tiss ue celi post-larval development of the commerciai
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ELSEVIER
Tiss ue &CeliTissu ••and èdl19 (1007) 325-134
\\'WW.e1se\' ier.comil ùt.'llitilice
Post-larval development of the commerciaI spongeSpongia officinalis L. (Porifera~Demospongiae)
• Ulllvmifll tÙg/J Stl/di di Ptmgla. DlpanfllltlllQ di Blalagla C<!llulaM e Ambientare - Via EICBai Satta - 06123 f'entgill. ltùlyb Univmità a~li Studi di Bclr~ Dipa~IJIO di ZoologIa - "o Ol'(lM(l, ,,- 7Q12:iBari.ltal,
lkuivcd 28 Marcl12007: rectived inrn'Ylsed fOl'ill131uIle 2007; a«q>ted 19 ]\111$ 2007AvailabIc Dnlinc IO Septembu 2007
Abstrnct
This srody inv&9tigated !.hodcvelopment or tbc Jamle of Spongla officln(l/4 in experimentnl conditiolls, afte.rsettlement 011 plastic suootralt-S,
using clccm:>n and light microsoopy. The released lt1I'Vl.le show i!Idark pigmcntcd ring dist.ingulshc-5 the p()3terlor IltrVal pOlo. The Y()\lD~esl
larvne, oovered wilh a nagellale epithclium. movc onwards by rOUl!ing On d-.eir longitudÌJllÙ ll..xk Over time a Creepi(lg-uke motiol1 pre\>ails,
probably linkcd IO tlle necd for seltlemem. After il free-s\.vimlniIlg period or 24-48 h, larvae settle on tbc artìlìcial SUbSI~IC by tbc llnleriorpole. AI Sèlliemear, th~ llageUute epitilelìum is substituled by f1atlencd cells, whkh delimit the òmennl}~t surfuce_ PMt-llirVlle WeIe renred lO
aboUI ~ months. Tbc early phQse (lf pasl-Iarval ditferentiation sb.ows Il solid interior mainly consisting of granular cclls \'lU)'Ì.ng in shape
and 811:e.They are lncluded in a dense col1~en matrlx !hai contains a conspicuO\ls amount or baclerla. Lacul1ae $re 8lteady evidenl in tbe
inltial pbase of metamorphosis. In severa! of lhem, ceU debrls and nucleare ce.lls llte vi&.ible. This feature is consÌslenl wi!h a pIQgre..'lsiverc.dllctioll or the ccll mass (olutolysìs). Neither choanocyte chamoors nor canals differcntiate. The mOJphogeJleUc p~$lealh to IlmetamorphQnly consistillg or vacuolated cells lI11d collagcn fibrils included in IIlhin fibr(m~COal.
<O2007 Ehevler Lld. All rights Wlerved.
1. Inll:odudlon
Sponge rcproduction, sexuality, larva! development andensulng rdense represent research fields useful lo \Irlder- .standing how mese sessile organisms cali colornzc d.iffereQt
environrnents and to whnt extent population genetic struclureìs affected by dispersa! pOlential (Wbalan el al .. 2005).
Larva! orgalÙzation hali attI'acted lhe interest of many
Icsearchers ~ to analyse larva l developme~t ilIld further metamorphosis. also in considemtion ofthe re1ntionshipswithin Pori.fcm (Boury-BsnauHet 111•• 1999; Le)"'et lÙ" 2006),and bctween these basicMetazQlI and higber aniroal~ (EeIk~Medrano and teys. 2lJ06). In addition, data 00 seqlJential
e-venls oooul'I'ing in tbe brief life of a released larYa lite es~en
lial to undetsland specific ecologica l Jleeds (M<Ùdonado.
• Com:.:spOnding llllthOt. Tel.: +39 OSO 5443357; Iu: +390805443357.
E-m(1'f (1tf(/res:s: [email protected](O. Corrieru).
