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 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.     

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.     

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.     

Evolutionary systematics of the Australian Cyzicidae (Crustacea,Branchiopoda, Spinicaudata) with the description of a new genus

In Australia's arid and semi‐arid zone, most aquatic habitats are nonpermanent. Although approximately 70% of its land surface belongs to these zones, very little is known of the iconic ‘large branchiopods’ that inhabit these important and widespread habitats. In the present study, we investigated 737 Australian specimens of the spinicaudatan taxa Caenestheria and Caenestheriella with a combination of one mitochondrial (cytochrome oxidase subunit I; COI) and three nuclear (elongation factor 1α, internal transcribed spacer 2, and 28S) markers to assess the diversity of species, their phylogenetic relationships, and phylogeographical history. The initial species delimitation was based on COI employing a combination of phylogenetic analyses and two automated approaches to species delimitation (general mixed Yule coalescent model and Automated Barcode Gap Discovery). The outcome was tested by the nuclear markers and considered under differing species concepts. The number of delineated species ranged from 14–27, in no case being in full agreement with any of the two automated approaches. The lower numbers resulted if inferred reproductive isolation, as required for the biological or Hennigian species concept, was employed. Although nuclear markers did not indicate ongoing reproduction, the lack of sympatric co‐occurrences inhibited inferences of definitive reproductive isolation in several instances. If monophyly or an ‘independent evolutionary fate’ was employed, as required for the phylogenetic or evolutionary species concepts, the species' distribution was of no importance and up to 27 species could be delimitated. Because the Australian representatives of both studied genera could not be clearly separated from each other but constitute a single monophyletic clade separated from all available non‐Australian representatives of these genera, we describe a new spinicaudatan genus Ozestheria gen. nov. to accommodate these species. Populations revealed relatively small levels of genetic differentiation over large areas of central and eastern Australia. By far the most pronounced levels of genetic differentiation were observed towards the north‐eastern regions, a pattern possibly explainable by ecological conditions and the movement of nomadic water birds that disperse resting eggs. © 2015 The Linnean Society of London     

SEM investigations of the larval development of Imnadia yeyetta and Leptestheria dahalacensis (Crustacea: Branchiopoda: Spinicaudata)

This paper presents a SEM documentation of the larval development of the two most abundant Austrian conchostracan species, Imnadia yeyetta (Limnadiidae) and Leptestheria dahalacensis (Leptestheriidae). As in several previously examined spinicaudatan species, five larval stages were documented: Nauplius 1, Nauplius 2, Metanauplius, Peltatulus, and Heilophore. Additionally, three postlarval stages of L. dahalacensis and the first larval instars of Eoleptestheria ticinensis and Limnadia lenticularis are shown and compared with the examined stages. Species identification of conchostracan larval stages is possible by using surface structures, and using SEM methods, except for L. lenticularis which can be identified more easily on the characteristic shape of the labrum.     

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.     

On the ontogeny of Leptodora kindtii (Crustacea,Branchiopoda, Cladocera), with notes on the phylogeny of the Cladocera

Leptodora kindtii, a large predaceous cladoceran, is among the most deviant species of the Cladocera. Therefore, its phylogenetic position has traditionally proven difficult to determine. Its many peculiar features include, among others, long, stenopodous, forwardly directed trunk limbs, a posteriorly placed dorsal brood pouch, a tri-lobed lower lip, and a long, segmented abdomen. This study describes the ontogeny of L. kindtii (Haplopoda), including general body proportions, appendages, the carapace, and other external structures in an attempt to facilitate the comparison of its aberrant morphology to that of other branchiopods. In general, the early embryos are similar to the early embryos of other cladoceran taxa with respect to body shape and size and position and orientation of the early limb buds. Many of the unusual features of L. kindtii appear late in ontogeny. The carapace appears at an early stage as a pair of dorsolateral swellings in a position corresponding to the gap between the mandibles and the first pair of trunk limbs; it later becomes posteriorly transposed by a gradual fusion of its more anterior parts to the dorsal side of the thorax. The tri-lobed "lower lip," under the labrum of the late embryo and the adult, develops as a fusion of the first maxillae (lateral lobes) to an elevated sternal region behind the mouth (median lobe). The stenopodous, segmented trunk limbs in the adult develop from embryonic, elongate, subdivided limb buds, similar to those seen in early stages of other branchiopods. Two conflicting possibilities for the phylogeny of the Cladocera, involving two different positions of L. kindtii (Haplopoda), are discussed. Several characters support a sister-group relationship between the Haplopoda and Onychopoda. However, some characters support the Anomopoda and Onychopoda as sister groups, leaving the Haplopoda outside this clade. In contrast to recent suggestions, we prefer to retain the term "Cladocera" in its original sense as comprising the Haplopoda, Ctenopoda, Anomopoda, and Onychopoda.     

