A morphological study of Chaetoceros species (Bacillariophyta) from the plankton of the Pacific Ocean of Mexico

73 Pages·1996·34.6 MB·

by  David U Hernandez-Becerril

Bull.not. Hist. Mus. Lond. (Bot.)26(l): 1-73 Issued27June1996
A
of Chaetoceros
morphological study species NATURAL
HISTORYMUSEUM
(Bacillariophyta) from the plankton of the
Pacific Ocean of Mexico 01 JUL 1993
DAVIDU. HERNANDEZ-BECERRIL ^
DepartmentofBotany, UniversityofBristol, WoodlandRoad, BristolBS81UG
Presentaddress:LaboratoriodeInvertebrados, FacultaddeCiencias, UNAM, Apdo.postal70-371,
Coyoacdn, Mexico, D.F. 04510Mexico
CONTENTS
Introduction 1
General 1
Historicalbackgroundandtaxonomicrelationships 2
Recentstudieswithelectronmicroscopy 2
Materialsandmethods 2
Sourceofmaterial 2
Methods 3
Terminology 3
Systematicaccount 4
Discussion 67
Morphology 67
Taxonomicrelationships 68
Classification 68
Biogeography 70
References 71
Index .. ..73
SYNOPSIS. An analysis of 65 preserved marine plankton samples from waters of the Pacific Ocean of Mexico was
undertaken in order to investigate the morphology of species of the diatom genus Chaetoceros Ehrenb. Forty-six
Chaetoceros taxa were recorded from the samples. Of these, 35 were studied using light, scanning and transmission
electron microscopy; a further 11 species were also recorded as present in the material, but these have been treated
elsewhere. Mostofthetaxastudiedarecharacteristicofwarm-waterregions.Theirmorphologyisdiscussed,especially
whereitdiffersfromthatpreviouslydescribed.Mostofthetaxaareillustratedbylightandelectronmicrographs.Anew
section, Peruviana Hern.-Bee., within subgenus Chaetoceros (Phaeoceros), is proposed. New observations by electron
microscopyarecontributedforthefollowingtaxa: C.atlanticusvar.neapolitanus,C.atlanticusvar.skeleton,C.brevis,C.
compressus, C. densus, C. denticulatus, C. distorts, C.pendulus, and C. vistulae. Phylogenetic relationships with other
generaandaspectsofdistributionandbiogeographyarealsorevised.
INTRODUCTION
General identifying species. Hargraves (1979) considered that resting
sporescanalso aid identification, although theseare limited to
Chaetoceros species are an important and often abundant speciesbelongingtosubgenusHyalochaete.
componentofthemarinephytoplanktoncommunity; however, Many Chaetoceros species from the plankton of temperate
the great number of species makes positive identification andcoldwatershavebeendescribedand studiedusingelectron
difficult. The major characters traditionally used for microscopy (EM). However, tropical and subtropical species
identificationatthespecieslevelare:theformandrelativelength havebeenlessstudiedusingsuchmodemtechniques.
ofthechain,thefrustuleshape(girdleandvalveviews)andsize, This work is a study of the morphology and taxonomy of
the structure and size of the girdle and valve mantle, the somespeciesofthegenus Chaetoceroswhichwereencountered
orientation and form of the setae, and the number of intropicalandsubtropicalareas,inordertopresentasystematic
chloroplasts. Evensen & Hasle (1975) found that the structure accountofthespeciesfromthoseregionsandcontributetothe
and size of the rimoportula is another important feature for taxonomyofthegenus.
TheNaturalHistoryMuseum,1996
D.U.HERNANDEZ-BECERRIL
Historicalbackgroundandtaxonomicrelationships proposed by Round & Crawford in Round et al., 1990); the
presentstudyfollowsthislatterclassification.
The genus Chaetoceros was erected by Ehrenberg (1844), who
described the type species, C. dichaeta, as well as three allied Recentstudieswithelectronmicroscopy
genera: Dicladia, Goniothecium, and Syndendrium; the last two
were at spore stage and all three are now considered to be Studies of Chaetoceros using electron microscopy began with
synonyms of Chaetoceros (VanLandingham, 1968). Later, Okuno (1951), when he published microphotographs of C.