0040-816M; ~ see l'ronl malter 1\:l2Wll!l.scvjer ~d. A1l rigbts n=rved.doi:1O.10Wj.tk;c.W07 .06.006
2006) and inteIpret spooge popu1.3tion dìstribution (Kaye andReiswig, 1991),
In thìs J:cgard, severa! llrticlcs have focused 00 lar<ial
behllviour, $ettlc:ntc:nt artd metamorphosis by considerÌi1glartae unde.r two differènt perspecti~: (1) to provide abetler dclÌnilion of their architetture by means of uUrastructural 8IIalysis (WooUacott. 1990; Boury-Esnault el al., 2003;
Maldooado cl 81.,2003; Ereskovsky and1okioa, 2004; Usher
andEreslroV"sk:y,2005; Eerkes-Medrano andLeys, 2006; Leysand Eresl(òvsky, 2006; Leys el al.•20(6); (ii) to test, in experirncnhù (.'Ondiliolls, I:he larval response lo some parametenin order ro make predictions OD their possible response wheo
cxposed 10 the natural enviromnent (Raye, 1990; WoollacOltand Hadlield, 1996i Maldonado el 81., 2003). In addilion,
tho study of sponge larvae represents a source of diagnosticcharactors al tbe ordt.r leve! (Ereskovsky and Toma. 2(04).
So far, nine larval types have been idenLified .in Poti!era
(Maldonado artd Bergquist, 2002) even though in demo-
326 E. Gaf11() el a/./1Jnu8 and CeiU9 (2007}J2S-3J4
sponges, a group including the largest taxonomic class, lhe
production of parenchymeUa larvae repl"esents the mO$tcommon pattem of development. Parenchymellae lU'eoften
retained by the parent io il brooding chamber (Kaye, 1990iWoollacott, 1993; Leys aod Degnao, 2002; Maldl)nado etal., 2003; Whalao et al .. 2005), a feature that offers a better
opportunity lo investigate their organization before and afterrelease.
Spollgia officinalis L, ìs li worldwide known sponge,
widely utilli:ed for C05metic purpoSM. Its over-exploitation
and repeated epidemics bave C3USedits disappearance fromwide Mediterranean 8l1'!as(Gaino el al., 1992; Pronzato et
al., 1996; Cenano et al., 2000), thus detennining the inclusion or thi~ bath spongc among tbe marine endangeredspccies requiring specific management measures (Anl\ex 3of thc Dern Conyention on tbe Frotection of WildIife). In
th1s contell.t, knowledge on tbe reproductive pllttem aod lar~val behaviour of this species are esseotial for understanding
the biologica! and ecological needs of tbe sponge populalions (Kaye and Rei$wìg, 1991), and may yield informationuseful for its proper management, here inc1uding COl1llerVll.tion planes. In thi~ specles tbe progressivo deve10pment ofembryQS and larvac was tbe subject of a previou!> investi
gation càIried out On post-fertilized eggs up to tbe newlyreleased parenchymellae (Bnldncconi et al., in press).
TIte present srndy was undertaken as Il second phase of
tho investigution OD the larvae of S. offidllalis in orde!; loanalyse larval behavioUJ in experimental conditions and tbe
bnsic anatomy of the post-hu'Vae after their setllement onan artificiill subWate. The "im was lO add SOme informa·
tion tQ the mlltux or knowledge On the metamorphosis of tbepareochymeUll in this eè(lBÒmiCally celevant species.
2. Mater1als and methow
The current srndy is mainly based on the swimming
. behaviour of newly released plU'enchymellae of S. offici1ll1lis
and on tbe ultrastructural aspects of their organization dwing
metamolphosis.
2.1. COlltClion of /onrae
Several hundred newly released brvae Were collected bySCUBA divers after hllving removed tbem from a plnstic
trap overlapping sponge specimens in the month of theirmain reproductive period (June) from IOlÙan coaStS (portoCesareo (LE) SE Italy-N40° 16'3 12" E17°SI'593"). Larvll.ewere immediate)y retumed to Ihe University or Bari labo
ratory where tbey were placed in glass lIerated containerswitb natllril' ftItered sea water. Tbc bottom of the containers
was CQvered with thin pIastic fragment:s (li few millimetresin thi.ckuess) to allow free-swÌII1IDing larvae to ~lt1e andauach to thernselves. Each container WllS emiched wìth nat
ural sea water daily, after having removed li çertain (jU~ntityor water. This procedure reduced me risk of natut'al. reSO\l{ce
deprivation and bacterial pollution due IO the experimenta!conditions. In order to test tho exact age of the post-Iarvae,
lhey Werc COnsidered actually settled if they did not resumeswimming when disturbed by moving me plastic ftilgments.
