Higher classification of the Monostilifera (Nemertea: Hoplonemertea) Author Kajihara, Hiroshi text Zootaxa 2021 2021-01-28 4920 2 151 199 journal article 8401 10.11646/zootaxa.4920.2.1 ec1a3d33-651e-499c-b775-b42a131ec75a 1175-5326 4475126 C369AA2D-29D5-4DDF-BFE2-EA4FC4AD2703 Family PLECTONEMERTIDAE Gibson, 1900a Morphological circumscription Oerstediina having a wickerwork rhynchocoel wall; the cephalic vessels protrude into the rhynchocoel as they pass through the cerebral ring to form a pair of vascular plugs; the mid-dorsal vessel does not penetrate the rhynchocoel to form a vascular plug. Clade definition Eumonostiliferans that are more closely related to Plectonemertes sinensis Gibson, 1990a than to Oerstedia dorsalis ( Abildgaard, 1806 ) . Plectonemertes sinensis has hitherto been known only from the original morphological description ( Gibson 1990a ). For practical purposes, therefore, it has to be proxied by other plectonemertids for which sequence data are available, such as Argonemertes australiensis ( Dendy, 1892 ) (cf. Kvist et al . 2014 ), until Plectonemertes sinensis is eventually sequenced. If Plectonemertes sinensis appears in a different clade, e.g., Cratenemertea , then this taxon will be referred to as either Acteonemertidae Chernyshev, 2005a or Potamonemertidae Chernyshev, 2005a . Constituent subtaxa Currently, 14 species in eight genera are recognized in Plectonemertidae ( Table 2 ). Remarks TABLE 2. List of eight genera and 14 species in Plectonemertidae Gibson, 1990a .

Genus	Species
Acteonemertes Pantin, 1961	Acteonemertes bathamae Pantin, 1961
Antiponemertes Moore & Gibson, 1985	Antiponemertes allisonae (Moore, 1973)
ditto	Antiponemertes novaezealandiae ( Dendy, 1895 )
ditto	Antiponemertes pantini ( Southgate, 1954 )
Argonemertes Moore & Gibson, 1985	Argonemertes australiensis ( Dendy, 1892 )
ditto	Argonemertes dendyi ( Dakin, 1915 )
ditto	Argonemertes hillii ( Hett, 1924 )
ditto	Argonemertes stocki ( Moore, 1975 )
Campbellonemertes Moore & Gibson, 1972	Campbellonemertes johnsi Moore & Gibson, 1972
Katechonemertes Moore & Gibson, 1981	Katechonemertes nightingale nsis ( Brinkmann, 1943 )
Leptonemertes Girard, 1893	Leptonemertes chalicophora ( Graff, 1879 )
Plectonemertes Gibson, 1990a	Plectonemertes sinensis Gibson, 1990a
Potamonemertes Moore & Gibson, 1973	Potamonemertes gibsoni Hickman & Moore, 1990
ditto	Potamonemertes percivali Moore & Gibson, 1973

Crandall’s (2001) morphology-based cladistic analyses of monostiliferous hoplonemerteans with interwoven rhynchocoel musculature suggested that i ) the marine genus Plectonemertes Gibson, 1990a , ii ) the freshwater genera Campbellonemertes Moore & Gibson, 1972 and Potamonemertes Moore & Gibson, 1973 , and iii ) the terrestrial genera Acteonemertes Pantin, 1961 , Antiponemertes Moore & Gibson, 1981 , Argonemertes Moore & Gibson, 1981 , Katechonemertes Moore & Gibson, 1981 , and Leptonemertes Girard, 1893 could each warrant a separate family. Chernyshev (2005a) implemented Crandall’s (2001) results and established Acteonemertidae (for Acteonemertes , Antiponemertes , Argonemertes , Katechonemertes , and Leptonemertes ) and Potamonemertidae (for Campbellonemertes and Potamonemertes ). However, recent molecular phylogenetic results are not necessarily concordant with Crandall’s (2001) morphology-based tree topology. For instance, in Kvist et al . (2014) , Argonemertes australiensis ( Dendy, 1892 ) is more closely related to Potamonemertes percivali Moore & Gibson, 1973 than to Leptonemertes chalicophora ( Graff, 1879 ) , making Acteonemertidae (or, Acteonemertinae, if placed at the subfamily rank) nonmonophyletic. Implementation of a subfamily classification for Plectonemertidae (in the sense of this paper) thus seems premature. The type species for the Plectonemertidae , Plectonemertes sinensis Gibson, 1990a ( type locality: Hong Kong , subtidal, 21 m depth), has been described morphologically from only a single specimen. Sequence data for Plectonemertes sinensis are a prerequisite for plectonemertid systematics, but attempts to collect more individuals of this species have so far been unsuccessful ( Chernyshev 2011b , 2016 ). Nomenclatural note As discussed by Crandall (2001: 105) , the authorship of the generic names Argonemertes and Antiponemertes is ascribed to Moore & Gibson (1985) , who made the names nomenclaturally available, although these were first proposed without type designation by Moore & Gibson (1981) .