Morphology of the Brain of Crayfish, Crabs, and Spiny Lobsters: A Common Nomenclature for Homologous Structures

23 Pages·1992·10.3 MB·English

by  D Sandeman

Reference: Biol Bull 183: 304-326. (October, 1992)
Morphology of the Brain of Crayfish, Crabs, and
A Common
Spiny Lobsters: Nomenclature
for Homologous Structures
DAVID SANDEMAN1 RENATE SANDEMAN1 CHARLES DERBY2
, , ,
AND MANFRED SCHMIDT3*
1School ofBiologicalScience, University ofNew South Wales, Sydney, NSHr2033. Australia.
2Department ofBiology. Georgia State University. Atlanta, Georgia, and 3Whitney Laboratory.
University ofFlorida. St. Augustine, Florida 32086
Abstract. The morphologies of the cerebral ganglia (Wiersma el a/., 1982; Glantz and Pfeiffer-Linn, 1990)
(brains) ofthree infraorders of the decapod crustaceans and theendocrine systemsin theeyestalkshave been par-
(Astacura-crayfish; Brachyura-crabs; Palinura-spiny lob- ticularly well investigated (Cooke and Sullivan, 1982;
sters)aredescribed. A common nomenclature isproposed Arechiga el a/.. 1990). Thedevelopment ofa semi-isolated
for homologous nerve roots, brain regions, tracts, com- preparation ofthe crab and then crayfish brain allowed
missures, neuropils, and cell body clusters. the investigation ofeye withdrawal, statocyst driven re-
flexes, chemoreceptive responses, and antenna II reflexes
Introduction (Sandeman. 1969, 1971. 1989; Sandeman and Okajima,
Decapodcrustaceanshavebeen favoredanimalsamong 1972; Silvey and Sandeman, 1976; Ache and Sandeman,
neurobiologists for many years because they are compar- 1980; Sandeman and Wilkens, 1982). Recently there has
ativelylargearthropods, havewell-organized nervoussys- been a renewed interest in the crustacean cerebral gan-
tems and interesting behavior patterns ranging from re- glion, stimulated by more detailed anatomical studies and
flexes to complex social interactions. Several fixed action thedescription ofa numberofneuronal systemsrevealed
patternsconcerned with protection orescapeare mediated byantibodies raised against various neurotransmittersand
by particularly well-defined sensory inputsand large neu- neuromodulators (see Wiese el al. 1990).
romuscularsystems, and, much research hasbeen focused The entry ofresearchers from many different fields into
on these. The crayfish ventral nerve cord survives well in crustacean brain research hasbeenaccompaniedbyacer-
isolationand hasalsobeenexploited in thestudyofmany tain confusion about the names ofdifferent parts ofthe
aspectsofthe neurophysiologyoftheventralganglia(e.g.. brain. This confusion is probably the result ofa large lit-
Hoyle, 1977; Atwood and Sandeman, 1982; Wine and erature on the brains ofthe crustaceans, not all ofwhich
Krasne, 1982; Wiese el ai. 1990). belongedtothedecapods. Within thedecapods, problems
There is a growing interest, however, in the cerebral have been caused by various interpretations ofthe works
ganglia (brains) ofthe crustaceans. Initial studies on the ofpreviousauthors, andbytheearlierauthorsthemselves
brains of the spiny lobsters by Maynard in the 1960's changingtheir minds about what to call a particular neu-
(Maynard. 1962; Maynard, 1966; Maynard, 1969; May- ropil (e.g., Hanstrom. 1924, 1925; 1947). Many recent
nard and Sallee, 1970) came to an untimely end, but the descriptions ofthe brains ofvarious decapods have per-
description ofthe impulse traffic between theeye and the petuated the errors or misconceptions ofthe earlier au-
brain was continued by Wiersma and his colleagues thors. Progress toward a standard nomenclature for the
component neuropils. tracts, and cell bodies ofthe deca-
pods was made by Tsvileneva and Titova (1985) who
Received 14 February 1992; accepted22July 1992.
