A new deep-water lancelet (Cephalochordata) from off Cape Nomamisaki, SW Japan, with a proposal of the revised system recovering the genus Asymmetron

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ZOOLOGICAL SCIENCE 21 : 1131-1 136 (2004) @ 2004 Zoologica Slociety of Japan
A New Deep-water Lancelet(Cephalochordfartoam) Cape
off

Nomamisaki, SW Japan, with a Proposal of the Revised
System Recoveringthe Genus Asymmetron

TeruakiNishikawa'
77ieNagoya UniversitMyuseum, Chikusa-ku,Nagoya 464-8601,Japan

ABSTRACT-Asymmetron interum n. sp. is established for the holotype collected durin gthe Hyper-Dol-
phinfNatsushi mcaruise in 2003 of the Japan Marine Science & Technolog yCenter {JAMSTEC )off Cape
Nomamisaki, southwestern end of Kagoshima Prefectur aet, a depth of 229 m. A. inierum is very similar
to it scongener, A. Iucayanum Andrews, 1893 (forme rcalllyed EPigonichthys lucayanus) but easily distin-
guishabl efrom i tby the larger number of total myotomes {83 in the former vs. 55-72 in the latter),The
genus Asymmetron has been treated as a juni osyrnonym of EPigonichth ybsu,t is recovered as a valid
genus distinc mtorphologically from another valid genus EPigonichbys (sens ustricto).
Key vvords:cephalochordates, new species, deep water, morphology, recovery of Asymmetron
INTRODUCTION new species is the firs tto be established in the lancelet sin
about 40 years since the proposals of Branchiostoma
During the Hyper-DolphinfNatsushima cruise in 2003 of benneth Boschung and Gunter ,1966 and B. moretonense
the Japan Marine Science & Technology Center (JAM- Kelly,1966,

STEC), several iancele tspecimens were col[ected from bot- The present findi ngof the true deep-wate rlancelet
tom sand near the bones of the sperm whale Rhyseter mac- sheds new ligh ton the biodiversit sytudies of the Iancelets,
rocephalus Linnaeus, 1758 at a depth of 229 m, off Cape as the closest relative ot the vertebrates.
Nomamisaki, southwestern end of Kyushu lsland ,Japan.
th e pThhyel ulmanCcheolredtas t,aor, itnhcel usdubepchay,lu3m0 knCoewpnhalIoMcnhgorsdpaectiae so,f TAXONOMIC DESCRIPTION