2.2. Observaf/on on generai slVimm/ng parrerns
Labofi1.t01')' observatioJls on tbe larva! movement were
detected by viewing larvae in glass Petri disl1es fiHed with filleroo seawater collected f:rom me habitat of S. officinalis. and
mamlaIDoo at room temperature (20-21 0c). Larva1 swimming (n == 30 specimens) was monitored and recorded witb adigital video camera connected lo a dissecting and light Leicllstereomicroscope.
2.3. Ul/rastrUCfural analysis
Post-larvae were bolli partially detàched from lheSUbStrat6
with a razor bIade without dismption and pllrtially placedwith their substrate into 2.5% glutamldehyde in artificial seawater used as buffer (pH 7.8) for five hOlll'S. Por transmissionelectron microscopy (TEM). samples were tinsed in actifìcial
sea warer used IlS buffer and posl-fixed for lhìrty min\ltes inosmium telroxide (1 % in sea water). Afterwards they were
repeatedly rinsed in the same buffer, dehydrated in a gradedetillmoi serie.<;and embedded in an epon-araldyte mi:xturel.lllnl·thin sections We.re obtained with an LKB ultnl.IOmt,
contTasted with manyI aCctatc and kad citrate, and examined
with li. Philips EM 208 transmission electron microscope.
Preparati0D: for scannin,g electron microscopy (SBM) werecarried out on tl1e glutMllldehyde tìxed materiat. then dehydrated ina graded ethanol series aod criticaI PQint dried using
a C02 Pabish CPD 750 apparatus. mounted 00 stubs with sil
ver conducting paint. and coated with gold palladium (20 nm)in Il Bahers Union EvapornlQr. SpeCimens were observed
under Il Philips XL 30 scanning electron microscope at the
acceler.lting voltage of 18kV,
3. Results
Brooded làrVae are easily detectable inside the mother
spongo, where tbey tend to gather together to fonn clumps(Fig. la). Released larvne (Fig. lb) show a black pigmented
ring locate<! at one of tbe larva! poles, surrounded by longftagella wllich greatly protnlde outside.
The latVae moved "P and do\Yn in lhe Petri dish. The 8wimming tak:es pIace by a rotation movement on ilS longitudinal
axis. with the posteriOI dark-ringed pole closer to the substolte and the anterior one uplifted. Larvae tended to direct
towards the shadowed border of the dish where the light wasIess intense. The locomolion atternates with a short period
of non-translocation. At intervals, Ihe larva seems lO explorethe substrate witb its anterioI' pole and move 0.11 fairly parat
leI to and aimost in contact wilh il. TIùs creeping-like mQtionbecOInCS more frequent as time goes by and it seems lo beIink:cd lo tbe need for settlemenl.
E. Gaino gt QI.l1bsJI/~ and C~1I39 (2007) 325-334 321
Fig.!. VIewoflhe larvaeofSpclIs/aoffie/lkllfg. (a) Broodroparenchymellacgalhtmd within the mothet sponge (arrows) (bar: l cm). (b) l'amlcbymeUaoboenocd under SEM (bar: 100 110m). Note the b/lICk: plgmenred J'Ùlg al oneofthe l~ pol~ (lIJTOw).
Larva! selliement takes pIace 24-48 h after release fromthe parent when larvae rest fllirly vertìcnIly and show !ho
anterior pole very dose lo lhe substrllte.
The onset of metamorphosis is marlred by the spre.ading
out of the cells of the contsct region and the ensuing progressive flattening òf the larv31 body that assumes a roùndshape in about 6-8 h fiom thc first suhs!:rate contllct The
main eell rnass is centraIly located and the peripheral bar
der lacks the typicnl ftngellated cover of tbe free-swimminglarva. ilnd graduaIly extends on me 9urface.