* Presentaddress: InstitutfurBiologic. T. U. Berlin. 1000 Berlin 10. adoptedtheoriginal nomenclature ofHelm ( 1928) intheir
Germany. description ofthe brains ofthe crayfish and crab.
304
DECAPOD BRAIN MORPHOLOGY 305
The largerdecapod crustaceans have life spans ofmany Antenna I (ANT I): Basal segments contain the stato-
years and a brain that, in size and complexity, lies some- cysts and muscles, and bear two sensory flagella both of
where between the octopus and insects. Indications are which carry mechanoreceptive and chemoreceptive sen-
that the brain and behavior ofthe crustaceans will attract silla (Derby, 1982; Derby and Ache, 1984). The lateral
considerable attention in the future (Wiese ct ai, 1990). flagellum bears special olfactory sensilla; the aesthetasc
It is therefore timely that a nomenclature for brain mor- sensilla (Griinert and Ache, 1988).
phology ofthe decapods be compiled for the commonly Antenna II (ANT II): Basal segments contain muscles
used species. In this report we suggest names for homol- and bear a scale-like structure and a single long sensory
ogouscomponents (i.e., nerve roots, neuropils, tracts, and flagellum carrying both mechanoreceptive and chemo-
groupsofcell bodies) that can be recognized in the brains receptive sensilla (Tazaki and Shigenaga, 1974; Derby,
ofthreeinfraordersofthedecapodCrustacea;theAstacura 1982).
(clawed lobsters and crayfish), Brachyura (crabs), and
Palinura (spiny lobsters). We havechosen representatives NerveRoots
from these infraorders because preparations already exist We define the nerve roots as those bundles of axons
for the physiological investigation ofthe brains ofthese thatextend from thebrain orothercentral nervousganglia
animals, and further studies will therefore most likely be and contain either sensory afferents, motor efterents, or
done on them. both, but not interneurons. The tract of axons between
Inselectingnamesforthevariouscomponentswehave thebrain and theopticganglia in theeyestalk is, therefore,
sought, where possible, to keep terms that have been not a nerve root because it forms a connection between
commonly used and to prefer names that do not imply central ganglia.
function unlessthis hasbeenclearlyestablished. We have Anteriormedian nen'e(AMNv): Thisshort nerve bun-
triedto removeambiguitiesandshowthat thesamecom- dle projects from the anterior surface of the brain and
ponentscan beidentified in thethreedifferent infraorders. suppliesthemusclesofthemedian segmentoftheeyestalk.
We have included an Appendix which listssynonymsthat Thereisno information on afferentsin thisnervebundle.
have been used by other authors for the neuropil areas Oculomotor nerve (OMNv): The oculomotor nerve
and cell body clusters we describe. Earlier authors have carries motor neurons to the muscles ofthe eyestalk. It
used the terms "lobe", "body", and "bridge" for several also contains primary afferent axons from mechanore-
particularly clearly delineated neuropils. Although we ceptors in this area. Motor neurons to some eye muscles
preferthe term "neuropil." we have retained these terms havebeen found in the lateral protocerebral tract in crabs
as they are well entrenched in the literature on compar- (Sandeman, 1964) and crayfish (Mellon, 1977).
ative studies ofarthropod brains. Wedo not pretend that Antenna Inerve(A,Nv): Motor neuronsto the muscles
oursystem ofnomenclature will apply to all members of in the basal segments ofantenna I are contained in this
the Phylum Crustacea, given their diversity and the very nerve together with the primary afferents from the recep-
different morphologyofthecerebralgangliaofsomeforms torson the flagella and basal segments. To thebest ofour
(Elofsson and Hessler, 1990). knowledge, all axons from the olfactory sensilla (aesthe-
tascs) diverge from the main bundle and project exclu-
Material and Methods sively to the olfactory lobe (see below) (Sandeman and
Denburg, 1976; Mellon and Munger, 1990; Schmidt and
Brain morphologiesofthethreedifferent typesofdeca- Ache, 1990; Schmidt and Ache. 1992), non-aesthetasc
pod were compiled from serial sectionsofwax embedded chemosensory and mechanosensory afferents project to
andsilverimpregnated, orplasticembedded andosmium the lateral and median antenna I neuropil (Rove, 1986;
ethyl gallate stained material. Cheraxdestructorhasbeen Schmidt and Ache, 1990; Roye and Bashor, 1991;
taken asthe representative ofthe Astacura, Scylla serrata Schmidt el ai. 1992).
