Larval development of Japanese 'conchostracans': part 1, larval development of Eulimnadia braueriana (Crustacea, Branchiopoda, Spinicaudata, Limnadiidae) compared to that of other limnadiids

As a part of a project to compare phylogenetically the larval or embryonic development of all major taxa of the Branchiopoda (Crustacea), the larval development of the Japanese spinicaudatan clam shrimp Eulimnadia braueriana Ishikawa, 1895, is described. Seven naupliar stages are recognized, based mainly on significant morphological differences between them, but in one case, on size alone. The seven stages range in length from 156 µm to 760 µm. Nauplius 1 is nonfeeding with incompletely developed and nonfunctional feeding structures. Nauplius 2 has apparently functional feeding structures, including a well-developed mandibular gnathobase, setulate protopodal endites of the antennae, and setules on various setae involved in swimming and food manipulation. Nauplius 3 is morphologically identical to Nauplius 2, but more than 50% larger. In nauplius 4, the coxal endite (naupliar process) of the antennae develops a bifid tip. Nauplius 5 has a lateral pair of primordial carapace lobes, and the first 4–5 pairs of trunk limb buds are weakly developed, making the anterior part of the trunk wider than the posterior. In nauplius 6, five pairs of trunk limb buds are visible externally and a small carapace has appeared, reaching approximately to trunk limbs 2; also, the pair of large buds behind the mandibles in previous stages has become divided into a large, anterior, setose bud and two smaller, posterior buds. The identities of these structures as either paragnaths or maxillules/maxillae remain uncertain. In nauplius 7, about six pairs of trunk limb buds are visible externally. The general morphology of the nauplius larvae of E. braueriana is much like those of the well-known Limnadia lenticularis (Linnaeus, 1758) and Eulimnadia texana Packard, 1871, including an elongate, lanceolate labrum; however, because of various heterochronies, the correspondence between the larval sequences of these species is not perfect. There is even less correspondence with the 5-stage larval development reported for Limnadia stanleyana King, 1855, and the spatulate labra of that species and Jmnadia spp. are different from those of other known limnadiid nauplii. The larvae of E. braueriana possess many typical (and synapomorphic) branchiopod features, such as the general morphology of the appendages involved in feeding and the mode of trunk limb development, while the small buds of the first antennae and the exact number and development of the parts of the trunk limbs are typical for the Spinicaudata.     

On the larval development of<Emphasis Type="Italic"> Eubranchipus grubii</Emphasis> (Crustacea,Branchiopoda, Anostraca), with notes on the basal phylogeny of the Branchiopoda

Selected larval stages of Eubranchipus grubii (Anostraca) from Danish temporary waters are examined by scanning electron microscopy in a phylogenetic context. The study focuses on limb development and body segmentation. It is shown that the large, proximal endite of the trunk limbs in the adult Anostraca is actually a fusion product of two smaller endites which make their appearance in the early larval development. This gives a total of six endites along the inner margin of the trunk limbs. An unsegmented endopod follows more distally. A small additional, seventh endite makes a short appearance in late larvae, but has disappeared in the adults. The naupliar feeding apparatus is of the same type as found in other branchiopods, and has previously been suggested as an autapomorphy for the Branchiopoda. The similarities between the naupliar feeding apparatus of E. grubii and other branchiopods include the presence of a long protopod with a characteristic morphology of the coxal and basipodal masticatory spines/setae, and a three-segmented mandibular palp (basipod and two endopod segments) with a largely similar setation in all taxa. The mode of trunk limb development is also the same as seen in most other recent branchiopods. The phylogenetic significance for the basal phylogeny of the Branchiopoda of these and other morphological features is discussed in relation to the phylogenetic position of two branchiopod fossils, Lepidocaris rhyniensis and Rehbachiella kinnekullensis. While R. kinnekullensis has previously been suggested to be a stem lineage branchiopod, the position of L. rhyniensis is more uncertain. Three different possible phylogenetic positions of L. rhyniensis are discussed: (a) L. rhyniensis as a stem lineage anostracan, (b) L. rhyniensis as a stem lineage branchiopod or (c) L. rhyniensis as a stem lineage phyllopod. It seems most plausible to consider L. rhyniensis a stem lineage anostracan.     

