Keywords. Allometry; autotomy; chela display; cheliped; claw; handedness; regeneration
Decapod crustacean chelipeds: an overview
PITCHAIMUTHU MARIAPPAN, CHELLAM BALASUNDARAM and BARBARA SCHMITZ
The structure, growth, differentiation and function of crustacean chelipeds are reviewed. In many decapod crusta-
ceans growth of chelae is isometric with allometry level reaching unity till the puberty moult. Afterwards the same
trend continues in females, while in males there is a marked spurt in the level of allometry accompanied by a sud-
den increase in the relative size of chelae. Subsequently they are differentiated morphologically into crusher and
cutter making them heterochelous and sexually dimorphic. Of the two, the major chela is used during agonistic
encounters while the minor is used for prey capture and grooming. Various biotic and abiotic factors exert a
negative effect on cheliped growth. The dimorphic growth pattern of chelae can be adversely affected by factors
such as parasitic infection and substrate conditions. Display patterns of chelipeds have an important role in
agonistic and aggressive interactions. Of the five pairs of pereiopods, the chelae are versatile organs of
offence and defence which also make them the most vulnerable for autotomy. Regeneration of the autotomized
chelipeds imposes an additional energy demand called “regeneration load” on the incumbent, altering energy
allocation for somatic and/or reproductive processes. Partial withdrawal of chelae leading to incomplete exuvia-
tion is reported for the first time in the laboratory and field in Macrobrachium species.
1. General morphology
Chelipeds of decapod crustaceans have attracted human
curiosity and fired human imagination since Aristotle
(Hopkins 1993) probably because they figure so promi-
nently both in structure and function in the life of these
animals. Crustaceans are mostly aquatic arthropods which
breathe through gills, have two pairs of antennae, and
numerous paired appendages on thorax and abdomen
(Stebbing 1893; Schmitt 1965) that are grouped into cepha-
lic, thoracic and abdominal appendages in relation to the
body tagmata. The cephalic and thoracic regions are usu-
ally fused to form a cephalothorax and the appendages are
known as cephalo-thoracic appendages. Decapod append-
ages are the best example of serial homology with a serial
modification in basic structure from the first to the last
walking leg (Wood and Wood 1932). With the exception
of the antennules, which are uniramous, other appendages
are basically biramous and possess a basal segmented
protopod with a coxa and basis and may have lateral
(exites) or medial (endites) protrusions (Manton 1977;
McLaughlin 1982). From the protopod arise the exopod
and endopod. Of the two, the latter has undergone a variety
of specialisations resulting in its transformation for vari-
ous functions like sensory reception, feeding, walking,
burrowing and swimming while the exopod is drastically
reduced or may even be lost. This has further been facili-
tated by mineralisation of the exoskeleton endowing rigi-
dity and support to the appendages which are made flexible
by the arthrodial membrane.
All decapods usually have five pairs of well developed
walking legs with exceptions in the sergistid family of
the Dendrobranchiata, many of the Anomura, and a few
Brachyura. In these animals the fifth or fourth and fifth
pair of pereiopods are reduced in size for special func-
tions. Occasionally both pairs may be vestigial or absent
(McLaughlin 1982). Structural modifications of decapod
appendages due to diversified functions and life style have
been described in different groups (Tiegs and Manton 1958;
Kaestner 1970; Schram 1978). The major modifications
Journal
of Biophysical Chemistry, 2009, 1, 1-13

of the appendages have evolved essentially from the
feeding habits of the groups (either for filtering or for
predation). However, the functional and structural modifi-
cations of crustacean chelipeds are not only due to feed-
ing and locomotion (Dahl 1956; Bock and von Wahlert
1965; Manton 1977) but also change with environmental
conditions (Smith and Palmer 1994) and species specific
needs supplemented by hox genes (Averof and Patel
1997). Among decapods the chelate legs are unique with
the first (Brachyura) or the second pair (among Macrura
with first two chelate pereiopods) being the sole organ of
offence and defence.
