RESEARCH，NO. 35: 79-91，2006 79

Decorating behaviorof the majid H y astenus diacαnthus

Takao Yamaguchi，Hiroshi Honda，Hisamichi Aratake and Yasuhisa Henmi

Abstract. - The decorating behavior Halimus dicanthus (De Haao) (=均1α stenus of 17 newly molted individuals of the diacanthus) had sponges，barnacles and m 吋id crab Hyαstenus diαc α nthus (De sometimes bryozoao 00 its carapace. The Haan，1837) was recorded on VTR. The crab attached hydroids，spooges ，brγozoao s， attached various living materials compouod ascidians ，aod piecesof algae to hooked setae on the carapace and ooto its carapace and walkiog legs ，except walking legs after careful selection by for the tips of the chela of the cheliped the chelae and processing with the (Yamaguchi et al. ，uopublished). It was ve庁 mouthparts. The crabs used chelipeds di 血cult to fiod well-decorated crabs io oa胞子 in a fixed way in the attachment al habitats.The compositioo of attached process. Except for the horn and spots materials depeoded 00 habitat cooditioos. on the carapace，the crabs attached 羽市 ere sponges were abuodaot，the crabs materials using the chelipeds of the covered their bodies with sponges，aod in opposite side. Newly molted crabs had locatiooswhere compouod ascidiaos were almost finished attachment within 2 domioaot，the crabs attached them to their hours，but the crabs continued to work bodies. Although H. di αcanthus rarely deco- sporadically for another 1or 2hours. rated themselves with algae，the crabs used The average frequency of attachments pieces of algae io habitats where inverte- was 91 (N =7). The hooked setae cover brate materials were scarce，but they were only aportion of the body，and other usually covered with spooges，feathery areas，except for the tips of the chelae， hydroids，or compound ascidiaos. are covered with barbed setae. The Wicksteo (1975，1979 ，1980 ，1993) coo- barbed setae hold the materials，which ducted detail edobservatioos 00 the decorat- grow outside of the hooked setae sites. iog behavior of majid crabs，and showed the The crabs were indifferent to the set- sequence of decoratioo. The crabs attach a tlement of larvae of sessile ， piece of material to the carapace or walkiog such as barnacles，and did not remove legs .Rows of hooked setae occur 00 the them. Consequently，portions of the carapace aod walkiog legs and the crabs rub crabs were covered with sessile ani- the piece agaiost the rows usiog its chelae. mals. The slender setae on the dactyl of めlast enus diacanthus occurs io the lower walking legs and the short setae in the iotertidal shores aod shallow sea bottom of pits of chelae are likely sensory organs ]apao aod the adjaceot seas toward Australia to detect suitable materials for attach- (Miyake，1983). Our objective is to deter- ment. mine how H. di αcanthus decorated them- selves ，bas ed 00 the video recordiog of th e decoratiog behavior of oewly molted crabs lntroduction and observatioo of setae 00 carapaceaod Sakai (1965) mentiooed that the majid walkiog legs by scanoiog electroo crab 均lastenus diacanthus planted hydroids mlcroscopy. 00 its body. Dudgeon (1980) reported 80 T. YAMAGUCHI ETAL

Materials and Methods Results

The crabs used in the video recording Distributio 汎 ofsetαe were obtained by dredging ashallow subti- Rows of hooked setae occur on the divid- dal area with depths of 5to 15 m in the vicin- ed large rostrum (Fig. 1). A long row of ity of the Aitsu Marine Station ，Kumamoto hooked setae is present on the dorsal sur- University in the Ariake Sea (32 0 31'N， face of the three segments of walking legs ， 130 0 19'E) from April to August 1992. The i.e. ，the manus，carpus ，and merus. In addi- crabs without injuries were put in aquaria tion to the rostrum，portions of the carapace and were given pieces of sliced fresh sardine are covered with hooked setae. Thehooked as food. Thenewly molted crabs were trans- setae on the walking legs are in asingle row ferred to another aquarium and kept until as shown in Fig. 2A. Thesetae have afish- their bodies became hard and they were hook shape and are serrated but the se 汀 a- ready to decorate. Video recording was car- tion is shallow and not so conspicuous (Fig. ried out on the newly moulted crab kept in a 2B). On the lateral sides ，the hooked seta small aquarium placed in adark room under has agroove as reported for L. crispatus constant il1 umination. A video camera (Wicksten ，1978). Hooked setae are most attached on atripod was placed in front of well developed at the rostrum. Each of the the aquarium aiming to record not only the horns is covered with setae ，which form two

