Potamostoma shizunaiense gen. et sp. nov. (Nemertea: Hoplonemertea: Monostilifera): a new brackish-water nemertean from Japan

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ZOOLOGICAL SCIENCE 20i 491-500 (2003) @ 2003 Zoologica Slociet yof Japan
Potamostoma shizunaiense gen.et sp. nov. (Nemertea:

Hoplonemertea:Monostiliferaa):New Brackish-Water

Nemertean fromJapan

Hirosh iKajiharai R'a,y Gibson2 ,and Shunsuke F, Mawatarii
iDivision of Biologic Saciiences G,taduat eSchool of Science H,okkaido Univetsity)
Sapporo060-0810,Japan

2Schooi of Biologica aind farth Sciences, Liverpoo lJohn Anoore sUniversity,
Byrom Street,LivetpootL3 YtFLU.K.

ABSTRACT-ibtamostoma shizunaiense gen, et sp. nov. (Nemert eHaop:lonemertea :Monostilif erias)
describe fdrom the mouth of the River Shizuna iH,okkaido ,Japan ,This genus is readily distinguishe dfrom
other monostiliferans by an oesophagus opening fa ranteriorly int othe rhynchodaeum, a well developed
excretory system extending the whole body lengt ht,erminals of the excretory collecting tubules situated
between the body wall circular muscle laye rand the dermis ,and bilobed testes in males,
Key words:Nemertea, excretory system, Hokkaido, the River Shizunai
INTRODUCTION tmoon2osptisluif,erous hoplonemertea ninhabiti nign salinity down