so far collected from tropica lto cool-temperate shallow Genus Asymmetron Andrews, 1893
waters all over the world (Pos sand Boschung, 1996). The Asymmeton Andrews, 1893, p. 237 (Typ especies:
deepest known record for benthic adults of this subphylum A. iucayanum Andrews, 1893 by monotypy)
as reported by Wickstead (1975 )wa,s in collections made Notasymrnetron Whitley ,1932, p. 260 {Typ especies:
by Zietz <1908 p,. 288) from "about 1OO fathoms [=18 3m] of Asymmeton caudatum WHiey, 1896 by original
water about 49 miles east of Cape Spencer'' ,South Austra- designation)
lia .Thus, i tis clear that the presen trecord extends the Diagnosis: Cephalochordat eswith gonads only on right
depth range of lancelets downwards to 229 m, and also rep- side, and with a markedly elongated urostyloid proces sas a
resents the firs otccurrence of the adult lancelet sin the deep posterio rextension of notochord without myotomes.
water, which is usually define das the region deeper than Remarks: The genus Asymmetron Andrews, 1893 has
200 m. recently been regarded as a juni osyrnonym of the genus
Further ,the material appears to be a new species of the EPigonichthys Peters, i877 with the type species of E. cui-
genus Asymmeton, as distin cftrom EPigonichth yisn the tellu sPeters 1,877. Thus, the lance]e thsave been generally
revised system proposed herein ,based on morphological classified into the two genera Branchiostoma Costa, 1834
considerations (show ni nthe present study derived from and EPigonichth ysbo,th with many juni osyrnonyms, in a
Nishikawa and Nishida] s(1997 )and molecular studies single famil yBranchiostomatj da(esee ,e.g., Nishikawa,
(Nohar aet aL, accepted; Ken et al., submitted). The present 1995; Poss and Boschung, 1996). The two valid genera are
distinguis hferdom each other by the differen tpositio nof
'Correspondingauthor/Tel. FA X. ++88 11--5 522-- 778899 --5578 6916'. , gonolnya dosn, thie. er .ie,gnht esaidceh isni dEeP iign otnhiec ghetnhuyss ; tBher asynmcmehtriicstom <awi,h itnlhee
E-mail:[email protected],ac,jp former> or asymmetric (i nthe latte r)ending of metepleura
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Flg　l　Asymmetron　tnfe厂um 　n　sp　the　holotype（NUM 　Az　O363）from　off　Cape　Nomamlsakl　southwestern 　end 　Qf　Kagoshma　Prefecture　at
adepth 　of　229　m　lef　tslde　A　the　whole 　body　showlng 　pecultar　uro＄tylol　dprocess （arrow ）Banterlor 　par　tshowlng 　a　black　plgment　spot　ln
neural 　tube（whlte　arrowhead ）low（thln　arrow ）and　hlgh（thlck　arrow）1ntertentacular 　membrane 　and　short　mld 　ventral　tentacle（black　arrow
head）Cposterlor　part　showlng 　atrlopore（large　asterlsk）anus （small　asterisk）abrupt 　ending 　of　lef　tme 重apleuron （thlck　arrow ）and　a　vacuole
be電ween 　atrJopore　and 　anus ｛thl　narrow ）Scale　bars　Indlcate 　l　mm
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A New Deep-wate r La n c e] e t 1133
has often been mentioned as a differenc ebetween the two and ventral notches (Fi g1 .B>. Dorsal fin very low in anterior
(see e,.g., Poss and Boschung, 1996). However, thi sis not two-third sof body, while becoming much higher posterially,
always clear {se eNishikawa and Nishid a(1997 )and the Lef tmetapleuron terminated abruptly and markedly iust
Discussion below), The only recent exception to the prevail- behind atriopore, while the right confluent with well-devel-
ing two-genus system is Piyakarnchana's (1 962), where the oped ventral fi n<Fi gI.C), followed by thin and high caudal
genera Asymmetron and EPigonichth yarse both treated as fin ,somewhat higher than dorsal fin .Urostylo ipdrocess
valid (fo trhe generi cdistinct isoeen the Discussion below). separable from dorsal and caudal fin sby it sown lower dor-
