CRUSTACEAN RESEARCH，NO .29: 143-151，2000

Redescription of the megalopa of dentipes (Brachyura: ) from Japan

Juan Ignacio Gonzalez-Gordillo，Shinji Tsuchida，and Christoph D. Schubart

Abstract.-Several megalopae of the ing found in the southern hemisphere， plagusiid Plαgusia dentipes were while P .dentipes de Haan，1835 is the collected 企・ omTateyama at the Pacific only temperate representative of the coast of Japan. The comparison of these northern hemisphere. specimens with previous descriptions of Two species of Plαgusiαa r e known this stage fr ・omJapan，revealed alack of from Japanese waters，Pl α:gusiαdentipes detail in the earlier morphological ac・ and P. squamosα( t h e latter as P . counts. Therefore，the megalopal stage of tuberculatα; see Sakai，1976 ;Miyake ， Plαgusia dentipes is redescribed and 1983). While the occurrence of P .squa- once again illustrated. The new set of mosαi n Japan is r訂 e，P. dentipes is very morphological characters for this stage is common along the Japanese coasts. used for adetailed comparison with Tsuchida and Watanabe (1997)give ade “ other known megalopae of the genus tailed account on growth and reproduc- Plagusiα. The results allow preliminary tion of P .dentipes .Previously ，Watanabe conclusions on phylogenetic relation- et α1.(1 992)reported on the daily settle- ships within this genus of rafting . ment of megalopae of this crab species and the influence of environmental fac- tors .Larval and juvenile stages of P. Introduction dentipes have been known for more than In the most recent revision of the ge- 60 years and were already mentioned by nus Plagusiα，Dawson (1987) recognizes Aikawa (1936，1937). Zoeal stages were eight species (or subspecies) and provides later described by Terada (1 987). Ohtake akey for their identification.Of these spe- (1963) gives a brief account on the cies ，only one，P. depressα( F a b r i c i u s ， megalopa and the first juvenile stage， 1775)，is restricted to the Atlantic，while while Muraoka (1 963) only published the other seven species form part of the morphological details of sexual characters marine coastal fauna ofthe Indo-Pacific. from the megalopa and first two crab Thespecies-specific distribution is mainly stages. All of these descriptions are in determined by climatic regions.Most of Japanese. the species are predominant along tropi- In recent years，larval and postlarval cal coastlines: i.e. P .immacul αt α morphology became increasingly impor- Lamarck，1818 ，P . integripes Garth，1973 ， tant for systematic and phylogenetic P. speciosa Dana，1852 ，and P. squamosα studies (e.g. Rice，1980; Felder et αl. ， (Herbst，1790) (t he latter being the senior 1985; Martin，1988 ;Clark & Webber， synonym of P. tuberculαt αL a m a r c k ， 1991; Marques & Pohle，1995; Cuesta & 1818;see Schubart & Ng，in press). The Schubart，1999). Morphological studies remalmng specles are more common ln on larval or juvenile stages， temperate regions，with P. chαbrus especially those related to metamorphic Linne，1764 and P .glabr αD， a n a ，1852 be- molts such as crab megalopae，provide 144 J.1. GONZALEZ-GORDILLO ETAL imporlant information on the evolution of given are the arithmetic mean :t 95 % con- larval development within different phy- fidence intervals. The studied material