Brightwell (1856) provided an emended description of criophilusCastrac. Helmcke & Krieger (1953) also made TEM
Chaetoceros,includingtwonewspecies. Schiitt(1895)described observationsofChaetocerosspecies,asdidHendeyetal.(1954).
a new genus, Peragallia, which is also now considered to be a Desikachary & Bahadur (1954) provided a study of the genus,
synonymofChaetoceros(probablyC.peruvianusBrightw.). although gave few details. Desikachary (1956) attempted to
Gran (1897) divided Chaetoceros into two subgenera: summarizetheelectronmicroscopystudies(mainlyTEM)made
Phaeoceros and Hyalochaete (Hendey, 1964, has correctly on diatoms up to that time. However, his list of 11 species of
substituted Chaetoceros for Phaeoceros, as this subgenus Chaetoceros did not include C. densus Cleve, which had been
contains the type species). Ostenfeld (1903) divided the studied previously by Hendey et al. (1954). Okuno (1956)
subgenera into 16 sections (two in Chaetoceros and 14 in provided additional information on some partially described
Hyalochaete); further additions were made by Gran (1905). species. Later, Hendey (1959) prepared another list, this time
Recent additions to the classification include the proposal of including 19 species of Chaetoceros studied using TEM and
section Coarctata within subgenus Chaetoceros especially with regard to thecell wall. Okuno (1970)continued
(Hernandez-Becerril, 199la), section Conspicua within to provide more information on Chaetoceros, while Blasco
subgenusHyalochaete(Hernandez-Becerriletal., 1993),andthe (1970) made a detailed study of C. didymus Ehrenb. Other
proposal for a new subgenus, Bacteriastroidea observations combining LM and TEM were made during the
(Heraandez-Becerril, 19930). The present infrageneric study of life cycles (Hargraves, 1972; Stosch et al., 1973) and
classification includes three subgenera and 19 sections morphology(Dukeetal., 1973).
(includingtheoneproposedhere):fourinsubgenusChaetoceros Themostimportantrecentcontributiontoourknowledgeof
and 15insubgenusHyalochaete. the genus Chaetoceros was made by Evensen & Hasle (1975),
AccordingtoVanLandingham(1968)thereare 177speciesof who studied 14 species (four in subgenus Chaetoceros
Chaetoceros,includingonefossil,fourdescribedassporestages, (Phaeoceros), 10 in subgenus Hyalochaete) using SEM and
and five from freshwater environments, together with 36 TEM. Later, Fryxell (1978) studied three species of
infraspecifictaxa: 19varietiesand 17forms.However,Hargraves Chaetoceraceae, including two Chaetocerosspecies, with SEM.
(1979) considered that this number was an overestimation and Hargraves (1979) provided an important contribution on the
somespeciesshouldberegardedasformsorvarietiesofothers. resting spores of Chaetoceros by combining LM, SEM, and
Chaetoceros exhibits little variation in its general structure. TEM.Fryxell&Medlin(1981)studiedthreeChaetocerosspecies
Thesubgeneramaybedistinguishedbythefollowingfeatures: usingLM and SEM,especiallywith regard tochain formation.
I.Chaetoceros(Phaeoceros)-robustspecies;onepairofsetaeper Navarro (1982) listed and figured 25 species and onevarietyof
valve;setaethickandstrong,mostwithchloroplastsandspines; Chaetoceros using LM, but gave no new data on their cell
restingsporesknownonlyinonespecies. structure. Takano(1983)describedanewspecies, C.salsugineus
II. Hyalochaete - delicate species; one pair of setae per valve; Takano, accompaniedbyelectron micrographs. Koch&Rivera
setaethinandfragile,usuallylackingchloroplasts;restingspores (1984) studied nine species of subgenus Chaetoceros
inmostofthespecies. (Phaeoceros), two of them not previously studied with EM.
III. Bacteriastroidea-fairly robust species; three pairs of setae Additional observations have been made recently on valve
&
per valve (two pairs reduced), lacking chloroplasts; resting development(Li Volcani, 1985),morphology(Rogersonetal.,
sporesunknown. 1986; Giuffre & Ragusa, 1988; Hernandez-Becerril, 199la, b,
Evensen & Hasle (1975) noted that the rimoportulae in 19920, 19930; Moreno Ruiz et al., 1993), taxonomy (Rines &
subgenusHyalochaeteareshorterandlessprominentthanthose Hargraves, 1986; Hernandez-Becerril et al., 1993), and resting
insubgenusChaetoceros,andareconfinedtoterminalcells. spores(Stockwell&Hargraves, 1986).