It has, however, become clear by mo]ecular ana]yses of sal and ventra] fins ,Dorsal fin-chambers 270, relative length
many IMng species of both genera <Noha retaal., accepted; to width for posterio rtal lones up to 3.3 ;preanal fin-cham-
Kon et al., subm[tted) that the genus EPigonichthys repre- bers indiscernibl e,but instead ,an elongated vacuole
sents a group of paraphyly with the deepest branch between detected along ventral side of rectum between atriopore and
it sspecies havin gurostyloid proces ssuch as seen in E. anus (Fi g1,C). Myotomes 83 in total c,onsisting of 58 in pre-
iucayanus and allies ,and the remaining two monophyletic atrioporal region, 9 in region from atriopore to anus, and 16
c[usters (on ecomposed of EPigonichthJL sspecies lacking in postanal, thus giving the myotome formula of
the process and the other of Bnanchiostoma species), Thus, 58+9+16=83, A black pigment spot detectab lien neura[ tube
in the lancele twisth gonads only on the right side, the pres- jus tanterior to firs tmyotome (Fi g1 .B), Tentacular ring com-
ence of urostyloid proces smay well be regarded an apo- posed of ca. 30 tentacles (includ ian gfew dorsal-most
morphic character-state to detine one taxon at the generic minute ones), it santerior margin situated at leve lof axial
level ,markedly distinc tfrom the other taxon composed of (=proxim apalr)t of 5th myotome; intertentacul amrembrane
EPigonichthys species lacking the process. The former extremely higher in span of 6 tentacles next to much shorter
taxon should be called the genus AsyTnmetron, because its midventral tentacl ethan elsewhere. Mid-gu tcoecum elon-
type species is A. Iucayanum (=E .iucayanus) ,while the gated, ranging at ]evel from 20th to 48th myotomes, No
other the genus EPigonichthys (sens ustricto), which has gonad.Remarks:
been confirmed by the mentioned molecular analyses to The present specimen resembles A. iucayanum,
include it stype species, E. culteilus Peters, 1877. All the as the only valid species of the genus and recorded so far
known species of the genus Branchiostoma Iack the distinct from shallow waters of the lndo-West-Pacifi cand Western
urostyloid process, and therefore ,its existence is unique to Atlanti cregions, very much even in detail edfeatures,
the genus Asymmetron among the lancelets. excepting in the higher number of total myotomes; A. tucay-
The genus Notasymmetron Whitley ,1932 was estab- anum is recorded to have 55-72 myotomes, while the
lished ,with Asymmetron cauctatum Willey ,1896 being its present specimen has 83 <se eTable 1) .This marked mor-
type species by the original designation ;A. caudatum is phologica ldifferenc eseems signjficant for the specific
treated a juni osrynonym of A. Iucayaum (see ,e,g., Poss delimitatio inn the Iance]e ttaxonomy. Moreover, the validity
and Boschung, 1996). Judging from the origina[ description of this delimitatio nhas been confirmed on molecuiar basis
of the genus ,i tis doubtless that the genus Notasymmmet- <Kon et aL, submitted). Thus, the present specimen may
ron was defined as the lancelet swith gonads only on the well deserve a new species of the genus Asymmetron with
right side and with a urostyloid process. Consequently, the the binomen A. inierum ;the specific name derjves from the
genus can be treated as a juni osyrnonym of Asymmetron. lati nadjective ''inferus'' (=lo wun,derneath) after it sdeep-sea
For furthe rconsiderations on morphological peculiarity habitat .I tmay also be pointed out that A. interum has far
of the genus Asymmetron see Nishikawa and Nishida more dorsal fin-chambers than the previous records of A.
(1997 a)nd the Discussion below. Iucayanum (27 0in the former vs. 1Ol-220 in the latte rf;or
thedeta"ssee Table 1),when Poss and Boschung's (1996)