Nemertean worms (phyl uNmemertea) ,with approxi- Curren tclassifications of nemerteans, particu]arly
mateiy 1150 known species {Gibs o1n9,95) ,are typically above generi clevel ,are in need of thorough taxonomic revi-
marine invertebrate sbut several species are known to occur sion {Gibso n19,85). The tradition atlaxonomic scheme will
in brackish waters and some have been able to colonise change in the futur (eSundbe arndg Gibson ,1995). The new
either freshwater or terrestri ahlabitats ,Some species of species is not assigned to family for thi sreason,
brackish-wate rnemerteans are known to thriv ein stable,
albeit reduced, salinities .An example i sthe hoplonemertean MATERIAL AND METHODS
byanophtha olbmscaura (Schult z1e8,51) ,which has been
foundinsaltmarshes orsaltmarsh poolson theAtlantic Specimens of the nemerteans were collected from beneath
coast of Nor th Americ a (No renb ur19g8,6 }, and is very Jstaopneasn (o4n 2sean2d0 '1a4Nt2 ",t2h2'e Em)o ounth 9 Moafy t h19e 9R6,i v1e6r NSohviezmubneari 1,H9o9k7ka,i adnod,
common in the Gulf of Finland where salinities are below 5- 24 November 1999. Sampling was carried out at ebb t[d ewhen the
6 psu (Brunberg,1 O9n6 t4h)e .other hand, there have been sa)inity was about 2 psu. The nemerteans were anaesthetised
only a few reports on species inhabitin gin those environ- either in 4% MgC12 or MS222, fixe d[n Bouin' ssolution for 24hr,
mgaenrndot svQ,e i s ,ww1ah9merp9es1,; l twrhaievt ears , a1mlo9iun7tih0st; y Mf oloourrc etbu raaantdce k$ Griaispibhdsl-yo,lna , kl1(ei9esk8 e1, i) gGn (i.mTbansa-obnle e1mOme0bbt ehsdoeFdde,rmdv. abtMu[ otois fnn tos5 or n6so- ent5ceh7te' i Csoslnt isy dml,e ewptse, era erppLpa earsr astahtufaasfiein mne wadao txf ob1 xy1a y nldtsiph eaenscn iedmcMe taneisloolsnoiner dyw ewatartsre i6 c,um hsar7edo deo.mre
l). by the squeezing method describe dby Kirsteuer (1967>,
Durin gthe fir satuthor's fauna lstudy around Hokkaido, Type material and voucher specimens are deposite din the
northern Japan ,a hoplonemertea snpecies was obtained at Zoological lnstitut eH,okkaido Universit Jya,pan {ZIHU).
the mouth of the River Shizuna iS.ubsequen htistological Abbreviation sused in figures.
study revealed that the combination of morphological char- ae = apical organ: ap = anterior pouch of ]ntesti ncaalecum; br =
acters found in the presen tnemerteans excludes them from brain c;g = cephalic gland; cm = body-wal lcircular muscle layer c;o
aplal poef r tahiem sd etsoc rdiebse cdgreinb eetrha e ofn ewMo ngoesntuisl ianfd erT ahs,epe cpierses eofnt =de xmc e =r=e bderxoaclrrse otsovereynnsto rrcaoyll lmoeucrstgcilaneng;; c tvduv b= u =lc eem pi;hgda-lid iocr=s a olbrlao nvogedes s-veselst;saei len;pi n dg= e ea =cpii dddoepehrrLm[miiiscs;;
gland cell ;g2 = purple-stain ibnasgoph"ic gland cell; gc = glandular
'Correspondingauthor:Tel. [phone]; component oi cerebrai sensory organ; ic = intesti ncaalecum; i l=
FAX, [phone]. inner layer of body wall longitudi nmauslculature; in = intestine ;Id
E-rnaH/[email protected],ac,jp = later adliverticul uomf intestina lcaecum; lm = body-wal llongitu-
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Table 1. Nemertean species recorded trom estuarine or other brackish-wat eharbitats.
Species Comments
HETERONEMERTEA
Amniclineu szhttiangensis Gibso nand Qi ,1991 Found in the lower par tof the Pearl River ,People' sRepubRc ot China, mostly in
treshwate cronditions (<O .p5su) but the habita otccasionally reaches a maximum
salinity of about 1O.9 psu (G[bs oanmd Qi, 1991),
Ninumanemertes kikuch iliwata ,1970 ln mud, Lake Hinuma, Honshu, Japan; the salinit oyf the lake varies trom about 15
psu in summer to about 21 psu in winter (lwa t1a97,0>.
Micrur abattica Cantel l1,975 From a muddy substratum, Tvtiren Bay, the Balti ccoast of Sweeden; the salLnity
of the area is usually slightty above 6,5 psu (Berg 1h9,73),
HOPLONEMERTEAMONOSTILIFERA
Amphiporetl baaltic Fariedric h1,940 From the south-western Balti Scea, south of the islan dof Oland, east of Bornholm
(Friedrich,1940).
Amphiporus bicoloreu Ksorotkevic h1,977 Found in interti dsaallinitie dsown to about 18 psu in the Kuril lslands ,Sea of
Okhotsk,Russia(Korotkev19i7c7}h,,

Amphiporus korschei tFiriedrlc 1h9,40 South-wester nBalti Scea, west of the islan dof Bornholm.
Amphiporus obtusoiostris Korotkevjc h1,977 Brackish-wat eirntertj dian slalinities down to about 18 psu, Kuri llsland sS,ea of
Okhotsk,Russia(Korotkev19i7c7h),,

Arenonemertes minutus Fr[edric h19,49 lnterti dian lsand, south-western Balti Scea.
Communoporus cephalonephridialis (Friedr i1c94h0,) From the Balti Scea, west of the islan dof Bornholm.
Communoporus hagmeier i(Fried r1i9c40h), East of Bornholm in the Balti Scea,
Communoporus rhynchocoetomicus {Friedr i1c9h4,0) South of the southern tjp of Sweeden, Balti Scea,
qyanophthat mobascura (Schult z1e85,1) ln salt marshes or salt marsh pools ,Atlanti ccoast of North America (Norenburg,
1986), Balti cSea, and the Guif of Finlan din salinities below 5-6 psu.
Pantinonemerte swinsor Mioore and Gibson ,1981 In brackish-wat emorngrove swamps, under the bark or in cavities of rotting tallen
mangrove trunks, Queensland ,Austral i(aMoor eand Gibson ,1 981).
ProneurotesbalticFariedricht,940 BalticSea.