decorating behavior but also the manipula- double 司 rows as shown in Fig. 2C. Hooked tion at the mouthparts. The video camera setae occur along the anterolateral carapace was connected to adouble-cassette video margins as shown by RC and LC in Fig. 1. In recorder and amonitor television placed out- addition to these locations ，the hooked setae side of the dark room. The recording of a occur at six spots on the carapace as indicat- single crab was carried out for two to five ed by RA，LA ，RB ，LB ，RD ，and LD. Other hours. surfaces of the carapace and walking legs To determine the percentage of crabs are covered with short barbed setae. An with sessile animals such as barnacles，ca Ic i- electron micrograph of the short barbed fied annelid tubes，or tunicates on their bod- setae is shown in Fig. 2D. The setae are ies ，specimens deposited in the Aitsu Marine thick but pointed. About one-third of their Station were examined.τbey were obtained surface is covered with short spines. The without selection in the vicinity of the station barbed setae are found over large areas during the years from 1974 to 1990 and were except for the sites covered with hooked preserved in 75 %ethano l. setae and the chelae of adult males. The Scanning electron microscopy of the abdominal surface of the crab ，where no setaeon the carapace and walking legs was hooked setae occur，is also covered with carried out in 2006. The materials were barbed setae. dehydrated after sonication for 5to 15 sec- onds in 75 %ethanol in agraded ethanol-t- Attaching behavior butanol series and were then freeze-dried. Weobserved the behavior of 17 newly Thedried samples were attached with adhe- molted crabs (8 females and 9males). They sive tape onto ametal stub. After sputter were given stems of featherγhydroids and coating with gold-pal1 adium，they were pieces of sponges. They quickly started examined in a]EOL 5400-LV scanning elec- attaching the given materials and continued tron microscope with an accelerating voltage for 120 to 270 minutes. Crabs had almost fin- of5 KV. ished attachment within 2hours ，but contin- ued to work sporadically for another 1or 2 hours. Some crabs sometimes took apos- ture or aposition di 血cult to know how they DECORATING BYHYASTENUS D lACANTHUS 81

R-l st

Fig. 1. Thedistribution of hooked setae in adult male 均 astenus diacanthus. Thesites are shaded and each is given an abbreviated name.R indicates the right side and Lthe left sid e. were manipulating or attaching the decorat- apparent in the length of walking legs and ing materia 1. Weexduded such crabs and the size of chelae of the cheliped (Fig. 4). the results of seven crabs (4 females and 3 Large males develop wider and longer，mas- males) are presented in Fig. 3.Th eaverage sive chelipeds and longer walking legs and frequency of attachment was 91. 4. However， they usually move slowly. However，we considerable differences were observed could not discern any dear differences in among individuals. Crab F-2 (female) the treatment and attachment of decorating attached 117 times in 186 minutes but M-2 material between large and small crabs. (male) attached only 46 times in 185 min- Crabs attached materials most frequently utes. M-2 was alarge crab，59.7 mmCL to the walking legs. They tended to attach (carapace length including rostrum) ，and materials from the anterior half of the body. had well developed large chelae and moved Seven of the observed 17 crabs started slowly. In larger crabs，sexual dimorphism is attachment at the rostrum. Five others first 82 T 目 YAMAGUCHI ETAL.