logenetic units. However，the accuracy of has been deposited in the Instituto de the descriptions and setal counts is cru- Ciencias Marinas de Andalucia (CSIC) in cial for the use of larval and postlarval Cadiz (Spain) (no. PG/2000・1). morphology in systematics. Unfortu- nately，the descriptions and illustrations Description of the megalopal stage by Aikawa (1936， Plα.gusiαdentipes de Haan，1835 1937)，Ohtake (1963)，and Muraoka Megalopa (Figs. 1A-L，2A-E ，3A-C) (1963) are insufficient for modern stan- Aikawa，1936: 3-5 (only dards of morphological comp訂 ativework. second stage) ，p l. 2: figs. 2-3; Aikawa， Wetherefore redescribe and newly illus- 1937: 13ι137 (only second stage) ，fig. 36: trate the megalopal stage of Plagusia B-C; Muraoka，1963: 54-55，figs. 1A，2A ， dent中es 企omJapan. The new description pl. VI: A; Ohtake，1963 :ι9，pl. III: figs. 1- allows to distinguish the megalopa of P. 14. dentipes from any other megalopa of not Pla.g usi αdent伊 es; Aikawa，1936: 3・5 (only 日rst stage) ，pl. 2:figs 1，5; Aikawa，1937: Plagusiαs o far described on the basis of 136-137 (only first stage) ，fig. 36: A ，E its morphology. Dimensions.一CL= 7.4 8:t 0.78 mm Material and Methods (6.62 - 8.27 mm);CW = 5.60 :t 0.85 mm (4 .4 5-4 .86 mm). Megalopa specimens of Plagusiα dentipes were collected from drifting Description.-Carapace (Figs. 1A，B). seaweeds near the tip of Boso Peninsula， Longer than broad and without spines. Tateyama，Chiba Prefecture，Japan on 6 Frontal region with two antennal clefts . May 1992 and some were fixed in 4% Tubercles and setation as shown on the formaldehyde in sea water. Other figure. Sternum (Fig. 1C). No spiny pro- megalopae were reared in the laboratory jections; many short simple setae at the and molted to juveniles. These juvenile proximal end. stages were used to confirm the identifi ・ Antennule (Fig. 2A).Peduncle 3-seg- cation of P .dentipes .The description of mented with 4+7+8+2，3+24 ，12 setae; the megalopal stage is based on 10 speci- basal segment bulbous. Endopod mens. Allappendages were dissected in unsegmented with arow of 6setae and 9 sea water under aWild MZ8 stereomicro- terminal setae. Exopod 3-segmented with scope，mounted in lactophenol and drawn many aesthetascs grouped in tufts on two with the aid of acamera lucida attached last segments; 4，4， 2 setae ，respectively. to aZeiss Axioskop compound microscope Antenna (Fig. 2B). Peduncle 3 ・seg- with Nomarski interference. The recom- mented，with 2+13 minute simple setae mendations for standardization in larval on the first segment，21 simple setae plus descriptions proposed by Clark et αl. 3plumose setae on the second segment， (1998) were followed. and 4setae on the third segment. Flagel- Measurements of entire specimens lum 8-segmented with 0，3，3，3，3+2，3，4，4 were made with an ocular micrometer on setae. a microscope using a total of six Mandible (Fig. 2C). Mandibular palp megalopae. Carapace width (CW) is ex- 3・segmented with 1，4+2 ，32 setae，respec- pressed as the maximal width of the tively. megalopa; carapace length (CL) was mea- Maxillule (Fig. 2D). Coxal endite sured 仕omthe 企ont ofthe carapace to the 合inged with 75-78 setae，4 ofthem strong posterior carapace margin. The sizes and terminal. Basial endite with 40-41 MEGALOPA OFPLAOUSIA DENTIPES 145