The typical cheliped or ambulatory pereiopod com-
prises of an exopod and endopod of which the latter is
highly reduced or lost. The exopod comprises seven
podomeres: (i) coxa, a short, stout cylinder, moving anterio-
posteriorly in articulation with the sternum and epimeron,
(ii) basis, a short cylinder with lesser average diameter
than the coxa and articulated by hinge joints with
the coxa, moving dorso-ventrally, (iii) ischium, larger
and wider than the basis, fused immovably and curved
upward, (iv) merus, (v) carpus, (vi) propodus, and (vii) dac-
tyl. The basis and ischium when fused together form the
basi-ischium (Lochhead 1961).
Typically Caridean shrimps have chelate or subchelate
first and second pairs of pereiopods; however, among the
Processidae often only one pereiopod of the first pair is
chelate, while the opposing member is simple. A very
unique and exaggerated development of one chela of the
first pair of pereiopod is characteristic of snapping shrimp
of the family Alpheidae. After being cocked in the open
position and building up tension, this large snapper claw
(of up to half the animal’s size) closes rapidly forming
a thin water jet; its high velocity (25 m/s) results in the
formation of a small cavitation bubble (3⋅5 mm in dia-
meter), that collapses with an extremely loud and short
sound (up to 248 dB re 1 µPa at 1 cm distance for 240 ns)
(Schmitz 2000). This signal is used for intraspecific,
hydrodynamic communication (Herberholz and Schmitz
1998) as well as for territorial defence and to stun or even
kill small prey (small shrimp, crabs or fish) (MacGinitie
and MacGinitie 1949; Hazlett and Winn 1962; Schultz
et al 1998). Marked asymmetry of the first pair of chelate
pereiopods is also common in a number of other decapods
like lobsters and fiddler crabs.
2. Growth
Crustacean growth is discontinuous since the highly min-
eralised old exoskeleton is shed through a process known
as ecdysis (= moulting) whenever a certain growth incre-
ment is achieved, whereas growth in vertebrates is
continuous. In decapods three types of allometry exist:
(i) positive allometry or progressive geometric growth, in
which the dependent variable grows fast with respect
to body size, (ii) isometric or arithmetic growth, and
(iii) negative allometry or retrogressive geometric growth,
in which the dependent variable grows slower than body
size. Chelipeds are the best example of crustacean
allometric growth. In males of the crab Arenaeus carib-
rarius (Pinheiro and Fransozo 1993), crayfish Orconectes
virilis, and blue clawed (BC) males of Macrobrachium
rosenbergii (Kuris et al 1987), chela growth shows posi-
tive allometry (Aiken and Waddy 1992), while it is iso-
metric in juveniles and females (Pinheiro and Fransozo
1993). A detailed account of the types of allometric
growth of cheliped in various decapod crustaceans is
given in table 1.
In heterochelous decapods chelipeds are further differ-
entiated into major (crusher) and minor (cutter) based on
morphologically and functionally different dentition pat-
terns (Levinton et al 1995). The large and robust chela
with molariform teeth, known as the crusher, can yield
more force than the minor, which has many cutting teeth
and spiniform setae (figure 1) (Mariappan and Balasunda-
ram 1997). Major and minor chelae possess differential
operating forces measured as ideal mechanical advantage
(IMA) (figure 2) (Warner and Jones 1976; Brown et al
Figure 1. Morphological
variations in the propodus of
(a) major and (b) minor chela in Macrobrachium nobilii. D, Dac-
tyls; P, propodus (from Mariappan and Balasundaram 1997).
(a)
(b)
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P. MARIAPPAN ET AL.

1979). In male Uca and Alpheus, the major chela is used
for aggressive and courtship displays, while the other is
used for capture and manipulation of prey and grooming
(Hazlett 1962; Nolan and Salmon 1970; Crane 1975).
Many crustaceans have spatulate chelae which are used to
scrap algae from rocks (McLaughlin 1982). The atyid
shrimps use brush and spiny setae on chelipeds to scrape
up debris (Fryer 1960). In Macrobrachium australe the
minor chela endowed with abundant bristles serves as a
sort of net to catch prey while the major chela is used to
pick up prey. Such a differential function among cheli-
peds is also observed in Homarus spp. (Davis 1987).
Chela size is also related to feeding habits. For instance,
detritivorous crabs have small slender claws (Seed and
Hughes 1995) while carnivorous counterparts like Ocy-
pode spp. possess enlarged chelae to facilitate predation.