Fig. 2. Two kinds of setae occur on the surface of Hyastenus diacanthus. (A): Arow of hooked setae occur on the merus of the right 4th walking Ieg of a44.7-mm CL male.(B): Ahook edseta occurs on the right horn of the rostrum of a36 ふmmCL male. (C): Aphotograph of the right horn of the rostrum of a 38. O- mmCL newly molted female. On the horn，two doublerows of hooked setae occur. This is not an electoronmicrograph but aphotogaph by an ordinarily 35 mmcamera attached with aclose up lens . (D): Barbed setae occur at the posterior fringe of the carapace of a44 .7-mm CL male. attached material onto the 1st walking leg of the mouthparts，the crab rubbed or pushed either side. None of the crabs first attached it onto its body using the chela of either material onto the 2nd to 4th walking legs. side. Usually the attachment was finished in Crabs touched the material using the chela less than half aminute. of the cheliped or the dactyl of walking legs， No specific order was observed in the especially those of the 1st walking legs of attachmen t. Crab F-1 (female) in Fig. 3con- both sides，caught or grasped it using one ducted the first seven attachments in the fol- chela，and carried it to the mouthparts. lowing sequence: 1，carapace ;2 ，carapace; 3， th When the material was large，the crab cut a rostrum; 4，the 4 leg of the right side; 5，the th rd po凶 on of it using two chelipeds. One of the 4 leg of the right side: 6，the 3 leg of the chelae held the material while the crab cut it left side; 7，the 2nd leg of the right side. Crab using the other chela，and then carried it to M-1 (male) conducted attachment as fol- st st the mouth. After processing the material at lows: 1，the 1 leg of the right side; 2，the 1 DECORATING BYHYASTENUS DIACANTHUS 83

120

言 100 ω E z u .M-1 e判 官 80 』 o . F ・1 h z z 60 コo

ωσ』 h .M-2 方 40 百。 コ一 E コ ω 20 《

。 20 40 60 80 100 120 140 Time (minutes) Rostrum いlCa?戸 p仰 陥匂匂ケツ glゆ句ψs (，乍乍芋陥仰欣仇l F下-1川( ♀ ，削41.勾)3 昨 | I(73 times in 270mi川川1n1ut l 川凶Jte阿s幼) 9 18 26 20 F-2 49.6) (♀ ， 圃圃置 窃移勿グA I19 2minutes) 38 43 ω l(107times ln ど F-3 (♀ ，51.3) 園 物 物税物 180 minutes) ω 36 37 u- l (11 7times ln zo F-4 (♀ ，32.0) 園園協括協易協訪w o - ; ] ，' . 186 m inutes) υ 32 偲 28 Z (86 tim es in2 12minut es) d司 M-1 7 17 30

A E 戸 寸 n O匂 C n n H JV H - n d H u v M -2 (♂ ，59.7) 圃 雰弱 点会 ( b t o t ) E m m s 7 8 16 15 ! (100times ln M -3(♂， 44.5) ・・・伝移拐忽捻拾; ; : a 123 minutes) 30 30

Fig. 3. Attachment of decorating materials in sevennewly molted めlastenus diαcanthus crabs. Above， the accumula tedfreq uencies of attachment by thecrabs within a2 0- m inutein terva l. Below，the fre- quency histograms of attachment onto the four portions of the body: rostrum，carapac e，four walkin g legs of the left sid e，and walking legs of the right side.τnesize of the crab(CL ，mm) is shown in the round brackets . 84 T. YAMAGUCHI ETAL.

