Research Article Histological Examination of Precious Corals from the Ryukyu Archipelago - Hindawi

15 Pages·2014·8.48 MB·English

HindawiPublishingCorporation
JournalofMarineBiology
Volume2012,ArticleID519091,14pages
doi:10.1155/2012/519091
Research Article
Histological Examination of Precious Corals from
the Ryukyu Archipelago
MasanoriNonaka,1MasaruNakamura,2MakotoTsukahara,1andJamesDavisReimer3
1OkinawaChuraumiAquarium,424IshikawaMotobu-Cho,Okinawa905-0206,Japan
2SesokoMarineLaboratory,UniversityoftheRyukyus,SesokoMotobu-Cho,Okinawa905-0206,Japan
3TransdisciplinaryResearchOrganizationforSubtropicalIslandStudies,UniversityoftheRyukyus,1Senbaru,Nishihara,
Okinawa903-0213,Japan
CorrespondenceshouldbeaddressedtoMasanoriNonaka,m [email protected]
Received25March2012;Accepted9July2012
AcademicEditor:GarthL.Fletcher
Copyright©2012MasanoriNonakaetal. This is an open access article distributed under the Creative Commons Attribution
License,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperly
cited.
In this paper we examined the histology of three commercially valuable species of precious corals (Paracorallium japonicum,
Corallium elatius, and C. konojoi) from the Ryukyu Archipelago. In order to observe their inner structure, samples were thin
sectionedandexaminedwithadigitallightmicroscope.ColoniesofC.konojoihadthickercoenenchymeandlargerautozooids
than those of C. elatius and P. japonicum. The sclerites of the three species tended to be concentrated in the outer layers of
coenenchyme.Thegastriccavitiesofautozooidsofallthreespecieswerefoundtoberelativelyempty.Somesymbioticpolychates
were observed in the axis of P. japonicum. As well, a zoanthid (Corallizoanthus tsukaharai) was often observed living on the
coenenchymesurfaceofP.japonicum.ItishopedourobservationswillprovideagoodfoundationoffuturestudyofJapanese
Coralliidaecorals.
1.Introduction littleinformationaboutthebiologyofspeciesfromJapanese
waters.
SpeciesinthegeneraCoralliumandParacorallium(Subclass
Some taxonomical studies about Japanese species have
Octocorallia,OrderAlcyonacea,FamilyCoralliidae)arewell
beenpublished[e.g.,[3–11]].Regardingbiologicalinforma-
known for their red or pink skeletons that have been used
tion, Grigg [12], Kosuge [1], and Iwasaki and Suzuki [13]
sinceantiquityforornament,medicine,talismans,andcur-
have presented growth data. Ueno et al. [14], Iwase [15],
rency. Therefore, they have long been known as “precious
and Nonaka et al. [16] have reported on the raising of
corals.” Precious corals have been harvested routinely from
precious coral in aquaria. Recently, Iwasaki [17] edited a
theMediterraneanSeaforatleast5,000yearsandweretaken
comprehensivepublicationonscientific,cultural,andhistor-
even as long as 30,000 years ago or more. Products made
icalperspectivesofCoralliidaecorals.
fromCoralliumrubrum(Linnaeus,1758)arerecordedfrom
a Stone Age monument approximately 25,000 years old in However, there have been no studies on the histology
Germany [1], and precious corals and shells were found in or anatomy of Japanese precious corals, except for work
ruinsroughly30,000yearsoldinLausanne,Switzerland[2]. performed by Kishinouye [7, 8]. His “Sango no kenkyu (in
ThefirstrecordofcollectingpreciouscoralinJapanisfrom Japanese)” and “Notes on the Natural History of Corals
1812,whenafishermanfoundapreciouscoralentangledin (samecontentsofformerpublicationtranslatedinEnglish)”
hisnetoffMuroto,KochiPrefecture,andharvestcontinues werethefirstandlastpublicationsdescribingthetotalbiol-
to the present day in the Kochi, Kagoshima, and Okinawa ogy of Japanese precious corals. This work has some com-
regions. It is generally recognized that the biomass of pre- mentsontheanatomicalfeaturesofthreeJapanesespecies,P.