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.     

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.     

Taxonomic notes on Cryptamorpha sculptifrons Reitter (Coleoptera,Silvanidae), with description of its larval morphology

Cryptamorpha sculptifrons Reitter, 1889 is redescribed and a lectotype and paralectotype are designated. The mature larva of C. sculptifrons is described. It is hypothesized that a variety described by Grouvelle (1908), C. sculptifrons var. punctifrons from India, might not be conspecific with Japanese C. sculptifrons. It is also suggested that larvae of Cryptamorpha can be distinguished from larvae of the tribe Brontini by the relatively thick antennae and the 3rd antennomere which is less than 3/4 of the length of the 2nd.     

Further expansion of the genus Cercopagis (Crustacea,Branchiopoda, Onychopoda) in the Baltic Sea,with notes on the taxa present and their ecology

The onychopod cladoceran Cercopagis that recently invaded the Baltic Sea is reported from new zones of the northern Baltic proper. Because of successful survival and an expanding distribution range, the addition of Cercopagis to the Baltic fauna is considered to be permanent. What has previously been cited as Cercopagis pengoi encompasses the morphology of several other species, subspecies and forms. Either a number of morphologically similar species is present, or there is a number of spurious species in Cercopagis. The last hypothesis is favoured. The spatial distribution pattern of Cercopagis, as well as that of total zooplankton, was correlated with depth. Deep (>100 m) and shallow (<10 m) stations had significantly lower abundance than stations of intermediate depth (<100 m). An overview of the distribution of C. pengoi group in fresh and brackish waters suggests a high tolerance to environmental factors, but with differences among taxa. Due to this ecological flexibility, the colonization of the Baltic is not unexpected. Increasing salinity may restrict dispersal of cercopagids to the southern areas of the Baltic and to the North Sea, but inland lakes (e.g. in Sweden) present an ecological profile suitable for colonization.     

Characterization and mapping of sensilla on the head appendages of noterid larvae (Coleoptera: Noteridae), and development of a preliminary biometric method for taxa delimitation

Larvae of the burrowing water beetle family Noteridae are distributed worldwide and are often abundant in a broad range of aquatic habitats, playing an important role in structuring freshwater communities, yet they have remained among the most poorly studied groups of aquatic beetles. Studies on sensillar equipment of aquatic insect larvae are largely lacking, despite their potential use in phylogeny and biometric identification methods. In this article, the external morphology and distribution of sensilla on the head appendages of first instar larvae of selected genera of Noteridae were examined using scanning electron microscopy. Seven main types were distinguished based on their morphological structure: basiconica (3 subtypes), campaniformia (2 subtypes), chaetica (7 subtypes), coeloconica (6 subtypes), coniform complex (2 subtypes), placodea, and styloconica (3 subtypes). The apex of the labial palpus was found to be the most variable and informative region in regard to the number, relative position, and topology of sensilla. Fingerprint models were, therefore, generated for this region in each of the studied genera, allowing their identification.     

