Feeding habits of Calma glaucoides (Alder & Hancock, 1854): its adaptive structures and behaviour

4 Pages·2001·2.5 MB·English

by  G Calado

BollettinoMalacologico,Roma,37(5-8):177-180,2001 -SocietàItalianadìMalacologìa
Feeding habits of Calma glaucoides (Alder & Hancock, 1854): its
adaptive structures and behaviour
Gommalo Calado & Victoriano Urgorri
KEYwords: Aeoliclacea;Calmagla/midey.Feeding
ABSTRACT Calmaglaucoides(Alder& Hancock, 1854) isan aeolid nudibranch inhabiting European (Atlantic and Mediterranean)Westernand Southern coasts.
Adultsfeedonfisheggs, thusbeingfound nearspawningsitesontheundersideofbouldersorinsmallcrevices,wheremalefish nest.Thisaeolidhas
an atypical uniseriate radula. Littleis knownaboutformationorfunctionofthis radula, but it isbelieved that such apeculiarmorphology is related
toadult'sfeedinghabits.Thefeedingbehaviourofindividualscouldbeobservedinaquaria. Itwasalsopossibletostudynotonlyradulaefromindivi-
duals ofdifferent sizes but also the damage caused by radula action upon fish egg membranes. These were visible under SEM after critical point
dryingofemptyeggs. SEM imagessuggest that the radula is usedasasaw. Aftertheegg is "opened" theyolkandembryoaresuckedoutwith the
help ofstrong buccal musculature, leaving the external membrane ofthe egg almost intact. The way these animals puncture fish eggs, associated
withtheearlydevelopmentoftheirradula,leadustoconclude,thatthereseemstobenofoodsizeconstraint,aspreviouslyhadbeenthought.
RIASSUNTO Cí?/wí?g/íí/i'íWíí'er(Alder&Hancock, 1854)èuneolidiaceopresentelungolecostedell’Atlanticooccidentaleedelmediterraneo.L'adultosi nutredi uova
dipescievienespessoritrovatovicinoalleovature,sullatoinferioredei massioinpiccolefessuredellaroccia.Questoeolidiaceohaunaradulauniseriata
moltoatipica. Pococonosciutesonolasuaformazioneefunzione, masi pensachelatipicamorfologiadebbaesserecorrelataalcomportamentotrofico
dellaspecie.Graziealmantenimentodialcuniesemplari inacquario,èstatopossibilestudiareilcomportamentodiquestaspecie,lamorfologiaradulare
in individui di diversatagliae i danni causati dalla radulastessasullamembranadelle uovadei pesci. Immagini al SEM,dopo il criticai point, delle
uova indicanoche la radulavieneusatacome unasega. Dopochel’uovoèstatotagliato, il tuorloe l’embrionevengono risucchiati grazieall'azionedi
unatortemuscolatura, lasciandopraticamente intattalamembranaesternadell’uovo. Il modoconcui questi nudibranchi taglianoleuova, in rapporto
anchealprimosviluppodellaradula,suggeriscechelatagliadelleuovanonsiaunfattorelimitante,comeprecedentementesupposto.
G. CALADO. V. URGORRI
1InstitutoPortuguésdeMalacologia,ApartadoNo. 52,S. PedrodoEstoril,2766-501 Estoril,Portugal.E-mail: bacongasís’mail.telepac.it
2LaboratoriodeZooloxíaMariña,DepartamentodeBioloxíaAnimal,UniversidadedeSantiagodeCompostela, 15706SantiagodeCompostela,Spain.
INTRODUCTION collected individuals ofC. glaucoides were kept in small beakers
Most aeolid nudibranchs feed on cnidarians and therefore they with small stones containing portions of Parablennius pilicornis
possess strong jaws and uniseriare or triseriate radulae, with lew spawn. After consumption of the egg contents, empty egg
exceptions in both characteristics. Calma glaucoides (Alder & membranes were dehydrated in alcohol, and observed in SEM after
Hancock, 1854), an aeolid nudibranch inhabiting European criticalpoint treatment.
(Atlantic and Mediterranean) Western and Southern coasts, is
precisely one such exception. Adults (7 to 18 mm) are found on RESULTS
their food supply, the spawn of teleost fishes such as Lepadogaster Radularmorphology
lepadogaster, Lepadogaster candollei, Parablennius gattorugine and SEM images allowed a closer examination of seemingly
Parablenniuspilkomis, which deposit their eggs on the underside of important details. Small teeth ofthe serration measure about 1mm
boulders or empty bivalve shells. C. glaucoides has a very atypical (Eig. 1) and in high magnification (top image) it is possible to see
“uniseriate” radula, previouslydescribed as arowofverysmall teeth some erosion on their outer edges (Eig. 2). In small animals, the
and a group ol lew bigger teeth at the distal end. Little is known first-formed “big” teeth were smaller than in later ones, as ifthey
about theformationorfunctionofthisradula, but it isbelieved that were in formation after differentiation of the distal edges. Radula
such a peculiar morphology is related with adult’s feeding habits size differs relating little between animals having a body length of
(E'VANS, 1922; Ro'WETT, 1946). The extent ofsuch a relation is the 1.4 mm from those of 2.5 mm (Eig. 3). This suggests that the
subjectmatterofthisstudy. radular morphology, developed early in the ontogeny, is preserved
throughout adult life. Similar arrested morphological development
