Journal of the Marine Biological Association of the United Kingdom, 2009, 89(2), 379 –386 doi:10.1017/S0025315408002762 Printed in the United Kingdom #2008 Marine Biological Association of the United Kingdom Illustrated key for the identification of brachyuran zoeal stages (Crustacea: Decapoda) in the plankton of Peter the Great Bay (Sea of Japan) elena s kornienko and olga m korn Institute of Marine Biology, Far East Branch, Russian Academy of Sciences, 17 Pal’chevskogo Street, 690041 Vladivostok, Russia A dichotomous identification key for brachyuran zoeal stages from Peter the Great Bay (Russian waters of the Sea of Japan) is provided for the first time The key covers 16 taxa identified to species level and uses only the most conspicuous external characters of larvae that are easy to observe under a stereomicroscope without specimens dissection The key is based on the accounts by various authors and new original descriptions of larvae obtained both from plankton samples and from laboratory culture Brief descriptions of larvae of 16 brachyuran species are also included Keywords: zoea, Brachyura, crab, identification key, plankton, Sea of Japan Submitted 15 May 2008; accepted August 2008; first published online 16 October 2008 INTRODUCTION Larval development is one of the most important periods of the decapod life cycle; recruitment does not occur unless the larval period is completed Larval data can be useful in evaluating species diversity in a region and in specifying the reproduction time of brachyuran species Morphological features of larvae are complementary characters for crustacean taxonomy and phylogeny The study of larvae is important for the problem of introduced species arriving in ballast waters or on fouled ships However, insufficient attention has been paid to decapod larval development in the Russian Far East Seas Many keys exist for the identification of brachyuran larvae in different regions of the World Ocean (Ingle, 1992; Paula, 1996; Ba´ez, 1997; Pessani et al., 1998; Anosov, 2000; Puls, 2001; Santos & Gonza´lez-Gordillo, 2004; Rice & Tsukimura, 2007), but only one taxonomic guide is known for the Sea of Japan (Konishi, 1997) There is no comprehensive key for identification of the brachyuran larvae in Russian waters of the Sea of Japan; however, the species list of this region considerably differs from that of coastal waters of Japan The aim of this work is to provide a key for the identification of brachyuran larvae in Peter the Great Bay MATERIALS AND METHODS The key is based on the accounts previously published by various authors (Table 1) and new original descriptions of brachyuran larvae both taken from plankton samples and reared from ovigerous crab females in the laboratory Corresponding author: E.S Kornienko Email: kornielena@mail.ru Zooplankton was sampled in Vostok Bay (inner bay of Peter the Great Bay, Sea of Japan) between May and November 2002 using a Norpac net with a ring diameter of 40 cm and a filtering cone made of a 168 mm mesh, and in Amursky and Ussurijsky Bays (inner bays of Peter the Great Bay, Sea of Japan) between April and October 2007 using a Juday net with a ring diameter of 38 cm and a filtering cone made of a 168 mm mesh (Figure 1) It is very difficult to identify the larvae (especially the larvae of congeneric species) using drawings and descriptions of different authors in more or less detail So, zoeae of most considered species were obtained under the laboratory conditions This material was used for the construction of the key and the original figures Ovigerous crab females were maintained in an aerated seawater aquarium until larvae hatched After hatching, larvae were concentrated at the edge of the aquarium using a point-light source and transferred to 1-l glass vessels with filtered and UV-sterilized seawater and reared to the megalopal stage The density of larvae was about 100 specimens l21 The water in the vessels was changed daily The larvae were fed with newly hatched