Comparative postembryonic development of arachnids

8 Pages·1993·2.6 MB·English

by  A Canard

COMPARATIVEPOSTEMBRYONICDEVELOPMENTOFARACHNIDS
ALAIN CANARDandROLANDSTOCKMANN
Canard, A. and Stockman, R. 1993 11 11: Comparative postembryonic development of
arachnids.MemoirsoftheQueenslandMuseum33(2):461-468.Brisbane.ISSN0079-8835.
A common model is used to describe the growth of various arachnid groups. In these
predatorsthereisretardationofdevelopmentofthefirstinstars,alongwithgreatermaternal
care fortheclutchandeven, as faras some groups areconcerned, in aviviparous develop-
ment. Mites,whichhaveverydiversifiedbiologies,havedevelopmentswhichhaveevolved
inmanydifferentways.
Les developpements des differents groupes d'arachnides sontdecritsen suivantunetrame
commune. II apparait ainsi uneEvolution des groupes de predateurs qui se traduit parune
augmentationduretarddedeveloppementdespremiersstades,enliaisonavecdessoinsala
ponte croissants, avec meme pour certains groupes des developpements vivipares. Les
Acariens,debiologiestresdiverses,ontenconsequencedesdeveloppementsquiontevolue*
dansdesvoiestresdifferentes.[^Development, arachnids, growth.
AlainCanard,LaboratoiredeZoologieetd Ecophysiologie, UniversitedeRennes1,France;
RolandStockmann,LaboratoiredePhxsiologiedesInsectes, UniversitedeParisVI,France;
19March, J993.
Analysisofdevelopmentaltypesusedinarach- embryonic, starts with the first divisions of the
nids is very great diverse in the terms used to egg and continues with the formation oftissues.
describethesephenomena.Thisdiversitytendsto After hatching or birth, the development is
partiallyhide some similarpoints in thedevelop- qualified as postembryonic. The postembryonic
mental process. Authors often use terminology organismisthencoveredwithanexternalintegu-
and analyse specific to a single grouporspecies, ment and develops outside ofthe egg membrane
instead of referring to general concepts relating or the female's genital tract. Various organs ap-
toall arthropods. pear and develop, some will not be functional
This study compares the developmental until late developmental stages (e.g. genital or-
processesusingthe sameterms,and wewill only gans). Externally, the development is shown by
usespecialisedtermsifitisabsolutelynecessary. changesinthecuticle. Reiterationofthisconcept
All developments cannot be discussed in detail may seem pointless, but the study of arachnids
here; definitions and more precise descriptions requires some explanations about hatching and
can be found in Canard and Stockmann (1992). birth.
Hatching, i.e. theopening and release from the
METHODS
egg's membrane, can be a long process. It may
takea few days forsome spiders, and sometimes
Our study is based mainly on literature, en- somemoultscanbeobservedbetweenthebegin-
richedwithourobservationsonarachnidgrowth, ning ofthe opening ofthe egg's membranes and
particularly on spiders and scorpions. their complete liberation. Hence, the post-
First, we will evoke the main concepts and embryonic period does start with the opening of
definitions usedandwillthendefinethedifferent the egg's membranes. This does not make it
scalesofdevelopmentforeachtaxon.Taxawhich necessarytolookforaphenomenonbeforehatch-
areexclusively predatory arehererepresentedby ingas,forexample,Legendre(1958)andVachon
to the increasing level of care devoted to the (1958b)didastheychosethe 'inversion' todefine
clutch. Mites, which have diverse biologies, will the beginning of the postembryonic period.
be studied separately later. Moreover, this proposition has one drawback: it
makes the postembryonic development begin at
RESULTS a time when the organism is not covered by a
tegument.
Concepts and Definitions Birth appears as a well and easily defined
phenomenon, without ambiguity. However, in
postembryonicdevelopment,hatchingandbirth pseudoscorpions, the organism leaves the
The development, defined as initially female's genital tract and moves into a ventral
,
462 MEMOIRSOFTHEQUEENSLANDMUSEUM
liteonyolk freetile,twdmgrepn>y , rtdhifwmottor
fmchmg Jffl.
