Pair Of Walking Legs Research Articles

Expression of posterior Hox genes and opisthosomal appendage development in a mygalomorph spider

Spiders represent an evolutionary successful group of chelicerate arthropods. The body of spiders is subdivided into two regions (tagmata). The anterior tagma, the prosoma, bears the head appendages and four pairs of walking legs. The segments of the posterior tagma, the opisthosoma, either lost their appendages during the course of evolution or their appendages were substantially modified to fulfill new tasks such as reproduction, gas exchange, and silk production. Previous work has shown that the homeotic Hox genes are involved in shaping the posterior appendages of spiders. In this paper, we investigate the expression of the posterior Hox genes in a tarantula that possesses some key differences of posterior appendages compared to true spiders, such as the lack of the anterior pair of spinnerets and a second set of book lungs instead of trachea. Based on the observed differences in posterior Hox gene expression in true spiders and tarantulas, we argue that subtle changes in the Hox gene expression of the Hox genes abdA and AbdB are possibly responsible for at least some of the morphological differences seen in true spiders versus tarantulas.

Description of the mantle lure and novel mimicry of the endangered Cumberlandian Combshell (Epioblasma brevidens) in the Clinch River, eastern United States.

The Cumberlandian Combshell (Epioblasma brevidens) is an endangered freshwater mussel endemic to the Tennessee and Cumberland River drainages, major tributaries of the Ohio River of the eastern United States. We conducted mask and snorkel surveys in May and June of 2021 and 2022 to locate, observe, photograph, and video female E.brevidens to document their unique mantle lures at sites in the Clinch River in Tennessee and Virginia. The mantle lure is morphologically specialized mantle tissue that mimics prey items of the host fish. The mantle lure of E.brevidens appears to mimic four distinct characteristics of the reproductive anatomy of the underside (ventral) of a gravid female crayfish, to include: (1) the external apertures of the oviducts located on the base of the third pair of walking legs, (2) crayfish larvae still encased in the egg membrane, (3) pleopods or claws, and (4) postembryonic eggs. Surprisingly, we observed males of E.brevidens displaying mantle lures that were anatomically complex and closely resembled the female mantle lure. The male lure similarly mimics oviducts, eggs, and pleopods but is diminutive (2-3 mm smaller in length or diameter) to those same structures in females. We describe for the first time the mantle lure morphology and mimicry of E.brevidens, showing its close resemblance to the reproductive anatomy of a gravid female crayfish, and a novel form of mimicry in males. To our knowledge, mantle lure displays in males have not been previously documented in freshwater mussels.

Spider Origins: a Palaeontological Perspective

Spiders (Araneae) can be placed within a series of nested clades within Arachnida. Arachnopulmonata encompasses all arachnids with book lungs. Pantetrapulmonata encompasses arachnids with four pairs of lungs in their ground pattern. Tetrapulmonata potentially encompasses pantetrapulmonate arachnids which have reduced the number of lateral eye lenses and endites on the coxae of the first pair of walking legs. Serikodiastida encompasses arachnids with opisthosomal silk glands. Several spider-like fossils, some of which were previously interpreted as spiders, may belong either here or in the wider tetrapulmonate group. Araneida encompasses arachnids with spinnerets and a male palpal organ, and fossils reveal that the common ancestor of spiders would have retained a flagelliform telson. Araneae can thus be defined as spiders which have lost the telson, something which appears to have occurred multiple times among arachnids. The oldest fossil example of each of these clades is documented, and compared to molecular estimates of origination dates where available, to yield a broad temporal and phylogenetic framework for spider origins.

