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 OERSTEDIIDAE Chernyshev, 1993 Morphological circumscription Oerstediina having a two-layered rhynchocoel wall; the cephalic vessels protrude into the rhynchocoel as they pass through cerebral ring; the mid-dorsal vessel does not penetrate the rhynchocoel to form a vascular plug. Clade definition Eumonostiliferans that are more closely related to Oerstedia dorsalis ( Abildgaard, 1806 ) than to Plectonemertes sinensis Gibson, 1990a . See the clade definition for Plectonemertidae for the potential problem stemming from the absence of molecular sequence data for Plectonemertes sinensis . Remarks Thollesson & Norenburg (2003) were the first to recognize the clade Oerstediidae , as treated herein, which in their molecular phylogeny included Antarctonemertes varvarae Chernyshev, 1999 ; Nemertellina yamaokai Kajihara et al ., 2000 ; Oerstedia polyorbis Iwata, 1954 [two specimens, erroneously identified as Oerstedia venusta Iwata, 1954 and Oerstedia zebra ( Chernyshev, 1993 ) , respectively; see Akhmatova et al . (2012) for the corrected identifications]; ‘ Tetrastemma ’ elegans ( Girard, 1852 ) ; and ‘ Tetrastemma ’ wilsoni Coe, 1943 . Thollesson & Norenburg (2003) referred to this clade as Tetrastemmatidae , probably because it included two species of ‘ Tetrastemma ’; furthermore, Gibson (1982a) had placed Nemertellina Friedrich, 1935b in Tetrastemmatidae , and Bürger (1895) had once placed Oerstedia Quatrefages, 1846 in Tetrastemmatidae . In a subsequent study by Strand & Sundberg (2005a) , however, Tetrastemma flavidum Ehrenberg, 1828 ( type species of Tetrastemmatidae ) and Oerstedia dorsalis ( Abildgaard, 1806 ) ( type species of Oerstediidae ) appeared in different clades, representing the Amphiporina and Oerstediina , respectively, as treated herein. The name Tetrastemmatidae should thus be used to denote a subclade in the Amphiporina , given the species identification of T. flavidum (see Nomenclatural notes below). Listed in Table 3 are species that have been confirmed to constitute Oerstediidae by means of molecular phylogenetics. Among the 24 species listed, none is known to possess a mid-dorsal vessel that penetrates to form a single vascular plug, and 18 are known to lack a single vascular plug on the mid-dorsal vessel (see also Table 4 ; Fig. 2 A–I); the vascular-system anatomy is unknown for the remaining six species. Instead of a vascular plug from the mid-dorsal vessel, these 18 species tend to have cephalic vessels protruding into the rhynchocoel lumen as they pass through the cerebral ring ( Fig. 2 F–G; Kajihara et al. 2000 : fig, 19; Kajihara et al . 2011 : fig. 24), although the protrusions can be subtle in smaller specimens ( Fig. 2H, I ). In larger species and specimens, the vascular epithelium in these protruding portions may be thickened ( Fig. 2A ) and specialized ( Fig. 2D ), so that these could be referred to as ‘vascular plugs’ (perhaps a different terminology for the ‘plugs’ in Oerstediina may prevent confusion: Gibson [pers comm.] suggests ‘monovascular plug’ and ‘bivascular plugs’ respectively, which I now propose). The ‘vascular plug’ (or, vascular protrusion into the rhynchocoel) in hoplonemerteans presumably functions to facilitate material transfer between the blood vascular system and the rhynchocoel ( Crandall 1993a ). Therefore, small-bodied species may actually lack a vascular plug because diffusion could compensate for its function. FIGURE 2. A, ‘ Emplectonema ’ mitsuii Yamaoka, 1947 (ICHUM 5968), transverse section immediately behind proboscis insertion, showing cephalic vessels (arrowheads) with medially modified epithelium; B–D, Gononemertes parasita Bergendal, 1900 (ICHUM 5971); B, dorsal surface at anterior end, anaesthetized living specimen; C, ventral surface at anterior end, anaesthetized living specimen; D, transverse section through brain ring, showing cephalic vessels (arrowheads) protruding into the rhynchocoel; E–G, Oerstedia dorsalis ( Abildgaard, 1806 ) (ICUM 3274); E, anaesthetized specimen in living state; F, G, transverse sections through brain ring, showing cephalic vessels (arrowheads) protruding into rhynchocoel; H, I, Oerstedia polyorbis Iwata, 1954 (H, ICHUM 3287; I, ICHUM 3288), transverse sections through brain ring, showing cephalic vessels (arrowheads) protruding into rhynchocoel. Scale bars: 100 µm (A, D); 50 µm (F–I); no scales for B, C, E. TABLE 3. List of 24 species that have been confirmed by means of molecular phylogenetic analyses to constitute Oerstediidae Chernyshev, 1993 . Generic names in quotation marks indicate that the species should be transferred to a proper genus, because the type species of the genus belongs in Amphiporina .