Asymmetron inierur rn], sp, extraordinarily large counts attaining to 484 for the latter
(Fi g1,> species are excluded.
Holotype: Deposited in the Nagoya Universit yMuseum The high number of myotomes in A. inierum is reminis-
(NUM-A0z363),coHected fromthesand near thebonesof cent ofB.elongatum Sundevall1,852 fromthePeruvlanand

the sperm whale, during the Hyper-DolphinfNatsushima Chiiea ncoasts and the Galapagos lslands with 78 myo-
cruise of JAMSTEC (NT03-08 legl) ,off Cape Nomamisaki, tomes in an average (rangin fgrom 75 to 86) and E. hectori
Kagoshima Prefecture,Japan, 31020.72'N, 129059.29'E, (Benhaml901)endemic toNew Zealandwith 84 <84to85)

229 m deep, 27 July 2003, JAMSTEC No. 053540; tixed myotomes (th deata from Poss and Boschung, 1996). How-
with 10% formali nand preserved in 70% ethanol. ever, these species lack urostyloid process completely.
Descripti oBno:dy, 14.7 mm long and up to 1.5 mm high, The three specimens of this new species were exam-
elongated Iongjtudinal laynd much flatten eldateral tlayp,er- ined before used for molecular ana]ysis (se eabove), but
ing gradually towards both ends (Fi g,IA>; preatrioporal rather insufficien tbleycause they were somewhat deiormed
region 1O.9 mm, atriopore to anus 1.0 mm, postanal 1.8mm, due to fixati vovnjth pure ethanol, collected durin gthe Hyper-
and urostyloid process 1,O mm, Rostral fi nextensive and Dolphin/Natsushima cruise of JAMSTEC, from the same
semi-circular, clearly separable trom other part by dorsal localit yas the holotype ,28 July 2003 (JAMSTEC No$.
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t134 T. Nishikawa
Table 1. Comparison in the number of dorsal fin-chamber sand myotome formula of A. inierum n. sp. with all the previou$ with
enough informati oofn Asymmetron lucayanum and it sjuni soynronyms (A .caudatum, A. macricauctatum, and A. orientale)records
Average2) and range3) in number of
Speciesnamei}Locality dorsalfin-chambers myotomes References
preatrieporalatriopore to postanal total
anus
A . i n(fner=u1m )n.A s.p. Of f2K2y9u smh ud,eeJpapan 270 58 9 16 83 in the presen tsiudy
1 "(cnay=a2n2u)m Bahamas N.D. 48,8(4246} 8.7 (8-9) 12,7(11-14} 65.3(62-68) Andrews (IB93)
A . I u(cnay=a1n2u)m Bahamas N,D (43-46) (8-10} {12-13) (63-69) Kirkaldy(1895)
A . J u(cnay=a2n4u)m4) N WM aAltdliavnet$i &c (170-180) (42-46) (8-9) (11-14) (62-68)57, 7 <B5 i6 g-e l5o(9w 1}&9 4Fa8r)fante
A. Iucayanum R e"d mS edae ecpa. N.D. 42 .7((4n1-=434)) 6,9( n(=67-)8) 8. 4{ (n=79-)1O) {n=3) Steiniz(1962)
A . t u(anv=a3nu)mA. Persian GuH (114-142) (38-39) (e7)9.79 (12-16) (57-61) Davvson(1964)
i u(cna=y2an8u)m Maldives N,D,174.3( 1443.036- 2(2403)-46) (9-t3) 12,61 (11-13) 66.71(64-71) Punnett(1903)
A. tucayanum NewCaiedonia (n=44) 44 ,8({4n0=-448)3) B .4( n(=64-41)0) 1 3.(3n(1=14-41)61)1.9( 16 61.-(31 n(3!6)737-)7529).2 Wickstead (1 970)
A . I u(cna=y9va)nAu. m(A) Sdoolwonm otno 3l5s mls, 161.4(142-176) 39.2{38-41) 8.1 (e9) (58-61) G i bb s&0W9i6c9k)stead
t u(cna=y9on)uEm. (B) Sdoolwonm otne 3l5s mls. 189.5(166-214) 44,3(41-46) 8.7(8-10) 13.1 (12-14) 66,1 (64-68) G i bb s&{W1i9ck6s9te}ad
t u(cna=y2an7u)s (A) GRreeeaft,B 2a2r rmier N.D, 39-40{39-41) 8-10{7-12) 11-13(10-14) 60-61 (59-64) G i bb s&(W1i9c9k6st}ead
E . t u(cna=y4an8u)s {B) GRreeeatt, B2a2rr imer N.D. 43-45{42-tL7) 9-lt {8-12) 12-15(12-16) 66-69 (64-70) G i bb s&0W9i9c6k)stead