nauplii of Artemia salina Very small zoea of varunid and pinnotherid crabs were reared using nauplii of the rhizocephalan crustacean, Polyascus polygenea, as a food Earlier, this method was described in detail (Kornienko & Korn, 2005a) All larvae were fixed in 4% formaldehyde for light microscopic studies The dichotomous identification key is based mainly on external morphological characters, which are easy to observe under a stereomicroscope MBS-10 without specimen dissection When these features are insufficient, the morphology and setation of appendages has been included Moreover, new original figures were provided to make identification easier The outlines of the larvae were drawn using a camera lucida attached to a binocular Ergaval microscope (Carl Zeiss Jena) 379 380 elena s kornienko and olga m korn Table List of species and sources of descriptions of brachyuran zoeae included in the identification key Family Species Authors Dorippidae Epialtidae Oregonidae Pisidae Cancridae Cheiragonidae Paradorippe granulata (De Haan, 1839) Pugettia quadridens (De Haan, 1837) Chionoecetes opilio (O Fabricius, 1788) Pisoides bidentatus (A Milne-Edwards, 1873) Cancer amphioetus Rathbun, 1989 Erimacrus isenbeckii (Brandt, 1848) Telmessus cheiragonus (Tilesius, 1812) Charybdis japonica A Milne-Edwards, 1861 Pinnixa rathbuni Sakai, 1934 Tritodynamia rathbuni Shen, 1932 Pinnaxodes mutuensis Sakai, 1939 Sakaina yokoyai (Glassell, 1933) Eriocheir japonicus De Haan, 1835 Hemigrapsus sanguineus (De Haan, 1835) H penicillatus (De Haan, 1835) H longitarsis (Miers, 1879) Kurata, 1964; Terada, 1981; Quintana, 1987 Kurata, 1969; Ko, 1998: Kornienko & Korn, 2004 Kurata, 1963b; Motoh, 1973; Haynes, 1973, 1981 Kurata, 1969; Kornienko & Korn, 2007 Iwata & Konishi, 1981 Aikawa, 1937; Kurata, 1963a; Makarov, 1966 Kurata, 1963a Yatsuzuka et al., 1984 Sekiguchi, 1978; Konishi, 1983; Kornienko & Korn, 2005b Matsuo, 1998 Konishi, 1981b Not described Morita, 1974; Kim & Hwang, 1990 Hwang et al., 1993; Kornienko et al., 2008 Hwang & Kim, 1995; Kornienko et al., 2008 Park & Ko, 2002; Kornienko et al., 2008 Portunidae Pinnotheridae Varunidae The key was constructed for zoea I, but the characters used in the key not change or change slightly through the successive zoeal stages, with the exception of peculiar cases Main characters of brachyuran zoea used for the identification are represented in Figure RESULTS Key for the identification of brachyuran zoea I (interspecific distinctions) 1a Carapace with rostral, dorsal and lateral spines (Figure 3A) Fig Map showing the sampling area 1b Carapace with rostral spine only (Figure 3B) or with rostral and dorsal spines (Figure 3C), lateral spines absent 11 2a Abdominal somites 3–5 with well developed posterolateral spines; furcal rami with lateral and dorsal spines (Figure 4A) 2b Abdominal somites 3–5 with poorly developed posterolateral spines (Figure 4B, C); furcal rami without lateral and dorsal spines (Figure 4B) or with lateral spines only (Figure 4C) 3a Furcal rami longer than proximal part of telson; dorsal and lateral furcal spines short (Figure 5A) 3b Furcal rami shorter than proximal part of telson; lateral furcal spines long (Figure 5B, C) 4a All carapace spines spinulated; dorsal spine straight; posterolateral spines longer than half abdominal somite; each furcal ramus with three spines Chionoecetes opilio (Figure 11A) Fig Main characters used for the identification of brachyuran zoea key for brachyuran larvae Fig Telson of zoea in Chionoecetes opilio (A), Telmessus cheiragonus (B) and Erimacrus isenbeckii (C) Fig Carapace of zoea in Eriocheir japonicus (A), Sakaina yokojai (B) and Pisoides bidentatus (C) [Lateral spines long, slightly shorter dorsal and rostral spines Antenna biramous; protopod spinulated, approximately equal rostral spine; endopod with three terminal setae of unequal length Lateral knobs on abdominal somites – long, those of third one reach end of the same somite Larvae found from April to