六七六 i B

F E

H

A・C.F 'L

0 ・E

Fig.1. Plagusiαdentipes de Haan，1835 ，megalopa: A ，carapace (dorsal B! ca:aI!_ ace.O.ateral . w);CEsternum;D，nrst pleopod;E ，fourth pleopod;F ，abdomen (dorsal view);G，abdomen (lateral ÷i e w ); H ，arstpereiopod;I，second pereiopod;J，third pereiopod;K ，fourth Peraopod，L ， fifth pereiopod. Scale bars =1 mm . 146 J.1. GONZALEZ-GORDILLO ETAL .

C C A.B D.E

Fig.2. Plagusi αdentipes de Haan，1835 ，megalopa: A ，antennule; B，antenna ;C ，mandibule; D ， maxill 叫e;E ，maxilla .Scale bars =0 .5mm . setae，12 setae on the inner lateral mar- eral simple setae . gin. Endopod 2・segmented with 10 long First maxilliped (Fig. 3A).Coxal and 2short setae on the proximal seg- endite with 25 setae. Basial endite with ment and 9+3 setae on distal segment. 4 60-62 setae. Endopod unsegmented with short setae and 3long setae on the 1setae near the base，5+4 median plu- protopodal margin. mose setae，and 17 minute simple setae. Ma泊lla (Fig.2E) .Coxal endite bilobed Exopod 2・segmented with 6distal plu・ with3ι38 setae on the proximallobe and mose setae and 9plumose setae，respec- 13 setae on the distallobe .Basial endite tively.Epipodite triangular with 55-56 bilobed with 30 setae and 38 setae，re- long setae. spectively.Endopod unsegmented with Second maxilliped (Fig.3B) .Coxa 田 ld 10 setae on the inner margin and 15 basis not well differentiated with 3plu- plumodenticulate setae on the outer mar- mose long setae. Ischium slightly differ- gin.Scaphognathite with approximately entiated bearing 18 setae. Merus，carpus ， 180 marginal plumose setae and 15+5 lat- propodus and dactylus with 24，9 ，18 ，16 MEGALOPA OFPLAGUSI ADENTIPES 147

Fig.3. Pl α.g usiαdentipes de Haan，1835 ，megalopa :A ，fir 叫 maxilliped; B ，second maxilliped;C ， third maxilliped.Scale bars =0 .5mm .

setae respectively.Exopod 2・segmented Pleopods (Figs 1D，E). Biramous， with 6median modified serrate setae plus present on second to sixth somites. 6distaI plumose setae on proximal seg- Endopod offirst to fourth pair with 14，15， ment;9 on distal segment.Epipodite with 15，13 minute hooked setae，respectively. 78-80 marginal setae. Gill present. Exopod of first to fourth pair Third maxilliped (Fig. 3C).Coxa and unsegmented with 55，56 ，54 ，44 plumose basis not differentiated bearing 24+16 setae respectively. Exopod of the uropods plumose setae. Endopod 5・segmented 2-segmented，proximal segment with 8 with 70，30 ，30 ，23 ，19 setae. Exopod 2- plumose setae and distal segment with 36 segmented，not exceeding merus length， plumose setae. with 12 plumose setae 田 ld 3simple setae， Telson (Fig. 1F).Broader than long， respectively. Long epipodite with approxi- posterior margin rounded. Five pairs of mately 140 marginal setae.Gill bud mediodorsal setae.Margin with 8+8 present. minute simple setae. Pereiopods (Figs 1H-L). Allsegments well differentiated.Propodus of second to Discussion fifth pereiopods armed with apair of api- The usefulness oflarval and postlarval cal strong spines.Dactyli of second to fifth comparisons for brachyuran systematics pereiopods armed with 7strong denticles and has been recently demon- on the inner margin. strated within the genus Plα:gusiα:Adult Abdomen (Figs 1F，G ). Six somites. crabs of the Atlantic P .depress αa n d the First to fourth somite smooth. Fifth and Pacific P. squamosαa r e morphologically sixth somites with 4and 6posterolateral very similar and have therefore been plumose setae，respectively. treated as subspecies of P .depress α( s e e 148 J.1. GONZALEZ-GORDILLO ETAL

Table 1. Morphological differences between megalopal stages of P .dentipes ，P .depress α，andP .squ αmosa. (1): only setae number; (*): after figures from the original paper.

