Male Copulatory Organ Research Articles

Redescripción de Haliotrematoides mediohamides (Monogenea: Dactylogyridae), un parásito branquial del sargo Calamus brachysomus (Perciformes: Sparidae) del océano Pacífico oriental

The monogenean Haliotrematoides mediohamides Kritsky & Mendoza-Franco, 2009 (Monogenea: Dactylogyridae) is redescribed based on examination of the type specimen (paratypes) and newly collected specimens parasitizing the gills of the Pacific porgy, Calamus brachysomus (Lockington, 1880) (Perciformes: Sparidae) (type host), a neritic fish captured off the coastal zone of Puerto Pizarro, Tumbes, Peru. Even though this monogenean was described 12 years ago, that description did not report some of the unique morphological features of H. mediohamides and neither did it offer a whole-mount drawing of this species. The most important characteristics of H. mediohamides are: 1) a male copulatory organ with hook-shaped distal end, 2) a non-coiled vaginal duct, 3) numerous secretory gland-cells associated with the peduncle, 4) a chandelier-shaped extrinsic adductor muscles articulated with superficial roots of the anchors, 5) a single tadpole-shaped prostatic reservoir, and 6) a vas deferens anteriorly convoluted. In addition, the first whole-mount drawing of H. mediohamides, as well as morphometric data are provided. Haliotrematoides mediohamides represents the first record of Haliotrematoides in South America. Haliotrematoides mediohamides is the third dactylogyrid species recorded to infect C. brachysomus in Peru.

The Use of Prefemoral Endoscope-Assisted Surgery and Transplastron Coeliotomy in Chelonian Reproductive Disorders.

Throughout the last decades, the increased popularity of the keeping of reptiles has led to a better understanding of the captive needs of a wide variety of species. Although this is reflected by the successful captive reproduction in many of those species, reproductive disorders such as preovulatory follicular stasis, postovulatory dystocia, secondary yolk coelomitis, and prolapse of the oviduct and male copulatory organ are commonly encountered in veterinary practice. In comparison to squamates, chelonians with postovulatory dystocia seem to be more responsive to oxytocin treatment, even in cases of chronic dystocia. There are various conditions, however, that necessitate the use of surgical procedures for the treatment of dystocia and other reproductive disorders in chelonians. Although restrictions may be encountered, the endoscope-assisted prefemoral approach is the least invasive and thus preferred technique instead of the ventral transplastron coeliotomy. The present report describes the diagnostic and surgical approach applied in seven cases of female chelonians with reproductive disorders. The therapeutic efficacy largely relied on the choice of minimally invasive endoscope-assisted surgery versus transplastron coeliotomy that was primarily dictated by the involved species, etiology, and associated pathology.

Rediscovering Monogenoids (Platyhelminthes) Parasitizing Pomacentrid and Chaetodontid Fishes from Cayo Arcas Reef, Gulf of Mexico

During a research of gill ectoparasites on damselfishes (Pomacentridae) and butterflyfishes (Chaetodontidae) from the Cayo Arcas reef in the Campeche Bank (Gulf of Mexico), the following monogenoids (Platyhelminthes) were found: Paraeuryhaliotrema pomacentris n. gen., n. sp. (Dactylogyridae) on beaugregory Stegastes xanthurus (Poey, 1860) (Pomacentridae) that is characterized, in part, by possessing a haptor armed with a dorsal, ventral anchor-bar complexes, seven pairs of similar hooks; two pairs of eyespots; overlapping gonads; a copulatory complex composed of a male copulatory organ (MCO) and an accessory piece; MCO tubular with a bulbous base from which arises a coiled shaft in the clockwise direction; and a dextral vaginal pore; Neohaliotrema variabilis n. sp. on bicolor damselfish Stegastes partitus (Poey, 1868) (type host), beaugregory Stegastes xanthurus (Poey, 1860) and beaugregory Stegastes leucostictus (Müller & Troschel, 1848); Neohaliotrema manubrium n. sp., Neohaliotrema aliamanubrium n. sp. and Neohaliotrema bifidum n. sp., Neohaliotrema bychowskii Zhukov, 1976 and Neohaliotrema macracanthum Zhukov, 1976 on Sergeant-major Abudefduf saxatilis (Linnaeus, 1758) (Pomacentridae); Neohaliotrema similium n. sp. on S. xanthurus; Haliotrema brevicirrus Zhukov 1976 on spotfin butterflyfish Chaetodon ocellatus Bloch 1787 (Chaetodontidae); Microcotyle multilineatus n. sp. (Microcotylidae) on brown chromis Chromis multilineata (Guichenot 1853) (Pomacentridae). The new species are described and illustrated; new illustrations and measurements of the haptoral structures, and new redescription and illustrations are provided for N. bychowskii, N. macracanthum and H. brevicirrus, respectively. The present study represents the first knowledge about ectoparasitic monogenoids of fishes in the Cayo Arcas reef from the Gulf of Mexico.