ciouscoralshasbeendecreasedbyover-fishing,butthereis japonicum(Kishinouye,1903),C.elatius(Ridley,1882),and
2 JournalofMarineBiology
C. konojoi Kishinouye, 1903. Kishinouye found that auto- 2.MaterialandMethods
zooids and siphonozooids communicated with each other
2.1. Sampling. Samples were collected from the Ryukyu
by vascular canals, siphonozooids had reproductive ele-
Archipelago, the southernmost region of Japan (Figure1).
ments, and, therefore, reported that siphonozooids were
not immature autozooids but a different organ that takes Inthenorthernpartofthearchipelago(southofKagoshima
IslandsandincludingAmamiIslands),specimenswerecol-
partinreproduction.Kishinouyealsoincluded drawingsof
lectedbymannedsubmarineatdepthsofapproximately100
sectionsofacolonyofeachofthesespeciesharvestedfrom
to300m.Inthesouthernpartofthearchipelago(including
Japan. Outside of Japan, Lacaze-Duthiers [18] described
Okinawa Island, Miyako, and Ishigaki Islands), specimens
the anatomy of C. rubrum (Mediterranean) and included
were collected by remotely operated vehicle (ROV). As
drawings of a sectioned branch and of a polyp brooding
collections were made by a private company seeking large
larvae. Hickson [19] includes a diagram of a transverse
colonies for commercial purposes, sampling was not ran-
sectionthroughabranchofC.reginaeHickson,1905,from
dom. Instead, large colonies were selectively harvested, and
theFloresSea,Indonesia.Grilloetal.[20]analyzedaxisand
environmentaldata(depth,watertemperature,typeofsub-
scleriteformationinC.rubrum,includingsomemicrographs
strate,approximatelatitudesofthecollectinglocations)were
ofhistologicalsections.Recently,SimpsonandWatling[21]
recorded for the area immediate of the collection. From 4
described two new species of Coralliidae with histological
June2005to1March2006,83specimenswerecollected,and
sections of C. bathyrubrum [21]. They dissected the spec-
from23June2007to1September2009,105specimenswere
imens and showed that canals function in communication
collected.Environmentaldataandwholecolonysize(height,
among the polyps [21]. Also recently, Debreuil et al. [22]
width, and holdfast diameters) were reported in a previous
showedcross-sectionsofaxialskeletonswithtoluidineblue
publication [31]. Samples were divided into valuable parts
staining of C. rubrum, and also cross-sections of axes of
(base parts of colonies) and unvalued parts (broken tips
Coralliumspeciesforcomparison, C.secundumDana,1846
of branches; up to 15cm long). The former were used for
(from Hawaii), and two Japanese species: C. konojoi and C.
commercial purposes, and the latter were preserved and
elatius.
examinedinthisstudy.Allspecimens(tipsofbranches)are
Octocorallia corals are divided into three systematic preservedintheOkinawaChuraumiAquariumcollection.
orders: Helioporacea (Blue coral), Alcyonacea (soft corals
and sea fans), and Pennatulacea (sea pens) [23]. Order 2.2. Identifications. All samples were identified using ac-
Alcyonacea is divided into five suborders: Protoalcyonaria, cepted morphological characters, such as color, branching
Alcyoniina, Scleraxonia, Holaxonia, and Calcaxonia. These pattern,polyparrangementandsize,aswellasscleriteshape
suborders are delineated by the contents of their axial andsize.Colonycolorandbranchingpatternwereexamined
structure; suborders Protoalcyonaria and Alcyoniina have from in situ or shipboard photographs with a scale. Polyp
no axial skeleton; suborder Scleraxonia has axes with free arrangement and details were observed and measured by
axialsclerites;suborderHolaxoniahascontinuoussolidaxes light microscope. Sizes and shapes of sclerites were doc-
without free axial sclerites with a hollow cross-chambered umented by light and scanning electronic microscopy.