The genus Chaetoceroshas beenconsidered to belongto the Oneofthelatestcontributionstotheknowledgeofthegenus
family Chaetoceraceae Smith, together with Bacteriastrum wasmadebyRines&Hargraves(1988),whogaveanaccountof
Shadbolt and Acanthoceros Honigm. (Simonsen, 1979). speciesencounteredinRhodeIsland,U.S.A.,usingLM,butalso
However, Round et al. (1990) placed Chaetoceros within the discussing important taxonomic points within the genus as a
EM
family Chaetocerotaceae Ralfs, with Bacteriastrum and whole. Other studies with involve the discovery of more
GoniocerosH. Perag. &Perag., althoughCrawfordetal. (1994) than one rimoportula per valve (Rines & Hargraves, 1990;
latertransferredthetwoGoniocerosspeciestothegenusAttheya Hernandez-Becerril, 1991a, c; Hernandez-Becerril et al., 1993)
West, leavingthefamilywithonlytwogenera: Chaetocerosand and thedescriptionofnewspecies(Hernandez-Becerril, 1991c,
Bacteriastrum.OtherworkershaveincludedonlyChaetocerosin 19926).
Chaetoceraceae (e.g. Lebour, 1930; Hendey, 1964), but it is
evident,however,thatChaetocerosandBacteriastrumareclosely
related (Fryxell, 1978; Simonsen, 1979). Acanthoceros is now MATERIALSANDMETHODS
placedwithinitsownfamily,AcanthocerataceaeR.M.Crawford
(Roundetal., 1990).
In Simonsen's (1979)classification, Chaetoceraceae isplaced Sourceofmaterial
within thesuborderBiddulphiineae, orderCentrales. In Round
et al. (1990) Chaetocerotaceae is placed within the order This study was carried out using preserved marine plankton
Chaetocerotales, subclass Chaetocerotophycidae (both taxa samples,somecollectedbytheauthor,butthemajoritysupplied
STUDYOFCHAETOCEROSSPECIES
by the following colleagues: R. Cortes-Altamirano Table1 Planktonsamplesusedforthisstudy.
(ICMyL-UNAM), S. Gomez-Aguirre (IB-UNAM), and
institutions:CIBandCICIMAR(LaPaz,B.C.S.,Mexico). Sample
Sixty-five samples were obtained from the no.
tropical-subtropicalPacificOceanofMexico: 29fromtheGulf
ofCalifornia,31 fromoffthecoastofBajaCalifornia,fivefrom
offthePacificcoastofMexico(seeTable 1).
Methods
All material prepared for light and electron microscopy was
rinsedatleastfivetimeswithdistilledwater.Permanentslidesfor
light microscopy were made from the rinsed and cleaned
material.Themethodforcleaningdiatomsfollowedthatusedby
Simonsen (1974) and Hasle (1978), which is basically the
oxidation of the organic material (using KMnO4) followed by
acid treatment (HC1). Identification, preliminary observations,
and measurements were made with an Olympus CH light
microscope, phasecontrast, and an Olympus Bhwith attached
camera,phasecontrast,brightfieldanddifferentialinterference
contrast.
RinsedandcleanedmaterialwasusedforSEM. Dropsofthe
prepared material were put onto coverslips, air-dried, and then
coated with gold in a coating unit. Some previously identified
specimens were isolated with the aid of a micropipette, and
afterwardstheabovemethodwasfollowed.Criticalpointdrying
was used fora few samples, after rinsingand dehydration. The
scanning electron microscope used was a Phillips 501, usually
operatedat 10-12kv.
For transmission electron microscope studies, only cleaned
materialwasused.Thiswascarefullyplacedwithamicropipette
ontocopper,Formvar-coatedgrids,air-dried,andthenobserved
directly.TheinstrumentwasaJEOL 1200EX.