P. dentipes P .dentipes P. depressα P. squαmosα (Ohtake，1963 ) (Present study) (Schubart et al ，accepted) (Muraoka，1965) Size (mm):CUCW 7.4 /5 .2 7.5/5 .6 5.9/5.0 5.5/4 .5 Antennule peduncle 13，6，6* 21，27，12 17 ，12 ，5 11 ，10，5 endopod 0，6* 15 6 6 exopodえ(l) 3，0，1，2* 4，4，2 2，2，2 2，1，3 Antenna peduncle 10，10 ，1 15 ，24，4 7，6，1 0，9，0 flagellum 0，0，2，2，4，0，0，2 0，3，3，3，5，3，4，4 0，1，5，3，7，5，4，4 0，0，3，2，3，1，2，3 Mandible palp 0，4，15 1，6，32 0，20 0，1，20-30 Ma玄i U ule coxal endite 16* 75-78 48-49 ? basial endite 19* 52-54 37 31* endopod 5，8ホ 12，12 4，4 0，2 Maxilla coxal endite 3+12* 49-51 38 ? basial endite 8+17本 68 47 ? endopod 9* 25 13 19-20

scaphog.inner sur f. 20 13 15 本 First maxilliped

coxal endite 16 本 25 24 ワ basial endite 29* 60-62 40 ワ endopod 19* 27 26 14* exopod 6，7* 6，9 7，5 7，5

epipodite 37* 55-56 58 39本 Second maxilliped

coxal endite 5 3 ヲ basial endite 5 18 ヲ 巴ndopod 18，4，11 ，15 24，9，18，16 6，4，13 ，10 6，2， ?， ?* exopod 20，7 12，9 11 ，5 9，5 epipodite 30 78-80 57 Third ma豆 lliped coxal-basial endite 40 endopod 28，15 ，14，8，14 70，30，30，23，19 44，28，30，19，13 ?， ?， 16，8， 10* exopod 1，0 12，3 11 6-7，11-13 epipodite 59* 140 79 ワ Pleopod endopod 14-17 13-15 9 8-9 exopod 43-57 44-56 36-48 34-49 Uropod exopod 5，33 8，36 5，30 8-9，27 MEGALOPA OFPLAGUSIA DENTIPES 149

Dawson，1987). However，the comparison plete information provided by Aikawa of zoeal and megalopal characters (in ad- does not allow adetailed comparison with dition to sequences of mitochondrial our specimens.It can be said，however ， DNA) has shown that these two forms are that the characteristics of the rostrum of actually quite different and deserve full Aikawa's stage 1，do not agree with the species status (Schubart et al. ，accepted) . ones known for the other species of The present redescription of the Plαgusia. Consequently，this stage must megalopal stage of Plα:gusiαdent中es 企om correspond to the megalopa of another ge- Japan，introduces awhole new set ofreli- nus. As additional evidence serves the able morphological characters for detailed size of Aikawa's stage 1megalopa (CL = interspecific comparisons of this species 5，1; CW = 3，5) ，which is clearly smaller with other members of the genus than the one observed 企omthe specimens Plαgusiα( s e e Table 1) and related genera. ofOhtake (1 963) (CL =7 .4; CW= 5 .2) and Unfortunately，the megalopal stage is the specimens 企omthe present study (CL known for only four species of Plagusiα， =7.5; CW= 5 .6) . i.e. P. chαbrus (described by Barnard， Numerical differences in the setation 1950)，P. dentipes (described by Ohtake， of the megalopal appendages can also be 1963 and Muraoka，1963) ，P. depressα used for interspecific comparisons. The (described by Schubart et α1. ，accepted) ， consistent number of setae on the and P .squ αmosα (described as P . endopod of the antennule (15 in P . tuberculαt αb y Muraoka，1965). In the dentipes and 6in P .depressa 出 ldP.squa- case of P. chαbrus，only the carapace and mosα) and on the distal segment of the the pereiopods have been described first and second maxillipeds (9 in P. (Barnard，1950). The description of P . dentipes and 5in P. depressαa n d P .squ α- squamosa lacks details and no appendage mosα) allows to distinguish megalopae of is fully described. P. dentipes from the ones of P .depress α Ohtake (1963) published the only full 紅 ldP. squαmosα. Another character to be description that is currently known for used for interspecific comparisons is the the megalopa stage of P. dentipes. How- rostrum，which is rather short and broad- ever，as in the case of the descriptions P . ly bilobed in P .dentipes and P. chαbrus， chαbrus and of P .squ αmosα，some ofthe whereas the one of P .depressa and P . data are incomplete. The comparison of squamosαp r o j e c t s well forward and is bi- the description by Ohtake (1963) and the fid at the tip .Megalopae of P .dentipes can present one of the megalopa of P . also be distinguished by their size ，being dentipes，revealed agreat difference in larger than the same stage in P .depress α setal counts. The higher number of setae and P. squamosα( s e e Table 1) as well as observed in the present specimens is es- in P .ch αbrus (CL =45; CW= 50 mm; pecially evident on the antennal pe- Barnard，1950) .Based on these meristic duncle，the mandibular palp，the coxal features，the megalopal morphology and basial endites of maxillule，maxilla ， clearly suggests acloser phylogenetic re- and first maxilliped，as well as on the lationship between P. depressαa n d P. endopod ofthe maxillipeds .Many ofthese squαmosαa s compared to P. dentipes . setae were missed in the description and This supports the results from adult mor- illustrations of Ohtake (1963). phology by Dawson (1987) and mtDNAby Aikawa (1936，1937) also gives brief Schubart (unpublished). descriptions of carapace and antennal features of what he considers the Literature Cited megalopa of P. dentipes，and distin- Aikawa，H. ，1936 .Morphology ofthe first zoea guishes two successive stages.Th eincom- and megalopa in Plαgusia dentipesde 150 J.1. GONZALEZ-GORDILLO ETAL.