Fig. 4.Two left chelae of Hyastenus diacanthus underthe same magnification .Adult large males have considerably larger chela than adult females. (A): Chela of a69. 8- mmCL male. 百1e propodus (p ollex and manus) has alength of 35.1 mmand aheight (measured at th ecentral portion of 出e manus) of 13.1 mm. This chela is completely devoid of barbedsetae. (B) :Ch ela of a6 1. 2-mm CL female.Th e propodus has alength of 17.3 mmand ah eight of 2.8 mm. Although th epollex and most of the dactyl are devoid of barbed setae ，the manus is covered with barbed setae . leg of the right side; 3，the 1st leg of the right rating material to the right hom of the ros- side; 4，the right-sided hom of the rostrum; trum，and material was always attached to 5，carapace; 6，carapace; 7，the 1sl leg of the the walking legs of the right or left side by left side. However，crabs did not attach ran- the chela of the opposite side. No exception domly but rather attached evenly on the cho- was observed. However，usage was flexible ， sen sites of the body，where the hooked rather than completely fixed. Weobserved setae occured. Although considerable indi- that amale ，which had lost the left cheliped， vidual differences in attachment frequency could attach decorating material to the 1sl were observed，differences between the leg of the right side ，and LB and LD sites on right and left side of each crab were small the carapace. σa b l e 1). For instance，Crab F-2 attached at the right and left 1' 1 legs，15 and 16 times， Sessile animals respectively. This may indicate that the Many H. diacanthus had sessile animals crabs are able to determine how much mate- such as bamacles on the carapace or walk- rial has been accumulated at each site and ing legs. 羽Te examined atotal of 160 speci- can adjust further attachment accordingly. mens and found that 55 (34 %)had sessile When materials did not attach easily ，the animals attached to them. Of these 55 indi- crabs repeatedly rubbed or pushed them. viduals，33 had bamacles only (Balanus sp.). They ate or discarded material that did not Six crabs had one or two tunicates (Sかela attach. However，the percentage of success- sp.) on the carapace. Ahigher ratio of occur- ful attachments was high. In total ，565 trials rence of sessile animals was observed on in 8females and 456 trials in 9males were large crabs (Fig. 5). In afew crabs，the mass observed. Of those，females succeeded in of the attached animals had become very 503 trials (89 %)and males succeeded in 402 large and almost enguIf ed the crabs. Two 凶 als (88 %). examples are presented in Fig. 6.

Use 01 cheli;抑d Detection 01 decoγα tingmαte γi: αl Thecrabs attached material using apar- When newly molted crabs encountered ticular side of the cheliped (Table 2). Only sponges or feathery hydroids，they quickly the right chela was used for attaching deco- started to decorate. They were indi旺erent to DECORATING BYHYASTENUS DIACANTHUS 85

Table 1.百1e comparison of the frequency of the attachment of the livin gmat erial (a pi ece of sponge or astem of fea th ery hydroid) at right and left sides of th ebody. Seven crabs (4 females and 3males) were examined.η1ecrabs attached th ematerial where the hooked sites occurred.η1e loc atio nof each sit eis shown in Fig. 1. Carapace Walking legs Rostrum A B C D 1" t 2nd 3吋 4th F-1 (Female，4 1. 3mm CL) Right 4 2 2 4 2 7 9 3 7 μift 5 1 2 4 l 8 5 4 4 F-2 (Female，49 .6mm CL) Right 4 。1 7 1 15 7 7 9 μift 7 2 1 7 。 16 11 7 9 F-3 (Female，5 1. 3mm CL) * Right 4 1 2 9 2 。20 6 10 Left 5 1 3 5 2 15 13 9 。 F-4 (Female，32.0 mmCL) Right 5 4 4 13 3 11 7 7 3 Leβ 7 3 4 9 5 11 10 9 2 M-1 (Male ，34 .4 mmCL) Right 3 1 2 3 2 11 10 5 6 Left 4 1 1 5 2 8 10 6 6 M-2 (Male，59.7 mmCL) Right 5 。1 2 1 9 4 。3 μift 2 。1 5 。 5 4 3 3 M-3 (Male ，44.5 mmCL) R ig ht 6 1 2 9 2 11 7 8 4 Left 7 2 2 8 1 11 9 5 5 *Th e1 st walking leg of th eright side and the4 th walking leg of th eleft side are missing.