One·day.old posl.larva/'!. observed under SEM, presenta ftat shape (Fig, 2a) and adhere to the 9ubstrote wilh their
irregular surface (Fig. 2b). Semi,thin seclions reveal the pres
ence of Il dense population of ceIls, varying in shape and size(Fig.2e).
Eleçtron micrographs show that along the border in con~
tact with the :mbstràte (Fig. 2d) il thin fibrolls coat coversthe post-Iarva, 'J1ili; COllt ìs occasionalIy uplifted from tbe
substrate (Fig, 2e), even though tbc metamorph is stabiIized by the outennost librils thàt liok il lo the plastic
substrate (Fig. 2f). Collagen lilamenls enter the fibrou:>
COllt {Fig. 2g), a feature supporting their involvement in itsfonnation.
Tne uppersurface of!he posI-larva is delimited by .!tat cellsmat give rise lO a uniform layer (Fig. 30.). Some SEM images
show thal, at this smge of metamorphosis. the metamorphpossesses shon uplifts scattered on ìhe surface and layeredover collagen filaments (Fig. 3b).
Transmission electl'Dn micrograpbs confirm the oççur
rence of epithelial exopinacQCyte-lik:e cells delimiting tbeoutermost 5pOI1gesurfuce (Fig. 3c). Caviti~ llI'e lIlready evi·
dent beneath this epitllelial Jayer interspetsed among cellswhose cytoplasm is filled up by ekctron-dcnse granll/es
(Fig. le), Th.e.se cells constìtUte a rlch populatiQn and varyin sUe, shape nnd gnlnWar content, Some cells show intran
cytoplasmic vBcuoles (Fig. 3d). Moving towards tbc centmlregion ofthe post,buVBe, the lacunac become more numerous
and a.re scattered among me cells that are here present witbhigh dellsity (Fie. 3e). Symbiotic bacter1à fin tbe collagen
mntrix (Fig. 3t).
In fille,-day-old post-1arvae. semi-thin sections show acertain regionalisation of tbe celIs lhat have a different mor
phology and arrnngement in relation lo theìr position in themetamorphosing larva, Some region$ C(Josist vf cells elon
gated in .shape lInd /lrranged in roW'S (Fig. 48), whereas in
others the cells h8ve a round-shaped morphology (Fig. 4a).The coIlagen matrix below the epimeliallayer is crossed bycytvplasmic extensions of the gtllliular cells (Fig. 4b), whichwith tbe symbiotic bacterio fonn the main component of tbemetamorph (Fig. 4c). On occasiono ceUs with a llUge BudellI>and electron-translucent inclusions are associated with tbe
granular ones (Fig. 4d). Tbeìr periphera\ borde.- show$ short
cywpla5lDÌc protxusions. a featu.re eom).istent witb moilleactivity. LO\l'ger-sized laclInae persisl. bordered by bacte:ria
and cells, Lik:ewise the youngest pòSt.l3rYae. cclJs with Inrgeintra-cytoplasmic vacuoles persist (Fig. 4e).
The main aspeèt evident in nine.day-old p05t,lllTVtU: is
Ihe increasing number of lacunae (F't.g. Sa). occasionally
de1irnìted by ceUs 8n'8nged atong their b01der, 88 evident in semi-thin sections (Fig. Sa). TrllIlSmission electron
microscopy ShOW8 th.e presence of celI debris inside these
lacunne (Fig. 5b), along with nucleate cella with no apparenlsigns of degenerotion (Fig. Se).
111e ssme fearore is evident in 15-day"old post"larvaewhere tlle dense cellular mass (Fig. 5d) results from granular cells (Fig. Se). In this phase of developmem, lacunaeappear delimited by a denser fibrillar ring, and include dottedmateria! snd nucleolate ceUs (Fig. 50.