July.] Fig Abdomen and telson of zoea in Chionoecetes opilio (A), Tritodynamia rathbuni (B) and Pisoides bidentatus (C) 4b All carapace spines smooth; dorsal spine slightly curved; posterolateral spines shorter than half abdominal somite; each furcal ramus with two spines 5a Abdominal somite with a pair of lateral knobs; outermost pair of inner setae on posterior telson margin dentated on inside surface (Figure 6A, A0 ); posterolateral spines very short in zoea I and considerably lengthen in successive stages Cancer amphioetus (Figure 11B) [Antenna biramous; protopod with two rows of spinules, nearly half of rostral spine; exopod with Fig Abdomen and telson of zoea in Cancer amphioetus (A, A0 ) and Charybdis japonica (B) (after Yatsuzuka et al., 1984) 381 382 elena s kornienko and olga m korn two terminal setae of unequal length Larvae found from June to September.] 5b Abdominal somites and with a pair of lateral knobs; all inner setae on posterior telson margin plumodenticulate; posterolateral spines prominent in all zoeal stages (Figure 6B) Charybdis japonica (Figure 11C) [Antenna biramous; protopod with two rows of spinules, nearly half of rostral spine; exopod with two terminal setae of unequal length Larvae not found yet.] 6a Abdominal somite with a pair of lateral knobs; posterolateral spines of somite shorter somite 5; lateral telsonal spine shorter than half furcal ramus; each furcal ramus with three inner setae (Figure 5B) Telmessus cheiragonus (Figure 11D) [Dorsal spine straight; rostral and dorsal spines spinulated in distal part Antennal protopod spinulated, shorter than rostral spine; exopod with two nearly equal setae Abdominal somites – with long posterolateral spines Each furcal ramus with three spines: one long lateral spine and two short dorsal spines Larvae found in April and May.] 6b Abdominal somites and with a pair of lateral knobs; posterolateral spines of somite shorter than somite 5; lateral telsonal spine longer than half furcal ramus; each furcal ramus with four inner setae (Figure 5C) Erimacrus isenbeckii (Figure 11E) [Dorsal spine straight; rostral and dorsal spines spinulated in distal part Antennal protopod spinulated, shorter than rostral spine; exopod with two nearly equal setae Abdominal somites – with long posterolateral spines Each furcal ramus with three spines: long lateral spine and two short dorsal spines Larvae found in April and May.] Fig Antenna and carapace of zoea in Tritodynamia rathbuni (A) and Eriocheir japonicus (B) 7b Lateral carapace spines arranged more ventrally than in typical brachyuran zoea; abdominal somites 4–5 not cylindrical but laterally expanded; telson subrectangular; furcal rami without spines or with minute lateral spines (Figure 7D –F) 10 8a Dorsal and rostral spines longer than carapace; dorsal carapace spine straight; antenna uniramous (Figure 8A) Tritodynamia rathbuni (Figure 11F) [Antennal protopod with two rows of spinules and with short seta near base Posterolateral spines on abdominal somites – highly reduced Larvae found from June to September.] 7a Lateral carapace spines arranged as in typical brachyuran larvae; all abdominal somites cylindrical; telson triangular; furcal rami without spines (Figure 7A, B) 8b Dorsal and rostral spines slightly shorter than carapace; dorsal carapace spine slightly curved; antenna biramous (Figure 8B) Fig Carapace of zoea in Tritodynamia rathbuni (A) and Pinnaxodes mutuensis (C); telson of zoea in Tritodynamia rathbuni (B); Pinnaxodes mutuensis (D), Pinnixa rathbuni (E) and Sakaina yokoyai (F) Fig Antenna, antennule and abdomen of zoea in Eriocheir japonicus (A) and Hemigrapsus sanguineus (B) key for brachyuran larvae 9a Abdominal somites 2– with a pair of lateral knobs (lateral knobs on somite disappear in successive stages); antennule with aesthetascs; antennal exopod nearly half protopod (Figure 9A) Eriocheir japonicus (Figure 11G) [Rostral spine nearly one-third antenna; dorsal spine with sparse blunt spinules Antenna biramous; protopod and exopod sub-equal Abdominal somites with a pair of lateral [Antennal exopod as tapering spine with two small unequal subterminal setae Larvae found from June to September.] 