Sacconemertell lautulen tlawata ,1 970 In mud, Lake Hinuma, Honshu, Japan, salinit yranging from about 5 psu in summer
to 21 psu in winter, occasionally as high as 30 psu at the bottom (lwat a19,70),
Sacconemertes arenosa Karling ,1933 Western end of the Gulf ot Finland, salinity le$ sthan 5-6 psu {Karl i19n3g3},.
Sacconemertopsi sbetoguro Cvhiernyshe 1v9,91 In the upper estuarine region of the River Gladkaya ,Russia ,at salinities of 1-3 psu
(Chernyshev,1991).
Sacconemertopsi soliw'ies alwata ,1970 Lake Hinuma, Honshu, Japan, in mud, salinit yrange approximately 5-21 psu
between summer and winter (lwat 1a9,70).
fetrastemma tridentat aKorotkevich, 1977 Intertid ablrackish-wat edrown to salinitie osf about 18 psu, Kuril lslands ,Sea of
OkhetskR,ussia(Korotkev19[7c7>h,,

dina lmuscle layer I;n = later anlerve cord; lv = later abtlood vessel; coel reaching to posteri oenrd of body; rhynchocoel muscu-
nc = putativ neurse cell ;ng = neuroganglionic component of cere- latur ei ntwo separate layers ;proboscis anterior chamber
b=co repal ;rls oerbndso D=sry cri h syionnrcghsaoend;aret umoL;co np=;r o= c segpl rl=ou sbs; oubos-ecm ui=s sc up;olyea rs=op hp aygglluosar;nud s ;ors:vtc === sorthvoyamnarccyhho;: -pi wlitohn gtihtruede imnu sabclol}de;y -lwaayl emlurs cs(ulaotuuret eanrd w itihn ndeir acgirocnual allra, ymeir d,ldloen-
ts = testi sv;p = vascular plug, gitudin a)laye ranteriorly divided by posteri oerxtensions of
cephalic glands ;pre-cereb rasleptum absent; cephaiic
DESCRIPTION rmeutsrcaucltaotrure ;muscl esoeso pdheagruisved forpoenm inogute ri npto orrthiynocn hoofd aieounmgitu jdiunsalt
Potamostoma gen, nov, behin dprobosci spore ;intesti ncaaelcum with two anterior
fype species: Potamostoma shizunaiense sp. nov. pouches and Iater adliverticu lbal;ood system very well
Etymoiog)n The generi cname (neute irs )formed by combin- developed, with single vascular plug ;cerebral gangll awith
ing the Greek words potamos (= a river) and stoma (= a neither inner neurilemma nor neurochord cells; latera lnerve
mouth) to indicat ethe habjta tin which the animals were cords without accessory nerves but with myofibrillae; periph-
found livin Tgh.e specific epithet is derived from the name eral nervous system well developed ;single apical organ
of the River Shizuna iby adding the Lati nadjectival suffix present ,cephalic glands well developed, extending behind
-ense (= be]onging to), brain ,sub-muscular gland $present; cerebral organ$ close
Diagnosis: Monostiliferou shoplonemertean swith rhyncho- i nfron tof brain e;xcretory system well developed, extending
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throughout body length ,collecting tubule terminals situated method describe dby Kirsteue r(1967 4) s:pecimens, 9 May
between body wall circular muscle layer and dermis ;dioe- t996; 24 specimens, 16 November1997; 4 specimens, 24
cious, testes bilobed, November 1999. Holotype ,immatur efemale ,complete
series of transverse section$, 7 pm, 81 slides (ZIHU-2037>;
paratypes ,immatur emale, transverse sections of anterior
Potamostoma shizunaiense sp. nov. body region, 6 vm, 39 slides, {ZIHU-193 0an)d immature
Material examinect A tota lof 32 livin gindividual swere coi- female ,complete series of transverse sections, 6 pm, 84
lected ,of which 11 were examined in vivo by the squeezlng slides (ZIHU-20 4Ni0n>e .sectioned voucher specimens are
also deposite dunder ZIHU-1931, -1932 ,-1933 ,-2038, -
2039,-2041,-2042,-2043,-2044.