Moving towards Ùle centraI region. Ùle size and the Qum·ber oflacunae tend to increase. Their dotted content can be
Ilssociated with cell debris (Fig. 6a). In proximity of one ofthese lncunae. two adjacent cella show the presence of longcytoplasmic extensions emerging from d1eir apical region
(Fig. 6b). These extensions cross tbe collagen matrix and for
balf of their length are located just above tbe cavity border.No further differentiation was observed in me reared
posH8rVlle, and about three months (100 days) arter their
328 E. Gaino 61 al./TImle alld Ce/l 39 (2007) 31S~34
Fig.2. LaMlsettlernent. (a)S~ vicwofaooe-day-ollhettledlana (bar: 100 J1.IlÙ. (b}1be In~fflll."ebetween pareochymcUIlWva(l'L) and lheplMlièru~tnlle(l'S) \,bar.20 lUll) ..(c) S\:RÙ-rbbi ~Qn.sttl;lWinl5lbc:Uppu :sctdcnllrfsce (arnn>r.!)GDdtbc dense celi wmpomnt ~ 20 p.rn}, (d) Bl<ç!rollmicmS"'Ph sbowms1M~u bordu (lImlw) in eonlilct with tbe plastle subsll'3te (FS) (bar. 21UD). (e) The "'Ider bordeT (RlJèw) \Jpll& troll1lhe pll&Stlc mhsttate (P8) (bar. l p.m).
(f) TIIe ffielamorpl\ is Iìnkcd 1.0the plaslic subsllUte by oulerffiOSI fibrils (arrow) ~OOr.QA jJ.m). (g) Collagen filnrnent!l eRler Ihc lÌbrous OOlIt(DJTOwS)(bnr: 111m).
settlement, they are delimited by a thin fibrons coatthal substitutes tbe initial epithelial coat (Fig. 6c). Elle
teria tend to accumulate alQng the extemal fibrous conto
Crlls with electron-translucent vacul)les are scattered in
the collagen matrix and are almost the only celi typepresent (Fig. 6c). Neither çhQanocyte çh!Ullbers nor canalsdifferentiate.
4. Discussion
Investigations on d1e behavio\ltiÙ pattem of sponge larvae afe limited lo artificial conditions:, il felllurc [hat may
alter the !'esponse mat larvae could have in the natura!.
enviromnent (Kaye and Reiswig, 1991). Nevertheleu, e'l'en
though n certain caution can. be suggested in extending lllb-
e. Gai/!() e' al. l'li.tJlle and Ctl139 (2007) 325-<334 329
l'i!!. 3. SEM (li, b) aod TEM (c. O view of OlIe-day-oldpost-lnl'Yll_ (a) The nppllr surfnce b}lli cove. of flilI cells (b:lr: 25 p.m). (b) A short upUft dcUmited by
ti:!! l;elli. N'ole Ihe collugen lilamenrs lJooemealh (arrows) (~r; 20 14ID). (c) PiDacocytc-likc celb dc1i11Ùt thc:oIitenilOst surfaa (lIrIOW). Nolo the pI:llSelKe or
li lacuna (L)~_rh the c:pithc:liallll)'er lUld iidJaant \O granlllll1'rells (GC) (bar: " !Am). (d)O~lllt .;:(IllshowiDg iDlm-qtoplasmic vllCUo1es(uroWii) (bàr:4ILm). (e) Sevenù lacuoae (L) In !he Inner post-1aIval region (bar. 3ILm). (O Syll1biotic bl1tteria (B) fili me collageR ma!rlx.l.. laclloae (bw: 6 JLDl),
oratory resullS lO me larva! melllm.Olph.Oli~ taking pIace in
natural conditions, the progressive tmDsformation occurri.ng
aftec settlement provides data useful lo under$land the larval biology. This is particularly relevant fol' S, officina#s,in cOIl$ideration of its commercial importance ~nd il:ll. dras
tic decre3$e and disappeamnce from large areas (Cenano et
al., 20(0). The survival of patched populations (ProImltQ et
al., 1996) foslers sponge--culture projects to re-populale lhe
spoiled benthic substrata (Corriero el al., 2004; BaldaccoDÌet al., 2(06). In lhis regard, beyond tbe biological interestthst larval swinuning behaviour, settlement and me duralionof metamoxphosis can have, these slUdies deserve attenUon
:330 E. GaUIO ~t al. l1i.ull~ and Celi J9 (ZOO]) 315-334
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'. b .~~~ .. " .
.e> ,.'...•••• •... .
