Psettarium anthicum sp. n. (Digenea: Sanguinicolidae) from the heart of cobia Rachycentron canadum (Rachycentridae) in the northern Gulf of Mexico

Morphological features of the testis of freshwater blood flukes of the genus Sanguinicola Plehn, 1905, with consideration of the testicular patterns in the Aporocotylidae

This is the first detailed study assessing the morphological features of the testis and testicular sperm of members of the freshwater blood flukes Sanguinicola sp. from Leuciscus idus (Cyprinidae) and for S. volgensis from Pelecus cultratus (Cyprinidae), and the marine blood fluke Aporocotyle simplex from Hippoglossoides platessoides (Pleuronectidae). The present study reports a unique feature in the distribution of germinal cellular components in freshwater Sanguinicola sp., showing the presence of the individual spermatocytes or their clusters in the testicular lobes, and the gathering of spermatid rosettes and spermatozoa within middle testicular lumen, which extends along the entire length of the testis. In contrast, each testis of marine A. simplex contains the usual mixed distribution of germ cells at various stages of development. The first TEM data on spermatozoon character of studied species has shown, unusual for digenean sperm structure, the absence of cortical microtubules in sperm principal region. Moreover, a variation in axoneme patterns is revealed in the studied aporocotylids, belonging to the different aporocotylid lineages a 9 + 0 axonemal type observed for freshwater teleost-infective species, Sanguinicola sp. and S. volgensis, and a 9 + '1' axonemal type revealed in spermatozoa of marine teleost-infective species A. simplex. The results discussed with the published data on the digenean sperm structure and the testicular patterns in the Aporocotylidae likely represent additional characteristics supporting the divergent evolutionary lineages of freshwater and marine aporocotylids. We anticipate future morphological studies of the sperm structure in aporocotylids of three lineages for an understanding of their phylogenetic relationships.

Molecular phylogenetic analysis of the problematic genus Cardicola (Digenea: Aporocotylidae) indicates massive polyphyly, dramatic morphological radiation and host-switching

Novel multi-locus sequence data were used to assess the molecular phylogenetic relationships of fish blood flukes showing similarity to the genus Cardicola Short, 1953 (Trematoda: Aporocotylidae). Analyses of three ribosomal (ITS2, 28S & 18S) subregions and one mitochondrial (cox1) DNA subregion shows that the hitherto-monophyletic clade formed by species of Cardicola Short, 1953 also includes species of three other genera - Braya Nolan & Cribb, 2006, Elaphrobates Bullard & Overstreet, 2003 and Rhaphidotrema Yong & Cribb, 2011 - as well as a new, morphologically distinct species discovered from the heart of the yellowfin tripodfish, Tripodichthys angustifrons (Tetraodontiformes: Triacanthidae). In the context of conflicting morphological, molecular and ecological data, we argue that the recognition of seven genera produces a more satisfactory taxonomy for these parasites than considering them all as species of Cardicola. We thus recognise Cardicola (as an explicitly polyphyletic taxon) together with Braya, Elaphrobates, Rhaphidotrema and three new genera. We propose Allocardicola n. gen. for A. johnpagei n. sp. from T. angustifrons, Chanicola n. gen. for three species of Cardicola that infect the chanid Chanos chanos, and Spirocaecum n. gen. for six species of Cardicola that infect siganid fishes. We interpret the pattern of diversification seen in the clade of these seven genera as one of multiple host-switching events followed by diversification among closely-related hosts and differing levels of morphological divergence.

A new genus and species of fish blood fluke, Achorovermis testisinuosus gen. et sp. n. (Digenea: Aporocotylidae), infecting critically endangered smalltooth sawfish, Pristis pectinata (Rhinopristiformes: Pristidae) in the Gulf of Mexico