Terminology
The terminology adopted in this study generally follows that
proposedbyAnonymous(1975)andRossetal. (1979). Specific
terminology for Chaetoceros follows Brunei (1966, 1972) and
&
Rines Hargraves(1988).However,thefollowingtermsusedin
this paper have been modified from those cited
(Hernandez-Becerril, 199la,c, I992a):
- Thetermchainisused instead ofcolony, ascolonyimpliesa
more complex organization with some interaction between
itsmembers.
- Chainsarearbitrarilyconsideredshortifthenumberofcells
inthemislessthan 10,longif 11 cellsormore. Usually,there
is no overlap between these two categories, as species are
typicallylong-chainedorshort-chained.
- The term heteropolar is applied in the sense of Rines &
Hargraves (1988), where the two ends of a chain orthe two
valvesofacellaremarkedlydifferentfromeachother(PI. 1,
Figs3a, b). Thus, todistinguisheachend thetermsanterior
and posterior are used: the anterior end having valves with
curved setae, directed towards the chain or cell, and the
posteriorendwithsetaedirectedawayfromthechainorcell.
- Girdle view is regarded as the broad girdle view, unless
otherwisestated(PI. 1,Fig. 1).
- 'Aperture' is the space between siblingcells in a chain (PI. 1,
Fig. 1).Thisisdescribedasnarrowifitislessthan5um,and
aswideifmorethan 5 um. Afewspeciesshowaratherwide
range of variation in the size of aperture and in these cases
the average measurement is given. The term aperture is
D.U.HERNANDEZ-BECERRIL
chosen in preference to 'foramen' (e.g. Rines & Hargraves, and setae. Measurements: 7-13 um a.a., 17-25 jam p.a., 24-30
1988), because the foramen represents a structure in the umap.(PI.2,Figs 1,2)
valve, while the aperture is not considered to be a valve
structure. EM. Thegeneralmorphologyofthisspeciesisrelativelysimple.
- Sateentradmeithnhaeovilerobgpyeoseiinstoninoalnmyeipndartathcleycofcreoldllilno(gwBertduonhteehire,ei,r1ap9so6s6iit)t.isioHvneorwiynevcteoherm,pclhteahxii,ns Tcblyhoessemvaatllolvtephoferacboeia,dssem,sanaotlflteth,hoeaungsehdtwsaeeeta(aPkeI.bcao2s,setFsaieagrsaer3ei-r6sr;oemgPueI.ltai3r,mlyeFsipgea.rpf4p)oa.rraTethneetd
Ti)aPkoasniotio(n19i8n3)thaescthhaeins:et'ateerimnintahle' tiserumsiendalinvatlhvee,sneonstetohfe tvahlivcekeneidnggersuhnopwasralalelhytaolitnheelriinmesaonfdthiengitrhdelemiannstelretiorno(wPsI o3f,
terminalcell, in thechain; 'intercalary'refersto setaeofthe Figs 1, 2). Rimoportulaearepresent ineachvalve in thechain,
wtinehtriemcrihcnaaallraercyetlhvlia;clkv'eesrpseaacinnaddl'cleailsrlgs,uesrientdchlautnoditdnhegestcohtrehiebirenst,eirnfntuaeslrecdva,allaavrneydosfweittthahee olsoficmtaphtleeedsteuitbnaeestchhoeapnecgenenttsroaetthotehfeoiutrthvseeirdvyealb(vPaeIs.ef3aa,cneF.digaEslxst1oe-r3dn)ias.tlaTllyhl,ye.tsThtherseuecytaaurrreee
tbhieggseramsepinveasl,vei;i)'Phoestietrioovnalivnart'h,etcheell:se'tiasoevailnvadri'f,fetrheentsevtaaleveisn ctihrecvuallarvein(PcI.ro3s,s-Fsiegcsti1,on2)a.tTthheeybatshee,npceurrfvoeraatneddfbuysepowriotihdssibalsining
setae, beyond which point they become thicker, square in
- T(hPIe.tle,rFmig'.an1)n.ulus'(Stosch, 1977)isusedtonamethe'central cross-section, and spine-bearing; the spines run in rows along
hyaline field', as used by Evensen & Hasle (1975) and the each edge and the areola pattern comprisestwo striae between
'centralarea'inthesenseofOkuno(1956). twocostae(PI.2,Fig.7;PI.3,Figs5-7).