ofthe Brachyura. and Jasits novaehollandiae and Panu- AntennaIInerve(AHNv): Motorneuronstothe muscles
lirns argus ofthe Palinura. in the basal segments ofantenna II run in this nerve to-
gether with primary afferents from mechanoreceptors,
Results proprioceptors, andchemoreceptorson theflagellum and
HeadAppendages trohpeilba(ssaelebseelgomwe)n.tsA.nAullmbaexornosftseurbmdiivniastieonisn tohfethseaamnetennenua-
Several terms are used for the two pairs ofantennae. II nerve forcrayfish havebeen described (HabigandTay-
We believe the most unambiguous to be antenna I and lor, 1982; Sandeman and Wilkens, 1982; Tautz and
antenna II. Antenna I is equivalent to the antennule or Miiller-Tautz, 1983).
first antenna, and antenna II to antenna or second an- Tegumentary nerve (TNv): This is a purely sensory
tenna, terms that we also use. nerve carrying primary afferents from mechanoreceptors
306 D. SANDEMAN ET AL.
and other sensilla o i >rsal carapace (Kinnamon,
1979).
Posterior i re (PMNv): Projecting from the
posterior o lie median nerve carries interneu-
rons }>' ..in and the oesophageal ganglion.
Brain /> andNeuropils (Fig. I)
There are three main divisions ofthe brain, protocere-
brum, deutocerebrum, and tritocerebrum, reflecting the
three ganglia that have fused to form it. The neuropils of
the optic ganglia and lateral protocerebrum are located
intheeyestalksofcrayfish,crabs,andlobsters. Themedian
protocerebrum and tritocerebrum are located medially.
Protocerebrum
The protocerebrum can be conveniently subdivided
III
into three parts, the optic ganglia, the lateral protocere-
brum and the median protocerebrum.
OPTIC GANGLIA. Contains three neuropils that are Figure I. Brain regions and neuropils that can be identified in all
threebraintypesandthatareconsideredtobehomologous. Heavyblack
probably devoted to processing the information received bars represent the tracts and commissures linking the neuropil areas,
by the photoreceptors ofthe retina. shownasboxes.Theromannumeralsrepresentthedivisionsofthebrain
Lamina (L): The first neuropil behind the retina, the according to the way we have arranged them in the text ofthe paper:
lamina is geometrically structured. i.e.. I = protocerebrum (with three subsections); II = deutocerebrum;
Externalmedulla(EM): Lyingdirectly behind the lam- 111 = tntocerebrum. A key to the abbreviations is provided in Appen-
dix 2.
ina, the external medulla is similarly geometrically struc-
tured, but is also transversely layered.
Internalmedulla (IM): The most proximal ofthe three the median protocerebrum is made up of two anterior
neuropils in the optic ganglia, this too is geometrically medialprotocerebral neuropils and two posterior medial
organized and has clearly defined transverse bands. protocerebral neuropils). Whileclearlydiscernible in some
LATERAL PROTOCEREBRUM. Contains two neuropils. section planes, these four neuropils tend to fuse with one
In crayfish, crabs, and spiny lobsters the neuropils ofthe anotherdorsallyand ventrally, makingthedistinction be-
lateral protocerebrum lie in thedistal segment oftheeye- tween them somewhat arbitrary. No primary afferent
stalk, directly proximal to the optic ganglia. In some an- projectionstotheneuropilsofthemedianprotocerebrum
omurans the lateral protocerebrum is incorporated into have been reported.
the centrally located median protocerebrum. .-Interiormedialprotocerebralneuropil(AMPN): These
Terminalmedulla (TM): This complex neuropil is not twoneuropils lieon each sideofthe midlineattheanterior
geometricallyorganized but hasa numberofsubdivisions ofthe median protocerebrum.