Achorovermis testisinuosus gen. et sp. n. (Digenea: Aporocotylidae) infects the heart of the smalltooth sawfish, Pristis pectinata Latham (Rhinopristiformes: Pristidae), in the eastern Gulf of Mexico. Specimens of the new genus, along with the other blood flukes that infect batoids are similar by having an inverse U-shaped intestine and a curving testis as well as by lacking tegumental spines. The new genus differs from all of the other blood flukes infecting batoids by having an elongate body (>50 × longer than wide), a testis having >100 curves, and an ovary wholly anterior to the uterus. It differs from Ogawaia glaucostegi Cutmore, Cribb et Yong, 2018, the only other blood fluke infecting a rhinopristiform, by having a body that is >50 × (vs <30 ×) longer than wide, a testis that is >75 × (vs <40 ×) longer than wide and has >100 (vs <70) curves, an ovary wholly anterior to (vs lateral and dorsal to) the seminal vesicle, a uterus wholly posterior to (vs overlapping and lateral to both) the testis and ovary, and a sinuous (vs convoluted) uterus. The new species joins a small group of chondrichthyan blood flukes that lack tegumental spines: O. glaucostegi, Orchispirium heterovitellatum Madhavi et Rao, 1970, Myliobaticola richardheardi Bullard et Jensen, 2008, Electrovermis zappum Warren et Bullard, 2019. Blood flukes infecting batoids are further unique by having a curving testis. That is, the blood flukes infecting species within Selachii are morphologically distinct from those infecting species within the Batoidea (excluding Gymnurahemecus bulbosus Warren et Bullard, 2019). Based on the morphological similarity, we suspect that the new species shares a recent common ancestor with O. glaucostegi. The discovery of the new species brings the total number of chondrichthyan blood flukes to 11 species assigned to nine genera.

Blood flukes (Digenea: Aporocotylidae) infecting body cavity of South American catfishes (Siluriformes: Pimelodidae): two new species from rivers in Bolivia, Guyana and Peru with a re-assessment of Plehniella Szidat, 1951

Plehniella Szidat, 1951 is emended based on new collections from South American long-whiskered catfishes. It is clearly differentiated from Sanguinicola Plehn, 1905 by lacking lateral tegumental body spines and by having 6 asymmetrical caeca. Plehniella sabajperezi sp. n. infects body cavity of Pimelodus albofasciatus (Mees) from the Demerara and Rupununi Rivers (Guyana) and Pimelodus blochii (Valenciennes) from Lake Tumi Chucua (Bolivia) and Napo River (Peru). It differs from Plehniella coelomicola Szidat, 1951 (type species) by having a thin-walled vas deferens that greatly exceeds the length of cirrus-sac and that joins the cirrus-sac at level of ovovitelline duct and ootype, an internal seminal vesicle that is absent or diminutive, and a cirrus-sac that is spheroid, nearly marginal, and envelops the laterally-directed distal portion of the male genitalia. Plehniella armbrusteri sp. n. infects body cavity of P. blochii from Lake Tumi Chucua (Bolivia). It differs from P. coelomicola and P. sabajperezi by having a relatively ovoid body, a massive intestine comprising caeca that are deeply-lobed to diverticulate and terminate in the posterior half of the body, a testis that flanks the distal tips of the posteriorly-directed caeca, and a proximal portion of the vas deferens that loops ventral to the testis. Small adults (Plehniella sp.) collected from body cavity of Pimelodus grosskopfii (Steindachner) from Cienega de Jobo and Canal del Dique (Colombia) differ from congeners by having a posteriorly-constricted body region, an anterior sucker with concentric rows of minute spines, an elongate anterior oesophageal swelling, short and wide caeca, and a male genital pore that opens proportionally more anteriad. This study nearly doubles the number of aporocotylids documented from South America Rivers and comprises the first record of a fish blood fluke from P. blochii, P. albofasciatus and P. grosskopfii as well as from Bolivia, Colombia, Guyana or Peru.

Cardicola beveridgei n. sp. (Digenea: Aporocotylidae) from the mangrove jack, Lutjanus argentimaculatus (Perciformes: Lutjanidae), and C. bullardi n. sp. from the Australian spotted mackerel, Scomberomorus munroi (Perciformes: Scombridae), from the northern Great Barrier Reef

