Phylogeny and a revised classification of the Monogenoidea Bychowsky, 1937 (Platyhelminthes)

Abstract

A hypothesis (CI = 57.3%) on the evolutionary relationships of families comprising the class Monogenoidea is proposed based on 141 character states in 47 homologous series and employing phylogenetic systematics. Based on the analysis, three subclasses, the Polyonchoinea, Polystomatoinea and Oligonchoinca, are recognised. The analysis supports independent origins of the Montchadskyellidae within the Polyonchoinea and of the Neodactylodiscidae and Amphibdellatidae within the order Dactylogyridea (Polyonchoinea); the suborder Montchadskyellinea is raised to ordinal status and new suborders Neodactylodiscinea and Amphibdellatinea are proposed to reflect these origins. The Gyrodactylidea (Polyonchoinca) is supported by three synapomorphies and comprises the Gyrodactylidae, Anoplodiscidae, Tetraonchoididae and Bothitrematidae. The analysis supports recognition of the Polystomatoinea comprising Polystomatidae and Sphyranuridae. Evolutionary relationships within the Oligonchoinea indicate independent origins of three ordinal taxa, the Chimaericolidea (monotypic), Diclybothriidea (including Diclybothriidae and Hexabothriidae) and Mazocraeidea (with five suborders). The suborder Mazocraeinea comprises the Plectanocotylidae, Mazocraeidae and Mazoplectidae, and is characterised by two synapomorphies. The suborder Gastrocotylinea, characterised by presence of accessory sclerites in the haptoral sucker, is divided into two infraorders, the monotypic Anthocotylina infraorder novum and Gastrocotylina. Two superfamilies of the Gastrocotylina are recognised, the Protomicrocotyloidea and Gastrocotyloidea; the Pseudodiclidophoridae is considered incertae sedis within the Gastrocotylina. The suborder Discocotylinea comprises the Discocotylidae, Octomacridae and Diplozoidae and is supported by four synapomorphies. The monotypic Hexostomatinea suborder novum is proposed to reflect an independent origin of the Hexostomatidae within the Mazocraeidea. The terminal suborder Microcotylinea comprises four superfamilies, the Microcotyloidea, Allopyragraphoroidea, Diclidophoroidea and Pyragraphoroidea. The analysis supports incorporation of the Pterinotrematidae in the Pyragraphoroidea and rejection of the monotypic order Pterinotrematidea. The following taxa are also rejected for reasons of paraphyly and/or polyphyly: Articulonchoinea, Bothriocotylea, Eucotylea, Monoaxonematidea, Tetraonchidea, Gotocotyloidea, Anchorophoridae and Macrovalvitrematidae. The Sundanonchidae, Iagotrematidae and Microbothriidae were not included in the analysis because of lack of pertinent information regarding character states. 2

Hexabothriid monogeneans from the gills of deep-sea sharks off Algeria, with the description of Squalonchocotyle euzeti n. sp. (Hexabothriidae) from the kitefin shark Dalatias licha (Euselachii, Dalatiidae)

“…However, the hexabothriid literature is plagued with confusion and discrepancies (Vaughan & Christison, 2012) but probably no more than any large family of monogeneans. The Hexabothriidae are considered a basal group within the Polyopisthocotylea in phylogenies based on morphology (Boeger & Kritsky, 1993) and molecules (Mollaret et al, 2000;Jovelin & Justine, 2001;Olson & Littlewood, 2002). Our survey of deep-sea sharks, with many negative results, emphasizes one of the major problems with hexabothriids, which is that specimens are rare.…”

Neonchocotyle violantei n. sp. (Monogenea, Hexabothriidae) from Pseudobatos lentiginosus (Rhinopristiformes, Rhinobatidae) of Yucatán, Gulf of Mexico

“…Despite the increase in the number of studies of the phylogenetic relationships of monogeneans using morphological features (BOEGER & KRITSKY, 1989, 1993CHISHOLM et al, 1995;WHITTINGTON, 2004), there still exist confusion between characters (morphological features) and the states (derived forms) of those characters. All of the states of a particular character are homologous.…”

Branchotenthes octohamatus sp. n. (Monogenea: Hexabothriidae) from the gills of the southern fiddler ray, Trygonorrhina fasciata (Rhinobatidae) in South Australia: description of adult and larva

“…Most evolutionary hypotheses are based on the assumption that a reduction in the number of haptoral hooklets has occurred from the ancestral state, widely thought to be 16 (Bychowsky 1957, Llewellyn 1970, Boeger and Kritsky 1993. However, Malmberg (1986, 1990 expressed an alternative view, suggesting progressive rather than regressive evolution in the number of haptoral hooklets.…”