- The measurements given for Chaetoceros species are: apical DISTRIBUTION. 29,42,63.
aa.xai.s),(tpyeprivcaallvlyarthaexiwsi(dpt.ah.)i,natnhdebapreoratdurgeir(dalpe.)vi(ePIw.,1a,bFbirgesvi1a,t2e)d. REMARKS. Seefollowingvariety.
2. Chaetocerosatlanticusvar. skeleton(F. Schutt) Hust.
SYSTEMATICACCOUNT Hustedt, 1930: 643, fig. 365; Cupp, 1943: 104, fig. 59-Bb, c;
Sournia, 1968:46.
ChaetocerosskeletonF.Schutt
Thirty-five taxa belonging to the genus Chaetoceros are Schutt, 1895: 45, pi. 5, fig. 19; Peragallo & Peragallo,
described,thetaxonomicarrangementfollowingthetraditional 1897-1908:482,pi. 134,fig.9.
classification (e.g. Hustedt, 1930; Cupp, 1943; Hendey, 1964; ?ChaetocerospolygonusF.Schutt
Rines&Hargraves, 1988).Thelocaldistribution(inthematerial Schutt, 1895:46,pi. 5,fig.24;Hustedt, 1920:pi. 323,figs6,8;
studied)isindicatedbythesamplenumbers(seeTable 1). Lebour, 1930: 114,fig.80;Hendey, 1964: 120,pi. 14,fig. 1 (non
C.polygonusF.SchuttsensuHust., 1920:pi.322,figs5,6= C.
atlanticusvar.neapolitanus(Schrod.)Hust.).
CHAETOCEROS
Ehrenb.inBer.Akad. Wiss.Berlin1844:200 Pis4,5.
(1844).Typespecies: ChaetocerosdichaetaEhrenb. LM. Chains straight, short, delicate. In girdle view, cells
octagonal, the apical axis being longer. Valve face convex,
CHAETOCEROS bearing a short, cylindrical process, mantle very low, lines of
I.Subgenus (PhaeocerosGran) girdlestraight; apertureswide. Invalveview, cellselliptical, the
1.SectionATLANTICAOstenf. sspeitnaeeso;nlytesrlimgihntallydisveetrageing.esSseetnatieatlhliyck,ucnodairfsfee,rebnetairaitnegdmifnruotme
Centre of valve with prominent, tubular protrusion of the intercalary setae, the latterdiverging and curvingmore widely,
rimoportula.Apertureswide. almost parallel to the chain axis. Several small chloroplasts
presentincellandsetae.Measurements: 10-17uma.a.,8-11 urn
1. Chaetocerosatlanticusvar. neapolitanus(Schrod.) p.a.,8-10umap.(PI.4,Figs 1,2)
Must. EM. The valves are not as heavily silicified as those of var.
neapolitanus, but the structure is otherwise similar to that
Hustedt, 1930: 645, fig. 366; Hendey, 1937: 290; Cupp, 1943: described above. The costa pattern becomes more apparent in
Cha1e0t4,ocfeigr.o5s9n-eBaep,onliotnand;usSoSucrhnrioad,.1968:46. 4t)h.isAvariheytayliannedrraidmiaitsesaflrsoomptrheesecnetntroenofthtehevvaallvvee(ePId.ge4, Faingd.
Schroder, 1900:29,pi. 1,fig.4;Hendey, 1964: 119,pi. 16,fig.3. thickeningsinthemantlerunalongthelinesofthegirdle(PI.4,
Pis2,3. Fig.6).Eachvalvebearsarimoportula,locatedinthecentre(PI.
