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 Infraorder AMPHIPORINA Morphological circumscription Eumonostilifera with a two-layered (inner longitudinal and outer circular) muscular rhynchocoel wall and a single vascular plug; exceptions include Carcinonemertes Coe, 1902 , Ovicides Shields, 2001 , Malacobdella Blainville, 1827 , and certain species of Ototyphlonemertes Diesing, 1863 , which lack a vascular plug. Clade definition Monostiliferous hoplonemerteans that are more closely related to Amphiporus lactifloreus ( Johnston, 1828 ) than to Oerstedia dorsalis ( Abildgaard, 1806 ) . Remarks A clade of eumonostiliferan species more closely related to Amphiporus Ehrenberg, 1831 than to Oerstedia Quatrefages, 1846 was consistently recovered in previous molecular studies ( Thollesson & Norenburg 2003 ; Strand & Sundberg 2005a ; Sundberg & Strand 2007 ; Sundberg et al . 2007, 2009; Kajihara et al . 2011 ; Andrade et al . 2012 ; Kajihara & Kuris 2013 ; Taboada et al . 2013 , 2018 ; Kvist et al . 2014 , 2015 ; Chernyshev & Polyakova 2018a , b), but had lacked a formal scientific name before Chernyshev & Polyakova (2019) referred to it as Amphiporina , a rankfree clade name. The taxon is here assigned infraorder rank. As with the case in Oerstediina , I leave the ending as it was proposed by Chernyshev & Polyakova (2019) , although the suffix -ina should be used for the name of a subtribe in accordance with Article 29.2 of the Code (ICZN 1999) when the taxon is placed in any of the family-group ranks. The name Amphiporina was first proposed by Ehrenberg (1828 –1831: 60) (see Nomenclatural notes below). Table 5 lists species that have been molecularly ascertained to be affiliated with Amphiporina . Of the 54 species listed, 29 are known to have a single vascular plug ( Table 6 ; Fig. 3 A–E). Among the remaining 25, the six species, Nemertovema hadalis Chernyshev & Polyakova, 2018a , Nemertovema norenburgi Chernyshev & Polyakova, 2019 , Ototyphlonemertes correae Envall, 1996 , Ovicides paralithodis Kajihara & Kuris, 2013 , Proamphiporus crandalli Chernyshev & Polyakova, 2019 , and Proamphiporus rectangulus ( Strand et al ., 2014 ) have been reported to lack a vascular plug; for the rest of 19 species, the anatomy of the blood vascular system is unknown. Within Eumonostilifera , species with a single vascular plug have so far been found only in Amphiporina ; no species in Oerstediina have been ascertained to possess a single vascular plug ( Tables 2 , 3 , 5 ). Therefore, it appears certain that the 147 species listed in Table 6 —species reported to possess a single vascular plug—likely belong in Amphiporina . As noted above, however, the absence of a single vascular plug does not necessarily denote an affiliation to Oerstediidae . Interestingly, Amphiporina harbours more species than Cratenemertea + Oerstediina combined. One of the significant findings of Thollesson & Norenburg (2003) was that Malacobdella Blainville, 1827 nest-ed among monostiliferans. Species in Malacobdella live in the bivalve mantle cavity, attached to their host by their posterior ventral sucker ( Vázquez et al . 2009 ). Unlike other nemerteans, they are suspension feeders ( Gibson & Jennings 1969 ), and their proboscis completely lacks a stylet apparatus (e.g., Riepen 1933 ). Having a highly specialized morphology, Malacobdella had been placed outside Monostilifera in a different higher taxon variably named Bdellomorphae ( Blanchard 1847 ), Bdellonemertini ( Wijnhoff 1913 ) , Bdellonemertea ( Coe 1943 ; Iwata 1960 ), or Bdellomorpha ( Chernyshev 2003a ); Thollesson & Norenburg (2003) brought an end to these higher taxa. No mention has been made in previous literature to any contact between the rhynchocoel and the blood vascular system in Malacobdella (e.g., Kennel 1877 –1878; Oudemans 1885 ; Maclaren 1901 ; Riepen 1933 ; Gibson & Jennings 1967 ). My examination of Malacobdella japonica Takakura, 1897 revealed that the mid-dorsal blood vessel—while it does lack a single vascular plug—sends off at least three branches of vessels anterodorsally near its anterior end, each penetrating into the ventral portion of the rhynchocoel muscular wall without protruding into the rhynchocoel lumen, and terminating in a blind end that contains basophilic substances ( Fig. 4 A–D). While these branches may compensate for the function of the vascular plug in terms of material transfer between the rhynchocoel and blood vessel, their fine structure and taxonomic distribution should be further studied to understand their physiological function and evolutionary significance. In the tree in Thollesson & Norenburg (2003) , Carcinonemertes cf. carcinophila imminuta (K̂lliker, 1845) was the sister group to all other Distromatonemertea. This topology was probably due to long-branch attraction ( Felsenstein 1978 ; Philippe et al . 2005 ) caused by an increased substitution rate in these decapod-egg parasites. Subsequent molecular studies showed Carcinonemertes as either the sister group to all other Amphiporina ( Andrade et al . 2012 ; Kajihara & Kuris 2013 ) or nested among the latter ( Kvist et al . 2014 ). Species in Carcinonemertidae lack a middorsal vessel ( Humes 1942 ) and thus do not have a vascular plug. In Ovicides paralithodis Kajihara & Kuris, 2013 , the cephalic vessels do not protrude into the rhynchocoel as they pass through the cerebral ring, although they are tightly attached to the rhynchocoel wall ( Kajihara & Kuris 2013 : fig. 3). FIGURE 3. A–B, Amphiporus lactifloreus ( Johnston, 1828 ) (ICHUM 3280); A, anaesthetized living specimen; B, transverse section showing vascular plug (arrowhead); C–E, Quasitetrastemma stimpsoni ( Chernyshev, 1992 ) (C, D, unregistered specimen, 3 July 2004, Akkeshi; E, ICHUM 5972); C, dorsal surface at anterior end, anaesthetized living specimen; D, ventral surface at anterior end, anaesthetized living specimen; E, transverse section showing vascular plug (arrowhead). Scale bars: 2 mm (A); 50 µm (B, E); no scales for C, D. TABLE 5. List of 54 species confirmed by means of molecular phylogenetic analyses to constitute Amphiporina .