4 _ .' v i^^tg^raJ ih*^^"* fi"T g^^y
egg \JU >p7[>fj3ltp4li Jfi *s 37 ^108 ,i
*B
-r
FIG. 2. Postembryonicdevelopment scheme ofa soJ-
pugid, Eremobatesditrangoruts(afterMurna, 1966).
PIG- I. Stages of postembryonic development of an
opilionid, Ltobunum rotundum (Phaiangidae, Pal- DIFFERENTDEVELOPMENTAL ROUTES
patores)(afterGucutal, 1943andNaisse, 1959).(m=
moult,Ji=incompletedjuvenile,J=juvenile),
Opilionids
brood pouch which is like an external extension The eggs are laid isolated from each other and
of the female?'s genital tract. Once in the pouch, then abandoned. The emergent animal depends
development continues and the organism Mil] on its yolk reserves it looks like ajuvenile har-
receives nutritive fluid from the mother. There- vestman but morphologically differs from fol-
fore, thestartofthepostembryonic development lowing instars by the unpigmented integument
pf pseudoscorpions should be when they leave and lack of some characteristics, such as un-
the pouch, rather than when (hey leave the formed chcliccrac, unsegmented tarsus, absence
female's genital tract,asothershavestated. ofmedianeyes.etc. Thereforeitisanincomplete
luvemle: Jii (term taken from Holm, 1940 con-
1NSTARSANDS! '..SKS cerningspiders)(='lar idmgtoJiihcithiL.
GeTnehrealinlsyt,araimsotnhegoarrgtahnriopsomdbs,etIwheceenxttewronamlouflotrsm. e1g96g5)te.etIthalloscoatheadsotnemdpoorrsaurmyoofrcgeapnhsa(konnheoroarxt)w.o
does not significantly change between tbt>e (wo Afterthefirstmoult,theanimaldiffersfromthe
stages, except for the short periods of pre- and imago only by its size and by sexual eharac-
post-exuviation. However, among some mites, teristics. Itisajuvenile,thesecondofthejuvenile
the external morphology and biology are phase J: (~ 'nymphc' according to Juberthie.
modifiedwhilethecuticleremains.Hence,Herik- 1965). Although active, it still lives on its yolk
ing(1882)distinguishedtwoforms,calledinsUirs reserves,Afteronemoult, thejuvenileopilionid?-
('stade"), one active and the other motionless. (J3) scatter and then feed on prey they catch.
Although this use of the term 'instar* was fol- Usually, 6-7 iuvemle instars occur before
lowed only by a few authors to describe the comesanimago, morerarelythere are5to8.The
development of few mite?., another acarologist numberofmoulNnuy varyfromwithindividuals
(Grandjean, 1938), consideredthatthe term was ofaspecies, andaccording to the developmental
too indefinite and proposed theterm 'stase'.The conditions;this numberisgenerally the same fur
definition ofstase changed later, but this term is bothsexes.
thebasisforanevolutionaryconcept(Grandje;m On becoming a breeding instar (irnagos) the
1954; Andre andJocque, 1986; Andre, 1989). opilionid cease mi.ulltng (adults), although some
We use 'instar' here in its usual definition, may live forbe5-fi >bars (Juberthie, 1965).
which means an organism between two moults
(for endocrinal considerations, see Canard and SOUR.IGIUS
Stockmann, 1992). To keep the general defini- The female isolates herselfin burrow hutdoes
tion, we will discuss the concept of stase later. givecare to hereggs.