(Blaustein ct a/., 1988). It contains neurosecretory cells Posteriormedialprotocerebralneuropil(PMPN): These
ofthe X-organ and itsassociated neurohaemal organ, the two neuropils lie on each side of the midline, directly
sinus gland, which together constitute one of the most posterior to the anterior medial protocerebral neuropils.
important neuroendocrine systems in the crustaceans. Protocerebral bridge (PB): Embedded in the anterior
Hemiellipsoid body (HN): Positioned anterior to the edge of the anterior medial protocerebral neuropil, this
terminal medulla, this neuropil sometimes has a glomer- V-shaped neuropil has a characteristic form containing
ular structure, and is large and layered in some anomu- manylargethrough-runningaxonswith finesidebranches.
rans, a characteristic which led Hanstrom (1925) to pos- In the crayfish Clierax. extra-retinal photoreceptors lying
tulate that it ishomologouswiththecorpora pedunculata in the anterior ofthe brain terminate in the neuropil of
ofthe insects. the protocerebral bridge (Sandeman el ai. 1990).
MEDIANPROTOCEREBRUM. Formstheanterior part of Centralbody(CB): A cigar-shaped neuropil lyingacross
the medially situated neuropils ofthe brain. It contains the brain and dividing the anterior from the posterior
two paired medial and two unpaired median neuropils. medial protocerebral neuropils. Thecentral bodyisawell-
(Throughout this paper we use the term median to de- definedareaofneuropil that immunocytochemical studies
scribe a structure that straddles the midline, and medial have shown to contain a wide variety of different neu-
to describe paired structures nearorat the midline. Thus roactive substances (Schiirmann el a/.. 1991).
DECAPOD BRAIN MORPHOLOGY 307
Cherax Scvlla Jasus
TNv
.TNv
A Nv A.Nv
M
A.Nv
A Nv
TNv M
A.iNv
TNv
TNv
1mm 1mm 5mm
Figure 2. Camera lucida-traced outlines ofthe brains ofCherax. Scy/la and Jasus seen from the side
and from above. Anterior is to the left ofthe page. In the crayfish and crab, the oesophageal connectives
and the protocerebral tract lie in nearly the same horizontal plane. In the spiny lobster the protocerebral
tractsextend upwards, almost at right angles to the plane ofthe oesophageal connectives. Antenna 1 and
antenna2nerverootsofthecrayfishand thecrabpointanteriorlyandventrally. whereasthoseofthespiny
lobsterprojectalmost directly \entralh. Thesedifferencesarereflected intheorganization ofthe neuropils
within thebrainsofthethreeanimals.
Deutocerebrum neuronsthat control the movements ofthe ipsilateral an-
Olfactorylobe(ON): The olfactory lobesareclearlyde- tenna I (Roye and Bashor, 1991; Schmidt et ai. 1991).
lineated spheres lying on each side of the brain. They The lateral antenna I neuropils have sometimes been re-
contain cone-shaped areas of densely packed synaptic ferred to as "parolfactory lobes" (see Appendix 1).
fields the olfactory glomeruli arranged with their api- Median antennaIneuropil(MAN)'- A relativelydiffuse
ces pointing to the center of the sphere. The olfactory block of neuropil that lies across the brain between or
lobes receive the primary afferent endings of the che- dorso-anteriorto thelateral antenna I neuropils. The me-
moreceptorsonantenna 1 (Sandeman and Denburg, 1976; dian antenna I neuropil fusesanteriorly with the posterior
Mellon and Munger. 1990; Schmidt and Ache, 1990; medial protocerebral neuropils, and posteriorly with the
Schmidt and Ache. 1992). tegumentary and antenna II neuropils. Little is known
Lateral antenna I neuropil (LAN): Consisting oftwo about the projections to this area ofthe brain. Branches
clear subdivisions when viewed in frontal sections, the ofdescending interneurons related to statocyst inputsex-
lateralantenna I neuropil oneachsideofthebrain receives tend into the medial antenna I neuropil in both crabs
afferents from mechanoreceptors, statocysts, and non- (Fraser, 1974) and crayfish (Yoshino et al, 1983). In the
aesthetasc chemoreceptors from the ipsilateral antenna I blue crab, mechanosensory afferents from sensilla at the
(Sandeman and Denburg, 1976; Yoshino el a/.. 1983; base ofantenna I projecttothe medial antenna I neuropil,
Roye, 1986; Blaustein et a/.. 1988; Schmidt and Ache. where antenna I motorneurons also branch (Roye, 1986:
1990). It also contains the synaptic fields of the motor Roye and Bashor, 1991). Primary afferents from the base