A . c au<dantu=m2)E. Papua New Guinea N.D.133(101 -1 7 0)40, 44 99.2 11 60,6463.8 Willey(1897)
tucayRnus Australia (n=13) 42 .{8n(3=9t-34)6) ( n(=81-31)2) 1 2(.0n(=91-31)5) ( n(=5184-)71) R i c ha r ds(o1n9&9Mc4K}enzie
A . I u(cany=an1u)mA. Palau lsls, 170 41 9 il 61 Nishikawa(1980)
I u(canya=n1um4) Mindro ls. N.D. 43.1 (40-45) 9.4 (9-10) 11,6{10-14} 64.3 (62-67) Franz(1922)
A , i u(cna=y2an)uEm. caO.1k5midneeapwa ls. 140,170 42, 44 9,10 i2 63, 66 Ni$hikawa(1980)
I u(cna=y1an5u1s) Variousareas 3e7(167-484) 36,5(35-52[sLc]) 15,9U3-18) 7.7 (6-9} 60 (55-62) P o s s &( lBgo9s6ch}ung
N.D.= No daia
1) A. tucayanum (A) and (B) mean two forms found sympatrically and distingutshab flreem each other by ditfe rent number of myotomes (fo frurther details see Dis-
cussien)2)
Bigelow and Farfant e(1 948) ,Dawson ( 1964}, and Kirkald y(1895 g)ave no data ; the iigure sof the New Caledonian and Mindro population $were calculated here
basedonWickstead's(197e)andFranz's(1922}data,respectively;theilguresoftheGreatBarrierReefpopulationindicateforeachcolumntherange"containing
85% or mere of the samples", instea dof the average, iollewing Gibbs and Wickstead (1 996}.
3) ln parentheses.
4) 1nclude sthe syntypes of A. macricaudatum Parker ,1904 from Florid aand A. orientaSe Parker ,I904 from the Maldive lsls.
"Genus,
053515 to 053517) ; they were 10.7, 12.5, and 13.0 mm 288-289) South Australia nspecimen of the
long, furnished with ca. 80 myotomes, with the lef tmeta- Asym[sicletron ,Andrews'' ,the previous holder of the deep-
pleuron ending abruptly and markedly jus tbehind the atri- e"swta srecord as stated above, because durin gthe cruise it
opore, while the right confluent with well-developed ventral lost sight of for several days. When examining i tlater
fin ,with an urostyloid process, O.58, O.46, and O,58 mm i twas found to be decomposed".
long,respectively, but without any preanal fin-chambers;

gonads uncertain. The occurrence of urustyloid process, the DISCUSSION
marked asymmetry of metapleura, and ca. 80 myotomes are
the reasons for the present jdentificati onal,though the Asymmetry of metapleura in generi cdefinition
gonads were uncertain in the specimens. Piyakarnchana (1 962) rightly distinguishe dAsymmetron
Abandoned was my examination of Zietz' s(1908 ,pp. from EPigonichthys (sens setricto), both having gonads only
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A New Deep-water Lancelet 1135