When the animal presents separate biologies The animal which hatches is incomplete, mo-
linkedwithtwodifferentaspectsduringthesame tionless and lives on its yolkreserves. Itisunpig-
instar, we call them 'forms' and give them two mented, has noeyes and no racquet organs. Two
different names. types may be distinguished. The first is in the
Galcodidac (Vachon, 1958a, Junqua, 1966). It
SucWcef-slsiimointi>io-uJrnsst.atrusdy to a mnrph<>-biological ditochsandotwlhoioklelikuentdheerimtahgeo acnodnsktereapisnttheoafsptehcet
description of the successive instars. These in- membranes ofthe egg; it is a foetal instar F [-
stars can follow each other b phase (Vachon, Marve* of Vachon, 1958a or Junqua, 1966, =
1953) in whichallinstarsareofsamekind. These i-embryo" ofMurna, 1966). The second type
different types aredefined in Table 1 esent in some Solpugidae (Lawrence, lw7)
s
COMPARATIVEPOSTEMBRYONICDEVELOPMENTOFARACHNIDS 463
freelife,feedingonprey rnS m9 mtO wiltifhetohneymoolkther freeWe,feedingonprey
W V
9 wt mi ns -</ ' V
gigtg^m4 gin\5 g
i?8jj^j>' Nk®
FIG. 3. Scheme of the different stages of the pos-
tembryonic development ofan amblypygid. Taran-
tulamarginemaculata(afterWeygoldt, 1970).
FIG. 4. Scheme of the different stages of the pos-
and some Karschiidae (Thaler, 1982). It looks tembryonic development of Typopeltis stimpsonii
like the imagos (juvenile), but lacks some struc- (Thelyphonidae)(afterYoshikura, 1965).
tures and has temporary organs like thorny con-
adapted to this life, so with reference to Scor-
JtiiinAu(af=tuir'otpnhrseiromafmrtolhuaelrvlteegr'se.soufIlttTishsaailnnerai,nnc1ao9nm8ip2ml)ae.ltewjhuivcehnihlae:s WpPieeoyrngesoy,alwsdeltac1wa9zl7le0w)it.ath1e90pu1l,luas:ndJP'p(r=a'eenmybmrpyhoen'' ooff
all the adult organs, except those linked with Thepullus moultwhileon the motherand then
reproduction. This juvenile is, according to the leaves her. Through this moult it acquires all the
species, the first or the second of the phase (= characteristics ofthe adult (except the reproduc-
'nymphe' of Vachon, 1958a; Junqua, 1966;
Muma, 1966). Itremainswiththefemaleuntil its tgirveegoarrgiaonuss).peItriiosda,jutvheenjiulveeinnisltears:sJc2.atAtfetrearnadshloirvte
integument is hard enough, then it disperses and ontheirown, feedingthemselves.Thenumberof
lives on itsown, feeding itselfon prey itcatches. juvenile instars may vary between individuals
The number ofinstars before reaching the status
(Weygoldt, 1970) and, after one year, they be-
ofimagovariesaccordingtotheindividuals. The come an imago.
imagos have a short life expectancy comprising The imagos ofboth sexes go on moulting and,
only one instar (adult). undergoodconditions,thefemaleskeepgrowing
afterthis moult. Therefore, there are no 'adults'.
Amblypygids
The female carries the eggs under its abdomen Uropygjds
in a brood pouch generated by the genital tract The female isolates herself in a burrow, and
during egg-laying. The incubation period of the lays her eggs in a newly secreted transparent
clutch may last 3 months (Weygoldt, 1970). ventral sac.
Hatching takes place in the brood pouch. Hatching occurs in the brood pouch. It cor-
The organism released from the egg's responds to a quasi-simultaneous release of the
membranes has a foetal aspect with the prosoma egg's membranes and of the integument of an
bent towards the abdomen and its appendages instar similar to the foetal instar of the
tight along the body. It is very incomplete (ap- Amblypygids: F (= 'primarlarve' of Kastner,
pendages incompletely segmented, absence of 1949 and 'prelarva' of Yoshikura, 1965). This
setaeandofsensoryorgans,etc.), motionlessand instar, which was already formed in the egg, has
lives on its yolk. It is a foetal instar: F (= a very short postcmbryonic life.