Table2. 百1e usage of the right and left chelipeds (chelae) in the attachment of 出e decoratingmat erials onthe 9s ites of the right and left sid es of th ebody .Total of 7crabs' trial sare shown here.Th er es ult s of the 1st and fourth walking legs of Crab F-3 are notinclud ed.Th elocation of the four sit es of the carapace iss hown in Fig. 1. Carapace Walking legs Rostrum A B C D 1st 2nd 3吋 4由 Ri ght cheliped Right-side 31 9 14 。13 。。。。 μift-side 。 。。43 。59 62 43 29 Left cheliped Righιsi de 。 。。47 。64 64 36 32 37 10 14 。11 。。。。 artificial materialssuch as small pi eces of thes lender setae.τbey occur in low density fel t. When they were given only artificial only on the dactyl of the walking legs. We material，they decorated the rostrum or cara- suggest that the slender setae are related to pacewith it ，but soon discardedit when liv- thedetection of decorating materia l. Figure ing material was provided. They touched 7shows electron micrographs of the dactyl such material using thechelae of both che- tip of the first walking leg.Th ecrabs catch， lip edsand also the dactyls of the first walk- cut，and carry decorating materials to the in gl egs.τbecrabs havetwo kinds of setae mouthpartsusing the chelae of the two che- on the surface of the body，the hooked and lip eds; however，th ewalking legs，especially barbed setae. In addition to these，the crabs the 1stpair ，help in the detection and holding haveanoth ertype of setae. Wenamed them of materials. When crabs touched sponges 86 T. YAMAGUCHI ETAL.

20 E三; ] with sessile animals (n =27) 10

」 ω 20 30 40 50 60 70 D E Zコ

10 with sessile animals (n = 28)

20 female (n = 81)

30

Fig .5. Siz e- frequency distribution of 160 specimens of Hyastenus diacanthus obtained in the vicinity of the Aitsu Marine Station ，Kumamoto University ，from 1974 to 1990. H atched and dotted bars show the number of specimens with sessil eanima lssuch as barnac1 es orsolitary tunicates attached.

or hydroids with the dactyls of their walking should becut into pi eces bythe chelae. legs，出 ey held them using the walking legs， Figures 8A and8C show that the chela isan 加 d then beganhandlin gthem as decorating id ealshap efor use as apair of sCIssors. materials. Detection of decorating materials is also achieved usingthe chela of the cheliped. Discussion Several round depressions occur on the Wicksten (1979) examined the decorat- dactyl and poll ex on both sides of the chela e， in gb ehavior of Loxorhynchus crispatus and which contain several short setae (Fig. 8) .It L. grandis. Shereported that before the is very important for decorating crabs to attachment the crabsmanipulate the materi- detect and select suitabl emat erial s; there- al at the mouthparts，then took the rough- fore ，the crabs should possess asensory ened piece of it byone of the chelae and rub organ that can detect the presenceof such it against an area of th es hell covered with material s. Depressions of the outer surface hookedsetae. Woods & McLay (1994b) contain about ten short seta e(Fig. 8B). It is studied the decorating behavior of the m 司id likelythat the setae in the depressionscon- crab Notomithrax ursus. The crab carefully tribute to the detection of decorating materi- selected asingle piece of algae and trans- als. In addition to detecting suitabledecorat- ferredit to the mouthparts. At the mouth- ing materials ，th ecrabs have to render them parts，the fragment was cut，and the end of suitablefo rattachmen t. Large-sized material the piece was roughenedand trimmed of DECORATING BYHYASTENUS DIACANTHUS 87

Fig. 6. Two specimensof Hyast enus dia canthus ，h eavily attached with sessi leanimals. (A): Abdominal view of a38. 6- mmCL female. Al arge m ass of bryozoa cover the entire dorsalsurface and it was impos- sib leto see the crab from the dorsal side. (B): A43.1-mm CL female. Alarg emass of barnacles is attached to its carapace. Except for the right 3rd walking leg，th eother legs were devoid of barnacles， and 出is femaleh ad no di 血culty moving.

st Fig. 7. Electron micrographs of the dactyl of the left 1 walkin gl eg of a44.7 ・mmCL maleHyast en ω diacanthus. Beside numerous bar bed setae ，slender se ta eoccur in low density on the unders id eof the dacty l. (B): Severalsl ender setae are shown in this enlar ged photograph.

any projections. Then it was tr ansferredto a attachment of th emat erials well agree with part of the body. Woods & Page (1999) those of H. diacanthus. However，no expla- examinedanother majid crab，ThacanoPh ηs nation was given on th erole of the barbed βlholi ，a nd reported that the used setae.Wicksten (1980) m entionedth epres- chelipeds to cut or wrench api ece of sponge enceof such setae，but no further explana- from the original mass. Following the pro- tion was added. In H. diacanthus，the barbed cessing of the spongeby th emouthparts ，a setae play an important role in decoration. single cheliped was usedto rub the pieceof As shown in Fig.1 ，the hooked setae cover spongeagainst the hookedsetae at the cho- only asmall portion of thecarapace and sen site of attachmen t. These observations walking legs of crabs，but the entire surface on the procedureof the manipulation and of well-decorated crabs is completely cov- 88 T. YAMAGUCHI ETAL