7),pe iocali4 cMouth of the Rive rShizuna iH,okkaido, Japan
{42"20' N1,42022'E) ,under stones on a sandy bottom,
Salini taty ebb tide 2 psu.
E>cterri aiieature sB:ody slender, up to 6 cm long and 1.2
mm wide (Fi g1.) .Head oval or truncat etriangula rshape.
Eyes arranged in four groups ,each containing 2-22 black to
dark green pigment-cup ocelli {Fi g2). .White pigment spots
on mid-dorsal surface of snout, Two pair osf cephalic fur-
rows presen tp;osteri ofrurrows encircle the body, forming
caudally direct eVd-shape on dorsal sunface {Fi g2).. Body
graduaH ytapered posterior elnyd,ing in bluntl yrounded tail.
Genera lbody colour yellowi$h-gr eteo nolive, rhyncho-
coel appearing as yellowish-oc hrmeedian dorsal line
extending almost to posteri otrip O.varie sin ripening females
visible as deep greenis hbands arranged pseudometameri-
cally ln posteri ohral fof body. Latera lnerve cords also visible
through later ablody margins as dark orange line sfringed
with whltish dots.
Body MtalL musculat"re andparenchyma: Epidermi sciliated,
with maximum thickness of about 38 um in anterior body
regions general ltyhinner posterio ralndy in places only 15-
Fig.2 , Potarnostoma shizunaiense gen. et sp. nov, Enlargement
ef the head, viewed dorsally ,to show the arrangement of the eyes
and cephalic furrows T.he positi oonf the brai nlobes and anterior
Fig.1 .Potamostoma shizunaiense gen .et sp, nov, Photograp hof portion osf the later anlerve cords is also indicate dS.cale bar =1
a livin gspecimen, viewed dorsall yS.cale bar = 5 mm, mm.
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20 pm tal l<Fi g3,). Dermis consistently about 5 pm thick sphincter-like layer of circular muscles.
throughou btody {Fi g3),. Rhynchocoel reaching aimost to posterio rtip of body,
Body wall muscles consisted primari lofy outer circular with wall containing separate inner longitudina land outer
and inner ]ongitudi nlaalyer sc;ircular laye r3-7 pm thick and circular muscle Iayer s(Fi 3g). ,Each laye rmostiy 2-5 pm in
frequentl ymuch thinner than dermis ,longitudi nlaalye rvar- thickness ,but circular laye rin posteri oprorti oonf rhyncho-
ies in thickness from 20-55 pm depending upon local coel thickened to about 15 pm,
contraction (Fi g3.). In cerebral region iongitudina llayer Probosci sslightly shorter than body ,white i ncolour
divide dint oouter and inner zones by posteri oexrtensjons when everted. Larger anterior portio n3,0-47% of body
of cephalic gland s(Fi g4A.}, Outer portio nn,ot contributjng diameter when retracted, consisted of papillat eepithelium,
to proboscis inserti oenx,tended to head tip .Most of inner 60-80 pm or more tal l,containing acidophilic gland cel]s,
longitudin amluscle fibre tserminate idn probosci sinsertion, di$tin cctonnective tissue basement laye r,weak laye rof
but a few extended anteriorly surrounding rhynchodaeum outer circular muscles, inne rlongitudj nmauslcle stratum 15
{Fi 4gB,). Cephali cretractor muscles derived from outer por- pm in maximum thicknes sa, delica tienne rcircular musc]e
tion of longitudi nlaalye rT.hin diagonal muscle [ayer (Fig, layer and a flattene dinner linin gP,roboscis nerves running
4C), extending between the two main body wall muscie in longitudin amluscle layer (Fi g5A,); of 12 sectjoned spec-
coats, not enclosed by connective tissue .Dorsoventr amuls- imens one indMdua lpossessed 11 probosci snerves, one
cies moderately well develope din foregu tand intestinal had 12 nerves, and the remainder13.
reglons, Centra lstylet smooth {Fi g5B.) ,variable in lengt h8,2-
Parenchymatou sconnective tissues well developed 110 um long (mea n93 um); basi s98-158 pm long (mean
throughout body lengt h,most obvious beiow rhynchocoel 128 pm), 32-54 pm wide (mea n45 pm) (i vnivo observation;
jus tbehin dbrain. n=1D, Styletibasi rsatio O.62-O.88 (mea nO,73) ,Number of
