Bull. Bull. Kanagawa Pref. Mus., No. 18, March 1989 47

The Megalopa Stage of Eρ lumula ρhα langi um (De Haan) (Crustacea, Brachyura, )

Kensaku MuRAOKA 〔Kanagawa Prefectural Mus eum 〕

ミズ ヒキガ ニの メガロパ幼生（甲殻上綱， 短尾下目，ミ ズヒキガ ニ科 〉

日本の沿岸に分布するミズヒキガニ科のカニ類のうち， 属 と Eρ lumu 付 属に属 する 種はそれぞれ 1 種ずつ 生息、 している この 両属のいずれかに 属すると 思われるメガロパ を， 東京大学海洋研究所の白鳳丸の研究航海 （KH 81 ーの で，IKMT ネツ｜を用いて， 四国沖 の洋上で 4 個体得ることがで きた この 幼生 と既知の幼生 との外部形態の比較観察を行っ たと

ころ，甲殻上の？？械や額赫の 形態、， さらには 腹部の形態な どは 既報のオーストラリア産の Eρ － lumula australiensis 〔H enderson ）の幼生 とその一般的 な特徴は類似する 点が多く み られ た．このことか ら， この 幼生はおそら く Eρ lumu 付 属に屈 し， しかも本属 は 日本の沿岸には

ミズヒキガニ E. 1うha ！αngium (De Haan ）の 1 種のみ生息 していることから 考えて，このメ ガロ パは本程の幼生ではないかと 思われる．（村岡健作〉

Summary

Four specimens of megalopae of the family Latr eilliiclae were taken far off south of of Shikoku us ing a IKMT net. They ha vea pair of long and div e rgent supra -orbital spines spines and a prominent acute dorsal spin 巴 on the carapace. They are referable to the same species, and closely allied to tho s巴 which were attributed to E. australiensis Henderson by Williamson (1967). It may be assigned to the megalopa of Eρ hala ngium (De Haan ) rather than Latreilllia valida (De Haan).

Introduction

Th 巴 family Latreilliidae compris 巴 two related g巴nera Latreillia and Eρ lumula

(Williams, (Williams, 1982 ). Each of them has fi ve and two sp巴cies respectively. From ]apa nese nese waters, L. val ;"da D 巴 Haan and E. ρhalan gium 〔D 巴 Haan 〕hav 巴 been described.

Two forms of megalopa 巴 d巴scribed from Mediterranean (Cano, 1893) and the north

Atlantic Atlantic (Rice , 1982) was attribut 巴d to L. elegans Roux, and Williamson's (1967) me galopa galopa obtained off south - eastern Australia wa s att ributed to E. australiensis Hen- derson. derson. From Japan, two forms of megalopae ha ve been described: Aikawa ’s (1937) megalopa from Sagami Bay was attributed to Homola sp., and Takeda and Kura ta ’s (1984) (1984) megalopa, found in stomach contents of the fish taken from the Ogasawara 48 M U RAOKA: The megalopa stag 巴 of Eρ lumula phalangium (De Haan)

~ B

Fig. Fig. 1. Megalopa of Ep!u m ula 1うhalangium (De Haan 〕

A, lateral view. B, d orasl view. Bar scale repres 巴nts 1 mm.

Islands, Islands, was assigned to Eρ halan g ium CD 己 Haan) (=L.ρ halangium de Haan 〕，

based based upon a single damaged specim e n. This paper deals with four sp 己cim 巴ns of megalopae re ferable to Latreilliidae, which were collected far off south of Shikoku, with with IKMT net, during the cruise KH 81 5 of R. V. Hakuho Maru of the Ocean Re - search search Institute, University of Tokyo. On the critical examination, the specimens may

be be assigned to E. 1りhalangium with some doubt. I with to express my sincere thanks to Prof. T. Nemoto, Ocean Research Institute, University University of Tokyo, for providing the opportunity of this study. I am also grateful Bull. Bull. Kanagawa Pref . Mus. , No. 18 , March 1989 49

1, 1’， J,K ,L L---ーーー一一一~ B,H,M A,F,G －C,D,E M ’ Fig. Fig. 2. Megalopa of E 戸lumula ρhalangiuin 〔De Haan ) (A -M ’〉 A, A, antennule; B , antenna; C, mandible; D , maxillule, E , maxilla, F, first maxilliped , G, secon d maxilliped, maxilliped, H, third maxilliped ; I, cheliped; I’， stout basal spine on basis of chelip 己d. vent ral vi -

ew; J-L , fir st, s巴cond and fourth wa lking legs; M , la st two abdominal s~gments and telson with uropod s. dorsa l view ; M ’， basa l portion of uropod. ve ntral view (en, endopod; ex, exopod 〕． Bar sca l es represent 0.5 mm. 50 MuRAOI

Table Table 1. Comparison of main charact 巴rs of megalopae of Eplu mula and ei Latr ll ia