Two species of the genus Anchistrocheles (Bairdioidea: Ostracoda: Crustacea) from Japan and their developmental characteristics for adaptation to interstitial environments

A new species and an already known species of the genus Anchistrocheles Brady & Norman, 1889 from the Pacific coast of Japan, are described in detail using scanning electron microscopy of the carapaces and soft-part anatomy of the appendages. The new species, Anchistrocheles hayatotanakai sp. nov., is only the second to be described in the genus Anchistrocheles from Japan, and this study is also the first to describe the appendages of A. yamaguchii Yajima, 1987, previously only known as a fossil from Pleistocene strata of the Atsumi Formation in central Japan. The two species are considered to be closely related because they share many common characters in their appendages, but they are distinguishable from each other based on the male and female copulatory organs, furcal chaetotaxy, brush-shaped organs, number of lateral pore systems, and outlines of the carapaces in dorsal view. Ontogenetic changes of carapace sizes were compared between three interstitial species (Anchistrocheles hayatotanakai sp. nov., A. yamaguchii, and Neonesidea sp. I) and an epifaunal species (N. sp. S). The reduction in carapace width was found to be the primary reason for the reduction in the cross-sectional area and is probably related to the adaptation to interstitial environments. The brush-shaped organs located between the 6th pair of limbs are also shown. This study is the first to report the anatomically precise position of these organs.

Morphological description and molecular characterisation of Dactylogyrus matlopong sp. n. (Monogenea: Dactylogyridae) from the South African endemic Labeobarbus aeneus (Cyprinidae: Torinae).

Dactylogyrus Diesing, 1850 is the most species-rich genus in Platyhelminthes, with over 900 documented species, that are mostly strictly specific to freshwater cyprinoids. The morphological Dactylogyrus groups afrobarbae-type, carpathicus-type, pseudoanchoratus-type, and varicorhini-type are known to occur in Africa. This study describes a new species of Dactylogyrus of the varicorhini-type from the gills of the endemic smallmouth yellowfish Labeobarbus aeneus (Burchell) from the Vaal River, Free State Province, South Africa. Dactylogyrus matlopong sp. n. is unique among its varicorhini-type congeners mainly by the accessory piece of the male copulatory complex that presents a hook-shaped subunit with defined round base not reaching the male copulatory organ, combined with the presence of a conspicuous medial projection on the anterior margin of the ventral bar. Sequences of the partial 28S and 18S rRNA genes, together with entire ITS1 region, were generated for the first time for a species of Dactylogyrus from South Africa. Concatenated phylogenetic analyses of selected Dactylogyrus spp. showed that these parasites group according to their morphological types.

Proposal of Cynoscionella n. g. (Monogenea: Diplectanidae), with description of a new species from the gills of Cynoscion phoxocephalus (Actinopterygii: Sciaenidae) in Peru and reassignment of two species of Diplectanum Monticelli, 1903.

Cynoscionella n. g. is proposed for Cynoscionella sanmarci n. sp. and two previously described species of Diplectanum Diesing, 1858 were reassigned into the new genus. The three species are gill parasites of sciaenid fishes (Perciformes: Sciaenidae). The new genus is closely related with Diplectanum (sensu stricto), but is mainly distinguished by its male copulatory organ (MCO) having a slightly sclerotized sleeve-shaped base, lacking accessory piece and accessory copulatory organ. In addition, Cynoscionella n. g. differs from Diplectanum species by having the ventral anchors with well-developed roots, and a prostatic reservoir simple. Cynoscionella sanmarci n. sp. is a parasite of the cachema weakfish Cynoscion phoxocephalus Jordan & Gilbert, a demersal teleost collected from off the coastal zone of Puerto Pizarro, Tumbes region, northern Peru. Diplectanum bilobatum Hargis, 1955 from the spotted weakfish Cynoscion nebulosus (Cuvier) and D. monticellii Domingues & Boeger, 2003 from the smooth weakfish Cynoscion leiarchus (Cuvier), are transferred to Cynoscionella n. g. as Cy. bilobatum (Hargis, 1955) n. comb. and Cy. monticelli (Domingues & Boeger, 2003) n. comb. The present finding represents the first data on the monogenean parasites of C. phoxocephalus. This is the thirteenth marine diplectanid species recorded from Peru.