Larval development of Lynceus brachyurus (Crustacea, Branchiopoda, Laevicaudata): redescription of unusual crustacean nauplii, with special attention to the molt between last nauplius and first juvenile

The larval development of "conchostracans" has received only scattered attention. Here I present the results of a study on the larval (naupliar) development and the metamorphosis of Lynceus brachyurus, a member of the bivalved branchiopod order the Laevicaudata. Lynceus brachyurus is the only species of the "Conchostraca" in Denmark. The phylogenetic position of the Laevicaudata has traditionally been a source of controversy, and this study does not solve the question completely. This work focuses on features potentially important for phylogeny. The general appearance of the larvae of L. brachyurus has been known for more than a century and a half, and some of its unique features include a large, larval dorsal shield; a huge, plate-like labrum; and a pair of immovable, horn-like antennules. However, many details relating to limb morphology, potentially important for phylogeny, have not been studied previously. Based on size categories, five or six larval stages can be recognized. The larvae approximately double their length and width during development (length: 230-520 microm). Most morphological features stay largely unchanged during development, but the antennal coxal masticatory spines are significant exceptions: they become bifid after one of the first molts. In all larval stages only the antennae and the mandibles actively move. In late naupliar stages the trunk limbs become visible as rows of laterally placed, undeveloped, and still immovable lobes. Swimming is performed by the antennae, whereas the mandibles appear to be involved mainly in feeding, as in other branchiopod larvae. The last naupliar stage undergoes a small metamorphosis to the first juvenile stage, the details of which in part were studied by following the premolt juvenile condition through the cuticle of the last stage nauplius. Among other changes there is a characteristic change in the shape and morphology of the univalved dorsal naupliar shield to a bivalved juvenile carapace. The general morphologies of the antennae and the mandibles are very similar to those of other branchiopod larvae and fall well within the "branchiopod naupliar feeding apparatus" recognized as a branchiopod synapomorphy by Olesen (2003), but some specific features shared with the larvae of other "conchostracans" are also identified. These special "conchostracan" features include: 1) a similar antennular setation; 2) a similar comb-like setulation of the bifid antennal coxal processes; and 3) mandibular palpsetae with setules condensed. In light of recent suggestions concerning branchiopod phylogeny (Cyclestheria as a sister group to the Cladocera), these similarities probably do not support a monophyletic "Conchostraca" but rather are symplesiomorphies of this taxon. A final decision must await a phylogenetic analysis of a more complete set of characters.     

SEM studies on the early larval development of Triops cancriformis (Bosc)(Crustacea: Branchiopoda, Notostraca)

We investigated early larval development in the notostracan Triops cancriformis (Bosc, 1801–1802) raised from dried cysts under laboratory conditions. We document the five earliest stages using scanning electron microscopy. The stage I larva is a typical nauplius, lecithotropic and without trunk limbs. The stage II larva is feeding and has trunk limb precursors and a larger carapace. Stage III larvae have larger trunk limbs and a more adult shape. Stage IV larvae have well developed trunk limbs, and stage V larvae show atrophy of the antennae. We describe the ontogeny of selected features such as trunk limbs and carapace, discuss ontogeny and homologization of head appendages, follow the development of the feeding mechanism, and discuss trunk limb ontogeny.     