central core; suborder Calcaxonia has solid axes without SpecimenidentificationfollowedRidley[3],Kishinouye[5–
free axial sclerites and without a central core [23, 24]. 8],Bayer[9],BayerandCairns[10],NonakaandMuzik[11],
There are some exceptions: Keroeididae with an axial andNonakaetal.[32].InJapan,therearesevenspeciesinthe
sclerite despite belonging to suborder Holaxonia [25], and family Coralliidae, six described by Kishinouye [4–8], and
Keratoisdinae (Isididae) with a hollow central core despite one species by Ridley [3]. In this study, we only examined
belonging to suborder Calcaxonia [26]. Family Coralliidae species with commercial value; namely, P. japonicum, C.
belongs to order Alcyonacea, suborder Scleraxonia [23]. elatius,andC.konojoi.
Muzik and Wainwright [27] showed diagrammatic sections
ofsomespecimens ofAlcyonaceaoctocorals,including two
2.3. Observation of Histological Sections, Coenenchyme Sur-
sclerxonian species, Subergorgia suberosa (Pallas, 1766) and
face, and Sclerites into the Coenenchyme. The original spec-
Melithaeaochracea(Linnaeus,1758).Aswell,theCaribbean
imens were preserved in pure ethanol as specimens were
holaxonian species Plexaura homomalla (Esper, 1794) has
preservedfornotonlyhistologicalexaminations,butalsofor
had its anatomy and histology studied in detail, with 62
otherstudiesincludingmolecularanalyses.Smallsubsamples
beautiful, exquisite drawings [28]. These works by Muzik
(approximately 10–20mm long) for making sections were
and Wainwright [27] and by Bayer [28] are good for
separatedfromoriginalspecimensanddecalcifiedinBouin’s
comparisonswiththepresentstudy.Afewpublicationshave solution.Thesubsampleswereembeddedinparaffin.Tissues
described the details of general gorgonian anatomy and werethenthinsectioned(7µm),mountedonslides,stained
include detailed drawings of diagrammatic sections (e.g.,
with hematoxylin and eosin. Prepared specimens were
[29,30]).
observed and photographs taken with a digital microscope
Thus,currentlyonlyoldandlimitedinformationabout (Keyence VHX). Bayer [28] and Muzik and Wainwright
thehistologyandanatomyofspeciesofJapaneseCoralliidae [27] were referred to during our microscopic observations.
exists. In this study, we aim to clarify the histological Diameter of both autozooids and siphonozooids, thickness
biologyofCoralliidaefromJapanandinparticularthethree of coenenchyme, etc., were measured using accessory soft-
commercialspeciesoftheRyukyuArchipelago. wareofthedigitalmicroscope.Inserialsectionsofthesame
JournalofMarineBiology 3
Japan
N
Kyushu I.
N30◦ East China Sea
Amami I.
o
Okinawa I. pelag
hi
Arc
u
N25◦ uky
Ry
Pacific Ocean
Ishigaki I.
E120◦ E125◦ E130◦ E135◦
Figure1:MapofpreciouscoralsamplingareasinsouthernJapan.
autozooid or siphonozooid, the largest measurement was
selectedasrepresentingitsactualsize.
Forsupportingdata,wealsoexaminedthesurfacedetails
of samples (coenenchyme, polyps, axis, and sclerites) by
scanningelectronicmicroscope.Todoso,scleritesandaxes
were separated and cleaned using 5% sodium hypochlorite
solution (household bleach). The examination was per-
formedbyalow-voltagetypeSEM(KeyenceVE-8800).
Thediagramsofthethreespeciesexaminedweredrawn
from images captured by digital microscope and scanning
electronicmicroscope.
2.4.DataAnalyses. TheStudent’st-testwasusedtoanalyze
differences in coenenchyme thicknesses between anterior
sides and posterior sides of each species. Statistical analyses
wereperformedusingMSExcel.