In Macrobrachium nobilii, the robust second pair is used
for prey capture and the slender first pair functions to
deliver the food to the mouth (P Mariappan and C
Balasundaram, unpublished data).
The crustacean chelipeds, thus differentiated in size in
otherwise bilaterally symmetrical organisms, provide a
prominent example of asymmetry, which is referred to as
cheliped laterality or handedness (Govind 1989). The
presence of a crusher chela on the right or left side in
many decapod crustaceans and deviation from a 1 : 1 ratio
has been widely reported (table 2). In predatory
Brachyura the presence of the major chela on the right
side facilitates handling of asymmetric hard shelled
molluscan prey, providing a possibility for coevolution of
a predator–prey complex (Abbay-Kalio and Warner 1989;
Seed and Hughes 1995). This concept however becomes
untenable when the handedness changes (Ahmed 1978;
Govind et al 1988). Reversal of handedness from crusher
Table 1. Allometric growth of crustacean chelipeds.
Species Sex Allometric status Source
Arenaeus cribrarius M + Pinheiro and Fransozo 1993
F –
Austropotamobius pallipes M + Grandjean et al 1997
F –
Cleistostoma kuwaitense M + Clayton 1990
F –
Liocarcinus depurator M + Muino et al 1999
F +
Macrophthalmus birtipes F + Barnes 1968
Macrophthalmus setosus F 0
Macrobrachium nobilii M +
F 0 P Mariappan and C Balasunda- ram, unpublished
Macrobrachium rosenbergii M + Nagamine and Knight 1980
Orconectes propinquus M +
Orconectes rusticus M + Garvey and Stein 1993
Orconectes virilis M +
Trapezia ferruginea M + Finney and Abele 1981
F 0
B +
M, Male; F, female; B, berried; +, positive allometry; –, negative allometry; 0, isometry.
Figure 2. Ideal
mechanical advantage (IMA) measurements of
Macropipus depurator chelae (a) strong and (b) fast chela. The
arrows show the direction through which forces F1 and F2 act.
T, Tooth, N, notch (from Warner and Jones 1976).
(a)
(b)
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P. MARIAPPAN ET AL.

to cutter and vice-versa or from pincer claw to snapper
claw, when a chela is lost, has been well documented in
some heterochelous crabs, lobsters, and snapping shrimp
(Wilson 1903; Yamaguchi 1977; Mellon 1981; Govind
1989; Young et al 1994). In other species with plasticity
in chela development into major or minor forms, the esta-
blishment of laterality (handedness) is determined by eco-
logical factors (Davis 1987; Smith and Palmer 1994;
Goldstein and Noetzli 1997), and the reversal of handed-
ness depends on the age of the animal (Cheung 1976).
However, in species where there is no reversal, genetic
factors determine laterality (Bush 1930; Yamaguchi 1977).
Apart from functional differences, structural variations
between crusher and cutter also have been elucidated
(Ogonowski and Lang 1979; Ogonowski et al 1980).
After autotomy, the resultant changes in the composition
of chela muscles at the time of chela development,
reversal, and regeneration are well documented in lob-
sters (Homarus americanus), and snapping shrimp
Alpheus heterochaelis (Stephens and Mellon 1979;
Mellon and Stephens 1980; Govind and Lang 1981;
Quigley and Mellon 1984; Govind et al 1987, 1988;
Govind and Pearce 1988a, b, 1994; Govind 1989).
In Gecarcinus lateralis, there is an attendant break-
down in claw muscle protein that occurs at moulting
which allows the reduced claw to be drawn through
the comparatively small foramen at the proximal end
of the propus (Skinner 1966; Mykels and Skinner
1981).
Sexual dimorphism in cheliped size has also been esta-
blished in crabs (Crothers 1967), lobsters and crayfish
(Snedden 1990), mantis shrimp (Schuster and Caldwell
1989), snapping shrimp (Read and Govind 1997), and
freshwater prawns (Mariappan and Balasundaram 1997).