MATERIALS AND METHODS of the radula is known, forexample, from the Harpidae (HUGHES&
We worked with specimens obtained from the Iberian Atlantic Emerson, 1987).
NW
Coast (Galicia - Spam (43" 27’ N, 8" 16’ W) and Arrábida,
Portugal (38° 27’ N, 9° 0’ W)). They were preserved in 70% Feedingbehaviour
ethanol. Buccal masses were extracted and placed in a 5% NaOH In order toconsume an egg, Calmaglaucoides crawls over the fish
solution for 24 h at 40" C. When radulae were detached they were spawn. Then it proceeds to enwrap an egg with its oral tentacles;
abundantly rinsed in tap water. Six radulae for SEM were dried and immediately afterwards we can see, through the almost transparent
coatedwithgoldpriortoexamination. body,theeggcontentsbeingsucked in andrapidlymovedalongrhe
In order to observe their feeding behaviour, rhree recently oesophagus to the stomach. During the feeding^process,
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GongaloCalado&VictorianoUrgorri
Fig. 1 -SEMpictureofaradulawheresaw-liketeetharevisible.
Fig. 2-Topimageofserraredbarwithsaw-liketeeth.
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FeedinghabisofClamaglaucoides
Fig. 3-SEMviewsoftworadulae.Left: froma 1.4mm longspecimen. Right: froma2.5 mm longspecimen.Scalebarforbothpictures.
Fig.4- PredatedParahlevnimpilicurniseggs.
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Fig. 5 - Detailoftheincision intheeggmembrane.Arrowindicatesouterborder.
immediately beforesuction theanimal usually bends forwatds all its SEM imagesofempty fishegg membranesshowopenings, made
cerata, letting them return to the "normal” position after the actual by the molluscs, that are consistently regular as ifcut with a
suction begins. The opening ofthe egg membrane was observed to "surgical " instrument and not just torn open. The openings
be a quick task. If by any chance the egg already contains an observed were morphologically identical and suggest a sawing-like
embryo, it is apparently crushed during suctionprocess, as we see it method ofcutting, precise and efficient. The observation ofliving
into small pieces. Theprocedure above is repeated withasuccession animals while feeding also indicates that this procedure is a rapid
ofeggs, until the animal is satiated, leaving behind avariable band one. We conclude that the saw-like portion ofthe radular tooth is
ofemptyegg membranes. Under laboratory conditions weobserved used tocut open the membranewith aminimum effortallowing its
up to 30 eggs being continuously consumed, in less than one hour, innercontent(which maycontainhardparts, iffish's larvaisalready
byasingleadult individual. formed)tobeextracted.
SEM images ofempty fish egg membranes (figs. 4 and 5) allow
us to see the size and shape ofthe opening made by the mollusc. It ACKNOWLEDGEMENTS
clearlyshowsevidenceofradularactionasdiscussedbelow. Thisworkwascarriedoutwhilefirstauthorwas holderofagrant
from "Fundai^ao para a Ciencia e Tecnologia”- Portugal
DISCUSSION (PtaxisXXI/BD/11185/97). We thank Ilidio Félix-Alves (I. P. M. -
Erosionon theouterborderofteeth,on theserratedportionofthe Portugal) for his critical teview ofthe English version ofrhe text.
tadula, made us believe that these teeth ate functional, regardless of We also acknowledge Dr. J.L. Cervera, editor of this special issue,
their small size (as compared with those ofother aeolidaceans). and two anonymous referees, whose comments and criticism helped
Examination offish egg membranes after consumption seems to toimprovethecurrentversionofthepaper.
agree with this view. Moreover, there is a reduced radula size
differencebetween animals havinga markedlydifferent body length, REFERENCES
making ussuspect that theentire "adult-like" radular morphology is Evans T.J., 1922. Calmaglancoides'. a study in adaptation. QuarterlyJournalof
developed early in the ontogenetic process. In fact we have observed MicroscopicalScience,London, 66:439-455.
smalleranimalsfeedinginamannersimilartolargerones. HughesR.N. &Emerson W. K., 1987. Anatomical and taxonomiccharacteristics
Therefore, one can assume that juveniles already feed on fish ofHarpaandMorum(Neogastropoda:Harpaidae)TheVeliger,Berkeley,29:
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carnivores (Evans, 1922). Thus, there seems to be no food size
RowettH.G.Q., 1946. Acomparison oftliefeeding mechanismsofCalmaglaucoides
constraint.
and Nebaliopsistipica.JounialoftheMarine BiologicalAssociationofthe United
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juvenile phase onwards, making us believe that they may also be
useful for the adult’s feeding behaviour. EvANS (1922) suggested
that these teeth might be used only in tlie post-settlement phase,
beforejuvenilescould findfishspawn. Lavoroaccettalo7febbraio2000
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