3.Results
Figure 2: Commercial species of precious corals from Japan.
3.1.Identifications. Weidentified75coloniesasP.japonicum, Above left: Paracorallium japonicum (Kishinouye, 1903). Above
61 colonies as C. elatius, and 27 colonies as C. konojoi right:CoralliumkonojoiKishinouye,1903.Below:Coralliumelatius
(Figure2). (Ridley,1882).
4 JournalofMarineBiology
1 2
5
1
4 5 6
1000 µm/div
6
4
2

5
Figure 3: SEM image of coenenchyme surface of Paracorallium
1
japonicum; OCA-Cn20060211-031. 1: coenenchymal mounds, 2:
5
siphonozooidprojections.
3.2.ObservationandMeasurementofHistologicalSections 2
3.2.1. Paracorallium japocicum (Japanese Name: Aka- 3
Sango). Specimensofthisspecieshadaroughcoenenchyme 1000 µm/div
surface (Figure3), averaging 0.15mm in thickness
(±0.04SD, n = 29), but the coenenchyme was somewhat Figure4:HistologicalsectionsofParacoralliumjaponicum;longi-
thickerattheendsoftwigs(Figure4).Manywarts(Figures tudinalsectioninbasepartofOCA-Cn20080329-020(above),and
3, 4, and 5) were present on the coenenchyme surface, transversesectioninbranchtipofOCA-Cn20060212-033(below).
averaging 0.12mm in height (±0.024SD, n = 14). Many 1:axis,2:coenenchyme,3:autozooid,4:siphonozooid,5:vasucular
canals,6:wart.
minute openings (Figure5) were observed into the coen-
enchyme in histological sections, averaging 0.041mm in
diameter. There are some mesogloeal openings in the
coenenchyme [27, 28], but the mesogloea was minute and
made stippled pattern at this magnification (Figure5). 3
Scleritesofspecimenswereapproximately0.050mmlongin
SEM examination (Figure6). Therefore, we concluded that 4 1
theopeningswerelacunaeremainingafterthedecalcification
ofsclerites.Thescleritesfillingupthecoenenchymetended
6
to be closer to the surface side (Figure5). In transverse 5
sections, larger openings (Figure5) were more common
than sclerites, and in longitudinal sections, these openings
looked oval, elongate or formed longer “canals,” averaging
0.078mm in width (±0.022SD, n = 11), and they were
parallel with the axis (Figure4; top). They joined with 100 µm/div 2
7
organizations of autozooids and siphonozooids, and they
tendedtobeclosetotheaxialside(Figures4and5). Figure 5: Transverse section of Paracorallium japonicum; OCA-
All autozooids were contracted in the specimens exam- Cn20080405-022. 1: axis, 2: coenenchyme, 3: siphonozooid, 4:
ined. Contracted autozooids were covered by a thin coen- siphonozooidopening,5:gamete(oocyte),6:vasucularcanals,7:
enchyme composed of many sclerites, which appeared lacunaeofsclerite.
mound-like on the surface (Figure7). Recently, the term
“coenenchymal mound” has been used in the description
of Coralliidae [32, 33]. The coenenchymal mounds were similartoasseeninthecoenenchyme.Theseopeningsmay
almost uniform in shape and size (Figures 3 and 4). The havebeenthemarksofsclerites(Figure7).
diameter averaged 1.0mm (±0.12SD, n = 45), and their Siphonozooidshadundevelopedsepta,andoperculum-
heightaveraged0.47mm(±0.11SD,n=35).Inautozooids, like structures inside of their openings. Openings were
there were tentacles, gastric cavities, muscular tissue, and minute on the surface (Figure5), and their diameter aver-
mesenteries (Figure7). Their gastric cavities were empty. aged0.046mm(±0.016SD,n=43).Siphonozooidswereof
In part of the tentacles, there were many minute openings variousshapesandsize,withsomeforming“mounds”onthe
JournalofMarineBiology 5
Figure6:SEMimageofscleritesofParacoralliumjaponicum;OCA-
Cn20060211-031.