'deutembryo' ofWeygoldt 1970). Theanimalreleasedafterhatchingandafterthe
After one moult, the animals leave the brood first moult, can move and climb upon the
pouch and attach themselves underthe females' mother's back. In general morphology, it looks
abdomen. They still liveon theiryolk,can move, like the adult (juvenile phase), but lacks some
and look like imagos (juvenile), but some struc- organs (median and lateral eyes are not yet
tures are lacking and the internal organisation is visible, flagellum unsegmented, etc.). It has par-
incomplete (digestive tract, circulatory system, ticular organs linked with its life on the mother,
etc.).Itisanincompletejuvenileinstarwhichhas including pad-like organs at the tip of the legs,
particular organs on the legs, a dorsal continua- instead of claws. It is a pullus: JP (=
tion at the distal end of the tibiae (Weygoldt, \sekondarIarve' of Kastner, 1949; 'larva' of
1970)and, in some families,anadhesiveorgan at Yoshikura, 1965). After a 'diapause', there is a
the tip ofthe tarsus. It lives on the mother and is moult which releases a juvenile instar: J2 (=
,
464 MEMOIRS OFTHEQUEENSLANDMUSEUM
Forms Characteristics Symbols
embryonalaspectunsegmented
different motionlessinstarswhichdonotfeed appendages foetalinstar
morphologyfrom themselves
imagos segmentedappendages nymph
activeinstar larva
Non-breeding
incomplete
notemporaryorgans
juvenile
samemorphologyas severalorganswhichdonotfunction
imagos temporaryorganslinkedtolife pullus
onmother
onlynon-functionalgenitalorgans juvenile
Breeding(=imagos) withmoulting imago
TABLE 1. Characteristicsofdifferentkindsofinstars.
lifeonyolk freelife,feedingonprey
FIG. 5. Scheme of postembryonic development of
Prokoeneniawheeleri(afterRucker, 1903).
'pullus' of Kastner, 1949; = 'protonymph' of
Yoshikura, 1965). They are still gregarious but
move aroundtheburrow andbegin tofeedthem-
selves. Afterone winterspenttogether, theythen
moult and scatter. Subsequent moults usually
occur annually, but may be less frequent
(Yoshikura, 1965). FIG. 6. Postembryonic development in two spider
Imagos do not seem to moult (adults). Their speciesthat (a) abandons itsclutch(Larinioidescor-
size ofeach species does not vary much. nutus) (after Ysnel, 1992), and (b) cares for young
(Philaeus chrysops) (after Bonnet, 1933; Canard,
1984).
Palpigradids
unTkhneowsne.xuMaolreboivoelorg,ynoofbopdaylphiagsraedviedrssiusccaelemdoesdt cOthhaemrbserke(ee.pg.thseailrticcildust)c.h with them in their silk
in breeding palpigradids. Therefore, knowledge Hatching occurs in the cocoon and it some-
oabnouotbstehreviratpioosntsemobfrynoatnuircaldepvoepluolaptmieonnts.isUbnadseerd treilmeeassetda.keTshaisfeiwnshtaoruriss bgeefnoerrealtlhye ffioresttali:nstFar(i=s
theseconditionsthreeimmatureinstarshavebeen 'prelarve' of Vachon, 1958b, = 'pullus' of
determined formany species (Conde, 1984). Canard, 1984). Among some orthognathids it
The three instars ofProkoenenia wheelericor- remains intrachorional and is therefore not pos-
respondtojuvenile instars (Rucker, 1903). Their htaetmcbhriynogniwch.enItsthveeergygtmhienmbcrutaincelesboupresnt.sAdmuorinngg
morphology evolves in a quantitative manner
several species which give care to the clutch,
(numberofbristles,articulationsoftheflagellum,
there is a series of2 or 3 instars ofthis kind: Fi
evolution ofgenital parts, etc.). F2,F3(Canard, 1987).Astheycannotmove,they
stay in the cocoon.