Species	Source
Amphiporus allucens Bürger, 1895	Strand & Sundberg (2005a)
Amphiporus angulatus ( Müller, 1774 )	Thollesson & Norenburg (2003)
Amphiporus formidabilis Griffin, 1898	Thollesson & Norenburg (2003) ; Kvist et al. (2014)
Amphiporus imparispinosus Griffin, 1898	Thollesson & Norenburg (2003) ; Andrade et al . (2012)
Amphiporus lactifloreus ( Johnston, 1828 ) *	Thollesson & Norenburg (2003) ; Andrade et al . (2012)
Amphiporus ochraceus ( Verrill, 1873 )	Strand & Sundberg (2005a)
Annulonemertes minuscula Berg, 1985	Sundberg & Strand (2007)
Arenogigas armoricus Krämer & D̂hren, 2015 *	Krämer & D̂hren (2015)
Carcinonemertes carcinophila (K̂lliker, 1845)	Andrade et al . (2012)
Carcinonemertes conanobrieni Simpson et al ., 2017	Simpson et al. (2017)
Cyanophthalma obscura ( Schultze, 1851 ) *	Strand & Sundberg (2005a)
Emplectonema buergeri Coe, 1901 *	Thollesson & Norenburg (2003) ; Andrade et al . (2012) ; Chernyshev & Polyakova (2019)
Emplectonema gracile ( Johnston, 1837 ) *	Thollesson & Norenburg (2003) ; Andrade et al . (2012)
Emplectonema neesii ( Örsted, 1843 )	Strand & Sundberg (2005a)
Geonemertes pelaensis Semper, 1863 *	Mateos & Giribet (2008) ; Andrade et al . (2012)
Gurjanovella littoralis Ushakov, 1926 *	Thollesson & Norenburg (2003)
Malacobdella grossa ( Müller, 1776 )	Thollesson & Norenburg (2003) ; Strand & Sundberg (2005a) ; Andrade et al . (2012) ; Kvist et al. (2014)
Nemertopsis bivittata ( Delle Chiaje, 1841 )	Thollesson & Norenburg (2003) ; Andrade et al . (2012)
Nemertovema hadalis Chernyshev & Polyakova, 2018a †	Chernyshev & Polyakova (2018a)
Nemertovema norenburgi Chernyshev & Polyakova, 2019 †	Chernyshev & Polyakova (2019)
Ototyphlonemertes correae Envall, 1996 †	Andrade et al . (2012)
Ototyphlonemertes macintoshi Bürger, 1895	Andrade et al . (2012)
Ototyphlonemertes pallida ( Keferstein, 1862 )	Kvist et al . (2014)
Ovicides paralithodis Kajihara & Kuris, 2013 †	Kajihara & Kuris (2013)
Paranemertes peregrina ( Coe, 1901 ) *	Thollesson & Norenburg (2003)
Paranemertes sanjuanensis Stricker, 1982 *	Thollesson & Norenburg (2003)
Poseidonemertes collaris Roe & Wickham, 1984 *	Thollesson & Norenburg (2003)
Poseidonemertes maslakovae Chernyshev, 2002 *	Kvist et al . (2015)
Proamphiporus crandalli Chernyshev & Polyakova, 2019 †	Chernyshev & Polyakova (2019)
Proamphiporus kaimeiae Hookabe et al ., 2020	Hookabe et al . (2020)
Proamphiporus rectangulus ( Strand et al ., 2014 ) †	Strand et al. (2014)
Prosorhochmus americanus Gibson et al ., 1986	Andrade et al . (2012)
Prosorhochmus belizeanus Maslakova & Norenburg, 2008a *	Taboada et al. (2018)
Prosorhochmus chafarinensis Frutos et al ., 1998 *	Taboada et al. (2018)
Prosorhochmus claparedii Keferstein, 1862 *	Taboada et al. (2018)
Prostoma eilhardi ( Montgomery, 1894 ) *	Strand & Sundberg (2005a) ; Andrade et al . (2012)
Prostoma graecense (B̂mig, 1893) *	Strand & Sundberg (2005a)
Psammamphiporus elongatus ( Stephenson, 1911 ) *	Andrade et al . (2012)
Quasitetrastemma stimpsoni ( Chernyshev, 1992 ) *	Strand & Sundberg (2005a) ; Kvist et al. (2015)
Raygibsonia bergi Sundberg et al ., 2009 *	Sundberg et al . (2009)
Sacconemertopsis belogurovi Chernyshev, 1991a	Kvist et al . (2015)
Tetrastemma candidum ( Müller, 1774 ) *	Strand & Sundberg (2005a)