6
1
3
4
Figure8:SEMimageofaxis surfaceof Paracoralliumjaponicum;
2 OCA-Cn20051128-015.
8
100 µm/div 7
The axial skeleton was decalcified and, therefore,
5 appeared as a large gap at the center of the colonies in
the prepared slides. Axial skeletons were oval or rounded
in transverse sections (Figure8), but irregularly shaped at
thetipofthebranches(Figure4;bottom,Figure9).InSEM
2
3 examinations, the surface of axes was faintly longitudinally
grooved (Figure8; top), with grooves at intervals of an
averageof0.171mmapart(±0.045SD,n=26),andcovered
with minute tubercles ornamented with thorny projections
(Figure8; bottom). These axial grooves formed the canals
in the coenenchyme (Figure4; bottom). There were almost
no pits underneath autozooids in our specimens. Some
100 µm/div
specimens were decalcified incompletely, and thus the axis
Figure7:Longitudinalsection(above;OCA-Cn20070908-007)and structurewasobservable.Someringswerefoundaroundthe
transversalsection(below;OCA-Cn20051219-027)ofautozooidof centeroftheaxisintransversalsections(Figure9).
Paracoralliumjaponicum.1:mouthopening,2:tentacle,3:gastric In 21 specimens, unknown commensal animals were
cavity, 4: muscular tissue, 5: septum, 6: axis, 7: siphonozooid, 8: observed embedded into the axis. These organisms resem-
gamete(oocyte). bled polychaetes as they had annular structures, and one
individualhadgonad-likestructuresinitsbody(Figure10).
These organisms inhabited a “nest hole” that appeared to
either be bored through the host’s axis, or the axis had
surface(Figure5),andsomeunderneathautozooids(Figure secretedandgrownaroundthecommensals(Figure11).On
7;top).Somesiphonozooidscouldnotbedistinguishedfrom the surface of coenenchyme, we could find much larger,
the canals in the transverse sections. In some specimens, nonoctocorallian polyps growing on two specimens, with
siphonozooidsbecomelargerbecausetheyhaddifferentiated oneofthesespecimenspotentiallyharboringitsowngonads
gonads(Figures5and7). (Figure12).Thesepolypsturnedouttobezoanthidsofthe
6 JournalofMarineBiology
4
3
4
2
2
5
1
1
3
1 2
2
Figure 12: A section of Paracorallium japonicum; OCA-
Cn20060109-042 with a commensal zoanthid, Corallizoanthus
tsukaharai. 1: host axis, 2: host coenenechyme, 3: polyp of
Figure 9: The transverse section of Paracorallium japonicum; commensalzoanthid,4:gonadsofcommensalzoanthid.Scalebar
OCA-Cn20090504-039. 1: center of the axis, 2: growth rings, 3: is1.0mm.
coenenchyme,4:autozooid,5:associatedcommensal.Scalebaris
1.0mm.
4
2
3
1
1
2
Figure13:Acommensalzoanthid(yellowincolor),Corallizoan-
thus tsukaharai associated on the surface of Paracorallium japon-
Figure 10: An unidentified commensal organism (possibly poly-
icum;OCA-Cn20060109-042.Thescaledivisionsare1.0mm.
chaete) with potential gonads associated into the axis of Paraco-
ralliumjaponicum;OCA-Cn20090420-036.1:axis,2:autozooid,3:
gonads.Scalebaris1.0mm.
species,CorallizoanthustsukaharaiReimer,2008(Figure13)
[34].
Figure14showsadiagramofP.japonicumdrawnbased
ontheresultsoftheseobservationandmeasurements.