Spiders The following instars are mobile and look like
Thedegreeofmaternal caregiven totheclutch aspider(juvenile)butthefirstoneortwostilllack
varies between species. Some spiders abandon some adult characteristics: they are incomplete
their cocoon (e.g. araneids). Others carry it in juvenile (Ji) (= iarves' and 'prenymphes' of
their chelicerae or attached to their spinnerets. Vachon, 1958b). In somecases, thefirstinstarof
COMPARATIVEPOSTEMBRYONICDEVELOPMENTOFARACHNIDS 465
lifeonyolk freelife,feedingonprey Iryfoelwkitohrtnuhterimtoitveheflruiodns birth freelife,feedingonprey
hatching m3
^ ml m2 rr\3
J3
Nw
94
FIG.7. Schemeof postembryonicdevelopmentstages
of ricinuleid Ciytocellus palaezi (after Pittard and
Mitchell, 1972)."
FIG. 8. Postembryonic development ofa pseudoscor-
thisphaseis very incomplete,butin someothers, pion, Chelifercancroides(afterVachon, 1938).
some characters can only be shown absent using retains some non-evolved characteristics (sen-
alinveSEoMn.thTehiersyeolfkir,stbiuntcosmopmleetaeljsuovefneieldeoinnstuanr-s sorialsystem, silkglands, digestivetract,etc.). It
is an incomplete juvenile: Jii (= 'larve IF and
developed eggs, which they can pierce with a 'protonymphe' of Vachon, 1938; 'protonymph'
cheliceral blade. Dispersal takes place after the of Weygoldt, 1969). Some species apparently
moultwhichreleasesajuvenileequippedwithall retainafoetalaspect(Judson, 1990).Thefirstfree
its organs (J). Juveniles then live on prey they instarsometimesremainsandmoultsinthecham-
catch (= 'nymphes'; Vachon, 1958b). The total berconstructedby the female (Weygoldt, 1969).
number of juvenile instars may vary within a Theanimallivesaloneafterthismoult.Thenum-
species. Males often become an imago in fewer
ber offollowingjuvenile instars is fixed to two:
instars than females. J2(= 'deutonymphe'),J3(= 'tritonymphe').Each
Female orthognathids and filistatids can still instar can be identified through its
moult. In labidognathids, imagos do not moult trichobothriotaxy (Vachon, 1938).Imagosdonot
any more (adults). In nature, all male spiders die moult any more.
withoutmoulting.
Scorpions
Ricinuleids Eggs hatch in the female's genital tract
Hatching releases an active individual, which (viviparous species) or soonafter laying
catchespreybutwhichhasonlythreepairsoflegs (ovoviviparous species).
and therefore does notpresentthe general arach- Newly born scorpions climb ontothe mother's
nid characteristics. Itdiffers fromthe imago, and back and remain there, living on yolk reserves.
is a larva: L. The three instars that follow They resemble an adult (juvenile) but is incom-
resemble the imago, and possess 4 pairs oflegs; plete (without trichobothria, unpigmented in-
however, they lackgenitalic structures. They are tegument, without specific bristles, etc.). It has
juveniles instars: Ji, J2, J3 (= 'nymphes' ofPit- temporary organs linked to life on the mother's
tard and Mitchell, 1972). There is only one im- back, such as legs without claws but bearing
aginal instar (adult). adhesive organs at their tip. This incomplete
juvenile is a pullus: JP (= 'larve' of Vachon,
P.SEUDOSCORPIONS 1940).
The eggs are laid in a brood pouch where they After one moult on the mother's back, the
feed upon maternal nutrients with the aid of the juvenilesperiodically movetotheground, where
embryonic membrane. Growth of the embryos they begin hunting and eating for the first time.
bursts the chorion and the external side of the They disperse afterwards and live alone. The
broodpouchtowhichtheyremainattachedbythe second instaris acompleteone (J2). Thenumber
buccal region. Their form is not differentiated. of juvenile instars may vary according to sex.