Brazilian Boidae hemipenis morphology: Macroscopic and histological aspects.

Four genera of the Boidae family are found in Brazil: Eunectes, Corallus, Epicrates, and Boa. Male copulatory organs in snakes are located inside the tail and are called hemipenes. They are double structures in an inverted position that are exposed during copulation. This study describes the macroscopic and histological aspects of hemipenes in Boidae snakes. One Boa constrictor, three Epicrates cenchria, one Corallus hortulanus hemipenes, and one fragment of the muscular retractor penis magnus (m. retractor penis magnus) from Eunectes murinus were included in this study. The structures were evaluated macroscopically and photo-documented using a stereo microscope. Tissue fragments were included in glycol methacrylate plastic resin, cut into 3-μm-thick slices, and stained with 1% toluidine blue for microscopic evaluation. The macroscopic analysis showed that the arrangement and diameter occupied by the m. retractor penis magnus in the hemipenis and the internal and external cavernous bodies differ between species. The histological analysis showed that the hemipenis of B.constrictor, E.cenchria, and C.hortulanus has stratified epithelium in the external portion supported by dense connective tissue with blood vessels and muscle tissue. Although the literature reports the presence of skeletal musculature in the hemipenis, striated musculature with a centrally located nucleus in the fibre bundle, typical of cardiac musculature in mammals, was observed in the studied species.

Cosmetocleithrum infinitum sp. n. (Monogenoidea: Dactylogyridae) parasite of the gills of Anadoras grypus (Siluriformes: Doradidae) from the Amazonas river, in Loreto, Peru.

Among Siluriformes, fishes of the family Doradidae harbor dactylogyrids from Cosmetocleithrum Kritsky, Thatcher and Boeger, 1986. Anadoras grypus (Cope) (Siluriformes, Doradidae) locally named in Peru as "rego-rego" hosts a new species of Cosmetocleithrum described herein as Cosmetocleithrum infinitum sp. n. The male copulatory organ (MCO) and vagina of the new species reveal its morphological uniqueness among members of Cosmetocleithrum. The MCO in the new species is an elongate, sclerotized sinuous tube, with 12 expanded coils, with counterclockwise orientation; the accessory piece is sclerotized, comprising a kind of cone, with a large opening at its base, with a branch in the posterior middle part and with pointed ends. The vagina is a sclerotized long, winding, coiled tube with a cone-shaped opening.

Phylogeny and evolution of the land snail tribe Clausiliini (Gastropoda: Clausiliidae)

The phylogenetic relationships within the land snail group Clausiliini were analysed based on an almost complete taxon sampling (28 of 29 extant species) and a set of mitochondrial and nuclear markers. The phylogenetic analyses and character state reconstructions revealed several trends in the group that resulted in repeated convergences. The N-type closing apparatus was convergently transformed into a G-type clausilial apparatus in Graciliaria, Ruthenica + Micridyla and probably three times within Neostyriaca. There were parallel changes in the length of the male copulatory organs and repeated reductions of the basal keel in several lineages. Such trends resulting in repeated convergences are characteristic for several radiations of stylommatophoran land snails. They may reflect parallel adaptations of related lineages to similar environmental constraints. However, it is also possible that some of these transformations are not adaptive, but represent random changes in a restricted morphospace. We explored the timing of the Clausiliini radiation using different calibration strategies. Despite large numbers of fossils of Clausiliidae from Western and Central Europe, the results of these analyses and the fossil evidence for a Cretaceous origin of the Clausiliidae indicate that there are large gaps in the fossil record of the Clausiliini. Especially the origin and early evolution of the Clausiliini in Southeastern Europe is obscured by our insufficient knowledge of Neogene deposits there.

Six new species of Rhamnocercus Monaco, Wood & Mizelle, 1954 (Monogenea: Diplectanidae) infecting the gills from South American sciaenid fishes.

A parasitological survey searching diplectanids (Monogenea: Diplecatnidae) infesting the gills of marine fishes from South America was carried out during the 2019-2020 period. The gills of four sciaenid species, 2 Cheilotrema fasciatum Tschudi, 1 smalleye croaker Nebris microps Cuvier, 2 royal highhat Pareques lanfeari (Barton), and 1 minor stardrum Stellifer minor (Tschudi), were sampled. Six new species of Rhamnocercus Monaco, Wood & Mizelle, 1954 were described: Rhamnocercus chacllae n. sp. and Rhamnocercus chaskae n. sp. from P. lanfeari, Rhamnocercus fasciatus n. sp. from C. fasciatum, Rhamnocercus microps n. sp. from N. microps, and Rhamnocercus rimaci n. sp. and Rhamnocercus tantaleani n. sp. from S. minor. Rhamnocercus chacllae n. sp. can be differentiated from its congeners by its L-shaped male copulatory organ (MCO) and by having an anteromedial slight notch at ventral bar. Rhamnocercus chaskae n. sp. differs from the other species of the genus by its long and straight MCO with bifid distal end and by having haptoral accessory spines at level of ventral bar with quadrifid distal portion. Rhamnocercus fasciatus n. sp. is characterized by possessing a straight and long MCO with truncated distal end, haptoral accessory spines at level of ventral bar with bifid distal portion, dorsal bars with a knob at lateral extremity, and a large vagina with bell-shaped. Rhamnocercus microps n. sp. differs from all congeners mainly by having a short and straight MCO with the distal end of internal tube spatulate and uncovered by external tube. Rhamnocercus rimaci n. sp. is can be distinguished from all other species of Rhamnocercus by having an almost J-shaped MCO with the distal end of external tube slight expanded and the distal end of internal tube narrow and uncovered by external tube. Rhamnocercus tantaleani n. sp. is mainly characterized by its MCO, which is tubular and straight, having the distal end of external tube bifurcated (right branch well-expanded and left branch narrow) and the distal end of internal tube enveloped by left branch of the external tube. This is the first data on the parasites of P. lanfeari, a little known, but popular fish in local markets from Peru. Rhamnocercus microps n. sp. is the first described species of Rhamnocercus in Brazil. The present finding brings to 12, the number of known species of Rhamnocercus. A key to Rhamnocercus species is provided.

Bychowskicotylids (Monogenoidea: Gastrocotylinea) infecting the gills of the sweetlips Diagramma labiosum Macleay (Haemulidae) in Moreton Bay, Queensland, Australia, with the proposal of Lebedevia n. gen. and description of Lebedevia lebedevi n. sp.

Two species of Bychowskicotylidae (Monogenoidea: Gastrocotylinea) were collected from the gills of the sweetlips Diagramma labiosum Macleay (Haemulidae) obtained from Moreton Bay, Queensland, Australia, during January 2016. Lebedevia n. gen. is proposed for bychowskicotylids having 1) a bilaterally symmetrical haptor with four pairs of gastrocotylid-like clamps and lacking an armed lappet (anchors and hooks absent); 2) longitudinal sclerotized internal ridges lining the vas deferens, 3) an unarmed male copulatory organ, and 4) four interconnected vesicles located posterior to the genital atrium and lying on the body midline dorsal to the uterus and ventral to the vas deferens. Lebedevia lebedevi n. sp., the type and only species of the genus, is described, and Tonkinopsis transfretanus Lebedev, 1972 is recorded for the first time in Moreton Bay. Yamaguticotyla Price, 1959 (Bychowskicotylidae) is considered nomen nudum, and the authorship of the genus is corrected to Yamaguticotyla Yamaguti, 1963.

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.

Identity of Zorotypus juninensis Engel, 2000, syn. nov. revealed: it is conspecific with Centrozoros hamiltoni (New, 1978) (Zoraptera, Spiralizoridae)

Zorotypus juninensisEngel, 2000, was previously diagnosed based on the external morphology of female and male specimens without description of the male copulatory organ, which is an important character for classification in Zoraptera. Based on a detailed morphological study of theZorotypus juninensisEngel, 2000 type collections deposited in the American Museum of Natural History in New York, and based on the comparison with the holotype male ofCentrozoros hamiltoni(New, 1978), we have determined that these two species are conspecific. We therefore formally synonymizeZorotypus juninensisEngel, 2000,syn. nov.withCentrozoros hamiltoni(New, 1978). Morphological characters and phylogenetic relationships ofCentrozorosKukalova-Peck & Peck, 1993 are also discussed in this report.

Morphological types of male copulatory organs of Bicornucythere bisanensis (Ostracoda, Crustacea) and the description of a new Bicornucythere species.

This study is designed to evaluate the male copulatory organs and carapace size of the inner bay benthic ostracod Bicornucythere bisanensis. The male copulatory organs demonstrate noticeable intraspecific variation in the distal lobe, especially the length of the tip, which shows a gradual variation; whereas the thickness of the distal lobe is conservative within the species. The population from central Japan (Aburatsubo Cove) showed remarkable morphological variations, with four copulatory organ types, each type defined by a combination of four shapes of the right and left distal lobes (Shape R, r, L, and l). While the variety of carapace morphotypes have been previously reported, our findings suggest that one morphotype from western Japan (Misumi-cho) should be treated as a distinct species. Thus, we described it as Bicornucythere misumiensis sp. nov.

First record of the jumping spider Pancorius changricus Żabka, 1990 from India (Araneae: Salticidae)

Pancorius changricus Żabka, 1990 is recorded for the first time from India. Detailed illustrations of the general morphology and male copulatory organ are provided. The distribution records of the species are also mapped.

Neotropical Monogenoidea 64. Cosmetocleithrum falsunilatum sp. n. (Monogenoidea, Dactylogyridae) parasite of the gills of Megalodoras uranoscopus (Siluriformes, Doradidae) from the Solimões river, near Iquitos, Peru.

Megalodoras uranoscopus (Eigenmann & Eigenmann) (Siluriformes, Doradidae) (the giant-talking catfishorthe giant-raphael catfish), from the Peruvian Amazon, hosts a new species of Cosmetocleithrum described herein as Cosmetocleithrum falsunilatum sp. n. The male copulatory organ of the new species closely resembles that of Unilatus spp. - with multiple tight loops and non-articulated accessory piece - which reveals its morphological uniqueness among members of Cosmetocleithrum. A phylogenetic analysis using 28S rDNA of available sequences suggests that Cosmetocleithrum is composed by two basal clades, one of them composed by sequences of the new species and C. trachydorasi.

Morphology and molecular phylogeny of Pauciconfibuloides amazonica gen. n. sp. n. (Platyhelminthes, Monogenoidea) parasitizing the Amazonian croaker Plagioscion squamosissimus.

An integrative study was performed to understand the phylogenetic relationships of an undescribed, freshwater species of microcotylid parasitizing Plagioscion squamosissimus from the Amazon River Basin. Based on morphological and molecular analysis (18S rDNA and partial 28S rDNA genes), a new genus is proposed to accommodate this new species, Pauciconfibuloides amazonica gen. n. sp. n. The new genus is closely related to Protastomicrocotylinae and Pauciconfibula by sharing the vagina, male copulatory organ, and genital atrium all unarmed. However, Pauciconfibuloides gen. n. can be distinguished from those taxa by the prostatic system and position of the vaginal pore. Molecular phylogenetic inference suggests a sister relationship with species of Polylabris (Prostatomicrocotylinae), but to date, there are no available 18S or 28S rDNA sequences of Pauciconfibula to be compared. This is the first report of a microcotylid parasitizing a freshwater sciaenid from South America.

Orostylis gen. nov., a new genus of Dalytyphloplanida with seven new species (Platyhelminthes: Rhabdocoela)

We describe a new genus of dalytyphloplanid rhabdocoels, with seven new species. Orostylis gen. nov. has a unique combination of characters including the presence of a sclerotised stylet, an anteriorly positioned male copulatory organ with the male genital pore in the buccal cavity, and the absence of an oviduct. The ovary empties directly into the intestinal lumen. Orostylis dohae sp. nov., Orostylis asinaraensis sp. nov., Orostylis caecus sp. nov., Orostylis distortus sp. nov., Orostylis donanae sp. nov., Orostylis gallicus sp. nov., and Orostylis timucuorum sp. nov. are distinguished from each other by the structure of the sclerotised parts of the male copulatory organ. Molecular and morphological evidence place the new genus in Neodalyellida Willems et al. 2006, and similarities with other taxa are discussed.

Mating behavior and reproductive morphology predict macroevolution of sex allocation in hermaphroditic flatworms

BackgroundSex allocation is the distribution of resources to male or female reproduction. In hermaphrodites, this concerns an individual’s resource allocation to, for example, the production of male or female gametes. Macroevolutionary studies across hermaphroditic plants have revealed that the self-pollination rate and the pollination mode are strong predictors of sex allocation. Consequently, we expect similar factors such as the selfing rate and aspects of the reproductive biology, like the mating behaviour and the intensity of postcopulatory sexual selection, to predict sex allocation in hermaphroditic animals. However, comparative work on hermaphroditic animals is limited. Here, we study sex allocation in 120 species of the hermaphroditic free-living flatworm genus Macrostomum. We ask how hypodermic insemination, a convergently evolved mating behaviour where sperm are traumatically injected through the partner’s epidermis, affects the evolution of sex allocation. We also test the commonly-made assumption that investment into male and female reproduction should trade-off. Finally, we ask if morphological indicators of the intensity of postcopulatory sexual selection (female genital complexity, male copulatory organ length, and sperm length) can predict sex allocation.ResultsWe find that the repeated evolution of hypodermic insemination predicts a more female-biased sex allocation (i.e., a relative shift towards female allocation). Moreover, transcriptome-based estimates of heterozygosity reveal reduced heterozygosity in hypodermically mating species, indicating that this mating behavior is linked to increased selfing or biparental inbreeding. Therefore, hypodermic insemination could represent a selfing syndrome. Furthermore, across the genus, allocation to male and female gametes is negatively related, and larger species have a more female-biased sex allocation. Finally, increased female genital complexity, longer sperm, and a longer male copulatory organ predict a more male-biased sex allocation.ConclusionsSelfing syndromes have repeatedly originated in plants. Remarkably, this macroevolutionary pattern is replicated in Macrostomum flatworms and linked to repeated shifts in reproductive behavior. We also find a trade-off between male and female reproduction, a fundamental assumption of most theories of sex allocation. Beyond that, no theory predicts a more female-biased allocation in larger species, suggesting avenues for future work. Finally, morphological indicators of more intense postcopulatory sexual selection appear to predict more intense sperm competition.

A new microbothriid monogenean Dermopristis pterophilus n. sp. from the skin of the Critically Endangered green sawfish Pristis zijsron Bleeker, 1851 (Batoidea: Pristidae) in Western Australia.

A new microbothriid monogenean Dermopristis pterophilus n. sp. is described from the skin of the Critically Endangered green sawfish Pristis zijsron Bleeker, 1851 in the Ashburton River delta, northern Western Australia. Analyses of the 28S ribosomal DNA marker and the molecular barcoding markers Histone 3 and Elongation Factor 1 α confirmed position among the Microbothriidae, with close affinity to the only other sequenced representative of Dermopristis Kearn, Whittington and Evans-Groing, 2010. The new species is morphologically consistent with the concept of Dermopristis; it has two testes, lacks a male copulatory organ and has a simple haptor. It is smaller than its two congeners D. paradoxus Kearn, Whittington and Evans-Gowing, 2010 and D. cairae Whittington and Kearn, 2011 and is most similar to the former, distinguished only in that it lacks the strong, transverse, parallel ridges on the ventral body surface that characterise that species. It is more easily distinguished from D. cairae, differing in body shape, possession of a seminal receptacle, and relative position and size of the haptor. It may further differ from both species by fine details of the gut diverticula, although these details are difficult to ascertain. Spermatophores were observed in the new species, similar to those previously reported for D. cairae. The new species exhibits site attachment preference: infections were greatest on and immediately adjacent to the host pelvic fins (including male reproductive organs, i.e. claspers), moderate in proximity to the dorsal and pectoral fins, few on the caudal fin and peduncle, and infrequently, isolated worms occurred elsewhere on the dorsal and ventral surfaces of the body. There was no incidence of infection on the head (including rostrum). We presume D. pterophilus is restricted to P. zijsron and thus likely faces the same threat of extinction.