3.2.2. Corallium elatius (Japanese Name: Momoiro-Sango).
This species had a rather smooth coenenchyme surface
(Figure15),averaging0.51mminthickness(±0.16SD,n =
65), (Figure16). The coenenchyme was thicker on the side
withautozooids,averaging0.54mminthickness(±0.16SD,
n = 37), than on the posterior (without autozooids) side,
averaging 0.47mm in thickness (±0.15SD, n = 28), but
there was no significant differences (t-test, P > 0.05)
between coenenchyme thicknesses of the two sides. Many
minute openings were observed in the coenenchyme in the
histological sections, approximately 0.06mm in diameter
(Figure17). In SEM examination, sclerites of specimens
were approximately 0.05-0.06mm long (Figure18), so we
Figure11:SEMimageofParacoralliumjaponicumwithacommen- concluded that the openings were decalcified sclerites. The
salnestboredintotheaxis;OCA-Cn20051219-023. sclerites filling up the coenenchyme tended to concentrate
JournalofMarineBiology 7
Vascular canals
Coenenchymal
Sclerites
mound
Siphonozooid
opening
Gametes
Siphonozooid
Figure15:SEMimageofcoenenchymesurfaceofCoralliumelatius;
OCA-Cn20060210-029.
Autozooid with a diameter averaging 0.039mm (±0.010SD, n = 23).
Axis The insides of siphonozooids were of various shapes and
Autozooid sizes, and some harbored gonads, and almost all siphono-
zooidswerenotmoundedonthesurface(Figures16and17).
Coenenchyme
Siphonozooid and canal systems could be distinguished by
Vascular canals theirshapesandthepresenceofundevelopedsepta,however,
bothsiphonozooidsandcanalsystemsweregenerallyopen-
1 mm
ings round in shape in the transverse sections. Moreover,
attemptstoobserveseptainmoredetailwithothersections
Paracorallium japonicum (Kishinouye, 1903)
were not successful. Therefore, siphonozooids could not be
strictly distinguished from canals in the transverse sections
Figure14:DiagrammaticsectionthroughabranchletofParacoral-
(Figure16;bottom).
liumjaponicum,showingcoenenchymeandaxis.Thecoenenchyme
ofthisspeciesissothinthatcanalsystemsaredrawnmoresimply Axialskeletonsweredecalcifiedanditwasobservedthat
thaninactuality. there were large openings at the centers of the colonies
in the prepared slides. Axial skeleton cross-sections were
oval or rounded (Figure16; below). At the terminal parts
of the branches, no axial skeletons were observed. In SEM
on the surface (Figure17). In transverse sections (Figure
examinations, the surface of the axis was unremarkable
16; bottom), there were openings larger than the marks
longitudinallygrooved,atapproximately0.27mmintervals,
of sclerites, and in the longitudinal sections (Figure16;
andcoveredwithminutetuberclesornamentedwiththorny
top),openingswereoval,elongate,orformedlongercanals.
Canals averaged 0.095mm in width (±0.018SD, n = 19), projections (Figure20; bottom). There were no pits under-
neathautozooidsinthespecimensexaminedinthisstudy.
and roughly formed two lines along the axis, and, were
Figure21 shows a diagram of C. elatius based on the
connectedatautozooidsandsiphonozooids(Figure16;top).
resultsoftheseobservationsandmeasurements.
All autozooids were contracted in the specimens exam-
ined. Contracted autozooids were covered by a thin coen-
enchymecomposedofmanysclerites(Figure19;top).They 3.2.3. Corallium konojoi (Japanese Name: Shiro-Sango).