" _ . ~..:' : t
,>.~.~...,/\~:'\.'.-,";':':. j'
I
Fig. 4. Flvc-day-old post-lacva. (a) Sem!·th\n ~QI\ ~owin8 a rcgionaIisalion D! Ihe ce\1s; in some 1Uell5 cells ere elongated In wpe ;"'lI dls~ in IQW
(A.)). in otheta are round in shape (~) (bar: 151JlD}. (b) Cytoplasmic nlell!lioD.$ of tbc glllDular cells crossillll du: coUllgell matri.'o( (arrows) (bar: 2 v-m). (c)
Gmoollli' <:elb (OC) and bacleria (D) oonslilutc lbc lI1IIin Còmpònentutthe melainotpb. (1m: 51'-m), (li) Ceu with a large nuclcD.!l, cleclron-trIlmlUcent inclwiOTlll
and slunt cytoplllSnuc proInISiuns~; l Pom), (1;1)Cdl.i wilb Jarge inlr1l-qtol'lBlimic Y1lCÙO!e:s(E!; E2) (bar. 2 jl.0I).
because lhey suppl y dlllà !hat can be used lO direcr interven
tions IO safeguard biodiversity.
Therolalion and C{eeping be.baviour ofthe free-swimming
larvaehas been obsenred in olhcI commercia! sponges (Kaye,
1990; Kaye and Reiswig, 1991; Mllldodado and Young,1996). The presence or a pigmented ring has also beenobservedin anhaplosclerid p~~ncb.irnella(Leys and Degnan,2002). TIùs fearnre can be considered a marker allowing the
posterior larval pole lo be distingwshed froro the anterior
ODe,As ohsexved ìn some Haplosc1erida and in all the .lmown
Diclyoceratida (Ereskovsky and Thk:ina, 2004; Maldonado,2006), in S. offidna/is !he posterior region 8lso possessesa distincI rlng of long flagella, the ruft. Il is thought tbatthe force for forwOlrd mOvement is due lo Ibe short f1agelln
of the çells uJrifu:mùy C()vering !ha larva! surface whereas
directionality is conferred by irregular beating of tbc long
flagella (Leys and Degnan, 2001; MlIldolUldo et al" 2003iLeys snd Meech, 20(6). L..mae of S. officinali.r rotate for the
E.. Gamo el al./Tisl!ll! aliti Celi 39 (2007) 325-334 331
Fig. ~. Nine-dlly-old (Il-<) IlJ1d 15-day-old (d~) lIMt larva. (a) Seml·tbill 8e(llon showillg a large lac:una (LI,) and olbers smaller (SL) (bar. 10 f.tm). (b) A
\'l\CUOle inclllding ceti dehris (tlltùw) (bar; 5 1UJ1).(c) A IIÙdelllèèdl (ilttOw) inside Il.IIl.CIllla(bar: 2 Jilll). (d) Seml-Ihln seçlloll showi~ lhe de.tlSe ~ll OOlllpoll.ent
(bar: 20 P.D').(e) ~l;u çeU, re~nllha main çeU fractlon (bar; :) •.•.m). (f) U1cuIIllIRcluding t1o\1ed mnu=ri:1I and n nucleol<llecelL Nole lhe dense iibriunr
ring (arrow) (bar. 2 JLm).
332 1!.Oalno BI aL I7fSJUB Olld CBll39 (2()(JJ) 32~jj4
,'.r ..
