First Record of a Polystome from Alligator Snapping Turtle, Macrochelys temminckii (Cryptodira: Chelydridae) or Mississippi; with Comments on "Neopolystoma orbiculare (Stunkard, 1916)" and Its Junior Subjective Synonyms

Classification of pleurodire polystomes (Platyhelminthes, Monogenea, Polystomatidae) revisited with the description of two new genera from the Australian and Neotropical Realms

Polystomatids are platyhelminth parasites that infect mostly amphibian and chelonian hosts. Polystomatid of testudines were, for more than seven decades, classified in the three genera – Neopolystoma Price, 1939, Polystomoides Ward, 1917 and Polystomoidella Price, 1939. The genus delimitation was primarily based on the absence of hamuli in Neopolystoma, the presence of one pair of hamuli in Polystomoidella, and two pairs in Polystomoides. From 2016 to 2020, five new genera were erected - namely Uropolystomoides Tinsley and Tinsley, 2016, Uteropolystomoides Tinsley, 2017, Apaloneotrema Du Preez and Verneau, 2020, Aussietrema Du Preez and Verneau, 2020 and Fornixtrema Du Preez and Verneau, 2020. The generic diagnosis was based not only on the size and shape of morphological characters such as hamulus 1, uterus and eggs, but also on the site of infestation (i.e. urinary bladder, oral cavity or conjunctival sacs). Despite large advancements in polystome classification over the last decade, Neopolystoma was still polyphyletic with some species nested within Polystomoides and others being closely related to the Australian Aussietrema. Regarding the distribution of freshwater turtles of the two suborders Pleurodira (Southern continents) and Cryptodira (distributed worldwide except in Australia), one may wonder whether Australian chelonian polystomes of the genus Neopolystoma may have diverged from species infecting other pleurodires of South America. In the present study based on the analysis of several species selected among all genera, we reveal striking morphological differences within polystomes infecting pleurodiran turtles, which herein led to the proposal of two new chelonian polystome genera, Pleurodirotrema n. g. and Manotrema n. g. Pleurodirotrema n. g. is characterized by the absence of hamuli, presence of latero-ventral vaginae and includes species that infect either the oral region or the urinary bladder of Australian hosts of the Pleurodira. Manotrema n. g. is characterized by the presence of small hamuli, latero-ventral vaginae, deep incisions between suckers, a low genital spine number (<10) and includes species that infect the oral region of South American Pleurodira.

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Two new polystome genera are described from chelonian hosts.

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They differ from all other chelonian polystomes in that they only infect pleurodire turtles from the Australian and Neotropical Realms.

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Describing these two genera resolves a polyphyletic clade as pointed out by Heritier and others.

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Solid morphological characters are supported by molecular evidence for Pleurodirotrema.

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Haptor and suckers for Manotrema are unique among chelonian polystomes.

Resurrection and emendation of Pseudoparamacroderoides Gupta & Agrawal, 1968 (Digenea: Macroderoididae), description of a new species from Vietnam, and comments on the systematics of macroderoidid genera

We herein resurrect and emend Pseudoparamacroderoides Gupta & Agrawal, 1968 (Digenea: Macroderoididae) and describe a new species, Pseudoparamacroderoides dongthapensis n. sp., from adult specimens infecting the intestine of a riverine catfish, Mystus mysticetus Roberts, (Siluriformes: Bagridae) in the Mekong River, Vietnam. Pseudoparamacroderoides (Pseudoparamacroderoides seenghali Gupta & Agrawal, 1968 [type species]; Pseudoparamacroderoides vittati Kakaji, 1969 [= Ps. vittatusi]; Pseudoparamacroderoides raychaudhurii Agarwal & Kumar, 1983; and Pseudoparamacroderoides keni Agarwal & Agarwal, 1984) differs from other macroderoidid genera by having the combination of a subspherical oral sucker that lacks distinctly-enlarged circumoral spines; caeca that extend posteriad beyond the testes without forming a cyclocoel; testes that are approximately ≤1/3 maximum body width in diameter; a cirrus sac that is claviform, slightly dorsal to and predominantly lateral to the ventral sucker (cirrus sac partially dorsolateral to dextral or sinistral margin of ventral sucker); symmetrical vitelline fields that extend posteriad to the middle of the post-testicular space (not restricted to the inter-gonadal space) and that remain separate (not confluent) anteriorly and posteriorly; and an excretory vesicle that is I-shaped (with or without anterior swelling) and wholly post-ovarian, inter-testicular, or median to the posterior testis. Pseudoparamacroderoides dongthapensis n. sp. differs from its congeners by having an elongate hindbody (>2× forebody length) and an excretory vesicle that is approximately half as long as the body and that extends anteriad beyond the anterior testis. This is the first record of a species of Pseudoparamacroderoides from beyond the Indian sub-continent, from M. mysticetus, and from the Mekong River or from Vietnam. A diagnostic key to macroderoidid genera and a key to Pseudoparamacroderoides spp. are provided.

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.