werehemisphericinshape,andwecalledthese“coenenchy- Thisspecieshadaverysmoothcoenenchymesurface(Figure
mal mounds” on the coenenchyme surface (Figure15). 22), averaging 0.83mm (±0.32SD, n = 43) in thickness
The coenenchymal mounds were almost uniform in shape (Figure23; top), and the coenenchyme was significantly
and size (Figure15), and their diameter averaged 1.53mm thicker on the side with autozooids, averaging 0.94mm in
(±0.19SD, n = 22), while height averaged 0.54mm thickness (±0.34SD, n = 20), compared to the posterior
(±0.19SD, n = 22). Autozooids had tentacles, gastric cavi- (withoutautozooids)side,whichaveraged0.74mminthick-
ties, muscular tissue, and septae. Their gastric cavities were ness(±0.28SD,n=23)(t-test,P<0.05).Thecoenenchyme
empty. In parts of the tentacles, there were many minute was hypertrophic at the terminals of twigs (Figure23;
openings that may have been marks of sclerites (Figure19; bottom). Many minute openings were observed in the
top). coenenchyme in the histological sections, and they were
Siphonozooidshadundevelopedsepta,andoperculum- approximately 0.06mm in diameter (Figure24). In SEM
likestructureswereobservedinsideoftheopenings(Figure examinations,scleritesofthespecimenswereapproximately
17).Theseopeningswereminuteonthesurface(Figure17), 0.05–0.07mmlong(Figure25),and,therefore,weconcluded
8 JournalofMarineBiology
2
4
5
1
3
2
5
1000 µm/div 4
5
1
4 or 5
3
2
4 or 5
1000 µm/div
Figure 16: Histological sections of Corallium elatius; longitudinal section of OCA-Cn20050606-008 (above), and transversal section of
OCA-Cn20050620-021(below).1:axis,2:coenenchyme,3:autozooid,4:siphonozooid,5:vascularcanals.
7 2
1
4
3
6
5
6
100 µm/div
Figure 17: Histological section of Corallium elatius; OCA-
Cn20071202-007. 1: axis, 2: coenenchyme, 3: siphonozooid, 4:
Figure 18: SEM image of sclerites of Corallium elatius; OCA-
siphonozood’sopening,5:gamete(spermsac),6:vascularcanals,
Cn20060213-037.
7:sclerite’sopenings.
that these openings were decalcified sclerites. The sclerites oftenobservedthansclerites,andinthelongitudinalsection
filling up the coenenchyme were distributed more densely (Figure23;top,Figure24),openingslookedovalorelongate
on the surface side than on the axial side. In the transverse or formed longer canals, averaging 0.13mm in width
sections (Figure23; bottom), larger openings were more (±0.04SD, n = 20), parallel with the axis. They connected
JournalofMarineBiology 9
4
6
3
1
2
100 µm/div
5
3
8 7
100 µm/div
Figure 19: Longitudinal section (above; OCA-Cn20090413-047)
and transverse section (below; OCA-Cn20060214-041) of auto-
zooidofCoralliumelatius.1:mouthopening,2:tentacle,3:gastric
cavity, 4: muscular tissue, 5: septum, 6: axis, 7: siphonozooid, 8:
Figure20:SEMimageofaxissurfaceofCoralliumelatius;OCA-
gamete(spermsac).
Cn20050815-001.
partofthecoenenchyme.Somesiphonozooidscouldnotbe
to organizations of autozooids and siphonozooids, and to distinguishedclearlyfromcanalsinthetransversesections.
twoorthreelayersinthethickcoenenchyme(Figure23;top, Axial skeletons were decalcified and were found to
Figure24). have large openings at the centers of colonies (Figure23).
All autozooids were contracted in the specimens exam- Transversesectionsofaxeswereovalorrounded(Figure23;
ined.Contractedautozooidswerecoveredbycoenenchymal bottom). At the terminal parts of the branches, there was
moundsthatwerealmostuniforminshapeandsize(Figures no axial skeleton. In SEM examinations, the surface of the
22 and 23), and these mounds formed low hemispheres axis was faintly longitudinally grooved (Figure27; top), at
coveredbyathickcoenenchymecomposedofmanysclerites approximately 0.5mm intervals, and covered with minute
(Figure23, Figure26; bottom). Diameter of coenenchymal tubercles ornamented with thorny projections (Figure27;
mounds averaged 1.74mm (±0.30SD, n = 22), and height bottom).Somespecimenswereincompletelydecalcified,and
averaged 0.80mm (±0.32SD, n = 13). Autozooids were somestripeslikegrowthringspresentintransversesections
observed to have tentacles, gastric cavities and mesenteries. werefound(Figure28).