Species	Source
Abyssonemertes kajiharai Chernyshev & Polyakova, 2018a *	Chernyshev & Polyakova (2018a)
Antarctonemertes dilutebasisae ( Kulikova, 1987 ) *	Taboada et al . (2018)
Antarctonemertes phyllospadicola ( Stricker, 1985 ) *	Maslakova & D̂hren (2009); Taboada et al . (2013)
Antarctonemertes riesgoae Taboada et al ., 2013 *	Taboada et al . (2013)
Antarctonemertes unilineata ( Joubin, 1910 ) †	Taboada et al . (2018)
Antarctonemertes valida ( Bürger, 1893 ) *	Taboada et al . (2013)
Antarctonemertes varvarae Chernyshev, 1999 *	Thollesson & Norenburg (2003)
Diplomma polyophthalma ( Gibson & Sundberg, 2001 ) *	Strand & Sundberg (2005a) ; Kajihara et al. (2011)
Diplomma serpentina ( Stimpson, 1855 ) *	Kajihara et al . (2011)
‘ Emplectonema ’ mitsuii Yamaoka, 1947 *	Kajihara et al . (2011)
Galatheanemertes giribeti Chernyshev & Polyakova, 2019 *	Chernyshev & Polyakova (2019)
Gononemertes parasita Bergendal, 1900 *	Kajihara et al . (2011) ; Andrade et al . (2012)
Nemertellina yamaokai Kajihara et al ., 2000 *	Thollesson & Norenburg (2003) ; Kajihara et al . (2011)
Oerstedia dorsalis ( Abildgaard, 1806 ) *	Strand & Sundberg (2005a)
Oerstedia polyorbis Iwata, 1954 *	Thollesson & Norenburg (2003) ; Akhmatova et al . (2012)
Oerstedia striata Sundberg, 1988 *	Strand & Sundberg (2005a)
“ Prosorhochmus nelsoni” ( Sánchez, 1973 ) ‡	Andrade et al . (2012)
Tetranemertes antonina ( Quatrefages, 1846 )	Kvist et al . (2014)
Tetraneuronemertes lovgreni Sundberg et al ., 2007 *	Strand & Sundberg (2007)
‘ Tetrastemma ’ elegans ( Girard, 1852 )	Thollesson & Norenburg (2003)
‘ Tetrastemma ’ vittigerum ( Bürger, 1904a )	Kvist et al . (2014)
‘ Tetrastemma ’ wilsoni Coe, 1904	Thollesson & Norenburg (2003)
Vieitezia luzmurubeae Junoy et al ., 2011 *	Junoy et al . (2011) ; Andrade et al . (2012) ; Kvist et al . (2014)
Vulcanonemertes rangitotoensis Gibson & Strand, 2002 *	Strand & Sundberg (2005a)

*Lacks a single vascular plug from the mid-dorsal vessel (see Table 4 ; Fig. 2 ). †Judging from the shape of the head, Antarctonemertes unilineata ( Joubin, 1910 ) of Taboada et al . (2018) is different from Tetrastemma unilineatum Joubin, 1910 of Gibson & Tait (1984) ; furthermore, the latter has been reported i ) to lack an accessory lateral nerve and ii ) to possess a single vascular plug from the mid-dorsal vessel (see Table 6 ), each of which suggests a non- Antarctonemertes identity. ‡ “ Prosorhochmus nelsoni ” of Andrade et al . (2012) represents a different species, most likely as the result of mislabelling or a sample mix-up. Among specimens collected in Coquimbo ( Chile ) on 2 February 2009 by Per Sundberg were NemPhyl 27 (DNA105586 at Museum of Comparative Zoology, Harvard; COI accession number HQ848606 ) and the three specimens NemBar0842–0844 (COI accession numbers KU840164 – KU840166 ; identical sequences); NemPhyl 27 was used in Andrade et al . (2012) . BLAST searches with KU840164 – KU840166 (NemBar0842–0844) indicate a 100% match with EF157586 [ P. nelsoni identified by Maslakova & Norenburg (2008a) ] and close similarity to other congeners [ P. belizeanus ( EF157591 ), P. claparedii ( MH106532 ), and P. americanus ( HQ848595 )]. However, HQ848606 (NemPhyl 27) differs from KU840164 – KU840166 and EF157586 by 15.8% in uncorrected p -distance. Prosorhochmus nelsoni of Maslakova et al. (2005) ( Table 6 ) has been reported to possess a vascular plug. ‘ Emplectonema ’ mitsuii Yamaoka, 1947 , ‘ Tetrastemma ’ elegans ( Girard, 1852 ) , ‘ Tetrastemma ’ vittigerum ( Bürger, 1904a ), and ‘ Tetrastemma ’ wilsoni Coe, 1904 should each be transferred to a proper genus in the Oerstediidae , because the type species of Emplectonema and Tetrastemma belong in the Amphiporina . Within the Oerstediidae , at least Antarctonemertes Friedrich, 1955 , Gononemertes Bergendal, 1900 , and Oerstedia Quatrefages, 1846 (as currently recognized) seem to be non-monophyletic ( Taboada et al . 