Proboscis apparatus: Probosci spore ,opening ventral]y just accessory stylet pouches 2-4 {most l3)y, each containing 2-
behind head tip ,leading int oshort ciliated chamber (Fi 4gD,, 4 accessory stylets.
E). Rhynchodaeum with delicat eand uncMated epithelium, Posteri oprrobosci cshamber about 25-35% of the body
1O pm in average thickness (Fi 4gE., F). Immediately in front diamete rw,ith wall containing basophil igciandul aerpithe-
of probosci sinserti onr,hynchodaeum surrounded by lium not torming papilla eou,ter longitudin almuscle layer
e
$g
oe
Fig.3 ,Potamostomashizunaiensegen.etsp.novC.amera lucida drawing of atransverse section to show the organization of the body in the
foregu tregion. Scal ebar = 400 ym.
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iilgiififigg$g$eewwee.gg-Lm-.:
Fig.4 .Potamostomashizunaiensegen,etsp,novA.. Transvers esection through the brai nto show the div]de dbody-'wal llongitudi nmauslcle
Iayer A.rrowheads indica ttehe inne rportio nof the lon g i t u d l nm aus lc ul at u re , B , T r a ns v e r s es e ct i o n t hr o u g ht h e p ; o b o sc i sinsenio,nC.Tangen-
tia lsection through the body wall musculature to show t h e no n -f as c ia te d d i a ge n a li i b re s ,i n d i c at e bd y a rr ow h ea ds , D. Sagitt aslection through
the anterior ti pof the head. E. Higher magnification of the boxed area in D to show the oesophagus opening (indica btye tdhe arrowhead) from
the ventral wall ot the rhynchodaeum jus btehind the probosci spore ,F. Transvers esection near the ti pof the head at the point where the
oesophagus is about te branch off from the rhynchodaeum. Scale bars :A, B, D, F= 1OO pm; C, E = 5e pm.
about 5 um thick ,thin and indisti nicntne rcircular muscle Stomach epithelium <Fi g3,, 5C), reaching to 70 pm or
Iaye rand delica tleini nlgayer N.o nerves were distinguished more in heigh t,dominate dby basophil igcland sbut also
in posterio rportio nof proboscis, contained a few acidophils. Degree of epithelial foldi nvgar-
Afimentary canat Oesophagu smoderately thick-walled, ied among individual sS.tomach gradual lnyarrowed posteri-
opening at ventral wall of rhynchodaeum jus btehin dprobos- orly, with both epithe[ial height and gland cell number
cis pore {Fi g4D., E) .Oesophageal epithelium neither cili- decreasing posterior llye,adln gint onarrow pylori ccanal
ated nor glandula rA.tte rpassing below ventral cerebral (Fi g5D,) opening int odorsa iwall of intestine.
commissure, oesophagus expanded leading to stomach; Intesti ncaalecum with a pair of anterior pouches and
transition ariegion between oesophagus and stomach con- several pair sof deep Iater adlivertic u<lFai 5gD,, 6) :anterior
tained violet-staining basophili cgland cells with granular pouches extended forward to middle porti oonf stomach, not
cytoplasm. reaching brain .Intestin ewith distal lbyranche ddeep lateral
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Fig ,5, Potamostoma shizunaiense gen. et sp. nov. A. Transvers esection through the anterior portio nof the probosci sto show the 13 pro-
boscis nerves, indicated by arrowheads. B. Photomicrograph of a typic aclentral styke tand basis .C. Transverse section throug hthe posterior
region ot the stomach, D, Transvers esectbn throug hthe py)ori cregion of the gut ,E. Transvers esection to show the single vascular plug,
Foregu tnerves are indicat ebdy the arrowheads. Scale bars /A, B, E = 1OO pm; C, D= 200 pm,
diverticu laalong whole lengt h.Anus at posterio rend of
body.Blood
system Blood vascular system well developed .Pair
of cephaiic vessels joinni anngteriorly by loop running dor-
sally over front of rhynchodaeum {Fi g4,B, D). Posteriorly,
vessels entering cerebral ring, Mid-dorsa lvessel arises from
one of the lateralvessels. Behind brainthreelongitudinal