rLeMc.tanCghualianr,stshterapiegrhvta,lsvhaorratx,israbtehienrgrloobnugsetr.,tIhnegciorrdnleervsisewm,ooctelhl,s s5,hoFritge.r3()P.I.T4h,iFsigrses4e,m6b;lPeIs.t5,haFtigo.f1)t.heInpsriedecetdhienrgivmaorpioetryt,ulbautisias
sgwhftlieheridnexogeeahmlmrgtyialot.dlynhdlaeclylueTtv.r,ehavrilImecmvndakie.,nvntcaraVollolarveblneuevlsvreaotisw,ne,f,dwaa,cclnuiedcnrieesvsnlslltipiseinogrnghfecetlal-lsgilybimpaerotcrdaiooylrctneailvhn,selgstxe;ytr,thaiaaeinebtgtesheaetar;ntrucainaaeadnlpniganegfrorfalytteeusprdreeroitenofvastceeiaerwasabigtrsodieiuednsit,,gen cbftFsoihoiergemml.ppoCplrw.2rei)e.tasshhteTeleoshnalpcnteeotewiiswocnotiutfrststuhorctvofihtaauiurfect.rukebsenaerieot,oafwwnpeleotla(lhePrlienIg-t.edsatee5nwp,tuvooaseFre.lciooogiOi.pssdnett6sade)he.ealrtaTasenhbtamidehamaettreahekrbiaaesassbostillsretaeuhstcaopcittflahultadrattreehpeaserpcc(naPtrsIreiae.erbltnesa5itdoe,s
45 from the chain axis, terminal setae arise at a similar angle closetothetip,whichissharp(PI. 5,Figs4,5,7).
from the corners. Numerous small chloroplasts present in cell DISTRIBUTION. 42,45,48,52.
Pervalvar Axis
1.
Valve Face
Girdle
Aperture
Setae
Intercalary
Terminal Setae
Transapical
Axis
\^.
Plate1 Fig. 1:diagramillustratingterminologyusedtodescribeatypicalchainofChaetoceros(broadgirdleview).Fig.2:valveviewofaspeciesof
Chaetoceros.Figs3a,3b:examplesofaheterovalvarspecies:C.peruvianus(3a),andaheteropolarspecies:C.coarctatus(3b).
D.U.HERNANDEZ-BECERRIL
Plate2 Chaetocerosatlanticusvar.neapolitanus.Figs1,2:typicalchains.LM.Fig.3:completechain.SEM.Fig.4:wholecell.TEM.Fig.5:valve
showingsetaeandrimoportula.TEM.Fig.6:detailofchain.SEM.Fig.7:detailofseta.TEM.Figs1-3,bar=20urn;Figs4-6,bar= 10urn;Fig.
7,bar=2nm.
STUDYOFCHAETOCEROSSPECIES
Plate3 Chaetocerosatlanticusvanneapolitanus.Fig. 1:partofvalvewithbrokensetaandrimoportula.TEM.Fig.2:partofvalveshowingsetae
andrimoportula.SEM.Fig.3:detailofrimoportula.SEM.Fig.4:anothercellshowingsomethickeninginthemantle.SEM.Fig.5:setawith
rowsofspines.SEM.Fig.6:fusionoftwosiblingsetae.TEM.Fig.7:setashowingporoidareolae.TEM.Figs1-3,5,7,bar=2urn;Fig.4,bar=
10urn;Fig.6,bar=5urn.
D.U.HERNANDEZ-BECERRIL
Plate4 Chaetocerosatlanticusvar.skeleton.Figs1,2:partofchainandcompletechain,respectively.LM.Fig.3:partofchain.SEM.Fig.4:two
siblingvalvesshowingrimoportulae.TEM.Fig.5:detailofchain.SEM.Fig.6:onevalveshowinghyalinerimandthickeninginmantle.SEM.
Figs1-3,bar=20urn;Figs4-6,bar=5urn.
REMARKS. Chaetoceros atlanticus var. neapolitanus and var. 3. ChaetocerosdichaetaEhrenb.
skeleton are morphologically very similar to the type, as
indicatedbyEvensen&Hasle(1975)andKoch&Rivera(1984), Ehrenberg, 1844: 200; Hustedt, 1920: pi. 326, fig. 8; Hustedt,
and their taxonomic position is in little doubt. They differ in 1930: 648,fig. 367; Hendey, 1937: 291, pi. 6,figs9, 10; Cupp,
havinga more temperate or subtropical distribution. Contrary 1943: 106, fig. 60; Hendey, 1964: 119, pi. 13, fig. 1; Okuno,
to Simonsen's (1974) opinion that distinction 'seems to be 1970: pi. 652; Evensen & Hasle, 1975: 157, figs 1-5; Koch &
senseless' between these two taxa, I consider that their Rivera, 1984:64,figs6-12.
taxonomicseparationshouldberetained. ChaetocerosjanischianusCastrac.