2013 , 2018 ; Kvist et al . 2015 ). Although some well-supported subclades are evident [e.g., Gononemertes Bergendal, 1900 + Vieitezia Junoy et al ., 2011 (Ju-noy et al . 2011); Tetraneuronemertes Sundberg et al ., 2007 + Nemertellina Friedrich, 1935b ( Kajihara et al . 2011 )], implementation of a subfamily classification seems to be premature, especially in the absence of sequence data for Obuergeria palma Corrêa, 1954 , the type species for Obuergerinae. Species that have been reported to lack a single vascular plug are listed in Table 4 . Many of the species in Table 4 may belong to the Oerstediidae . However, lack of a vascular plug does not necessarily mean an oerstediid affiliation, because some Amphiporina species lack a single vascular plug from the mid-dorsal vessel ( Table 5 ). TABLE 4. List of 70 species reported to lack a single vascular plug on the mid-dorsal blood vessel, and thus possibly constituting Oerstediidae Chernyshev, 1993 . Generic names in quotation marks indicate that the species should be transferred to a an alternative valid genus, because the type species of the genus belong in Amphiporina .

Species	Source
Abyssonemertes kajiharai Chernyshev & Polyakova, 2018a *	Chernyshev & Polyakova (2018a)
Aenigmanemertes norenburgi Sundberg & Gibson, 1995	Sundberg & Gibson (1995)
Africanemertes ruetzleri Kirsteuer, 1965	Kirsteuer (1965)
‘ Amphiporus ’ atypicus Friedrich, 1935a	Friedrich (1935a)
Antarctonemertes dilutebasisae ( Kulikova, 1987 ) *	Chernyshev (1999)
Antarctonemertes papilliformis ( Korotkevitsch, 1977 )	Chernyshev (1999)
Antarctonemertes phyllospadicola ( Stricker, 1985 ) *	Stricker (1985)
Antarctonemertes riesgoae Taboada et al ., 2013 *	Taboada et al . (2013)
Antarctonemertes valida ( Bürger, 1893 ) *	Taboada et al . (2013)
Antarctonemertes varvarae Chernyshev, 1999 *	Chernyshev (1999)
Cryptonemertes actinophila ( Bürger, 1904b )	Gibson (1986a)
Correanemertes gordoni Gibson, 2002	Gibson (2002)
Digononemertes australiensis Gibson, 1990b	Gibson (1990b)
Diplomma albimarginata ( Kirsteuer, 1965 )	Kirsteuer (1965)
Diplomma bothwellae ( Gibson, 1982b )	Gibson (1982b)
Diplomma polyophthalma ( Gibson & Sundberg, 2001 ) *	Strand & Sundberg (2005a) ; Kajihara et al . (2011)
Diplomma serpentina ( Stimpson, 1855 ) *	Kajihara et al . (2011)
Elcania patagonica Moretto, 1970	Moretto (1970)
‘ Emplectonema ’ mitsuii Yamaoka, 1947 *	this study (Fig. 2A)
Galatheanemertes giribeti Chernyshev & Polyakova, 2019 *	Chernyshev & Polyakova (2019)
Gononemertes australiensis Gibson, 1974	Gibson (1974)
Gononemertes parasita Bergendal, 1900 *	this study (Fig. 2B–D)
Halimanemertes slacksmithae Gibson, 1990b	Gibson (1990b)
Ischyronemertes albanyensis Gibson, 1990b	Gibson (1990b)
Ischyronemertes erythrophleps Gibson, 1990b	Gibson (1990b)
Ischyronemertes heterophthalma ( Schmarda, 1859 )	Senz (1997)
Ischyronemertes tetrophthalma Gibson, 1990b	Gibson (1990b)
Meionemertes polygonimos Gibson, 1986b	Gibson (1986b)
Nemertellina tropica Kirsteuer, 1965	Kirsteuer (1965)
Nemertellina yamaokai Kajihara et al ., 2000 *	Kajihara et al. (2000)
Nemertopsis tetraclitophila Gibson, 1990	Gibson (1990a)
Nemertovema hadalis Chernyshev & Polyakova, 2018a †	Chernyshev & Polyakova (2018a)
Nemertovema norenburgi Chernyshev & Polyakova, 2019 †	Chernyshev & Polyakova (2019)
Noteonemertes novaezealandiae Gibson, 2002	Gibson (2002)
Obuergeria palma Corrêa, 1954	Corrêa (1954)
Oerstedia crassus ( Senz, 1993c )	Senz (1993c)

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