E. E. phalangium E. austlariensis Homola sp L. elegans (Pr 己記 nt author ) ( Williamson, 1967 ) ( Aikawa, 19 37 ) (Rice, 1981 〕

Carapace Carapace length (mm 〕 3. 5 3.9 不 3. 1* 4. 1 1st 1st Antenna endp od (s egment s〕 3 2 2 3 exopod exopod (s egments ) 7 7 5 7 2nd 2nd Antenna (segments) 10 10 12 10 Mandi bl 巴 palp palp (s 巴gments 〕 3 3 1キ 3 1st 1st maxilliped 巴ndp ocl (s egments ) 2 2 ？ 1 Pleopod s, 2-5 enclp ocl (hair s) 24 - 26 ？ ？ 20 - 25 exopod exopod (hairs) 5-7 ワ ？ 45 Urop ocl peduncle peduncle (hair s〕 ？ ヲ 。 巴ndpocl (hairs 〕 15 17 13 2 ? 11 exopod 〔hairs) 20 - 21 17 ？ 18 As terisk mark C 〕；caluculated from the figure s.

to to Prof. S. Garno, Yokohama Nat iona l Uni vers ity, for his valuable suggestions and critical critical rea ding of the manu scr ip t.

Materials and Methods

Four spec imen s of megalopae Latr eilliidae avai labl e for the st udy w 巴re collected at St. St. 1. (3 1°31.0' N, 133 °29.9'E ), far off south of Shikoku with an ob lique tow ing IKMT (Isacs (Isacs Kidd mid water tra w l) net, sa mpling l ayer 0 350 m, on 9S eptember 1981. during

the the KH -81 -5 crui se (7 S巴ptember to 20 No ve mber, 1981) of the R. V. H ak uho Maru

of of the Oc ea n R esearch In stitut 巴， Uni vers ity of Tokyo.

The y we re fi xe d in about 3 ~ぢ buffere d formalin made up with seaw ater and tra nsferr ed

to to 60% et hanol for preserv at ion. The sp巴cimen s were dissected wit h the aid of th e

di sse ctin g fine need l es and binocul ar micro scop 巴 w hile the sp 巴cimens were immer se d 50% ety lene glyco l.

De s cription : Megalopa of Eplumula ph αIα ngium (De Haan ) Figs. (Figs. 1. 2)

The four sp巴cim ens avail a ble for the study are simil ar in every respect. Dimen sion : Carapace length as m eas ured along the mid line, 3.5mm; length of th e supra -orbital spin e, about 6.0 mm; carapace width , 2.0 mm.

Carapace ( Fig. 1. A, B ) is almost rectangu l ar in shape as se 巴n from the dorsal side, and slightly wider po steriorl y. Ro st rum b ents downward, and is pointed and hardl y Bull. Bull. Kanagawa Pref. Mus., No. 18, March 1989 5 1 v i sible in dorsa l vi ew. Th e re are a pa ir o f very long and w ide ly di vergent supra - orbita l sp ines. The ir dista l end is provided w i th a sma ll anchor li ke pro ces s. Pro - minent acute -tipped dor som ed ian spine aris ing from the gastric reg i on is p rovided with a s maller anterior subsid i ary knob proc 巴ss ; the dor sa l sp in e is flanked by a few sma ll se tae. There is a swo ll en proce ss on the ca rdi ac reg ion.

Abdomen ( Fig. l, A, B ) is ra t her sl巴nder. Fir st so mi te is shor ter than the s巴con d, and bears a sma ll tubercle on dorsa l sur face. Second so mi te ha s a l arge st out acute dor sa l proce ss , which iss li ght ly directed forward at it se nd. Te lson (Fig. 2, M) is ell ip so idal in shape, almost thr ee time s as broad as l ong, and furni shed with no margina l spin es or se tae.

Eye (Fig. L A) is very l arge and ha ss hort p巴duncl e.

Antennu l ar ped u ncle (Fig. 2, A) is three segment 巴cl , enclopod consists of thr ee seg- ment s, each carrying a few short set ae ；巴 xop od seve n seg men ted, and prov ided with a tuf t of ae stheta scs on each of the fir st five seg m ent s.

Antenna l peduncle ( Fig. 2, B ) is three -seg m 巴nted , the proxima l seg ment carries a m i nute sca l e; the fl age llu m i s seve n seg me n ted, the pro xima l seg ment is very sma ll and without setae; distal fi ve seg ment s are ra t her slend 巴r and bea r long setae . Mandibu l ar pa lp (Fig . 2, C) consists of three segments, the di sta l one arm ed with about about sixte 巴n stiff spine s. Max ill ul ar endopod (Fig. 2, D) has two segments, each carry ing two setae .