Morphology of two marine euplotids (Ciliophora: Euplotida), Aspidisca fusca and A. hexeris,with notes on their small subunit rRNA gene sequences

We investigate the living morphology, infraciliature, and small subunit rRNA gene sequences of two poorly known marine euplotids, Aspidisca fusca Kahl, 1928 and A. hexeris Quennerstedt, 1869, isolated from intertidal sewage outfall, northern China and sandy sediments, southern China, respectively. Improved diagnoses and morphometric data are provided for both species. Aspidisca fusca is characterized by having a peristomial spur, seven frontoventral cirri in a “polystyla-arrangement”, and two oval macronuclear nodules. Aspidisca hexeris can be recognized by having an elliptical body shape, a peristomial spur, seven membranelles in the anterior portion of adoral zone and 11–13 in the posterior part, as well as seven frontoventral cirri arranged in two oblique rows. In addition, the presence and degree of projections along the left margin of A. hexeris are highly variable among populations. Phylogenetic analyses based on small subunit rRNA gene sequence data support the validity of both A. hexeris and A. fusca as distinct species, and indicate that A. fusca is most closely related to A. aculeata and A. steini, whereas A. hexeris shows a close relationship with A. magna.     

Egg production, hatching rates, and abbreviated larval development of Campylonotus vagans Bate, 1888 (Crustacea: Decapoda: Caridea), in subantarctic waters

Early life history patterns were studied in the caridean shrimp, Campylonotus vagans Bate, 1888, from the subantarctic Beagle Channel (Tierra del Fuego). As a consequence of very large egg size (minimum 1.4 mm), fecundity was low, ranging from 83 to 608 eggs per female (carapace length [CL] 11-22.5 mm). Egg size increased continuously throughout embryonic development, reaching prior to hatching about 175% of the initial diameter. Due to low daily numbers of larval release, hatching of an egg batch lasted for about 2-3 weeks. The complete larval and early juvenile development was studied in laboratory cultures fed with Artemia sp. nauplii. At 7.0±0.5 °C, development from hatching to metamorphosis lasted for about 6 weeks. It comprised invariably two large zoeal stages and one decapodid, with mean stage durations of 12, 17, and 15 days, respectively. Larvae maintained without food survived on average for 18 days (maximum: 29 days), but did not reach the moult to the zoea II stage. Size increments at ecdysis were low in all larval stages (2.1-3.9%), indicating partial utilisation of internal energy reserves. A clearly higher increment (14%) was observed in the moult from the first to the second juvenile stage. Low fecundity, large size of eggs and larvae, an abbreviated mode of larval development, high larval survival rates during absence of food, demersal behaviour of the early life history stages, and an extended hatching period with low daily release rates are interpreted as adaptations to conditions typically prevailing in subantarctic regions, namely low temperatures (causing long durations of development) in combination with a pronounced seasonality in plankton production (i.e., short periods of food availability).     

Phylogenetic position and morphology of Raphidiophrys elongata sp. nov. (Haptista: Centroplasthelida) with notes on cyst wall structure and evolution

The majority of centrohelids bear external coverings consisting of organic spicules or siliceous scales. Cyst coverings are usually reinforced with additional layers of modified scales. The cyst wall of Raphidiophrys heterophryoidea has an unusual and complex structure. It consists of three different types of scales and includes the mosaic scale layer not known in other centrohelids. During excystment, the cyst wall fragments along the sutures of the mosaic layer. For other Raphidiophrys species, cyst coverings are not studied. The present paper describes a new Raphidiophrys species, R. elongata, belonging to the NC7 environmental clade. Trophozoites bore thin plate scales with reduced upper plate. Under starvation, cysts emerged in clonal cultures. Cyst coverings of R. elongata and R. heterophryoidea were studied in comparison with the use of FIB-SEM. Cyst wall of R. elongata was significantly thinner than in R. heterophryoidea and was formed with 3–5 layers of uniform overlapping scales. No mosaic scale layer was present. During excystment, trophozoite exited cyst shell through random fissure. Possible evolutionary events and driving forces behind the complication of cyst wall within Raphidiophrys were discussed.