308 D. SANDEMAN ET AL.
ofthe antennule ha <Iserved that project to the ropil which also contain the synaptic fields ofthe motor
medialantenna T il in spinylobsters(Schmidt, un- neurons that control the movements of antenna II
pub. obs.) (Sandeman and Wilkens, 1982; Habig and Taylor, 1982;
Acces^ i: The accessory lobes lie directly Tautz and Muller-Tautz. 1983).
poster? u) the olfactory lobes. Theyare larger Teguineniarv neuropil(TN): Each tegumentary nerve,
than il lobes in the crayfish, about the same carrying the afferent input from the dorsal carapace
.:iory lobesin spiny lobsters, and very much (Sandeman, 1969; Kinnamon, 1979), endsinatight knot
smaller than the olfactory lobes in crabs. They contain ofneuropil dorsal and somewhat anterior to the medial
large numbersofsmall round glomeruli. In thespiny lob- margin ofthe antenna II neuropil.
ster, the accessory lobes are subdivided into medial, cen-
tral, and lateral layers containing glomeruli of different Tracts and Commissures (Fig. 1)
sizes (Maynard, 1966, 1971; Blaustein et a!., 1988). The
accessory lobes do not appear to receive a direct input Many tracts in the brains ofthe crustaceans link areas
from primary afferent axons, nor have motor efferents of neuropils, and a number of axon bundles cross the
been found that have their synaptic fields there. brain. We haverestricted ourselvesheretothe largestand
Deutocerebral commissure neuropil (DCN): Small best known that can be unequivocally identified, when
round ventrally situated neuropils characterized by re- present, in the three infraorders.
ceiving strong projections from the deutocerebral com- Optic tract (OT): The optic tract links the last ofthe
missure and from the medial protocerebrum. Clearlyde- optic ganglia (internal medulla) to the lateral protocere-
fined in crayfish and spiny lobsters with large deutocere- brum. Veryshortintheastacurans, brachyurans, andpal-
bral commissures, these neuropils have not yet been inurans, it is often confused with the much longer pro-
identified in the crab brain. No primary afferent inputs tocerebral tractthatlinkstheterminal medullatotheme-
are known that project to the deutocerebral commissure dian protocerebrum in these groups.
neuropils, nor has the nature ofthe interneuronal input Protocerebral tract (PT): Axons in this tract link the
been defined. The subject ofmuch confusion, these neu- terminal medullaand hemiellipsoid bodywiththeanterior
ropils have been called "parolfactory lobes" in several medial protocerebral neuropilandotherareasofthebrain.
recentpublications (TsvilenevaandTitova, 1985; Sande- Sometimes inaccurately referred to as the "optic nerve"
man et al, 1988; Blaustein cl til.. 1988) and are renamed or "optic tract" (see Appendix 1).
here in accordance with our policy to avoid functional Olfactoryglobulartract (OGT): The olfactoryglobular
names where we can. See Appendix 1 for synonyms. tract linksthe hemiellipsoid bodiesandterminal medullae
Olfactoryglobulartradneuropil(OGTN): Firstpictured with the olfactory and accessory lobes on both sides of
in crayfish by Helm (1928) and labelled "z", attention the brain by crossing the brainjust dorsal to the central
wasagain drawn tothis neuropil byTsvileneva and Titova body neuropil. It typically contains very large numbers
(1985). It appears to lie within, or very closely associated ofsmall diameter axons (1 ^m and less).