Within a few seconds, the mother injects a nutri- Mostly there are 6 to 7 instars, but it may vary
tive fluid which trebles their volume (= 'larves from5 (Orthochirus)to 10(Diplocentrus)(Polis,
gonflees' of Vachon, 1938; 'deutembryons* of 1990). Imagos do not seem to moult, but it may
Weygoldt, 1969).Organogenesiscontinuesand a be possible (Stockmann, 1968).
moult occurs which releases an animal which
emerges by an anteriorcephalothoracic tooth. Mites
The released instar looks like the imago, but The Acari have many more developmental
166 MEMOIRSOFTHEQUEENSLANDMUSEUM
lifconyofc freelifefeedingonnnoosstl I I
H
M\ZL
freelife
**
(04]
FIG. 9. Postcmbryonicdevelopment Stages 01 a scor- stching ml m2 w3 yr- '
pion, Euscorpiusitalicus(afterAngermann. 1957). L jTptgt J3
types than other arachnids. The eggs are often ' ffl
abandoned. There is a first instar which has a
foetal aspect, but it remains intrachorionic, ex- 94
cept in some cases (Coineau, 1977). This instar
can be compared with foetal instars of other FIG. 10. Succession of stages in postcmbri
arachnids (F), butit is not postembryonic. development ofmites, (a) Argasidae. OfhtthodoT06
Thefirst free instar is obviouslydifferent from maritime (after Guiguen, 1990); (b) Orih.iiul.w
(Carahodes wllmarmi) (afterBellido. 1983).
the imago because it usually has only 3 pairs of
legs. It moves and can feed itself. It is alarva: L. tcmaticgroupoftheimago,thereforetheyarenot
Thefollowinginstars areeight-leggedandonly larvae, but genital organs and furthermore some
differ from the imagos by some quantitative or
other structures are lacking. This 'incomplete'
sexual characteristics: they are juveniles (J) (= situation is not always easy to observe mor-
f^onrymapshpeesc'i)e.s,Tahte1nourm2b,emroroefionfstteanrsaimsaofxtiemnufmixeodf pusheofluolg,icbaelclya.usHeowtehveseer,inbsitoalrosgiacraelnienafrolrymaatliwoanyiss
3, but up to 4-5 in the Argasidae. unable to liveontheirown.
After these immature instars imagos appear,
which do not moult anymore (adults) (= Trie pullus (Pavlovsky, 1924) is an incomplete
juvenile instar with special adaptations to life on
'prosopon' ofRenter, 1909).
the mother, such as pad-like organs on the tipof
In the thrombidiids, there are periods of inac
the legs.
tivity between larval andjuvenile stages and be-
The presence oftwo morpho-biological forms
tween juvenile and adult stages. At such times,
the animal is covered by theoriginal cuticle, but during the same instar among mites is rare
secretesanew tegumentunderit, whichbecomes amongst the arthropods {except Diptera), but it
the tegument of the next instar. In many other does not raise any problems of description and
does not require any fundamental vocabulary
cases, motionless instars can he distinguished,
sometimes comparable to real nymphs or to changes: it simply requiresmoreaccuratedefini-
specific survival-forms, which allow for disper- tions.
sal.
Chronologicaland Morpijo-biological
DISCUSSIONANDCONCLUSIONS Descriptions
In the development of a systematic group of
Terminclogv and Concepts arachnids,exceptinricinuleids,pseudoscotpions
Mostterms used inotherarthropodscanalsobe and perhaps palpigradids, there is nofixed num-
used inarachnids.Wehave usedonly theoriginal ber of instars Therefore it would be unwise to
terms of pullus. foetal instars and incomplete base a study on few species and to fix the
juvenile. chronology, because some still unknown
The foetal instar, although it has been defined developments may modify the established sys-
for arachnids (Canard, 1987), is not specific to tem. Theoretical systems of this kind were
this group. Ft is evident in some insects and proposed by Reuter (1909) for mites and by
myriapods (= 'prolarves\ 'prelarves\ 'pseudo- Vachon (1958b) for spiders. Thus, the constant
foetus' etc.). presence of three post-larval juvenile instars
,
The incomplete juvenile instars belong to the (=nymph) in mites stated by Reuter and often
juvenile phase of which Ihey form a part (Jii followed (protonymphe, deutonymphe,
followed by J2). One can recognize the sys- tritonymphe.i does not conform to most species.