9b Abdominal somites 2–3 with a pair of lateral knobs; antennule with aesthetascs; antennal exopod nearly 2/3 protopod (Figure 9B) Hemigrapsus sanguineus, H penicillatus, H longitarsis (Figure 11H) [Antennal exopod as tapering spine with small unequal subterminal setae Larvae found from June to September.] 10a Abdominal somites 4–5 expanded; furcal rami shorter than proximal part of telson, with minute lateral spines (Figure 7D) Pinnaxodes mutuensis (Figure 11I) [Antenna uniramous; protopod with two rows of spinules Lateral telsonal margins slightly convex Larvae found in July.] 10b Abdominal somite as a horseshoe; furcal rami longer than proximal part of telson, without lateral spines Pinnixa rathbuni (Figure 11J) [Rostral and dorsal carapace spines straight Antenna uniramous; protopod with two rows of spinules and with short seta near base Furcal rami without spines (Figure 7E) Larvae found from May to November.] 11a Carapace with rostral spine only Sakaina yokoyai (Figure 11K) [Antenna uniramous; protopod with two rows of spinules Abdominal somites – as a horseshoe Telson nearly rectangular; furcal rami shorter than proximal part of telson, without spines; median notch virtually absent (Figure 7F) Larvae found in June – August.] 11b Carapace with rostral and dorsal spines (Figure 10) 12 12a Rostral and dorsal spines three times longer than carapace; dorsal spine straight Paradorippe granulata (Figure 11L) [Dorsal spine with blunt spinules, rostral spine with acute spinules Antenna biramous; protopod and exopod sub-equal Abdominal somite with pair of lateral knobs Telson narrow and long, with a pair of lateral spines; furcal rami twice exceeding proximal part of telson Posterior telsonal margin with two inner setae only (Figure 10A, A ) Larvae found in July and August.] 12b Rostral and dorsal spine shorter than carapace, dorsal spine slightly curved (Figure 10B) Pugettia quadridens, Pisoides bidentatus (Figure 11M) Fig 10 Carapace (A) and telson (A0 ) of zoea in Paradorippe granulata; carapace of zoea in Pugettia quadridens (B) 383 384 elena s kornienko and olga m korn Fig 11 Lateral view of zoea in Chionoecetes opilio (A), Cancer amphioetus (B), Charybdis japonica (C), Telmessus cheiragonus (D), Erimacrus isenbeckii (E), Tritodynamia rathbuni (F), Eriocheir japonicus (G), Hemigrapsus sanguineus (H), Pinnaxodes mutuensis (I), Pinnixa rathbuni (J), Sakaina yokoyai (K), Paradorippe granulata (L), and Pisoides bidentatus (M) knobs Furcal rami with lateral spines (Figure 4C) Larvae found from June to September.] Most Brachyura from Peter the Great Bay pass through five zoeal stages Majiod crabs (Pisoides bidentatus, Pugettia quadridens, and Chionoecetes opilio) have an abbreviated development including only two zoeal stages Two of three pinnotherid crabs also undergo an abbreviated development: Sakaina yokoyai passes through probably three zoeal stages; Pinnaxodes mutuensis, through four zoeal stages Four zoeal stages are known also for Paradorippe granulata Different zoeal stages of brachyuran crabs (age distinctions) are easily determined using the number of natatory setae on the exopods of maxillipeds, the number of setae along the posterior telsonal margin, the presence of uniramous or biramous pleopod buds and some other morphological features The same stages in the species with abbreviated development are more advanced in the number of characters over those of the species with longer development Identification of different zoeal stages of brachyuran crabs (age distinctions) Zoea I Eyes sessile; exopod of maxilliped each with natatory setae; abdomen consists of somites and telson; posterior telsonal margin with þ setae (in Paradorippe granulata, posterior telsonal margin with two setae only in all zoeal stages) Zoea II Eyes stalked; exopod