However, their gastric cavities were found to be empty. In In one specimen, a commensal animal (Platyhelmin-
part of the tentacles, there were many minute openings, thes?) was observed in the coenenchyme (Figure29). How-
similar to as seen in the coenenchyme (Figure26; bottom). ever,nootherorganismswereobservedinthesespecimens.
Thesemayhavebeenmarksofthesclerites. Figure30 shows a diagram of C. konojoi based on the
Siphonozooidshadundevelopedsepta,andoperculum- resultsofobservationsandmeasurements.
likestructuresinsidetheopenings(Figure24).Theopenings
wereminuteonthesurface(Figure24),averaging0.045mm 4.Discussion
in diameter (±0.012SD, n = 16). The insides of siphono-
zooidswereofvariousshapesandsizes,andsomeharbored TheonlyreportofhistologicalexaminationofJapanesepre-
gonads (Figure24). No siphonozooids formed hemispheres ciouscoralswaspublishedinmorethan100yearsago[7,8].
and some siphonozooids were distributed near the core Althoughtheobservationsinthisstudywerecarriedoutby
10 JournalofMarineBiology
Autozooid
2 4
3
1
Autozooid
3
Siphonozooid
opening 5 2
Vascular canals
1000 µm/div
Siphonozooid
Coenenchymal
2
mound Gametes 5
Sclerites
Axis
1
3 3
Coenenchyme
1 mm
5
1000 µm/div
Corallium elatius(Ridley, 1882)
Figure23:HistologicalsectionsofCoralliumkonojoi;longitudinal
section of OCA-Cn20090428-038 (above), and transverse section
Figure21:DiagrammaticsectionthroughabranchletofCorallium of OCA-Cn20060221-043 (below). 1: axis, 2: coenenchyme, 3:
elatius,showingcoenenchymeandaxis. autozooid,4:siphonozooid,5:vascularcanals.
hasacomplicatedsystem,withthreeormorelayersofcanals
[7,8].Theseresultsareallsameasourobservations.
1 Inthisstudy,coenenchymethicknessesandpolyp(auto-
zooid and siphonozooid) sizes were measured by histolog-
ical sections. This is a more exact method than former
studiesthatmeasuredexternalmorphology.Kishinouye[8]
describedthethicknessofthecoenenchymeinthreespecies:
“thin” in P. japonicum, and “thick” in C. elatius and C.
konojoi. In this study, we give a numerical value to the
coenenchymethicknessofeachspecies.Thecoenenchymeof
2 P.japonicumwasthethinnest,averaging0.15mmthickness,
only 29% of C. elatius’s coenenchyme, and 18% of C.
konojoi’s coenenchyme. From the results of Kishinouye [7,
8] and the present study, thicker coenenchymes tend to

have more complicated systems of vascular canals, while
Figure 22: SEM image of coenenchyme surface of Corallium
species having thinner coenenchymes tend to have rough
konojoi; OCA-Cn20050619-020. 1: coenenchymal mounds, 2:
surfaceswithminute warts.These results suggestthat there
siphonozooidopenings.
isarelationshipbetweenthicknessofthecoenenchymeand
status of the coenenchyme surface. In other words, there is
primitivemicroscope,Kishinouyegaveaverydetailedreport enough space for structures in a thick coenenchyme, and
of the examination with hand-written figures. Kishinouye suchspecieshavecomplicatedorgansintheircoenenchymes,
explained how gonads differentiated in siphonozooids, and but as there is no space in a thin coenenchyme, in these
that the thin coenenchyme of P. japonicum has simple speciesstructuresmustprojectoutofthesurfaceorbeneath
vascularcanals,whilethethickcoenenchymeofC.elatiushas theaxis.Forexample,thecoenenchymesurfaceofP.japon-
twolayersofcanals,andthethickcoenenchymeofC.konojoi icumhasdistinct coenenchymalmounds coveringretracted