with, the olfactoryglobulartractat a pointjust beforethe Deutocerebral commissure (DC): This commissure is
tract reaches the olfactory and, when present, accessory large in crayfish and spiny lobsters, but cannot be iden-
lobes. Present also in crabs, this neuropil has assumed a tified with certainty in crabs. In crayfish it contains two
greater significance since the branches oflarge serotonin populationsofaxondiametersthatcrossthebrainbetween
immunoreactive neurons, associated with the accessory the two accessory lobes.
and olfactory lobes, have been found in this neuropil Oesophagcal connectives (OC): These two large tracts
(Sandeman and Sandeman, 1987; Beltz et al.. 1990; link the brain with the suboesophageal ganglion and the
Schmidt et al.. 1991). Connections between the olfactory ventral cord.
globulartract neuropil andotherpartsofthe nervoussys-
tem have yet to be determined. Cell Body C'/i/.v/m
Homologous cell bodies are more difficult to identify
Tritocerebrum
than neuropils, tracts, and commissures. In some cases,
Antenna Hneuropil(AriN): Thesecylindrical neuropils suchasthecellsassociatedwiththeolfactoryandaccessory
are posterior to the accessory lobes in crayfish, posterior lobes, the cell bodies can be identified by theircharacter-
to the olfactory lobes in crabs, and postero-dorsal to the istic morphology, but in others there are no such criteria
olfactory lobes in the spiny lobster. They are tapered lat- available. Theprojectionsoftheprimary neuritesofafew
erally and often have ageometrically arranged pattern of cell bodies are known, but these are in the minority, and
axons running antero-posteriorly across them. The pri- then information is often available for only one brain
maryafferentsfrom antenna II end in theantenna II neu- type.
TNv
A,,NV
dorsal view
OMNv
OGT
A Nv
''
(
AMPN
?
TNv
CB - /-*$8,<&
PMPN s ;; ON
DCN tgjjjj^
..
13
MAN
AcN
LAN
m
Nv
A|| AnN
x
OC ventral view
Figure3A, B. Graphic reconstruction ofthe neuropilsand cell clustersin dorsal and ventral viewsofthe brain ofthecrayfish. This figure, and
those forthecraband spiny lobster,were reconstructed from sectioned material, so that the proportionsofthebrain areasand positionsofthecell
clustersare reasonahh accurate!} retained. The numbersandsizeofthecell bodiesshown, however,do not represent thetruesituation, apart from
indicating the difference between the characteristically small "globuli" cells associated with the accessory and olfactory lobes, and the larger cell
bodiesfoundelsewhere in the brain. A key totheabbreviations isprovided in Appendix 2. Seetext fordetails.
309
310 D. SANDEMAN ET AL
PT
AcN
v
NV
"
\ >_-_. AnN >; / '%:-
"""-'
\^ ." ";-^_
'- .' j. '.i..'''*&|*fcf4\* ,
* ' '
,
:'
's
:.
m
:
i
<-:
*-
'
V *17
^
Figure4. Horizontal sectionsofthe brain ofCherax. Inthisand in the following figures, the planesof
thesectionsareindicated on theinsetdiagramwhichshowsthebrain insideviewwithanterioron theleft.
Figure4A includesthe olfactoryglobulartract(OGT)which formsachiasm at thecenterofthebrain and
then diverges to end in the olfactory (ON) and accessory (AcN) lobes. All the main neuropilscan be seen
inthisplane. Figure4Bisasectionthrough amoreventralplaneandshowsthedeutocerebralcommissure
(DC)extendingacrossthebrain between thetwoaccessorylobes. Aand Bshow how theolfactoryglobular
tractpassesdorsallyoverthedeutocerebral tractinthemidlineandthen ventrallybeneath itbeforeentering
theolfactory and accessory lobes. Scalebars = 100^m.
>" Kt -
*
"<*'.
,
-
Figure5. A.A horizontalsection neartheventralsurfaceoftheChcraxbrain. Atthislevelthevcntrally
situateddeutocerebralneuropilscanbeseen(DCN).ThemedialantennaI neuropilisnolongerintheplane
ofthe section, but the lateral antenna I neuropils (LAN) are still present as round areas, medial to the
accessory1 lobes. Bundlesofaxons at their anterior margins are the beginning ofthe antenna I nerve root.