vessels, one mid-dorsal and two later aiex,tend through
aP remaining body lengt hwithout connection until meeting pos-
terior lyby supra-intestinal Ioop. Mid-dor$al vessel, soon
after erigin, entering ventral rhynchocoel wall formin gsingle
Iarg evascular plug up to 55 um wide and 30 pm tal l(Fig,
5E). Blood vessels with distin wcatlls throughout, up to 60
ym wide anteriorly; gradually narrower in posterio rintestinal
reglon,Nemous
ld system: Brai nmoderately large ,with dorsa land
ic ventral lobe sof similar size (Fi g4,A) ,Dorsa iand ventral
commissures 20-25 pm and 45-50 pm thick ,respectively.
py Thin outer neurilemma investin gcerebral gangli ab,ut with-
out inner neurilemma. Latera lnerve cords, lacking accessory
nerves and neurochords, meeting posteriorblyysupra-intes-

tina lcommissure,
Fig. 6. Potamostoma shiiunaiense gen. et sp. nov. Schematic dia-
gram to $how the arrangement of the anterior pouches and latefal
divertjc uolf athe inte$tina icaecum, drawn trom livi nmgaterial,
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Fig. 7, Potamostoma shizunaiensegen. et sp. nov, A. TTansvers esection through the pre-cerebral region. B, Transvers e$ection throug hthe
stemach region to show the sub-muscular glands ,with the aperture ot one of the glands indicat ebdy the arrowhead. C. Transvers esection to
show the appearance ot a cerebral sensory organ. D-G. Ser[a ltransvers seections through the stomach region to show the excretory coliect-
ing tubules i,ndicated by black arrowheads. White arrowheads in E-G indica taenother collecting tubul eleadin gto it stermina lregion situated
between the dermis and body wall circula rmuscle layer .H. En)argement of the boxed area shown in F. White arrowheads indicat aen excre-
tory tubule leading to it sterminal region which is $urrounded by small cells (indlca tbye dblack arrowhead). I .Longitudin aselction to show a
putativ teermina lregion of an excretory collecting tubule, indicate bdy arrowhead. The asterisk indicat etshe rhynchocoel circular muscie layer.
J. Transvers esection through the poster isotormach region to show one of the nephridiopores, indicat ebdy the arrowhead, K. Transverse sec-
tion through tne posteri obrrain region to show one of the sinuses, indicat ebdy the arrowhead, contalning unidentified cells, situated in the
parenchym aL.. Transverse section through the intesti nraeglion to show the dark pigment granule sin immature ovaries (indic abty eardrow-
heads }M,. Transvers esection through the intesti nraeglion of an immature male with evidence of early spermatogenesis to show the bilobed
appearance of a testi sN.. Transvers esection through the intesti nraeglion of an immature female to show the appearance of a developing
ovary. Scale bars :A, J, N = 1 OO -m; B-G = 50 ym; H = 15 pm; t ,K = 20 pm; L, M = 200 "m.
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Periphera lnervous system rather well deve[oped A.nte- bosci sinsertion,
riorly ,several cephalic nerves extending from front of both Cerebra lsensory organs (Fi g7,C) comparatively large
dorsa land ventral brai nlobes ,innervatin gproboscis and and $ituated close below anterolateral margins of cerebral
ocelli mostly. Pai rof stout and prominen tnerves emerging gangli ao,pening to exterior via distinc vtentrolateral ciliated
lateral lfyrom dorsa igangli al,eadin gto neuroganglionic tis- cerebral canal$ of about 45 pm in diameter, leadin ignwards
sues of cerebral sensory organs. Pair of foregu tnerves, from anterior pai rof cephalic furrow sC.anals surrounded
originating from ventral cerebral ganglia ,running posteriorly posteriorl yby neuroganglionic tissues ,flanke dabove and
in parenchyma above oesophagus and stomach (Fi g5E.), below by cap-like glandular portions ,Cerebra lorgans ellip-
Apica loigan and cephalic glands S:ingl eapica[ organ, com- tica lin cross-section, 60 pm wide and 200 pt' mtall,
prisi nogf ciliated pi t35-55 Ltm i ndiamete rand line dby neu- Excretory system: Excretor ysystem very weil developed
trophil ivcacuolate epithelium of 1O-25 pm thick ,opening at and extending throughout the lengt hof body, including
tip of head (Fi 4gD.). Cephalic gland sdischargi ntgo exterior head, Termina lregions of excretory system embedded
via apical organ. between dermis and body-wall circular muscle layer (Fig,
Cephali cgland scomparatively [arge ,irregular lsyhaped 7D-H). Terminals surrounded by small but unidentified cells;
and vacuolated in appearance, occupying much of cephalic flame cells not found .Thick-wall e(d10-1 p5m) collecting
space (Fi g7A,), and extending back behin dbrain A.s well tubules ,35-45 pm or more jn diamete rh,ighl yconvoluted
as typica lvacuolate basophil ilcobule sc,ephalic gland salso and ramify around rhynchocoel, ]ater anlerve cords and ali-
contain two other distinc tgland types; yellow -to orange- mentary canal (Fi g3,) ,Nucle iof cells forming collecting
staining acidophils and purple-stain ibansgophils with Mal- tubules locate dclose to tubule lumen, Final region of each
lory 'tsrichrome {Fi g7,A), collecting tubule thick-walle dand surrounded by unidentified
Sub-muscula rglandS :Sub-muscula rgland s(Fi g7B.} scat- cells similar to cells around termina l(Fi g7.1) ,Numerous
tered amongst fibre osf body-wal llongitudi nmauslcle layer nephridiopores opening latera l{lyFi g7,J) ,ln holotyp e17
in foregut region on all sides of body. Each gland opening and 15 nephridiopores opening on right and Ief tside of
to exterior by own pore. body, respectively. Each nephridiopore leading to distinct
Sensory oigans: 1O-70 ocelli ,arranged into two groups on co]lecting tubules and terminals.
each side of head (Fi 2g}., 3040 pm in diameter, with dark Numerous sjnuses containing highl yvacuolated cells
green to blac kpigmen tcup (Fi g7C,), Anterio grroups situ- with small and dense nuclei (Fi g7K,) found in parenchyma;
ated near head tip ,posterio rgroup sat about leve lof pro- each sinus isolate ndo,t opening int oeither blood vessels or
Table 2. Monostilifer ohuosplonemertea ngenera with a bilayere rdhynchocoel war1 and an oesophagus emerging from the rhynchodaeum
close behind the proboscis pore .Data compiled from Friedri c(h194 019,55, 1957) ,Gibson (1973 }S,anchez and Moretto (l988 )S,enz (1993)
and the presen tstudy,
Genus 1 11111IV v vjVll
Arctonemertes Fariedrich ,1957 +o?oo+ ooooo+ ++?+Oe+ ++?+o+ ooo+oo ++++d+++++o??ot+
Atrionemerte sSbenz, 1 993
Communoporus Friedrich,1955