of maxilliped each with natatory setae; in most species abdomen consists of somites and telson; pleopod buds absent; posterior telsonal margin with þ setae In Pisoides bidentatus, Pugettia quadridens, and Chionoecetes opilio, zoea II is the last stage; hence, the sixth somite is delineated, somites 2–6 with biramous pleopod buds In Sakaina yokoyai, pleopod buds uniramous In Charybdis japonica and Chionoecetes opilio, posterior telsonal margin with þ setae Zoea III Exopod of maxilliped each with natatory setae; the sixth somite delineated, with the exception of Pinnixa rathbuni which has somites in all zoeal stages In Cancer amphioetus, Trithodynamia rathbuni, Erimacrus isenbeckii, Telmessus cheiragonus, Eriocheir japonicus and Hemigrapsus species, posterior telsonal margin with þ setae; in Charybdis japonica and Pinnaxodes mutuensis, with additional small unpaired setae In Sakaina yokoyai, pleopod buds biramous Zoea IV Exopod of maxilliped each with 10 natatory setae; somites 2–6 with uniramous pleopod buds In Cancer amphioetus and Tritodynamia rathbuni, posterior telsonal margin with þ setae Zoea V Exopod of maxilliped each with 12 natatory setae; pleopod buds biramous In Eriocheir japonicus and Hemigrapsus species, posterior telsonal margin with þ setae key for brachyuran larvae DISCUSSION REFERENCES According to Adrianov & Kussakin (1998), 20 brachyuran species belonging to families and 16 genera inhabit Peter the Great Bay (Russian waters of the Sea of Japan) We found larvae of only 16 species from families and 14 genera occurring in the plankton of Peter the Great Bay (Table 1) To date, we have not found both adults and larvae of Goetice depressus (de Haan, 1835), Helice tridens de Haan, 1833, and Paradromia japonica (Henderson, 1888) According to Vassilenko (1990), adult specimens of Pinnixa tumida Stimpson, 1858 are found only in Possyet Bay (eastern Peter the Great Bay) Brachyuran larvae occur in Peter the Great Bay from April to November Zoea of each species represented in this key has been previously described Only the larvae of Sakaina yokoyai are not known yet; however, the morphology of closely related species, S japonica, has been described (Konishi, 1981a) Both adults and larvae of S yokoyai are rarely found in Peter the Great Bay, so we failed to obtain the total series of their larval stages Nevertheless, we believe that S yokoyai, like S japonica, passes through three zoeal stages Frequently, the distinction between larvae of congeneric species is based on slight differences The larvae of congeneric species, described on the basis of specimens hatched in the laboratory from ovigerous females, can be identified only to the generic level when collected in nature In our case, the specific identification of three Hemigrapsus species (H sanguineus, H penicillatus and H longitarsis) is very difficult Zoea I and zoea II of these species are nearly identical The larvae are distinguishable only from zoea III Zoea III –V of Hemigrapsus species differ in the number of dorsomedial setae on the abdominal somite I and in the number of setae on the posterodorsal arch It is pertinent to note that among the three Hemigrapsus species, zoea and megalopa of H penicillatus differ greatly (Kornienko et al., 2008) Despite the great similarity of larvae in varunid crabs of the genera Hemigrapsus and Eriocheir, the latter possess a number of distinctive features in all developmental stages (Kornienko & Korn, 2005a; Kornienko et al., 2008) It was recently shown that zoea of Pisoides bidentatus and Pugettia quadridens belonging to different families are also nearly identical, with the exception of a more intensive coloration of the latter Some differences appear only in the megalopal stage Based on the larval similarity (Kornienko & Korn, 2007) and high genetic identity of adults (Zaslavskaya et al., 2007) these two species should be assigned to one genus The larvae of the other ten 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