Theolfactory lobesareenclosed by the fine fibersofthe axons from the chemoreceptors. These axonsare
also contained in the antenna I nerve root. B. The small olfactory globular neuropil (OGTN) contained
within the fibers ofthe olfactory globular tract (OGT) at the point where the olfactory globular tract and
the deutocerebral commissure (DCN) cross before projecting to the neuropils to the olfactory (ON) and
accessory lobes (AcN). C. Darkly stained axons (arrows) from the deutocerebral tract (DC) penetrate the
accessory lobe from the periphery toend in twolayersofglomeruli inthe lobe. Scalebars = 100^m.
311
312 D. SANDEMAN ET AL.
A,Nv
TNv
A Nv
n
dorsal view
A,,NV
ventral view
Figure 6A, B. Dorsal and ventral views ofthe brain ofScylla scmila asan example ofa hrachyuran.
See text lordetails.
DECAPOD BRAIN MORPHOLOGY 313
-V" >-;-^WW:3p( gg*
'.,
-
m
<&/?&,-*'v$8is^-% In
: ;
cI. <-,;--^---;"NT.iMWitoKiV.--."
;;;<0JpvlX
,
s
?
/
^r x ^^^^;,
, v j
? - -^: "
^'S/ -
;
Figure 7. A honzontal section through the brain ofSo'//a. This section is slightly oblique, passing
through more dorsal neuropils on the left (A) and more ventral neuropils on the right (B). The anterior
medialprotocerebral neuropils(AMPN)arelargerthan theposteriorprotocerebral neuropils. Theolfactory
lobes (ON) are also large and enclosed by many chemoreceptive fibers projecting from the antennules in
theantenna I nerveroot. Thetegumentary nerveroot and neuropil areprominent (A), whereasthe lateral
antenna I neuropil andthe antenna II neuropilare relatively small (B). Scale bar = 100^m.
The cell bodiesarecontained in clusters; some ofthese lie distal or adjacent to the external medulla, and (3) cell
clusters are clearly recognizable in all brain types, some bodiesthatlieadjacenttotheinternal medulla, orbetween
are not. In previous studies, cell body clusters have been the internal and terminal medulla.
given specific names, and these names differ from one Detailed information about the projections ofmany of
brain type to another. Here, we describe the cell clusters the cell bodies in the optic ganglia is available for some
accordingto the brain region in which they are found. In crustaceans (Nassel, 1977; Sandeman, 1982).
this way we avoid functional names for cell clusters that LATERAL PROTOCEREBRUM. The lateral protocere-
may be highly heterogeneous and that may contain the brum contains (4) cell bodies that lie adjacent to the ter-
cell bodiesofneuronswith widelydiffering functionsand minal medulla, and (5) cell bodies that lie adjacent to the
projections. hemiellipsoid body.
We
recognize 17 different clusters of cell bodies that Detailed information about the projections ofsome of
appear to be common to all brain types; to simplify mat- the cell bodies in the lateral protocerebrum ofspiny lob-
ters we have numbered the cell clusters, 1-17, from an- stersandcrayfish isavailable(Blaustein eta!., 1988; Derby
terior to posterior. Tables in Appendix 1 provide cross and Blaustein, 1988).
references to the descriptions provided in this paper and MEDIAN PROTOCEREBRUM. The median protocere-
by previous authors. brum includes (6) a prominent medial cluster of cell
bodies, some of which are very large; lying around the
Protocerebrumf front ofthe brain and extending from the dorsal to ven-
tral surfaces; (7) lateral cell bodies that may appear in
OPTICGANGLIA. In the optic ganglia we recognize (1) some preparations as extensions ofcell cluster 6 on the
cell bodiesthat liedistal tothe lamina, (2)cell bodiesthat ventral surface of the brain and in others as separate
groups: and (8) small lateral groups of cell bodies that
*Numberscorrespond tocell bodieslabeled in Figures. lie on either side ofthe central body at thejunction be-