Comparative morphology among trunk limbs of Caenestheriella gifuensis and Leptestheria kawachiensis (Crustacea: Branchiopoda: Spinicaudata)

Morphological differences among groups of the 24 trunk limbs of Caenestheriella gifuensis (Ishikawa, 1895) and differences between males and females are described and illustrated. A setose attenuate lobe located proximally near enditic lobe 1 and a discoid lobe covered with small setae proximal to enditic lobe 1 are newly described. The five ventral enditic lobes, endopod, exopod, and dorsal exite of traditional spinicaudatan morphology are redescribed. Trunk limbs 1–4 of females bear a palp on enditic lobe 5 and trunk limbs 1–15 of males bear a similar palp. A second, articulating palp is associated with the base of the endopod of trunk limbs 1–2 of males. The proximal part of trunk limbs 19–24, bearing enditic lobe 1, articulates by an arthrodial membrane with the remainder of the limb, and the exite is distal to this arthrodial membrane. Development of trunk limbs, ascertained through an examination of early juvenile instars of Leptestheria kawachiensis Uéno, 1927, includes an asetose limb followed in time by a series of setose limbs that increase in morphological complexity with age. The number of lobes on the asetose limb varies from seven (corresponding to five enditic lobes, an endopod, and an exopod) on anterior limbs to five on trunk limb 24, which lacks the lobes corresponding to enditic lobe 4 and the endopod; these two structures are added later to setose limbs. The attenuate lobe, the discoid lobe, the exite of all trunk limbs, and the palps of the anterior trunk limbs are added to the setose limbs. Development of anterior limbs is accelerated relative to that of posterior limbs, and development of the more posterior limbs is truncated relative to that of limbs immediately anterior to them. Enditic lobe 4 and the endopod of limbs like trunk limb 24 develop from, or are patterned by, enditic lobe 5; the articulating palp of male trunk limbs 1–2 also may be added in this way. A comparison of these observations with development of the copepod maxilliped suggests that the spinicaudatan trunk limb is composed of a praecoxa with three lobes, a coxa and a basis each with one lobe, and an endopod of three segments in females and four in males. This is similar to the homology scheme previously proposed by Hansen in 1925. A critique is given of attempts to homologize parts of arthropod limbs based on developmental gene expression patterns. Stenopodal to phyllopodal transformations of maxillipeds in copepods provide a model at least partly applicable to spinicaudatans, and a ‘multibranched’ interpretation of spinicaudatan (and by extension branchiopodan) limb morphology is rejected. There is nothing intrinsic to the structure of the adult trunk limbs suggesting that they are similar to the adult limbs of the ancestral branchiopod or the ancestral crustacean, but early developmental steps of more posterior limbs are good matches for the morphology of an ancestral crustacean biramal limb predicted by a hypothesis of duplication of the proximo‐distal axis. © 2003 The Linnean Society of London, Zoological Journal of the Linnean Society, 2003, 139 , 547–564. No claim to original US government works.     

Review of naupliar development among Miraciidae (Copepoda,Harpacticoida) with a naupliar description of <Emphasis Type="Italic">Paramphiascella</Emphasis><Emphasis Type="Italic">choi</Emphasis> sp. nov. from Thailand

Both genders of Paramphiascella choi sp. nov. were collected from the green alga Enteromorpha clathrata in Rayong province, Thailand. P. choi shares with other species of the genus: cylindrical body shape, rostrum not bifid, eight-segmented antennules, three-segmented exopodal antenna, and female P5 exopod with five setae. The new species distinguished from other conspecific species by: three-segmented exopodal antenna, inner edge of basis of male P1 and P2 bear a bare ovate-knob each. Enp-1 very elongate, Enp-2 of male P2 transformed into a large, strong, slightly curved and tapering attenuation with two central chitinous ridges, and bearing one medially directed knob close to enp-1. At the base of this knob arise three plumose setae of unequal length. These characters are suggested to be autapomorphies of the new species. Six naupliar stages are obtained and described a key for the identification of stages is provided. Nauplius I has one pair of caudal setae; three-segmented antennules; antenna consists of a coxa, basis, endopod and exopod; mandible has a coxa, basis, endopod and exopod; hindbody bears two caudal setae. Nauplius II develops one aesthetasc on the antennule; antenna has added an arthrite arising from the coxa; mandible has a row of tiny spinulose setae. Nauplius III has added two pairs of caudal setae. Nauplius IV bears bilobed bud of the maxillule armed with two setae and four pairs of caudal setae. Nauplius V bears a multilobed bud of the maxillule with three setae and five pairs of caudal setae. At Nauplius VI, the buds of swimming legs 1 and 2 are added.     