Fig.8. Elec甘on micrographsof th echelae of 均lastenus diacanthus. (A): Outer surface of the chela of a 48.3-mm CL male. (B): An enl argedphotograph of th epit soccurring on theda cty lsho wn in A. (C): Inn ersurfa ce of the chela of a39 .4 -mm CLmale. ered with sponges or compound ascidians (1980) showed that th ecarapace ，cheliped with no areas undecorated. It appears impos- and walking legs of Oregoniαgrα，cilis are sible to attach decorating materials without covered with decorating material but the help of barbed setae. Podochela hemρhilli has hookedsetae with τb e range of distribution of hooked setae an interval on the walking leg. Juvenile is greatly different by the species. Wicksten Pugettia troducta possesses two rows of DECORATING BYHYASTENUS DIACANTHUS 89 paired hooked setae on the upper rostral between adult males and females suggest surface and attaches algae but in the adult that the chelae of males of H. diacanthus crabs these setae are lost and the crabs lose have an alternate function than that of atool these ability to decorate (Mastro，1981). for use in decoration. They are likely to be Dudgeon (1980) examined the decorat- important in sexual display to attract ing behavior of 10 majid crab species females. obtained from the sea northeast to east of Woods &Mc Lay(1994a) studied the uti- Hong Kong. He reported that neither of 10 lization of attached algae as food in species including H. di αcanthus had decorat- Notomithrax ursus and reported that the ing materials on the cheliped. In the present daily consumption of attached algae was 2.8 study，newly molted crabs of H. diacanthus %under conditions in which an alternative did not attach materials onto the cheliped. source of food was available. Cruz-Rivera However，well-decorated individuals had (2000) examined how three Mediterranean sponges，hydroids ，or compound ascidians majid crabs used algae in decoration. He on the cheliped as well as on the walking reported that the attachment of algae had lit- legs. tle value as storage of food. 九九 Ticksten (1975) Weobserved that many H. diacanthus reported that newly molted individuals of had sessile animals such as barnacles Loxorhynchus crispatus removed the decorat- attached to the carapace or walking legs. It ing materials from the exuvia of newly molt- is unlikely that the crabs attached such ani- ed individuals. Weobserved that in H. dia- mals by themselves. Wesuηnise that the lar- canthus，the crabs ate attached materials vae of sessile animals settled onto the sur- when they were not given food. The face of the crabs and grew before the crab attached sponges and hydroids gradually had molted. According to Dudgeon (1980) disappeared from the surface of the exam- the decoration comprises two independent ined crabs. 百le decoration of H. diacanthus components. The first ，and major，compo- has afunction of food storage. However，in nent is material attached to the hooked setae the natural habitat，individuals of H. diacan- by the crab itself. Thesecond is the accep- thus were usually surrounded by plenty of tance of various kinds of organisms.This decorating materials (Yamaguchi et al. ， passive process involves the non-removal of unpublished) . foreign bodies sett1 ing on the carapace. Wicksten (1979) reported that for L. Sessi1 eanimals occurred at ahigher ratio on crispatus and Loxorhynchus grandis，the ros- large crabs of H. diacanthus (Fig. 5). Such trum is decorated before the other parts of individuals molt less frequently than smaller the crab. In H. di 町 anthus，the decoration of individuals; therefore，larval settlement can the rostrum was not given priority as in L. occur over alonger period of time. It is crispatus. Of 17 newly molted H. diacanthus unc1 ear that the two crabs shown in Fig. 6 crabs，7 first attached decorating material to were in acondition of the terminal anecdysis the rostrum，but the decoration of the ros- because they were not the largest but medi- trum was not 自nished quickly. Theaverage um-sized females (see Fig. 5). time needed to accomplish attachment to Allfemales and small males of H. diacan- the rostrum in the seven crabs (Fig. 3) was thus have barbed setae on the pollex of the 99 minutes. Such interspecific differences chelae as shown in Fig. 4B. However，the might be related to the structure of the ros- chelae of large males are very large com- trum. In H. di αcanthus，the rostrum is large pared to those of females and are completely and divided into two