Generally such a dimorphism between a cheliped pair
(Darby 1934) is mainly based on size rather than form
(Lee 1995) and when adjusted for size variations their
functions are similar as in Ozius verreauzii (Hughes
1989). However in Alpheus heterochaelis the male pincer
claw really differs in form from that of the female struc-
turally (Read and Govind 1997). The development of a
dimorphic pattern begins at the time of puberty moult
(Hartnoll 1974; Pinheiro and Fransozo 1993, 1998),
which is a prerequisite for functional sexual maturity (see
e.g. Hyas lyratus, Stevens et al 1993). In some decapods
the attainment of puberty moult is identified by the level
of change in propodus length (e.g. Nephrops norvegicus,
Farmer 1974). Differences in chela allometry are used to
Table 2. Handedness in decapod crustaceans.
Species Handedness Source
Calappa philargius R Ng and Tan 1985
Callinectes sapidus R Hamilton et al 1976
Carcinus maenas R Abby-Kalio and Warner 1989
Glabropilumnus laevimanus R Tweedie 1950
Globopilumnus globosus R Tweedie 1950
Heteropanope glabra R Tweedie 1950
Heterozius rotundifrons R Jones 1978
Macrobrachium nobilii R Mariappan and Balasundaram 1997
Menippe mercenaria R Cheung 1976
Necora puber R Norman and Jones 1991
Neopanope texana R Swartz 1972
Pilumnus hirtellus R Tweedie 1950
Uca lactea R Yamaguchi 1973, 1977
Uca vocans R Barnwell 1982
Uca tetragonon R Barnwell 1982
Uca formosensis R Barnwell 1982
Ocypode gaudichaudii L Trott 1987
Synalpheus brevicarpus L Herrick 1911
Alpheus dentipes – Dawes 1934
Alpheus heterochaelis – Young et al 1994
Chlorodopsis melanochira – Tweedie 1950
Homarus americanus – Herrick 1911
Macrobrachium australe – Davis 1987
Nephrops norvegicus – Farmer 1974
Ocypode quadrata – Haley 1969
Thalassina anomala – Pillai 1990
Uca formosensis – Shih et al 1999
Xantho exartus – Tweedie 1950
R, Right handed; L, left handed; –, equal distribution of right and left handed animals.
4
P. MARIAPPAN ET AL.

differentiate immature from mature phases in Pagurus
prideauxi (Paulian 1936). Factors like feeding, mate-
guarding, and fighting influence the development of such
dimorphic patterns of chelipeds (Vermeij 1977; Hughes
1989). Parasites exert a remarkable negative effect on the
growth of chelipeds in various crustaceans. Bopyrids,
entoniscids and sacculinids are the common parasites
known to affect the normal growth of chelipeds. Infection
of a bopyrid Gyge branchialis on Upogebia littoralis and
Probopyrus pandalicola on Palaemonetes, Ione thoracica
on Callianassa laticauda, an entoniscid Entonella mono-
ensis and a sacculinid Sacculina polygenea on Hemigrap-
sus sanguinesus showed a significant reduction of chela
size when compared to uninfected forms (Tucker 1930;
Reverberi 1943; Morris 1948; Hartnoll 1960; Yamaguchi
and Aratake 1997).
In Macrobrachium rosenbergii the development of
polymorphic males is common in natural as well as com-
munally cultured populations. These males are differenti-
ated into (i) small males (SM), with delicate, clear or light
pink claws and with a low ratio of claw to body length
and much smaller than the other two morphotypes,
(ii) orange-clawed males (OC) with non-spineous, often
orange claws, having a higher claw to body length ratio,
and (iii) blue-clawed males (BC) with blue, spineous
claws and a high ratio of claw to body length. Small males
can transform into blue-clawed males through orange-
clawed forms in the absence of dominant BC males or
when raised in isolation (Ra’anan and Cohen 1985; Kuris
et al 1987). Among mature males of Pisa spp., Jassa fal-
cata and Inachus leptochirus, even within the same age
group there is a remarkable difference in the size and
Table 3. Variations in the percentage of limb loss in field populations of various decapod crustaceans.