Haan. Suisangaku Kaihou，7: 1-5.(In Muraoka，K. ，1963 .On the secondary sexual Japanese) characters of the post-Iarval stages of a 一一一一， 1937. Further notes on brachyuran shore crab，Pl α:g usiαdentipes de Haan.Re- larvae.Records ofOceanographic Works in searches on Crustacea，1: 54-65 .(In Japa- Japan，9(1) :87-162. nese) Barnard，K. H .，1950. Descriptive catalogue of 一一一一一， 1965.On the post-larval stage of South A 企ican decapod Crustacea. Annals Plαgusiαdepressαt u b e r c u l a t a Lamarck (= of the South A 企ican Museum，38 :1-8 24. P .tuberculata ). Researches on Crustacea， Clark，P. F .，Calazans ，D. K.， &Pohle ，G. W .， 2:83-90 .(In Japanese) 1998.Accuracy and standardization of Ohtake，H .，1963 .Morphological changes of brachyuran larval descriptions. Inverte- the megalopa with metamorphosis in brate Reproduction and Development，33: Plα:gusiαdentipes de Haan.Kagakukyoiku 127-144. Kenkyusitsu Gyoseki Manazuru Marine Clark，P. F .，& Webber，W. R. ，199 1. Arede- Laboratory for Science Education，Faculty scription of Macrocheirαh α empferi of Liberal Arts and Education，Yokohama (Temminck，1836) zoeas with adiscussion National University，6: 7-12 (In Japanese) of the classification of the Majoidea Rice，A. L .，1980. Crab zoeal morphology and Samouelle，1819 (Crustacea:Brachyura ). its bearing on the classification of the Journal ofNatural History，25 :1259-1279 . Brachyura.Transactions of the Zoological Cuesta，J .A .，& Schubart，C .D. ，1999. First Society London，35 :271 -424. zoeal stages of G eogrα:p sus lividusand Sakai，T .，1976 .Crabs of Japan and the Adja- Goniopsis pulchrαf r o m Panama confirm cent Seas. Kodansha，Tokyo .Vo l. 1. xxix + consistent larval characters for the sub- 773 pp. family Grapsinae (Crustacea: Brachyura: Schubart，C .D. & Ng，P .K. L. ，in press.On the ).Ophelia ，51 :163-176. identities of Cα ncer depressus Fabricius， Dawson，E. W.，1987 .A key to the world spe・ 1775，Pl αgusia immαculatαL a m a r c k ， cies of Plαgusiα( C r u s t a c e a : Brachyura)， 1818，Cα ncersquαmosus Herbst，1790 ，and with a new record of P .d epress α Plagusia tuberculata Lamarck，1818 tuberculata Lamarck from New Zealand. (Crustacea: Brachyura:Pl agusiidae). National Museum ofNew Zealand Records， Raffies Bulletin ofZoology. 3:37 -45. Schubart，C .D .，Gonzalez-Gordillo ，J . 1.， Felder，D .L. ，Martin ，J .W .