Cardicola Short, 1953 is a genus of the Aporocotylidae Odhner, 1912 (Digenea), with 25 currently recognised species described from 32 species of Perciformes and Mugiliformes fishes around the world, including eight species from the Great Barrier Reef. Here, we describe two new species from this region, namely Cardicola beveridgei n. sp. from the ventricle and atrium of the mangrove jack, Lutjanus argentimaculatus (Forsskål) (Perciformes: Lutjanidae), and Cardicola bullardi n. sp. from the ventricle of the Australian spotted mackerel, Scomberomorus munroi Collette & Russo (Perciformes: Scombridae), from off Lizard Island, Queensland, Australia. These two new species are most easily distinguished from the 25 current members of Cardicola in having the combination of i) a spinous oral sucker, ii) an anteriorly intercaecal ovary, iii) a uterus that extends anteriorly from the oötype, iv) the number of spines per ventrolateral transverse row, and in v) body size and the length/width ratio, vi) the oesophagus and caecal length(s) relative to body total length, vii) the length of the posterior caeca relative to the anterior pair, viii) the testis length/width ratio and its total size relative to that of the body, ix) the postovarian field as a percentage of body length, and x) egg size. In addition, C. beveridgei n. sp. is further differentiated by possessing a female genital pore that opens anterodextral to the male pore while C. bullardi n. sp. differs further in possessing a testis that is almost entirely intercaecal and does not extend anteriorly to the level of the intestinal bifurcation. Employing genetic analysis of ITS2 rDNA sequence data, representing these species and a further 13 recognised and three putative species of Cardicola, we were able to unequivocally confirm these specimens as distinct (9-22% different over 420 nucleotide positions). Distance analysis of ITS2 showed that i) species of Cardicola from the Siganidae formed a monophyletic clade, to the exclusion of other Cardicola species reported from the Scombridae, Sparidae, Lutjanidae and Chaetodontidae, ii) a general phylogenetic isolation exists between the species of Cardicola reported from scombrid fishes, and iii) C. beveridgei n. sp. and Cardicola milleri Nolan & Cribb, 2006 from lutjanids and Cardicola chaetodontis Yamaguti, 1970 from chaetodontids are phylogenetically close, despite the evolutionary remoteness between the host groups and their highly disparate biology. Given the likelihood of many additional species being attributed to Cardicola, we predict that continued molecular analyses will indicate that this genus will prove to incorporate a series of radiations in association with particular fish taxa as well as evidence of host-switching. (Nucleotide sequences reported in this paper are available in the GenBank database under accession no. KF752497).

Littorellicola billhawkinsi n. gen., n. sp. (Digenea: Aporocotylidae) from the myocardial lacunae of Florida pompano, Trachinotus carolinus (Carangidae) in the Gulf of Mexico; with a comment on the interrelationships and functional morphology of intertrabecular aporocotylids

Littorellicola billhawkinsi n. gen., n. sp. infects the myocardial lacunae of the ventricle and atrium of Florida pompano, Trachinotus carolinus in the northern Gulf of Mexico. It differs from other aporocotylid genera by the combination of having a body 10-30× longer than wide, a posterolateral body protuberance, lateral spine rows, an aspinous anterior sucker comprising a slightly muscular rim circumscribing the mouth, asymmetrical posterior ceca 14-20× length of the anterior ceca and lacking diverticula or secondary rami, tens of testes distributing in a cobblestone-like field anterior and posterior to the distal ends of the posterior ceca, an oviducal seminal receptacle comprising the distal portion of the oviduct, and a post-cecal ovary plus by lacking rosethorn-shaped spines, a pharynx, and a Laurer's canal. The new species appears host specific to Florida pompano because no conspecific infection was detected in 134 carangids of 8 species in 4 genera captured nearby the type locality. Psettarium sebastodorum Holmes, 1971 is transferred to the new genus, as Littorellicola sebastodorum (Holmes, 1971) n. comb., because it and the new species differ from species of Psettarium by the combination of having multiple testes plus 8 other features detailed herein. This report brings the number of nominal Gulf of Mexico aporocotylids to 12 species of 8 genera, represents only the second record of an aporocotylid from a carangid there, and supports the notion that elongated, "thread-like" aporocotylids with lateral spine rows are seemingly well-adapted for infecting myocardial lacunae or embedding in the myocardium of their definitive fish hosts.