Species Category Per cent Source
Atergatis flloridus M 41⋅30 Norman 1995
F 18⋅40
Callinectes sapidus – 24⋅80 Smith 1990a, b
Cancer magister – 25⋅00 Shirley and Shirley 1988
Cancer magister – 45⋅00 Durkin et al 1984
Cancer pagurus M 13⋅20 Bennett 1973
F 9⋅90
Carcinus maenas M 12⋅50 Abello et al 1994
F 7⋅90
Carcinus maenas M* 1⋅70 Sekkelsten 1988
M** 17⋅90
Carcinus maenas M 53⋅30 McVean 1976
F 55⋅00
Chionoecetes bairdi J 34⋅60 Edwards 1972
M 43⋅00
F 23⋅00
Cyrtograpsus angulatus – 80⋅00 Spivak and Politis 1989
Homarus americanus M 44⋅40 Moriyasu et al 1999
F 61⋅30
Homarus americanus – 21⋅00 Estrella and Armstrong 1994
Homarus americanus M 40⋅00 Briggs and Mushacke 1979
F 30⋅20
Macrobrachium nobilii J 10⋅90
M 15⋅22 Mariappan and Balasundaram 1999b
F 22⋅30
Necora puber J 23⋅00 Norman and Jones 1991
M 32⋅80
F 28⋅80
Nephrops norvegicus M 62⋅00 Chapman and Rice 1971
F 41⋅00
Panulirus argus – 40⋅30 Davis 1981
Paralithodes camtschatica J 29⋅40 Edwards 1972
– 14⋅80
Paralithodes camtschatica M 15⋅30 Niwa and Kurata 1964
F 19⋅50
J, Juveniles; M, males; F, females; –, not categorised.
Carapace width: *20–34⋅9, **65–79⋅9 mm.
5
P. MARIAPPAN ET AL.

shape of the chela (Sexton and Reid 1951; Hartnoll 1963).
Season-induced cyclic changes in chela polymorphism has
been reported in males of Orconectes propinquus (Stein
1976).
3. Autotomy
Autotomy refers to a reflex severance of one or more
limbs in response to injury or its threat, which occurs al-
ways in a predetermined breakage plane (Wood and
Wood 1932; Robinson et al 1970; McVean 1982). A
number of factors contribute to the prevalence of auto-
tomy, which has been extensively studied and reviewed
from time to time (Wood and Wood 1932; Bliss 1960;
McVean 1982; Juanes and Smith 1995). Crustaceans
widely practice self amputation of one or more limbs dur-
ing inter- and intraspecific competition for limited re-
sources like food, shelter, mate and also as a strategy
to avoid predation and wound limitation (Wood and
Wood 1932; Bliss 1960; McVean 1982). Apart from such
biological reasons, commercial factors like intentional
harvesting of chelipeds in species like Menippe merce-
naria (Savage and Sullivan 1978), incidental damage by
fishing gear (Kirkwood and Brown 1998), and culling of
undesirable individuals (Kennelly et al 1990) are also
responsible for the loss of chelipeds. In the polymorphic
male population of M. rosenbergii, cheliped loss is a
periodic event among the dominant blue-clawed males
(bulls) on attaining a critical value of 1 : 2⋅8 ± 0⋅18 body
length/chela length as a growth strategy (Schmalbach
et al 1984). Males of M. nobilii (28%) (carapace length:
1⋅6–2⋅5 cm) resort to chela autotomy during exuviation
even when reared individually under ideal laboratory
conditions (Mariappan and Balasundaram 1999a); even
multiple limb autotomy occurs in M. malcolmsonii in the
field (P Mariappan and C Balasundaram, unpublished data).
The limb loss varies from species to species (1⋅7% in
Carcinus maenas, Sekkelsten 1988; 80% in Cyrtograpsus
angulatus, Spivak and Politis 1989), within a species (C.
maenas, 1⋅7%, Sekkelsten 1988; 55%, McVean 1976)
and as a function of size within a species (Necora puber,
12% in juveniles and 38% in adults, Norman and Jones
1991) (table 3). To a certain extent temporal and geo-
graphic variations also contribute to autotomy in a given
population (Shirley and Shirley 1988; Smith 1990a).
Though the autotomised animals get immediate advantage
in terms of survival, in the long term the need to divert
body resources for regeneration has an adverse effect on
the regular energy budget. Further the injured animal
becomes less dominant and remains more vulnerable to
further attacks in a community; autotomy also limits its
access to shelter, food gathering potential, and its abi-
lity to find a mate (Kuris and Mager 1975; Sekkelsten
1988; Davenport et al 1992; Abello et al 1994; Smith
1995).