The larval development of an Australian limnadiid clam shrimp (Crustacea, Branchiopoda, Spinicaudata), and a comparison with other Limnadiidae

The adult morphology of the Australian Limnadopsis shows some remarkable differences to that of other Limnadiidae. These differences are not reflected in its larval development. In Limnadopsis parvispinus, larval development comprises six stages. In stages I and II only the three naupliar appendages are present: the antennule as a small bud, the biramous antenna as the main swimming organ, and the mandible. The antennal protopod bears two endites, the proximal naupliar process and a more distal endite. In stage III a bifid naupliar process (in earlier stages not bifid) and the first signs of the carapace and trunk limb anlagen (undifferentiated rudiments) appear. In stage IV the carapace anlagen become more pronounced. The number of trunk limb anlagens increases to five, and differentiation has commenced. In stage V the first five pairs of trunk limbs are differentiated to varying degrees. The anterior-most four pairs of trunk limbs are subdivided into five endites, a small endopod, an exopod and an epipod. The bivalved carapace covers the anterior-most limbs. In larval stage VI the carapace is larger and the trunk limbs are further differentiated. A general pattern in the sequence of larval stages is the increasing number of sensilla on the antennules. From the last larval to the first postlarval stage, a significant change in morphology takes place. The trunk limbs are now used for swimming. Typical larval organs are much smaller than in the last larval stage. A comparison with other representatives of the Limnadiidae shows a high degree of correspondence, with most differences explained by the heterochronous appearance of characters during development. Five to seven stages are described for all studied Limnadiidae, including one particular stage in which four fully developed setae, a bifid naupliar process and the first signs of carapace anlagen are present. These characters are found in stage III in L. parvispinus, Limnadia stanleyana, Eulimnadia texana, and Imnadia yeyetta but in stage IV in E. braueriana and L. lenticularis. Based on a comparison of the larval stages of six limnadiid and one cyzicid species, we conclude that at least six naupliar stages belong to the limnadiid ground pattern.     

Naupliar and Metanaupliar Development of Thysanoessa raschii (Malacostraca,Euphausiacea) from Godth?bsfjord,Greenland, with a Reinstatement of the Ancestral Status of the Free-Living Nauplius in Malacostracan Evolution

The presence of a characteristic crustacean larval type, the nauplius, in many crustacean taxa has often been considered one of the few uniting characters of the Crustacea. Within Malacostraca, the largest crustacean group, nauplii are only present in two taxa, Euphauciacea (krill) and Decapoda Dendrobranchiata. The presence of nauplii in these two taxa has traditionally been considered a retained primitive characteristic, but free-living nauplii have also been suggested to have reappeared a couple of times from direct developing ancestors during malacostracan evolution. Based on a re-study of Thysanoessa raschii (Euphausiacea) using preserved material collected in Greenland, we readdress this important controversy in crustacean evolution, and, in the process, redescribe the naupliar and metanaupliar development of T. raschii. In contrast to most previous studies of euphausiid development, we recognize three (not two) naupliar (= ortho-naupliar) stages (N1-N3) followed by a metanauplius (MN). While there are many morphological changes between nauplius 1 and 2 (e.g., appearance of long caudal setae), the changes between nauplius 2 and 3 are few but distinct. They involve the size of some caudal spines (largest in N3) and the setation of the antennal endopod (an extra seta in N3). A wider comparison between free-living nauplii of both Malacostraca and non-Malacostraca revealed similarities between nauplii in many taxa both at the general level (e.g., the gradual development and number of appendages) and at the more detailed level (e.g., unclear segmentation of naupliar appendages, caudal setation, presence of frontal filaments). We recognize these similarities as homologies and therefore suggest that free-living nauplii were part of the ancestral malacostracan type of development. The derived morphology (e.g., lack of feeding structures, no fully formed gut, high content of yolk) of both euphausiid and dendrobranchiate nauplii is evidently related to their non-feeding (lecithotrophic) status.     