Ma xillary 巴nclopod ( Fig. 2, E) consists of one segment and carries about six plumo se hair s on the late ral mar g i n; scaphognath ite is pro vid ed with more than SO margina l plumo se ha irs. F irst max ill iped ( Fig. 2, F) ha s l arge epipod; endopod is two -seg me nte d, th e di stal seg m e nt w i th a termina l expa ns ion ; exopod cons ists of two seg ment s, the di sta l seg - ment carry ing four plumo se hair s. Seco nd max illi ped (F ig. 3, G) is furni shed with as len der setose ep ipod ; endopod of ha s five segments , each of which carri 巴sa n umb 己r of setae ; the isc hium not clear ly se parated from the basi s, exopod armed w i th eight plurnose hair s marginally on the dista l portion . Third rna xilliped (Fig. 2, H ) ha s a se to se epipod, endopo d ha s five seg ment s, the inn er marg in of the isc hium is pro vided w ith se to se and about s ix sm all te eth, and that that of the m eru s with a se ri es of long se tae; exop od w ith fi ve plumose ha irs on its di sta l end. Che li ped s (F ig. 2, I, Iつis sl ender; the basi s arm ed with a sma ll hook like spin e. Fir st to thre 巴 wa lking l egs (Fig. 2, J, K) have sword -lik e dacty lus , w hic h carr ies a ser ie s of fine setae ventrally and dorsally, th 巴 prop od us bears two or three s trong spin es di sta lly on the inner margin . Fourth wa l king leg ( Fig. 2, L ) is pro v ided w ith thr ee lo ng se ns ory ha ir s di sta ll y on th e dact ylus.

Abdominal som ite s 2-5b ear a pair of biramou s pl eopods; the endor 】ods each armed 52 M URAOK A: The m 巴galopa stage of Eplumula phalangiu.m (De Haan )

with five to sev 巴n hook 巴d hair s and the exopod of the p!eopods 2 to 5 carrying 24, 24 - 26, 25 -26 , 25 plumo se hairs, re spect ively. Uropod (Fig. 2, M, M ’） is furnished with subequal rami; basis bears a p lum o se hair on the outer margin; endopod has 15 17 and exopod carrie s 20 - 21 mar g in al plum ose hair s.

Remarks

The pre se nt four specimens of m ega lopae co ll ected far off Shikoku are referab le to the the same spec ies, and bear som e s uperfic ial rese mblanc e to tho se which were attri - buted to the fo ll owing s pecies, 1) L. elegans Rou x (Cano, 1893, Rice, 1982 ). 2) L. va li da

De Haan or E. ρhalan giu m CD 巴 Haan) by Ric 巴（ 1982) and Aikawa (193 7: as Homola sp.). The main charact e rs of the m ega lopa e are li s ted in Table 1. They are di s tinguishable from one another by the use of some feat ur es, such as cara pace length, and seta l for mula e of antennae, mouth part s and pleopods.

In In genera l appearanc 巴， the meg a lopae designat ed as Homola sp. by Aikawa (1937)

and as E. ρhalangiut η （＝L.ρ halangium) by Tak eda & Kurata (1984 ) are very lik e tho se of L. elegan s de scr ib ed by Cano (1893) and Rice (198 2). Wherea s the present specim ens are very clo sely allied to the me ga lopa whic h wa s de signated as E. aus- trali ensis by William son (1967) in having a pa ir of very prominent and widely diver gent supra orb ital s pines, and an acuminated dorsa l sp in e with a sma ll anterior knob on the carapace, and also in ha v ing the s imilar se gmentation of the fir st and sec ond antennae. antennae. The prese nt megalopa e ma y be ass ig ned to Eρ halangium (De Haan ) w ith some doubt. It will require mo re extens ive collecting and mor e rear in g in labo ratory,

to to make more definit 巴 specific identificat i on.

Literature Cited

A1K AWA , H., 1937. Furth er not 巴s on brachyuran Jarva. Rec. oceanogr . Wk s. Japan , 9(1〕： 87 162.

C ANO, G., 1893. Svillupo dei Dromidei. Atti Accad. Sci . fis. mat. Napoli, 6 ・ 1 23, 2 pi s. M uRA OK A, K., 1986. The megalopa s tage of a belonging to the family La treilliidae ( Crus tacea, tacea, , Brachyura ) . Zool. Sci., 3(6) : 1112 (Summary ）‘ R1 cE , A. L., 1982 . The megalopa s tage of Latreillia elegans Roux (Decapoda, Brachyura, Homo loi- dea ). Crustaceana 43 (2) : 20 5-210. T AK EDA, M . & Y. K uRATA , 1984 . Crab s of the Oga sawa ra Islands VII. Third report on the species obtained obtained from stomac hs of fishe s . Bull. Natn . Sci. Mu s., Tok yo, Ser. A, 10 (4) : 195 202.

羽TrLLI AMS, A. B. , 1 982. Revi sion of the ge nu s Latr 巴ill ia Roux (Brach y ura: ). Quad. L ab.

Tecnol. Tecnol. P 巴sea, 3 227-255.

WrLLI AMSON , D. I., 1967 . The megalopa s tage of th 巴 homolid crab Latreillia australiensis Rend 巴rs on and and comments on other homolid mega lopas. Australian Zoologi st, 14: 206-211.