on the right ,on the basis of the differenc ethat the former existence of the chamber in the former,
genus was fumished with "right metapleuron continuous The lack of distinc tpreanal fin-chambers is recognized
with ventral fin ,Ief tmetapleuron terminatin gbehin datri- as a diagnosti cfeature ot A. Iucayanum by Poss and Bos-
opore", whiie EPigonichthys with `[both metapleura terminat- chung (1996 )an,d followed in the present study. Althoug hit
ing a short distance behind atriopore" (p .96). However, the is true that a few old records of this specjes show the exist-
metapleuran asymmetry, as claimed in Asyrnmeton by Piy- ence of preanal fin-chambers (fo rthe detai lssee Bigelow
akarunchana above, is often detectab l(ethou gunhclearly) and Farfante (1948> t)h,ere is agreement among all of the
also in EPigonicht hasy sd,iscussed in detai [by Nishikawa recent literatu rwehich includes any reference to this char-
and Nishida (1997 o>n the basi sof the examination of spec- acter that i tis not present. Thus, the old informati woans put
imen$ and the literatu rseurvey. So fa ras 1am aware, the aside here, ljk eNishikawa (1986).
mentioned asymmetry ls marked]y observable only in A.
Iucayanum and A. inieru mbecause their ventral fi nin New explanation on pelagic larva ewith many myotomes
between atriopore and anus is always high enough to allow Gibbs and Wickstead <1996 )proposed a beautiful
for easy recognition of it scontinuity with the right metapleu- hypothesis to explain the variation in the myotome formula
ron and the abrupt disappearanc oef the lef tone jus tbehind of A. Iucayanum, based on thei rdiscoveri etshat it scertain
the atriopore <se eFig .IC). Thus, Piyakarynchana's defini- adult populations were composed each of the two forms (A
tjon of the genus AsymmetTon is not adopted here. and B), distinguishe dtrom each other by the dMerence in
myotome formula (se eTable 1); typicall yt,he tota land pre-
Some features peculia rto known species ef Asymmet- atrioporal numbers were 58-61 and 3840, respectively in
ron the form (A) ,while 65-69 and 43-45 in the form (B) .The
Nishikawa and Nishid a(1997 c)lajmed that EPigonich- hypothesis suggests "that the ful lcomplement of myotomes
thys lucayanus (=A .Iucayanum in the presen tstudy} has was formed prior to the compietion of metamorphosjs" (for
two more teatures unique among all the known species of original references see Gibbs and Wickstead), and holds
lance]et sot,her than the existence of elongated urostyloid that the two forms are 'Ederived from differe lnatwal stages"],
proce$s and the marked metap[euran asymmetry stated the form (A )"from an amphioxus larva-li ksetage that has
above. One is the peculia rmorphology of the intertentacular metamorphosed after a $hort plankton istcage" and the form
membrane which is "much highe raround the ventral side of <B )"from the amphioxides stage which has undergone a
oral hood than ]aterall yw,here the tentacles on either side long, more wide[y dispersed ,planktoni cexistence" (p ,615}.
are interconnecte don]y near their bases" {Bigel oawnd According to this hypothesis ,amphioxides larvae with 83-88
Farfant e,1948, p. 21), thus the membrane changes its tota lmyotomes, which have been rarely collected offshore,
height abruptly between latera land ventral ones; further t,he are regarded to be "held in oceanic currents until death" (p.
membrane of the ventral tentacles is also much higher than 524).
it sventral neighbor interconnect itnheg most ventral one of Another hypothesis is also possjble ,however, that the
the tentacles with the midventral tentacle <se ee.g., Fig .6 of presen tnew species A. interum ,so far known to have 83
Pi, 13 of Andrews (1893 )F]ig ,2 of Nishikawa {1 980)); in the tota lmyotomes, may represent adults of the mentioned
other lancelet sth,e membrane's change in heigh ti squite amphioxides larvae with 83-88. I tis true that in the sea area
gradual ,with the height gradual lyincreasin gventrally, not far from it stype Iocalit yt,wo such larvae were recorded:
slightly <i nmany species of Branchiostorr} ao)r remarkably one, having 80 myotomes, from the Tsushima Strait ,less
(e.g ,i,n EPigonichth ymsaldivensis; unlike Poss and Bos- than 200 m deep, and the other with 83 myotomes from the
chung's (1996 m)isinterpretation ot its description sgiven by southern end of East China Sea, 2,080 m (Nishikawa,
Nishikawa (1980 e)tc.). The other i sthe posterio rshift of the 1981). Then, the forms {A )and (B )might possibl bye two
tentacular ring, with it santerodorsal extremity Iocate dat (or good species, instead of representing two phenotyp[c forms
sometimes behind) the 4th myotome; in other Iancelets ,the of a single species as predict ebdy Gibbs and Wickstead's
extremity is discerned around the 1st myotome. These two hypothesis ,Molecular analyses will be indispensable to
features are shared with A. interum (se eFig ,1B). examine the validity of these hypotheses.
Preanal vacuole in A. inferum ACKNOWLEDGEMENTS
ln the holotype of A. inierum ,a longitudinai leylongated
vacuole is detectabl ealong the ventral side of the rectum Sincer ethanks are due to Dr. Y. Fuiiwara ot JAMSTEC for the
between atriopore and anus (Fi gI.C), This structure is not material, to Prof .M. Nishid aand Dr. T. Kon of the Ocean Research
detectedinthepureethanol-preserved specimens identified Instjtut eof Universi tofy Tokyo and Dr. M. Nohara of HITEC Co. for
with this sp ecie s, an d therefore ,may be unstable. It strue cBi.t aCtiuotnl oef ro ft hHea runvpaubrldi sUhnedive rdsait tfay oor tc rmiotlieccaul lraeradi nagna loyfs etsh,e mtano usPcrroipft. .E.
nature remains open until histologic asltudies on additional Financiai[ ysupported in part by the Grant$-in-A ifdrom JSPS (Nos.
material are performed .The structure might possibi ybe 13440253 and 16370044>,
explained as the preanal fin-chamber .I fthi sis true ,A.
interumcan also bedistinguishferdomA.Iucayanum bythe

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1136 T. Nishikawa
Nohara M, Nishida M, Miya M, Nishikawa T (2005 E)volutio onf the
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