STUDYOFCHAETOCEROSSPECIES
Plate5 Chaetocerosatlanticusvar.skeleton.Fig. 1:terminalvalve.TEM.Fig.2:insideviewofvalveshowingrimoportulainternally.SEM.Fig.3:
singlecell.SEM.Fig.4:detailofsetawithporoidareolae.TEM.Fig.5:tipofseta.TEM.Fig.6:pointoffusionintwosiblingsetae.TEM.Fig.7:
detailofanotherseta.TEM.Fig. 1,bar=5\an;Figs2,4-7,bar=2um;Fig.3,bar= 10nm.
10 D.U.HERNANDEZ-BECERRIL
Castracane, 1886:77. fromtheapicalaxis.Setaethick,coarse,bearingspines;terminal
Pis6,7. setae differ from intercalary setae only in direction of
divergence,intercalarysetaearisingalmostparalleltotheapical
LM. Chains straight, of variable length. In girdle view, cells axis, terminal setaecurving to thechain axis. Numerous, small
rectangular, nearly octagonal, corners smooth. Valve face chloroplastspresentincellandsetae. Measurements: 38-45 um
gmeannetrlaelllyowf,lalti,newsiotfhgiardtlheins,traciyglhitn;draipcearltuprreoscveesrsyawtidteh.eIncevnatlrvee, a.a.,32^8ump.a.,3^umap.(PL8,Fig. 1)
view, cells nearly circular or elliptical. Setae thick, coarse; EM. The valves follow the general pattern of structure for the
intercalary setaecurve smoothly and fuse furtherout from the genus: heavily silicified and perforated by poroids, but here a
cellsthanterminalsetae;terminalsetaecurvetowardsthechain weak costa pattern is observed and the poroids become scarse
axis. Numerous, small chloroplasts present in cell and setae. close to the valve centre (PL 8, Figs 2-4). The annulus is an
Measurements:6-11 uma.a., ll-12ump.a., 13-22umap.(PL6, oblong hyaline field in the valve centre (PL 9, Figs 2-4). The
Figs 1,2) rimoportula is located at the very centre of the valve, being a
otsnsaEtithtpohMmrehpto.pueeeuvlcragdaetsSrhl,uhisvorsnoceuehryttstoalthor;iinatsnbdrnecdeserhoripainle(pciciPcratnoIgielh.sshesettste7lau,mwny(ebaetPFesInrwi,i.toegelln6i.ore,cpeoi.1tFfeb)ihio.TnsegebhedH.streyvoae6vaa)rnpetl.lvdrhdviTeeeendhpseo(eeeePu(rdnIrtPgf.rcIiseoie.im,rmd6so6a,eo,fst,opeocFFotadiimcrhngguteib.dsrcuyklrw4o3eea-si)nln6m.tcai)ahtotn.liTnhgnvlsehHeoiwaelpesaiylotdrsasrgvl-boaeoaloiilnliafodvgsktfas,eoee patPosP5.ehrifLLerem6afo9p)b9r,lo.la,earesFoTaeiplFhth,gaaioeestgbld(ytsue5Pebt,Lrbiy16bnne)-9saea.4i,irs)cdfF.ooeirifnmogwAeesowitmsntf1eheo,tosu4hsafr)het.-rsasiomTlvaiaftehdlbereeplreydontspraawebortfteaioetaedsteessernr,puaatisrornwseifeehooassontclerohommotesnbuodttlsiatssitseehinttecdg(aaieenPera,cL(cdeuPcg8tleLe(,harsPretF8L,aiaciwgl9nFna,soidlsgtF6le.,yitpght75iesoe;;s
structure inside (PI. 7, Figs 1-3, 5). Setae differ from the DISTRIBUTION. 16,42,45,48.