4. Regeneration
Crustaceans have the ability to replace lost limbs by
means of regeneration, which is linked with moulting
(Prizbram 1901; Bliss 1960; Skinner 1985). However,
at any given time, in a wild population of Cancer magis-
ter the proportion of animals with regenerating limbs
(5%) is comparatively lower than that of animals with lost
limbs (18%) (Shirley and Shirley 1988), suggesting an
increased vulnerability of autotomised animals to preda-
tion (McVean and Findlay 1979). In some species the
process of limb regeneration affects the moult increment
and moult interval but in others no such effect has been
reported (Smith 1990b; Spivak 1990; Cheng and Chang
1993). Regeneration of a lost limb to its original size
depends upon age and time of loss in a given moult
cycle. Normally the lost limb regenerates within 2–3
moults, faster in juveniles than in adults (Skinner 1985;
Smith 1990b).
5. Abnormalities in chelipeds
Abnormalities or malformation of chelipeds have been
reported widely in various decapod crustaceans like lob-
ster (Homarus americanus, Faxon 1881; H. gammarus
and Nephrops norvegicus, cf. Shelton et al 1981), crayfish
(Procambarus clarkii, Chokki and Ishihara 1994; Naka-
tani et al 1997), crab (Geryon affinis granulatus, Oka-
moto 1991; Macrophthalmus japonicus, Suzuki 1963),
and the Japanese edible crab (Chionectes japonicus, Mo-
toh 1971). Most of these claw abnormalities are mainly due
to a lateral outgrowth in the propodus, which results es-
pecially from abnormal wound healing following the
damage of the propodus (Okamoto 1991; Nakatani et al
1992); this phenomenon could also be induced in the
laboratory (Murayama et al 1994; Nakatani and Kitahara
1999).
6. Cheliped display
Communication in crustaceans often involves the display
of antennae and chelipeds. The roles of the chelipeds in
agonistic and aggressive interactions during inter- and
intraspecific competition for a limited resource is well
documented in the literature (Hazlett 1972; Salmon and
Hyatt 1983). The possession of chelipeds plays a major
role in acquisition and retention of shelters in Homarus
americanus (O’Neill and Cobb 1979) and Macrobrachium
nobilii (Balasundaram and Mariappan 1998). Different
6
P. MARIAPPAN ET AL.

kinds of acts or movements for cheliped presentation have
been reported in various crustaceans (Liocarcinus depura-
tor and Necora puber, Huntingford et al 1995; H. ameri-
canus, Atema and Cobb 1980; Macrobrachium
rosenbergii, Barki et al 1991; M. australiense, Lee and
Fielder 1983). A detailed account of the use of chelipeds
in communication is provided by Salmon and Hyatt
(1983). Cheliped extension, meral spread, strike, lifting of
claw, scissoring, thrust, cheliped striking, embrace, nip
and push are the major events mediated by chelipeds
(table 4 and figure 3).
7. Courtship and mating
The role of chelipeds in courtship display and the pres-
ence of chelipeds as an aid in mate access have been
extensively studied. In Uca pugilator there is a marked diffe-
rence in display patterns between mature and immature
males (Salmon et al 1978). Since chelae have a
major role in displays during agonistic interactions, the
degree of dominance is expressed by the type of chela
morphometry. An animal with robust chelae has easy
access to mates during inter-male competition and also
through sexual selection by females. Autotomy also plays
a crucial role in mating since such handicaps lead to a
negative effect on mate access as observed in small and
medium sized males of Carcinus maenas (Sekkelsten
1988). Variations in mating and reproductive patterns are
observed among polymorphic males of Macrobrachium
rosenbergii. The dominant blue-clawed males (bulls, BC
males) effectively court and protect mates (Ra’anan and
Sagi 1985), while intermediate males (OC males) show
reduced reproductive activity in the presence of BC males
(Ra’anan and Cohen 1985). Submissive small males are
also sexually less competent, but mate successfully in the
absence of BC and OC males (Sagi 1984).
8. Implications of chelae for decapod culture
In communal culture of crustaceans, the possession of
large crusher chelae triggers aggression between individu-
als leading to physical damage of body parts (especially
chelipeds) aggravating the rate of limb loss and mortality.
Indeed chelipeds constitute 10–26% of the body weight in
Table 4. Cheliped mediated displays in decapod crustaceans.
