A. bivaginalis were distinct from those of Pseudaxine trachuri Parona & Perugia, 1889 (distance > 15%) and of several other gastrocotylids. Finally, we could not distinguish our Mediterranean specimens from A. bivaginalis, neither on the base of morphology (because the original description is incomplete) nor on molecules (because molecular information is lacking on A. bivaginalis from Venezuela) and ascribe them to A. bivaginalis. However, hosts are different, and localities are widely separated, so it is likely that future study will show that the species from the Mediterranean is a distinct, new, species.