，& Goy，J. W .， Re戸lS，N .，Liu ，H .-C. ，& Cuesta ，J .A.， ac- 1985.Patterns in early postlarval develop- cepted. AreAtlantic and Indo-Pacific popu・ ment of decapods.In :Larval growth，Crus- lations of the rafting crab，Plagusia taceans Issues 2，B alkema，pp .163-225. depressa，distinct? New evidence from lar- Haan，W. de，1835. Crustacea. In :P. F .von valmorphology and mtDNA. Raffies Bulle- Siebold，(ed .) ，Fauna Japonicasive descrip- tin of Zoology. tio animalium，quae in itinere per Terada，M. ，1987 .Zoeal forms of 14 species of Japoniam，jussu et auspiciis superiorum， crabs from Enshunada.Researches on qui summum in India Batava imperium Crustacea，16: 93-120.(In Japanese) tenent，suscepto ，annis 1823-1830 collegit， Tsuchida，S .，& Watanabe，S .，1997 .Growth notis，observationibus et adumbrationibus and reproduction of thegrapsid crab illustravit，pp . 1-243，Lugduni- Plagusia dentipes (:Brachyura ). Batavorum，Leiden . Journal of Crustacean Biology，17 (1):90- Marques，F .，& Pohle，G .，1995 .Phylog enetic 97. analysis of the Pi nnotheridae (Crustacea， Watanabe，S. ，Tsuchida ，S .，& Nakamura ，N .， Brachyura)based on the larval morphol- 1992.The daily settlement of megalopae of ogy，with emphasison the Dissodactylus the grapsid crab Plagusia dentipes de species complex.Zoologica Scripta，24 : Haan (Brachyura: Grapsidae) in relation to 347-364. environmental factors .Researches on Martin，J. W .，1988 .Phylogenetic significance Crustacea，21 :153-158. ofthe brachyuran megalopa: evidence from the Xanthidae.Symposia of the Zoological Society London，59 :69 -102. Addresses: (JIGG)Instituto de Ciencias Mari- Miyake，S .，1983 .Jap anese Crustacean Deca- nas de Andalucia (CSIC)，Poligono de Rio podsand Stomatopodsin Color. Vol. 11 SanPedro s/n ，Apartado Oficial ，Puerto Brachyura (Crabs).Hoikush aPublishing . R ea111510，Ca diz ，Spain ;(ST )Marine Eco- 277 pp. (In Japanese) systems Research Department，Japan Ma- MEGALOPAOF PLAGUSIA DENTIPES 151 rine Science and Technology Center，2・ 15 Biologie 1，Universitat Regensburg，93040 Natsushima-cho Yokosuka，Kanagawa ， Regensburg，Germany. 237・0061，Japan; (CS) Department of Bio- E-mails:(JIGG) nacho.gonzalez@icman. logical Sciences，National University of csic .es; (ST) [email protected];(CS) Singapore，10 Kent Ridge Crescent， cd_schubar憾ケ ahoo.com Singapore 119260;current address: