R. A. Bray

The nature and evolution of the association among digeneans, molluscs and fishes

Patterns of association of digenean families and their mollusc and vertebrate hosts are assessed by way of a new database containing information on over 1000 species of digeneans for life-cycles and over 5000 species from fishes. Analysis of the distribution of digenean families in molluscs suggests that the group was associated primitively with gastropods and that infection of polychaetes, bivalves and scaphopods are all the results of host-switching. For the vertebrates, infections of agnathans and chondrichthyans are apparently the result of host-switching from teleosts. For digenean families the ratio of orders of fishes infected to superfamilies of molluscs infected ranges from 0.5 (Mesometridae) to 16 (Bivesiculidae) and has a mean of 5.6. Individual patterns of host association of 13 digenean families and superfamilies are reviewed. Two, Bucephalidae and Sanguinicolidae, are exceptional in infecting a range of first intermediate hosts qualitatively as broad as their range of definitive hosts. No well-studied taxon shows narrower association with vertebrate than with mollusc clades. The range of definitive hosts of digeneans is characteristically defined by eco-physiological similarity rather than phylogenetic relationship. The range of associations of digenean families with mollusc taxa is generally much narrower. These data are considered in the light of ideas about the significance of different forms of host association. If Manters Second Rule (the longer the association with a host group, the more pronounced the specificity exhibited by the parasite group) is invoked, then the data may suggest that the Digenea first parasitised molluscs before adopting vertebrate hosts. This interpretation is consistent with most previous ideas about the evolution of the Digenea but contrary to current interpretations based on the monophyly of the Neodermata. The basis of Manters Second Rule is, however, considered too flimsy for this interpretation to be robust. Problems of the inference of the evolution of patterns of parasitism in the Neodermata are discussed and considered so intractable that the truth may be presently unknowable.

A review of the Apocreadiidae Skrjabin, 1942 (Trematoda: Digenea) and description of Australian species

The Apocreadiidae is reviewed and is considered to include genera recognised previously within the families Apocreadiidae, Homalometridae, Schistorchiidae, Sphincterostomatidae and Trematobrienidae. Key features of the family are extensive vitelline follicles, eye-spot pigment dispersed in forebody, I-shaped excretory vesicle, no cirrus-sac and genital pore opening immediately anterior to the ventral sucker (usually) or immediately posterior to it (Postporus Manter, 1949). Three subfamilies and 18xa0genera are recognised within the Apocreadiidae. The Apocreadiinae comprises Homalometron Stafford, 1904 (new syn. Barbulostomum Ramsey, 1965), Callohelmis n. g., Choanodera Manter, 1940, Crassicutis Manter, 1936, Dactylotrema Bravo-Hollis & Manter, 1957, Marsupioacetabulum Yamaguti, 1952, Microcreadium Simer, 1929, Myzotus Manter, 1940, Neoapocreadium Siddiqi & Cable, 1960, Neomegasolena Siddiqi & Cable, 1960, Pancreadium Manter, 1954, Procaudotestis Szidat, 1954 and Trematobrien Dollfus, 1950. The Schistorchiinae comprises Schistorchis Lühe, 1906, Sphincterostoma Yamaguti, 1937, Sphincteristomum Oshmarin, Mamaev & Parukhin, 1961 and Megacreadium Nagaty, 1956. The Postporinae comprises only Postporus. A key to subfamilies and genera of the Apocreadiidae is provided. It is argued that there is no convincing basis for the recognition of the genus Apocreadium Manter, 1937 and all its constituent species are combined with Homalometron. The following new combinations are proposed for species previously recognised within Apocreadium: Homalometron balistis (Manter, 1947), H.xa0caballeroi (Bravo-Hollis, 1953), H.xa0cryptum (Overstreet, 1969), H.xa0longisinosum (Manter, 1937), H. manteri (Overstreet, 1970), H.xa0mexicanum (Manter, 1937) and H.xa0vinodae (Ahmad, 1985). Apocreadium uroproctoferum Sogandares-Bernal, 1959 is found to lack a uroproct and is made a synonym of H.xa0mexicanum. Homalometron verrunculi nom. nov. is proposed to replace the secondarily pre-occupied H.xa0caballeroi Lamothe-Argumedo, 1965. Barbulostomum is made a synonym of Homalometron and H.xa0cupuloris (Ramsey, 1965) n. comb. is proposed. Neochoanodera is made a synonym of Choanodera and Choanodera ghanensis (Fischthal & Thomas, 1970) n. comb. is proposed. Species within the Apocreadiinae and Postporinae are reviewed and the following are recorded or described from Australian fishes: Homalometron wrightae n. sp. from Achlyopa nigra (Macleay), H.xa0synagris (Yamaguti, 1953) n. comb. from Scolopsis monogramma (Cuvier), H.xa0stradbrokensis n. sp. from Gerres subfasciatus Cuvier, Marsupioacetabulum opallioderma n. sp. from G.xa0subfasciatus, Neoapocreadium karwarensis (Hafeezullah, 1970) n. comb. from G.xa0subfasciatus, N.xa0splendens n. sp. from S.xa0monogramma and Callohelmis pichelinae n. g., n. sp. from Hemigymnus melapterus (Bloch), H.xa0fasciatus (Bloch), Stethojulis bandanensis (Bleeker) andChoerodon venustus (De Vis). Callohelmis is recognised by the combination of absence of tegumental spines, caeca terminating midway between the testes and posterior end of body, ventral sucker enclosed in a tegumental pouch, prominent muscles radiating through the body from the ventral sucker, vitelline follicles not extending into the forebody, and a very short excretory vesicle that opens ventrally. New combinations for species previously recognised within Crassicutis are proposed as follows: Neoapocreadium caranxi (Bilqees, 1976) n. comb., N.xa0gerridis (Nahhas & Cable, 1964) n. comb., N.xa0imtiazi (Ahmad, 1984) n. comb. and N.xa0marina (Manter, 1947) n. comb. The host-specificity and zoogeography of the Apocreadiinae are considered.

Superfamily Gymnophalloidea Odhner, 1905

Fellodistomidae are common parasites of a wide range of marine and freshwater fishes and some marine invertebrates. They are characterized by a smooth tegument, a V- or Y-shaped excretory vesicle, post-gonadal uterus, restricted vitelline fields, uterine seminal receptacle and an anterior opening of Laurer’s canal (Bray, 2002). Brooks et al. (1985) in their phylogenetic analysis of Digenea have not included Fellodistomidae which they have considered ‘insertae sedis’ and polyphyletic. Subsequently, Hall et al. (1999) supported the polyphyletic nature of Fellodistomidae and based on molecular evidence, distributed the members of the family in three families: Fellodistomidae Nicoll, 1909, Faustulidae Poche, 1926 (Syn. Baccigerinae Yamaguti, 1954) and Tandanicolidae Johnson, 1927.

Monorchis lewisi n. sp. (Trematoda: Monorchiidae) from the surf bream, Acanthopagrus australis (Sparidae), in Moreton Bay, Australia

We describe Monorchis lewisi n. sp. (Monorchiidae) from the surf bream, Acanthopagrus australis (Günther, 1859) (Sparidae), in Moreton Bay, eastern Australia. The new species differs from most existing species of Monorchis Monticelli, 1893 in its possession of an elongate I-shaped excretory vesicle, and from other congeners in the relative configuration of the gut and suckers. Ovipusillus mayu Dove & Cribb, 1998 is re-reported from Gnathanodon speciosus (Forsskål, 1775) (Carangidae) from Moreton Bay. We report new second internal transcribed spacer (ITS2) and 28S rDNA sequence data for both species. Bayesian inference and Maximum Likelihood analyses of the 28S rDNA dataset suggest that existing subfamily and genus concepts within the family require substantial revision.

Postlepidapedon quintum n. sp. (Digenea: Lepocreadiidae) from the bastard trumpeter Latridopsis forsteri (Perciformes: Latridae) off the coast of northern Tasmania

The new lepocreadiid species, Postlepidapedon quintum, is erected for worms recovered from the perciform fish Latridopsisftrsteri off the ncoast of northern Tasmania. It is distinguished from its congeners by the vitelline extent and the shape and thickness of the wall of the ninternal seminal vesicle. A key to the genus Postlepidapedon is given. P. quintum is likely to be endemic to southern Australia and New nZealand, as is its host.