Blood flukes (Digenea: Aporocotylidae) of stingrays (Myliobatiformes: Dasyatidae): Orchispirium heterovitellatum from Himantura imbricata in the Bay of Bengal and a new genus and species of Aporocotylidae from Dasyatis sabina in the northern Gulf of Mexico

We redescribe Orchispirium heterovitellatum based on the holotype and 3 original voucher specimens collected from the mesenteric blood vessels of scaly whiprays Himantura imbricata (Bloch and Schneider, 1801) (as Dasyatis imbricatus) captured in the western Bay of Bengal off Waltair, India. We emend the diagnosis of Orchispirium to include anterior sucker present, testis looping, cirrus sac enveloping large internal seminal vesicle, oviducal seminal receptacle present, and metraterm short and thin-walled. We describe Myliobaticola richardheardi n. gen., n. sp. based on live observations, light microscopy, and scanning electron microscopy of adult specimens collected from between the cardiac trabeculae of Atlantic stingrays Dasyatis sabina (Lesueur, 1824) captured in Mississippi Sound (type locality), Mississippi, and Apalachicola Bay, Florida. The new species has a minute, aspinous body lacking lateral tubercles; an aspinous and eversible anterior sucker lacking a peduncle; a posterior esophageal swelling; an inverse U-shaped intestine; smooth ceca terminating in the anterior body half; a looping testis lacking lobes; a cirrus sac enveloping a large internal seminal vesicle; a medial and primarily post-testicular ovary; an oviducal seminal receptacle; a postgonadal uterus flanking the internal seminal vesicle; a short and thin-walled metraterm; and a common genital pore. It lacks a pharynx and Laurer's canal. No other named aporocotylids infect a member of cohort Batoidea or have the combination of an aspinous body, an aspinous anterior sucker, a posterior esophageal swelling, an inverse U-shaped intestine, a looping testis, a cirrus sac enveloping a large internal seminal vesicle, and a common genital pore; these observations indicate that O. heterovitellatum and M. richardheardi are closely related. The discovery of a second species representing a second genus of Aporocotylidae in diamond stingrays (Dasyatidae) suggests that Batoidea is an undersampled host group for aporocotylid infections.

Historical account of the two family-group names in use for the single accepted family comprising the “fish blood flukes”

The family-group name for the “fish blood flukes” is unstable, with both “Aporocotylidae Odhner, 1912” and “Sanguinicolidae von Graff, 1907” in use for the single family. Although “Sanguinicolidae von Graff, 1907” (or. Graff, 1907.) has been a widely-accepted family-group name for the fish blood flukes subsequent to Yamaguti’s 1954 and 1958 synoptical publications (“Systema Helminthum”), a critical examination of the relevant literature, much of it published in German during 1900 through 1926, reveals that “Aporocotylidae Odhner, 1912” is the earliest available family-group name for these flukes. The name Aporocotylidae, moreover, was in wide usage by alpha taxonomists before 1954 and by several authors between 1954 and the present time. We speculate that the recent long-standing uncertainty about the earliest available family-group name primarily stems from the (1) logistics of Ludwig von Graff’s tome published in 1904–1908, (2) bibliographic confusion between that work and another Graff work published in 1907 (both of which treat Sanguinicola but not Aporocotyle), (3) initial ambiguity regarding the phylogenetic relatedness of the first four aporocotylid species that were named, (4) lack of consensus on the status of Aporocotylidae and Sanguinicolidae and the genera included within them, and (5) misleading application of. Graff, 1907. to Sanguinicolidae by Poche in 1926, Fuhrmann in 1928, Yamaguti in 1954 and 1958, and subsequent review articles that treated fish blood flukes. Under the International Code of Zoological Nomenclature (ICZN, Article 8.3), “Sanguinicolidae” was not made available by Graff because he disclaimed the name in the same, and only, work wherein he used the name (ICZN, Article 8.3). Sanguinicolidae was first made available in 1926 by Poche, who referenced Graff’s 1907 work. Hence, “Poche, 1926” comprises the correct authority and date for that family-group name, not “von Graff, 1907” or “Graff, 1907”. Since we presently accept only a single family for all fish blood flukes and abide by the Principal of Priority (ICZN, Article 23), we herein regard Sanguinicolidae Poche, 1926 as a junior subjective synonym of Aporocotylidae Odhner, 1912.