First report of antennular attachment organs in a barnacle nauplius larva

Larvae released from Newmaniverruca albatrossiana were cultured in the laboratory until the cypris stage. The brood size of individuals was low, about 60 larvae per brood. The exact number of instars was not determined. Early instars had the morphology normally seen in lecithotrophic nauplii of thoracican cirripedes. They had uniramous antennules with a few apical setae and biramous antennae and mandibles equipped with natatory setae only. Neither antennae nor mandibles carried any enditic spines or setae and the mouth cone was diminutive. The last nauplius stage obtained in our cultures was typical except in the structure of antennules. The head shield was enlarged but not flexed down, the antennae and mandibles were virtually unchanged from earlier instars, and the ventral thoracic process was well developed but without any external appendages. In contrast, the antennules had the complex shape and segmentation otherwise seen only in cypris larvae, where they are used for bipedal walking on the substratum in search of a settlement site. The similarity included the specialized shape of the first two antennular segments and the specialization of the third as an attachment organ. Nauplii just prior to this last instar had simple, straight antennules but completely lacked setae and instead terminated bluntly in what appears to be an incipient attachment organ. The presence of cypris-like antennules in late nauplii has not previously been recorded in cirripedes. We suggest that this will allow the larvae to attach on the substratum temporarily before they reach the cypris instar and this will increase the chance of settling successfully on their rare substratum (sea urchin spines). The specialization in late N. albatrossiana nauplii will therefore decrease mortality during the larval phase and thus counterbalance the very low breeding potential in this deep-sea species.     

Larval development of the pedunculate barnacles Octolasmis angulata Aurivillius 1894 and Octolasmis cor Aurivillius 1892 (Cirripedia: Thoracica: Poecilasmatidae) from the gills of the mud crab,Scylla tranquebarica Fabricius, 1798

Detailed studies of larval development of Octolasmis angulata and Octolasmis cor are pivotal in understanding the larval morphological evolution as well as enhancing the functional ecology. Six planktotrophic naupliar stages and one non-feeding cyprid stage are documented in details for the first time for the two species of Octolasmis. Morphologically, the larvae of O. angulata and O. cor are similar in body size, setation patterns on the naupliar appendages, labrum, dorsal setae-pores, frontal horns, cyprid carapace, fronto-lateral gland pores, and lattice organs. Numbers of peculiarities were observed on the gnathobases of the antennae and mandible throughout the naupliar life-cycle. The setation pattern on the naupliar appendages are classified based on the segmentation on the naupliar appendages. The nauplius VI of both species undergoes a conspicuous change before metamorphosis into cyprid stage. The cyprid structures begin to form and modify beneath the naupliar body towards the end of stage VI. This study emphasises the importance of the pedunculate barnacle larval developmental studies not only to comprehend the larval morphological evolution but also to fill in the gaps in understanding the modification of the naupliar structures to adapt into the cyprid life-style.     

Larval and post-larval development of the branchiopod clam shrimp Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Conchostraca, Spinicaudata)

The larval and post-larval development of Cyclestheria hislopi is examined by SEM. There are at least nine stages (excluding the adult) – six larval and three post-larval stages. The first four stages are passed within the egg-membrane. The larval and the post-larval phase are separated by a profound change in morphology that takes place between stages VI and VII. The larva shifts from a dorso-ventrally flattened 'larval' appearance up to stage VI to a laterally flattened, more 'adult' appearance from stage VII. New morphological data have been revealed by this study, including (1) a large and globular larval dorsal organ; (2) the carapace starts its development from the segments of the first and second maxillae; (3) the anterior ramus of the second antenna in adult Cyclestheria hislopi is the endopod, and the posterior ramus the exopod. Direct development of the brood in Cyclestheria hislopi – unique among conchostracans – is compared with that of the Cladocera. If Cyclestheria is the sister group to the Cladocera, as favoured in this work, the classical neoteny theory of the Cladocera must be reconsidered, as there is no particular similarity between any adults of the Cladocera and any of the larval stages of Cyclestheria . It is suggested that Cyclestheria displays the type of development present in a cladoceran ancestor. A comparison between Cyclestheria and the Upper Cambrian 'Orsten' fossil Rehbachiella kinnekullensis reveals a remarkable similarity in the endite morphology of the trunk limbs.     