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Species	Source
Tetrastemma coronatum ( Quatrefages, 1846 ) *	Strand & Sundberg (2005a)
Tetrastemma flavidum Ehrenberg, 1828 *	Strand & Sundberg (2005a)
Tetrastemma laminariae Ushakov, 1928	Strand & Sundberg (2005a)
Tetrastemma longissimum Bürger, 1895 *	Strand & Sundberg (2005a)
Tetrastemma melanocephalum ( Johnston, 1837 ) *	Strand & Sundberg (2005a)
Tetrastemma peltatum Bürger, 1895	Strand & Sundberg (2005a)
Tetrastemma pseudocoronatum Chernyshev, 1998b *	Chernyshev & Polyakova (2019)
Tetrastemma robertianae McIntosh, 1874 *	Strand & Sundberg (2005a)
Tetrastemma vermiculum ( Quatrefages, 1846 ) *	Strand & Sundberg (2005a)
Tortus tokmakovae Chernyshev, 1991b	Chernyshev & Polyakova (2019)
Zygonemertes simoneae Corrêa, 1961 *	Thollesson & Norenburg (2003)
Zygonemertes virescens ( Verrill, 1879 ) *	Thollesson & Norenburg (2003) ; Strand & Sundberg (2005a) ; Andrade et al . (2012)

*Possesses a single vascular plug on the mid-dorsal vessel (see Table 6 ). †Reported to lack a vascular plug (see Table 4 ). TABLE 6. The 147 species reported to have a single vascular plug on the mid-dorsal blood vessel, and thus to constitute Amphiporina .

Species	Source
Aegialonemertes chlorophthalma Gibson, 1990b	Gibson (1990b)
Africanemertes swakopmundi Stiasny-Wijnhoff, 1942	Stiasny-Wijnhoff (1942)
Alaonemertes michaelseni Stiasny-Wijnhoff, 1942	Stiasny-Wijnhoff (1942)
Alaxinus oclairi Gibson et al ., 1990	Gibson et al . (1990)
Ammonemertes erseusi Gibson, 1990b	Gibson (1990b)
Amphiporus antifuscus Iwata, 1954	Kajihara (pers. obs.)
Amphiporus arcticus Punnett, 1901a	Joubin (1890 : pl. XXX, fig. 7, as A. marmoratus )
Amphiporus cruciatus Bürger, 1893	Bürger (1893)
Amphiporus cruentatus Verrill, 1879	Coe (1904)
Amphiporus dubius Hubrecht, 1879	Bürger (1895 : pl. 15, fig. 20)
Amphiporus fuscosparus Korotkevitsch, 1977	Korotkevitsch (1977)
Amphiporus korschelti Friedrich, 1939	Friedrich (1939)
Amphiporus lactifloreus (Jonston, 1828) *	Oudemans (1855); this study
Amphiporus microocelli ( Sun, 1995a )	Sun (1995a)
Amphiporus mortonmilleri Gibson, 2002	Gibson (2002)
Amphiporus spinosissimus Bürger, 1893	Bürger (1893)
Amphiporus spinosus Bürger, 1893	Bürger (1893)
Amphiporus superbus ( Stimpson, 1854 )	Berg (1973)
Amphiporus vaillanti Joubin, 1902	Joubin (1902)
Amphiporus virgatus Bürger, 1895	Bürger (1895) ; Gibson & Crandall (1989) commented that this species may be related to Nipponnemertes
Arctonemertes ussuriensis Chernyshev, 1998a	Chernyshev (1998a)
Arenogigas armoricus Krämer & D̂hren, 2015 *	Krämer & D̂hren (2015)
Arhochmus korotneffi ( Bürger, 1895 )	Maslakova & Norenburg (2008a)
Atrionemertes greenlandica Senz, 1993b	Senz (1993b)

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