"";,,;.,<;.:~
Fig. 6. Flfieen-day-old (a, b) and loo-day-old (e) posl·l~. (a) Cenll'U ~gioo oC 1110met3DlOlpb showing ~ lnc;rell$ing Dumber or I~ (t) \Yithdolte4conlcol and cell debris (lUtOw) tbar: 41Ul\). (1)) Two BdJl\Cent ~ (C,. C't) whos~ long cytoplasmlc ~xlellSlolIS (atrows) eIllelge!rom Ihelr aplcal regloR. Note
thek l~tiOD in pIWÌIIlÌty In a lacuna (t) (bar: llLm). MCella with e1eclIoo-tnmll1cenl 'VlIcilnle3 IIICIhc pn:vaknt componcnt ne Ihc melllmolph dclimiled bytllbintiblOlIS roal (rutOlllS). Nole Ihe presence Qfbacteriil (B) ~Iong \he eJllcm~llibrous COlI (NI'; 2,...m),
E. Galno e/al. /ns~lI~iJJfd C~Ji39 (2007) 32S-JJ4 333
main swimnùng peri(ld (24--48 h), during which they prefershaded areas or lhe Petri dish, thereby snggesting il negative
phototMis, likewise ob.setved in some dictyoceratid$ (Kaye,1990; Maldonado el al., 2003; Ereskovsk:y and Tokina, 2(04)
and haplosclerids (Leys llnd Degnan, 2001; MaldoWldo etal., 20(3), In conlIast, the 18IVa or Cacospòngia molliòrwas
de.scribed a.$ photopositi:ve Upon relcasc, but subscquenUyshifting to photonegati\Te aller a few hours (Maldonndo ot al.,
2003), In tbc bap10scierid Reniera sp. the pOllterior regi.on isre.sponsible Ior a coordinated response ofthe parenchymeUa
k) tbe yariations in lìght int.ensity (Leys and Meech, 2006).'!Wo distinct rodopsin peaks oblained for Rentera sp. &reCOD
sistent with the involvo.ment of tbe cells of this region inlight perception (Lo.ys and Meecb, 2006). It Ì8 weU known
mat rhodopsin acts as a photosensitive pigmenl not olÙY inMetI1zoa, but also in fungus zoospores (Samnak: and Foster,1997) and green algae (Poster el al., 1984). Maldonado elal. (2003) in tbeir exhauslive investigiltion on tbe mechani~m
by which light affects tbe beating pattem of parenchymellae,correlilte larva! phototaxis and ultraslIUcturo by stressing mal
the pigmc:nt~lilled pcollUsions of the tuft cells nct llS simple
eyecup pholoreceptors of many lower in'\'ertebrstes in dis
criminllting Ihe direction of light. Tile long tlagella of someadjacent ceUs seo.m 10 group togeLher to beat 88 Il cohesiveunit. '!bis arrnngement giving rise to Il compound f1agellacould enhance the beat as a unit.
In S. offic/nalis lhe larval rotaliOll is gradually substiwted
by a creeping-lik:e motion, which becomes more and morerelevant at tbe end (lf the free-swimmìng period, probably inrelation lo tbe ensuing settlement.
In tbe ncw1y rclcascd parenchymeUa of S. offiCinalis the
postcrior ring ot long-ftagellate cells have distai proti~usionsand numerous elecuon-Iucent vacuole..'1filled witb li homogerteous matrix (Baldacooni Cl al.. in press). Their morphology
is similar lo thal described by!.eya and Degnan (2001).The tirst adhesioll of tne pareocbymella of S. offidnalis
J to the plastic subslrate is assured by a groundroat lhat fonns, discontinuous adhesion points. Tbe formation of an adhesivelamella secreted by basopinacocytes has been observed in
melanIorphosÌIJ.g demospollg~ (aorojevic and Uvi, 1965;Boury-EsnauIt, t976; :Bergquist and Green, 1977; E;Vllns,
1977; Kaye and Reiswig. 1991).
Additional data in (bis field could help understanding ofthe larval ability lo in~ct with the substrate and select il, aprocesso that co\Ùd be at tbe ba$i$ of tbe complex mcchanisrnof selfll1QD-~elf recognitkm in $pQnges (see revÌeW in Gaino
et al., 1999). A collagenll\yer, giving ~e 10a n3I1:QW .spQngin
layer, hlls been also observed in tbe encrusting sponge Sco.paliTlQ lQphYl'Opoda. in whiçh tbe secrelion or this matri:x: bytbe basaI pinacocytes realises a spongelsubslnlte connection(MaIdonado and Uriz, 1999).