The first-stage zoeas of Carpilius convexus (Forskal, 1775) and Carpilius maculatus (Linnaeus, 1758) (Crustacea: Decapoda: Brachyura: Xanthoidea: Carpiliidae): an example of heterochrony

The first-stage zoeas of Carpilius convexus (Forskål,1775) and Carpilius maculatus (Linnaeus, 1758) are describedand fully illustrated. Both these Indo-West Pacific speciesexhibited a unique xanthoidean character for the basis of thesecond maxilliped, which possesses five (arranged 1,1,1,2) setaeinstead of the expected four (arranged 1,1,1,1). A comparisonwith the zoeal stages of Carpilius corallinus (Herbst, 1783)as reported by Laughlin et al. (Laughlin et al., 1983) revealedmarked differences including the possession of carapace lateralspines (v. absent in C. convexus only), the subterminal setationof the distal maxillule endopod segment with two subterminalsetae (versus one subterminal seta in Indo-West Pacific species),the terminal setation of the distal maxillule endopod segmentwith four setae (versus three setae in C. convexus only), twolateral spines on the telson (versus three in Indo-West Pacificspecies) and the number of zoeal stages. The first-stage zoeasof the two Indo-West Pacific species appear to have hatchedin a more advanced state of development than those of C. corallinus,and the expression of a number of characters has been accelerated(early onset). In fact, the zoeal stages of both Indo-West Pacificspecies and carpiliid species appear to be abbreviated becausethe first zoeas are considered to be equivalent to the third-stagezoeas of C. corallinus.     

<Emphasis Type="Italic">Foxtosognus rarus</Emphasis> gen. n., sp. n.—A new genus and species of copepods (Copepoda: Calanoida) from the abyssopelagic zone of the Kuril-Kamchatka Trench

A female of Foxtosognus rarus gen. n., sp. n., a new genus and species of copepods, is described from the abyss of the Kuril-Kamchatka Trench. The new genus is placed in the family Arctokonstantinidae, whose diagnosis is emended and supplemented with the following characters: mandibular basis with one to two setae; mandibular endopod one without setae; maxillular distal basal endite plus endopod with two to four setae or without setae. The features that distinguish Foxtosognusgen. n. from other representatives of this family are as follows: mandibular palp with a long endopod segment one, endopod segment two with seven setae, and exopod segment five with two setae; maxillula with distal basal endite lacking setae and separated from endopod bearing three setae; maxillular precoxal arthrite with seven to eight setae and exopod with four setae; maxilliped syncoxa without setae on precoxal endites and endopod of three segments. The genera Sognocalanus and Foxtonia earlier included in the Spinocalanidae are herein transferred to the Arctokonstantinidae.     

External morphology of the male of Cyclestheria hislopi (Baird, 1859) (Crustacea, Branchiopoda, Spinicaudata), with a comparison of male claspers among the Conchostraca and Cladocera and its bearing on phylogeny of the 'bivalved' Branchiopoda