dwhbpiourhflteifecceenrh(deoanihntnac,ogsopwsvelitaaontrenihi.gnefitgiTti?veuhe)sdeoi(iornPrfaLslipC7x.or,lsoaFiywtdiglsegoassnn,ota4fai,lncb7udi)ss.ghtcahphpeoieerrfooliiyundnsicdnr(eotPdshLset-i7asp,resecFhotiailgvoasnep3aa,itss6tm,eaarl8lns)l,o, HottRhhpaEieisMssnlAesietRos'usKnpdeS(ycw1.io9he7nisT5cha)Chir.seodmbstesaphneeseyrcuvpisaboe.tsseHiiitooscinwcooselnnovfoseoiefrfrl,ymCte.rhtdeewbloroabrtimyeemaadoljcptioooosrmrCwptd.iuaibtflrohfairener(tagiehlnnoicsECsee.vsBeadmbnieealsnetdesywneu,esaei&innnt
DISTRIBUTION. 12,48. is central and in C. borealis it is located to one side) and the
pRrEeMsAeRncKeS.ofEvweenaskenco&staHeasilne t(h1e97v5a)lvecsomomfentthaitsedspecoines,thae bpruetsleancckeinogfipnorCo.ibdosreianltish.esetaebases,characteristicofC.densus
characteristicnotfoundinthematerialused forthisstudy. The
hair-like structures on thevalveedge have been found by some 6. ChaetocerostetrastichonCleve
authors (e.g. Evensen & Hasle, 1975; Koch & Rivera, 1984). Hernandez-Becerril, 1992a:367,figs 1-8.
ThesesameauthorshavealsostatedthatthesetainC.dichaetais
circular in cross-section, which differs from my observations DISTRIBUTION. 12.
whereithasclearlybeenseenaspolygonal.
7. ChaetocerosseychellarusG. Karst.
2.SectionBOREALIAOstenf.
Hernandez-Becerril, 1993a: 121,figs 16-27.
Tubularrimoportulausuallyabsent.Aperturesnarrow. DISTRIBUTION. 18, 19,45,48,63.
4. ChaetocerosoctagonusHern.-Bee. 8. Chaetocerosdenticulatus Lander
Hernandez-Becerril, 19926:218,figs 1,3-15. Lauder, 1864:79,pi.8,fig.9;Hustedt, 1920-1921:pi.324,fig.
&
DISTRIBUTION. 7, 12. 7, pi. 337, fig. 7; Allen Cupp, 1935: 135, fig. 53;
Subrahmanyan, 1946: 129,figs 188-190;Sournia, 1968:47,pi.
5. ChaetocerosdensusCleve 3,fig.24;Simonsen, 1974:31;Desikachary&Prema, 1987:pi.
258,fig. 5.
Cleve, 1901:299;Meunier, 1913: 14,pi. 1,figs 14-28;Hustedt, ChaetocerosnanodenticulatusOkamura
1920:pi.325,fig.9;Hustedt, 1930:651,fig.368;Lebour, 1930: Okamura, 1907:91.
115,fig. 81;Cleve-Euler, 1951: 96,figs 184a-c; Hendeyetal., Chaetocerosdenticulatusf.angustaHust.
1954: 28,pi. 1,fig. 1; Hendey, 1964: 120,pi. 17,fig. 1;Drebes, Hustedt, 1920:pi. 324,fig.5
&
1974: 64, figs 48a, b; Rines Hargraves, 1988: 50, figs 100, Chaetocerosdenticulatusf.lataHust.
101. Hustedt, 1920:pi. 324,fig.6.
Chaetocerosborealisvar.densaCleve PL 10.
Cleve, 1897:20,pi. 1,figs3,4.
Pis8,9. LM. Chains straight, ofvariable length, robust. In girdle view,
cellsoctagonal,withsmoothcornersandconstrictionsatgirdle
LM. Chains straight, usually long, robust. In girdle view, cells level. Valve face conical, mantle high, lines of girdle straight;
rectangular or nearly eight-sided, with smooth corners and apertureswide. Invalveview,cellselliptical, thesetaediverging
constrictionsatgirdlezones;aperturesnarrow.Valvefaceflator atanangleofabout 15-20 fromtheapicalaxis.Setaearisefrom
slightly convex, mantle high, lines of girdle straight. In valve close to the valve centre, thick and coarse, with a tooth-like
view,cellselliptical, thesetaedivergingatanangleofabout30 projectionnearthebaseincontactwiththatofthesiblingsetae.