horns. devoid of barbed setae as shown in Fig. 4A. Woods & Page (1999) described how the Wehave not yet observed the courting cheliped was moved in the decoration of behavior of H. diacanthus but the size and 7為αcanophrys βlholi. Each cheliped masked morphological differences of the chelae its half of the carapace and the branchial 90 T 目 YAMAGUCHI ETAL region on the opposite side of the carapace， perfectly." Crabs must either move to where as well as the walking legs on the opposite the color and texture of their decoration side of the body. ThacanoPhηs β lholi has a matches the background or they must deco- relatively larger and longer cheliped com- rate to match their background. Their dis- pared to H. diacanthus，but no difference cussion indicates that H. diacanthus is agen - was observed in the usage of the cheliped in eralist species. It attaches living decorative attaching decorating materials between materials，which are easil yavailable in the these two species. habitat，to make it di血cult for the crabs to Wesuggested that the slender setae befound by predators. Thanh et al. (2003) occurring on the dactyl of the walking legs experimentall ystudied the di 宜erence of sur- might be adetecting apparatus of the deco- vivalrates of the decorated and non-decorat- rating material. Hamilton et al. (1985) edindividual sof the majid crab，Tiarinia reported that the plate setae of the dactyls of cornigera ，released in an intertidal poo l. the kelp crab Pugettia producta，are τb e y confirmed that the survivalrate of the chemosensitive. Schmidt & Gnatzy (1989) decorated crabswas significantly hi gher studied the chemosensory cells of the fun- than that of non-decorated crabs. nel-canal organs on the dactyls of Carcinus maenas and concluded that the organ served agustatory function. Theshape and appear- Literature Cited ance of these structures are veηrdifferent Cruz- Ri vera ，E. ，2000. Generality and specificity in from the slender setae. Presence of the feed in gand decoration preferences of chemoreceptors on the feeding chelae of the three Mediterranean crabs. Marine Biology， 137: 70 714. fiddler crab Ucαpugilator was reported by 5- Dudgeon，0. ，1980. Some inter- and intraspecific Robertson et al. (1981). Weissburg et al. differences in the decorating pattems of majid (1996) examined the feeding chela of two crabs (Crustacea: ) 仕omthe coastal fiddler crabs，U. ρugilator and U. ρugnax，by waters of Hong Kong. 1n: Morton，B. S.，& SEM and found that the claw contained a Tseng，C. K. (eds .)，Proceedings of the first large number of small pit-type structures at International Marine Biological Workshop: the tip and suggested the structures were TheMarine Flora and Fauna of Hong Kong and Southern China，Hong Kong，1980: the chemosensory organ. Thepit 匂 pe st ruc- 82 5-835 .Hong Kong University Press ，Hong tures occur on the surface of the chela not Kong. on the setae.Not only behavioral but also Hamilton，R. A.， Linberg，K. A. & Case，]. F. ， anatomical st udies are needed to know the 1985. Structure of dactyl sensilla in the kelp function of the slender setae and the setae crab ， Pugettia producta. ]ournal of located in the pits of the present species. Morphology，183: 349-366. Sato & Wada (2000) discussed the func- Mastro，E. ，198 1. Algal preferences for decoration by the Cali fomian kelp crab ，Pugettia ρroduc- tion of decoration. Themain function of dec- ta (Randall) (Decapoda， Majidae). orating in spider crabs has been considered Cructaceana，4 1: 64-70. to be camouflage. Di旺erent tactics to pro- Miyake，S. 1983. ]apanese crustacean decapods duce the e宜.ect of camouflage can be hypoth- and stomatopods in co lor ，II. pp. i-viii ，pp. esized between generali sts and specialists in 1-277，plates 1-64. Hoikusha，Osaka. (I n resource utilization patterns for decoration. ]apanese) & Thetactic for ageneralist is “to look less like Robertson ，]. R.， Fudge，]. A. Vermeer，G. K.， 198 1. Chemicaland live feeding stimulants of acrab ."In this case，crabs need to attach the sand fiddler crab ，Uca tugilator (Bosc) . large amounts of decoration to themselves ]ournal of ExperimentalMarine Biology and in order to blur their outlines and not be rec- Ecology，53: 47-64. ognized by predators as prey. 1n contrast， Sakai，T. ，1965. The crabs of Sagami Bay. pp the tactic for aspecia li st is “to match th e i-xvi ，pp. 1-20，plates ，1-100 ，pp. 1-92 ，pp. decoration of the crab to the background 1-32 ，1 map .Maruzen ，Tokyo. DECORATING BYHYASTENUS DIACANTHUS 91