The adult male of Cyclestheria hislopi, sole member of the spinicaudate conchostracan clam shrimp family Cyclestheriidae and a species of potential phylogenetic importance, is described for the first time. Several previously unknown features are revealed. Among these are (1) the morphology of the dorsal organ, which is roughly similar in shape to the supposedly homologous structure in other clam shrimps but bears a relatively large, centrally located pore unique to the species; (2) an anterior cuticular pore presumably leading to the ‘internal’ space surrounding the compound eyes, and thereby homologous to the same pore in other clam shrimps and in the Notostraca; (3) the spination and setation of the antennae and thoracopods, and (4) the mature male first thoracopods (claspers). The male claspers are paired and essentially equal in size and shape on right and left sides of the body. The second pair of thoracopods are not modified as claspers, a situation different from all other spinicaudate families but shared (plesiomorphic we propose) with the laevicaudatans and most cladocerans. The claspers bear a field of special spine-like setae on the extremity of the ‘palm’; this setal type, previously unrecognized, is unique to Cyclestheria. The palm of the clasper also bears two palps (one very small), as in other conchostracan species (both laevicaudatans and spinicaudatans). The movable finger of the clasper, modified from the thoracopod endopod, bears a row of long setae along its outer extremity, also unique. Cyclestheria exhibits a mixture of characters, some unique and others typical of the Spinicaudata (Conchostraca). Cladoceran clasper types are briefly reviewed. as are the claspers in the Spinicaudata and Laevicaudata (Conchostraca). Morphology of the clasper of Cyclestheria shows typical spinicaudate characters. It is suggested that claspers on the first thoracopods may be a synapomorphy for the Conchostraca and the Cladocera. The possible role of Cyclestheria or a Cyclestheria-like ancestor in cladoceran phylogeny is briefly discussed in light of recent suggestions (Martin and Cash-Clark, 1995) of cladoceran monophyly and possible ancestral relationships with this genus. Some possibilities concerning the phylogenetic position of Cyclestheria–either as a sister group to the rest of the Spinicaudata or as a sister group to the Cladocera—are discussed.     

Larval development of Balanus reticulatus Utinomi, 1967 (Cirripedia, Thoracica) and a comparison with other barnacle larvae

The morphological features of the cephalic shield, labrum, abdominalprocess, antennules, antennae and mandibles of Balanus reticulatusare described and illustrated. The size and setation formulaeof the larvae are given at each stage. The trilobed labrum andlateral margin of the cephalic shield with numerous small spinesare diagnostic features for all the subsequent nauplius stages.Numerous small denticulate processes on the surface of the cypridcarapace are major morphological characteristics not found inother balanomorph species. We have constructed keys from stageII to stage VI for the predominant barnacle nauplii of Koreancoastal waters, based on morphological traits such as totallength, shield width, labrum shape, the presence or absenceof posterior shield spines and dorsal shield spines in stagesIV, V and VI, the specific setal type in the fourth segmentof the antennal endopodite, and setation formulae of Pollicipesmitella, Chthamalus challengeri, Megabalanus rosa, B.reticulatus,Balanus amphitrite and Balanus albicostatus.     

Redescription of the Chengjiang arthropod Squamacula clypeata Hou and Bergström, from the Lower Cambrian, south-west China

The anatomy of the arthropod Squamacula clypeata Hou and Bergström, 1997 from the Lower Cambrian Chengjiang Lagersta¨tte is redescribed based on four newly excavated specimens. The new material was collected from localities recently discovered in the Kunming area, Yunnan Province, south-west China, and preserves remarkable details of the ventral morphology, revealed by preparation. Squamacula clypeata is dorsoventrally flattened and rounded in outline. The cephalon was covered by a wide, short shield, with a large doublure and a pair of uniramous antennae on the ventral side. The thorax consists of nine somites, each protected by a tergite and carrying at least one pair of biramous limbs. The pygidium is covered with a small rounded tergum. The endopod is segmented, equipped with short spines on the inner margin of the coxa and a claw-like structure distally, and the exopod flap-like, fringed with setae. The limbs in the pygidium are like those in the thorax in shape. Squamacula was most probably a nektobenthic predator. The spinose endopod could walk, grasp and grind. The large flap-like exopod was adapted for swimming and respiration. Its affinities lie with the Arachnomorpha, but the relationships with other known taxa remain ambiguous.     