Divanell aGCibson ,1 973
Koinoporu sSanchez and Moretto ,1 988
Potamostoma gen, nov,
1 Body-wal lmusculature with (+ )or without {O )diagona lmuscle layer.
i lBody-wal llongitudina lmuscle layeranterio rdliyvide d{+ )or not divide d(O},
11 1Rhynchocoel shorter than body {O o)r as bng as body (+).
IV lntestina lcaecum presen t(+ )or absent {O).
V Cerebr aslensory organs replaced by neuroglandular complex (+ )or with typical structure (O),
Vl Excretor ysystem restricted to foregu tregion of body (+ }or extending throughout body length (++).
Vll festes ln mature males bilobe d{+ )or slmpie (O).
a Friedri c{h195 714:3) noted that in Arctonemerte"sD etrhor iFriedric h1,957, the rhynchodaeum opens fa ranteriorly and dorsall tyo the oesoph-
ageal openjng, He ajso stated (1957 1:44) that Oesophagus mUndet subterminal aus und nimmt ganz vorne das Rhynchodaeum aut",
Chernyshev (1998 )h,owever, made no mention ot the oesophagus-rhynchodaeum relationship in A. ussuriensis Chernyshev ,1998.
b Senz ( 1993) reported that in Atrionemertes greenlandic Saenz, 1 993, there was ne oesophagus, the foregut instea depening direct liynt oand
atrium,C
Gibson { 1973: 802> noted tha tthe rhynehodaeum "opens lnt othe oesophagus close to the common probosci sand oral aperture" in Divanetla
evelinae Gibson, 1973.
d Gibson (197 3re)corded tha tin D evefinae the excretory system was very indistinc atnd at best poorl ydeveloped.
e Sanchez and Moretto ( 1988/ 199) stated that the rhynchocoel "extends up to two-third sot the total lengt hot the body, "in Kbinoporu smapochi
Sanchez and Moretto 1,988,
f K, mapochiis hermaphroditic and possesses ovotestes {Sanch eanzd Moretto 1,988).
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A NewBrackish-WaterNemertean 499
excretory tubules. conditions; invertebra tleisvjn gi nsuch regions are not sub-
Reproductiv seysten?: Dioecious .Gonads arranged pseudo- jec tto the rapid salinity fluctuatlon asssociated with estuar-
metamerically, alternating with latera lintestin adlivertic uilna ies ,The Amphiporus and letrastemr rsipeacies, which were
immature .Gonads in individual scol[ected in November reported from Sea of Okhotsk by Korotkevi c(h1977 a)re, not
identifiab iteo sex; early spermatogenesis or developin ogva found in salinitie sles sthan 18 psu (Tabl 1e) and their excre-
seen in indMduals collected in May. Sexuall ymatured indi- tory systems are restricted to the foregut region of the body,
viduals exhibiting colour dimorphism t;este skhaki in colour, On the other hand, those euryhaline species, including
whereas ovaries deep green ,ln immature females ovaries Amnictineu zshLu'angensis Gibson and Qi ,1991 , Hinumane-
fill ewdith dark green pigment granule s(Fi g7L.), Testes mertes kikuchi ilwata, 1970, Sacconemertel lalutuienta
approaching maturity are dorsoventrall ybilobed (Fi g7M,), lwata ,1970, Sacconemert(rpsis belogurov iChernyshev,
each lobe about 1OO um by 400 pm in dimension D.evelop- 1991, S. olivetera lwata ,1970, and the present species,
ing ovarie$ up to about 300 pm by 600 pm; each ovary con- which liv ein salinities fluctuat idnogwn to 1-6 psu, possess
tainin gat leas t30 eggs. Putativ neurse cells situated along excretory systems extending throughout most of the body,
inne rwall of each ovary; some eggs connected to nurse These finding ssuggest the critica lsalinity ,where nemerte-
cells by short stalk {Fi g7,N). ans have to develop thei rexcretory system throughout the
Systematic remarks: Comparative[ yfew hopionemertean body tor survjve, would Ijkel yto be between 6-18 psu,
genera that have two separate muscle layers in their
rhynchocoel wall have been reported in which the oesopha- ACKNOWLEDGEMENTS
gus, as in the present specimens, emerges from the
rphryenscehondt aeunmew fgae nriusn f roclnot soefl yt he rberseamib lnleosbe s A{rTcatob nl2e)em, eTrhetes tIhe ec teWxiei nsto gelanircgeeo chga reotaie tsteht eu ftplor roDerm s tYhe.e n Tsmtapoeukctaihmsehn soi,fm tah eft ooRr uibnvrdei r nwSghhiilins zttg uo hnHeaK if'woas rs nao tctioacelx--
Friedrich ,1957, but can be distinguishe dfrom the latt ebry onomic inve$tigation ,We would also Iik eto thank Dr Jane tMoore
the anteriorly divided body-wal llongitudi nmuasclulature and for criticising and commenting on an earlier version ot this paper.
the extensive developmen tof the excretory system, None ot
the genera list eidn Table 2 possesses the anteriorly dMded REFERENCES
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