Sato，M. ，& Wada，K.， 2000. Resource utilization American ，242: 11 6-122. for decorating in three int ertidalmajid crabs 一一一一 ，1993. Areview and amod elof decorati ng (Brachyura: Majidae). Marine Biology，137: behavior in spider crabs (Decapoda， 705-714. Brachyura，Majidae). Crustaceana，64: Schmidt，M .& Gnatzy，W .，1989 .Specificity and 314-325. response characteristics of gustatory sensilla Woods，C. M. c.， & McLay，C. L. ，1994a. Use of (funnel-canal organ) on the dactyl of the camouflage materialsas afood stored by th e shore crab，Carcinus maenas (Crustacea， spid er crab Notomithrax ursus (Brachyura: Decapoda). Journal of Comparative Majidae). New Zealand Journal of Marineand Physiology A， 166: 227-242. Freshwater Research，28: 97-104. Thanh，P. D .，Wada ，K. ，Sato ，M. &Shirayama ，Y .， 一一一一 ，& 一一一一 ，1994b.Masking and ingestion 2003. D ecorating behaviour bythe majid crab preferences of th espider crab Notomithrax Tiarinia corrigera as protection against preda- ursus (Brachyura:Majida e) .N ew Zealand tors. Journal of th e Marine Biological Journal of Marineand FreshwaterRes earch， Association of th eUnited Kingdom，83: 28: 105-11 1. 1235-1237. 一一一一 ，& Page，M. ].， 1999. Sponge masking and Weissburg，M. J. ，P earce，]. ，Govind ，C. K. & related preferences in the spider crab Derby，C. D .，1996 .Sexually dimorphic pat- ThacanoPhrys filholi (Brachyura: Majidae). terns of neural organization in the feeding Marine and Freshwater R esearch，5 0: appendages of fiddler crabs. Cell & Tiss ue 135-143. Research，286: 155-166. Wicksten，M .K.， 1975.Obs ervations on decorat- ing behavior following molting in Loxorhychus Addresses: (TY) Obiyama， 5-36-71 ， crispatus Stimpson (Decapoda，Majida e). Kumamoto 862・0924，Japan;(HH) Jyouka 9-1 8， Crustaceana，29: 31 5-316 Hondo，Amakusa ，863-0016 ，J apan; (HA) ， 一一一一， 1978.Attachment of decorating materials Tunehisa，6143-35 ，Miyazaki ，880-0916 ，Japan ; in Loxorhynchus crispatus (Brachyura， (YH) Aitsu Marine Station ，Center for Marine Majidae).Transcripts of the American Environment Studies，Kumamoto University， Microscopical Society，97: 217-220. Matsushima，Ka mi-Amakusa 861-6102，]apan 一一一一 ， 1979. Decorating behavior in E-mails:(TY) [email protected]; Loxorhynchus crispatus Stimpson and (HH) hrshonda@ mx7l.t iki.ne.jp ;(HA) ararin@ Loxorhynchus grandis Stimpson (Brachyura， miyazaki-catv.ne.jp; (YH) [email protected] Majidae). Crustaceana，Supp l. 5: 37-46. u.ac. JP 一一一一 ，1980. Decorator crabs. Scientific