COMPARATIVE POSTEMBRYOMCDEVELOPMENTOFARACHNIDS 467
inwhichthereare lessthan3juvenileinstars and and, unlike otherarachnids, arcnotall predators.
even less to those with 4 to 6 instars (e.g. Or- Therefore, they have followed different evolu-
mihodorosmarinrmts). tionarypathwaysand sometimes metamorphosis
Developmentalanalysesbasedonafixednum- takes place, with larvae ar>d nymphs (similar in
ber of instars (chronological) establishes com- thesecases to those ofholometabolk:insect
mon points between instars ofdifferent species, With 'survival' instars which enable themtodis-
in order to envisage evolutionary pathways. But perse.
these common points will always remain Thisevolutionofclutchorjuvenilecarebythe
hypothetical, and moreover, these pathways can mother docs not indicate phylogenetic relations
be elucidated without this system. Therefore we in the different orders, because it is a general
do not wish Jo use a method with no decisive phenomenon within the animal world and can
advantages and, because of iis fixed character, appear independently in differentgroups.
limited development descriptions, because
Species which do not suit the established system LITERATURECITED
xcluded. In mites, forexample, the number
of instars is considered fixed to one larval, three ANDRE,H.M.19»9.Theconcepto!slasc.Pp.3-14 In
juvenileinstars and the adult. However, in many H.M. Andre and J.C Lioitt (eds). 'L'ontoe
species one ormore juvenile instars are missing ct le Concept tic Stase chaz lea Aniiropodc/.
AGAR- Wnvrv
saipnnesdtcaisresos.m,eaFtoivramreimsaibttlheeesrnetuahmrebereemroirso,feditnehspatnaernstd.hirenegjuovnenitlhee ANDRBlEat,SaosccHis.eJiMne.'spAKiodjeyrOaslCacQnUBdfeoiit,gheeftrd.a'IrE9amHco6hn.mioTdlsho.egMdieeetmi3on3.i:iru1,-i14.
ANCERMANN, H. 1957. Ubcr verhalten, Spcr-
Evolutionary Pathways mophorenbildung und Sinncsphysiologic von
Immature instars of arthropods are adapted to EuscorptHs kalians Hbst. und Vcrwandtcn Alton
speciallifestylesorenvironmentsandsometimes (Scorpiones, Cbactidae). Zeitschrift fttr
Tierpsychologie 14: 276-302.
differ from those ofimagos. Often these adapta- BELUDO, A. 1983. Etude morphoJogique ei
tions influence the morphology so deeply that it ^cologique de Carabodcs wilhmvwi Bernini,
is difficult to distinguish the imago from the ]°75 (Acan, Oribatci) dans une formation
immature forms(larva). Such differentes art piunnii^ de la landc armoricainc. Thdsc 3cmc
marked among the arachnids llarvae absent ex- cycle Rcnncs 1. 79pp.
cept in milesandrictnuleids). BONNET,P. 1933.Lecycle vitaldePhitoeuschtysops
A good correlate probably exists between the Pi»da (Anin&dc. Salticidc). ArchivesdeZoologie
ExperimcntaJe75: 129-144
ainncdrtehaeseidnclreevaelseodfncuarmtbebryotfheinmcooimhpelrettoeiitnssctalrustcaht CANAdReDv,elAo.p1p9e8m4.enCton,tribduetionId1eloalcoongniaci&saenlcctdiiie
the startofthe development. T^cophysiologie des Arancides dc landes ar-
Moreover,thebiologyandmorphci1<>gy*>fear!y Fnoric^ines. These Doci. Etat, Rennes: 389 pp,»
instars can be observed"and explained as adapta- annexe. t52pp.
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