Act Description
Cheliped extension2,3,5,6 Extension of chelae towards the opponent without contact
Cheliped presentation2 Ambulatory legs in walking position and both chelipeds in
presentation position
Cheliped shaking3,5 Rapid oscillations of the dactyls while (without touching
propodus) the claw is partly extended in the direction of
another prawn
Complete lifting3,5 Lifting of the claws and anterior part of the body towards
another individual
Incomplete lifting3 Similar to complete lifting, but the claws remain in the hori-
zontal plane
Crouching6 Chelipeds are folded tightly against the body
Fending6 Outward swinging of one or both chelipeds
Grasping1,6 Seizing of another individual with thoracic appendages 3–5
Meral spread1,3 Outward spreading of the enlarged meri of the appendages
Nip3,4 One animal closes down the tips of its chelae on a body part
of another animal
Push3,4,5
One animal pushes one of its chelae against a body part of
another animal
Shielding6 Holding the chelipeds like a shield
Strike1,3 A blow delivered by one individual to another with the dac-
tyls of one or both raptorial appendages
Scissoring3,5,6 Bringing the two claws together from the complete lifting
position in a scissoring motion
Thrust3 Rapid simultaneous opening of the two claws in the direc-
tion of another prawn
Sources: 1) Dingle 1969, 2) Hazlett and Bossert 1965, 3) Barki et al 1991, 4) Peebles
1979, 5) Lee and Fielder 1983, 6) Jachowski 1974.
7
P. MARIAPPAN ET AL.

Figure 3. Agonistic acts in decapod crustaceans (Jachowski 1974; Barki et al 1991).
8
P. MARIAPPAN ET AL.

Macrobrachium nobilii (Mariappan and Balasundaram
1999a), 20% in Carcinus maenas and Liocarcinus hol-
satus (Lee and Seed 1992), and 50% in Menippe merce-
naria (Simonson and Steele 1981). In H. americanus, the
possession of the crusher claw is essential for acquisition
of limited resources, as well as establishment and mainte-
nance of dominance hierarchies (O’Neill and Cobb 1979).
In such cases the autotomised animal becomes subjugated
and more subordinated during further attacks. In C.
sapidus, the loss of chelipeds was shown to have not only
a negative effect on foraging ability and prey handling
time (Juanes and Hartwick 1990; Smith and Hines 1991),
but also the incumbent has to channelise more metabolic
energy for the regeneration of chelipeds. Thus in species
like Callinectes sapidus (Ary et al 1987; Smith 1990b),
the loss of chelipeds leads to a reduction in moult incre-
ment due to energy diversion; such energy demand is
called regeneration load (Skinner 1985), which may
reduce reproductive output (Norman and Jones 1993;
Luppi et al 1997). Chelotomy, dactylotomy and immobi-
lisation of the dactyls have been shown to reduce the
degree of cannibalism in H. americanus (Kendall et al
1982) and in M. rosenbergii (Karplus et al 1989; Diaz
et al 1990). However the decreased survival rate due to
forced severance of limbs and subsequent regeneration are
major constraints that reduce the harvest size (Powell et al
1998).
9. Conclusion
Though autotomy, moulting and regeneration of chelipeds
have been reviewed periodically, a collective perusal of
literature attempted in this review reveals that the diverse
functional and structural modifications of chelipeds are
not only influenced by feeding and locomotion patterns,
but also by environmental conditions and species-specific
needs. A number of biotic and abiotic factors influence
the development of chelae. The chelae are most vulnera-
ble to autotomy and their regeneration imposes a regene-
ration load in the regular energy budget of the animal
resulting in a telling effect on the other regular somatic
and reproductive processes. In aquaculture experimental
removal of chelae minimizes aggressive interactions but
the problem is recurrent due to regeneration potential and
hence is of limited applicability. Since it takes more than
one moult for total regeneration of the chelae, their use as
a taxonomic character is doubtful.
Acknowledgements
Financial assistance from the Council of Scientific and
Industrial Research, New Delhi, to PM in the form of a
Senior Research Fellowship and University Grants Com-
mission, New Delhi, to CB in the form of a major research
project is gratefully acknowledged. Thanks are also due to
Dr S Prem Mathi Maran, Chennai, for line drawings.
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