The fÌfst event in tbe one-day-old post-lar\Tlle is the reCeS
sion of the f1agellale cover, io such a way lhal an actualflngellale epitbelial covering is limited lo me brooded nnd
free-swimming larvae (Baldacconi el al., in press). in agree
ment witb previous observalions OD commerciai sponges
(l(aye and Reiswig, 1991) andReniera s.p. (Leys and Degnan,2002), The fate of lhese cells is. stili conb;oversial but inReniera sp. il was lìrst demonstrat.ed using a 8uorescent celI
ttllcker !hat lhe outer epithelilll ce1ls of tbe parenchymelliltnrnsform into tbc flngellnte choanOéytes amI in an elon
gated coU type sca.ttered throUghoUl the juvenile sponge (Leysand Degnan, 20(2), lhereby corifirming obsc.rvations On thepoecilosclerid Hamigera hamigera (Boury-Esnault, 1976).
In one-day-old post-Iarvae of S. o.fficillali.r the outermos[ surface, oppOllico !he basai one, is defunited by a
coyeriog of ftat cells whose rnorphology recalls tbat of theexopinncocytes. Tbe meromoxphosing larvae have a solid
centraI mass moinl.y constituled of cells with e.lectron-denseinclusions immersed in 8 collagenous matrix enriched by
a marked amount or bacteria. These bacteria, presumablyderived from those already present in the free-swimIning
larva, can contribute to tbe feeding activity of the metamorphhy phllgocylo~ìs, li pnx:ess already evident in the cO\WJeQ(
larval development and in newly released l;u:vae (Baldllcconicl a!., in press).
Post-larvae show nUmerous lacunne bolli in thoir super·llcial und inner core. Likewise Obser\Tèd in olher Caribbean
commercia! sponges (Kaye snd Ro.iswig, 1991), tbei! deve1
opment beneath che epitheliallayer and within tho. centrai
mass of cells cm be re,garded as earIy alages in tbe fonnation ofthe canal system. As themetamorphosis proceeds. celIdebris aDlVor ceUs appear within these lacunae. thereby suggesling possìble llutolysis. This basic olgllmzation lasls fu•..a long period nnd remains unchanged in lOQ..daY-Q!dpostlarvae, which ate tbe last phase we obtained in experlmental
conditions. In mese specÌIneI1S, il is inreresting lO Ilotc tbcoccurrence ot a unjfonn tbin fibrous cont delimiting lbe meta
morph, which seo.ms lO act as a barrier IO prevent exogenousbacteria from penetrnting inwards. 111emo.tamorph seems toturn into a resistant body.
In conclusion, in· me larvae of S. officinalls, as well asin tbe above rnentioned Caribbean commerciaI sponges. acompletion of metamorphosis WQSnot Qltained. Presumably,the laborlllOey conditions could delay activalion of lhe nlter
feeding SY1item of post-setUetS and affect tbe. process ofceli dift'erentiation, On lhe other l1al\d, according to litera
Iute, tbe time required for tbe completion of metamolphosis
~eeID$ to var}' conside.rably (FeU, 1989; Leys and Degnan,2(02). Indeed, whereas in many sponges met;unorphQ$isis completcd within aboUI 24 h f(lllowing l:'lr\'al sctt1cment,$omclimes this process ~eds much m(Ire s::lowly. InHamigero hamigera inhalent opening$ and Qllculum deve.lop
after 9~10 dnys, but tbe flngelllltt::d chamoors do not 3ppe:lr
unti! after ODe month (BOllIy-Esnault, 1976),Insponges,!he te.rm "parencbymella" has been llttributed
to larvae that sbare Only ge.neral features. In lhis regard, sOme
au!hors Use the terminology ''parenchymeUa-t}lpe''. just lO
stress tbe varlability of tbe reference model. Consequently,
We cannot exclude tbat the dUl'ation of the IIlQqmogenetic
processes ClUl differ in "parenchymella" belonging lo differ
entgroups, In ex.per1mentaI conditions. rapid metamOIphosis
:334 E.. Gallio 6' al. In~JII6 and Ct!lI 39 (1007) 325-]34
is crociul for redùcing tbe risks of contamination and tissue
daIIt8ge, thereby allowing the organisational c\1cnts leadmg
(O lÌ ncW functional sponge lo be traced.
Acknowledgement
We thank tbe 8Ilonymous referees for their helpfu1 advice,
which greatly improved the content of tbe papero
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