Homology of Holocene ostracode biramous appendages with those of other crustaceans: the protopod, epipod, exopod and endopod

Unambiguously biramous appendages with a proximal precoxa, well-defined coxa and basis, setose plate-like epipod originating on the precoxa, and both an endopod and exopod attached to the terminal end of the basis are described from several living Ostracoda of the order Halo-cyprida (Myodocopa). These limbs are proposed as the best choice for comparison of ostracode limbs with those of other crustaceans and fossil arthropods with preserved limbs, such as the Cambrian superficially ostracode-like Kunmingella and Hesslandona. The 2nd maxilla of Metapolycope (Cladocopina) and 1st trunk limb of Spelaeoecia, Deeveya and Thaumatoconcha (all Halocypridina) are illustrated, and clear homologies are shown between the parts of these limbs and those of some general crustacean models as well as some of the remarkable crustacean s.s. Orsten fossils. No living ostracodes exhibit only primitive morphology; all have at least some (usually many) derived characters. Few have the probably primitive attribute of trunk segmentation (two genera of halocyprid Myodocopa, one order plus one genus of Podocopa, and the problematic Manawa); unambiguously biramous limbs are limited to a few halo-cyprids. Homologies between podocopid limbs and those of the illustrated primitive myodocopid limbs are tentatively suggested. A setose plate-like extension, often attached basally to a podocopid protopod, is probably homologous to the myodocopid epipod, which was present at least as early as the Triassic. Somewhat more distal, less setose, and plate-like extensions, present on some podocopid limbs (e.g., mandible), may be homologous instead to the exopod (clearly present on myodocopid mandibles). The coxa (or precoxa) is by definition the most basal part of the limb. A molar-like tooth is present proximally on the mandibular protopod of many ostracodes; it is the coxal endite and projects medially from the coxa (or proximal protopod). The Ostracoda is probably a monophyletic crustacean group composed of Myodocopa and Podocopa. All have a unique juvenile (not a larva) initially with three or more limbs. Except that juveniles lack some setae and limbs, they are morphologially similar to the adult. Thus the following suite of characters in all instars may be considered a synapomorphy uniting all Ostracoda: (1) Each pair of limbs is uniquely different from the others. (2) The whole body is completely enclosed within a bivalved carapace that lacks growth lines. (3) No more than nine pairs of limbs are present in any instar. (4) The body shows little or no segmentation, with no more than ten dorsally defined trunk segments. No other crustaceans have this suite of characters. A probable synapomorphy uniting the Podocopa is a 2nd antenna with exopod reduced relative to the endopod.     

Unusual sensory setae of the raptorial Branchinecta gigas (Branchiopoda: Anostraca)

In many vernal pools, visibility is very poor because of the turbidity from suspended clay particles. For predatory species like Branchinecta gigas, these conditions can be detrimental to successful prey capture. In vernal lakes in central California, B. gigashave developed specialized hunting modes to capture anostracan prey in pools of low visibility. The position of their body, the kinematics of their locomotion, and their reduced eye size suggested the possibility of novel sensory structures on their antennae and/or their cercopods designed to enhance their prey capture abilities. Using Scanning Electron Microscopy, we investigated the presence and design of sensory setae on the antennae and cercopods of B. gigas. On both males and females, there are dense patches of sensilla along the length of the antennae. They are oriented ventrally and slightly anteriorly. These antennal setae appear to be chemosensory in structure and position; they resemble antennal setae of other branchiopods. However, the setae of the cercopods are unusual in their morphology and location on the appendage. The cercopods, which are bent over the head in the hunting position, have a linear arrangement of specialized setae on their ventral side. They are jointed setae with an anterior crown of protective spines. The setal joint only permits limited abduction either toward the head in the hunting position or ventrally when swimming. These setae appear to be mechanosensory in function and may be adaptations to a raptorial lifestyle. They correlate well with the behavioral components of hunting in B. gigasand their complex prey capture mechanism.