Genomic resources and toolkits for developmental study of whip spiders (Amblypygi) provide insights into arachnid genome evolution and antenniform leg patterning

BackgroundThe resurgence of interest in the comparative developmental study of chelicerates has led to important insights, such as the discovery of a genome duplication shared by spiders and scorpions, inferred to have occurred in the most recent common ancestor of Arachnopulmonata (a clade comprising the five arachnid orders that bear book lungs). Nonetheless, several arachnid groups remain understudied in the context of development and genomics, such as the order Amblypygi (whip spiders). The phylogenetic position of Amblypygi in Arachnopulmonata posits them as an interesting group to test the incidence of the proposed genome duplication in the common ancestor of Arachnopulmonata, as well as the degree of retention of duplicates over 450 Myr. Moreover, whip spiders have their first pair of walking legs elongated and modified into sensory appendages (a convergence with the antennae of mandibulates), but the genetic patterning of these antenniform legs has never been investigated.ResultsWe established genomic resources and protocols for cultivation of embryos and gene expression assays by in situ hybridization to study the development of the whip spider Phrynus marginemaculatus. Using embryonic transcriptomes from three species of Amblypygi, we show that the ancestral whip spider exhibited duplications of all ten Hox genes. We deploy these resources to show that paralogs of the leg gap genes dachshund and homothorax retain arachnopulmonate-specific expression patterns in P. marginemaculatus. We characterize the expression of leg gap genes Distal-less, dachshund-1/2 and homothorax-1/2 in the embryonic antenniform leg and other appendages, and provide evidence that allometry, and by extension the antenniform leg fate, is specified early in embryogenesis.ConclusionThis study is the first step in establishing P. marginemaculatus as a chelicerate model for modern evolutionary developmental study, and provides the first resources sampling whip spiders for comparative genomics. Our results suggest that Amblypygi share a genome duplication with spiders and scorpions, and set up a framework to study the genetic specification of antenniform legs. Future efforts to study whip spider development must emphasize the development of tools for functional experiments in P. marginemaculatus.

Jurassic arthropod tracks from northern Iran

In 2010, a siltstone slab containing three arthropod trackways was discovered in the Middle Jurassic Dansirit Formation in the Ruyan region, central Alborz Mountains, northern Iran. Quality of preservation is varied, but the best-preserved track sequences consist of a chevron-shaped pair of outer tracks surrounding two pairs of inner tracks. These trace fossils are named herein as a new ichnogenus and ichnospecies, Porpaichnus dansiritensis. The depositional environment of the track-bearing stratum is enigmatic. If the sediment is of littoral origin, the footprints were likely made by a decapod crustacean. For a terrestrial deposit, the imprint morphology is possible evidence of an arachnid that used its pedipalps to supplement four pairs of walking legs. These morphological characteristics suggest the track-maker is may have been an early member of the Infraorder Mygalomorpha. If so, the 170 Ma trackways are the earliest known evidence of a tarantula-like spider. Although the oldest known tarantula fossils date to the Miocene, fossil evidence of mygalomorph spiders dates to the Cretaceous, and molecular clock evidence suggests that divergence of spider families occurred in the late Paleozoic.

External morphogenesis of the tardigrade Hypsibius dujardini as revealed by scanning electron microscopy.

Tardigrada, commonly called water bears, is a taxon of microscopic panarthropods with five-segmented bodies and four pairs of walking legs. Although tardigrades have been known to science for several centuries, questions remain regarding many aspects of their biology, such as embryogenesis. Herein, we used scanning electron microscopy to document the external changes that occur during embryonic development in the tardigrade Hypsibius dujardini (Eutardigrada, Parachela, Hypsibiidae). Our results show an accelerated development of external features, with approximately 30 hrs separating the point at which external structures first become recognizable and a fully formed embryo. All segments appear to arise simultaneously between ∼20 and 25 hrs of development, and no differences in the degree of development could be detected between the limb buds at any stage. Claws emerge shortly after the limb buds and are morphologically similar to those of adults. The origin of the claws is concurrent with that of the sclerotized parts of the mouth, suggesting that all cuticular structures arise simultaneously at ∼30 hrs. The mouth arises as an invagination in the terminal region of the head at ∼25 hrs, closes later in development, and opens again shortly before hatching. The anlagen of the peribuccal lobes arise as one dorsal and one ventral row, each consisting of three lobes, and later form a ring in the late embryo, whereas there is no indication of a labrum anlage at any point during development. Furthermore, we describe limited postembryonic development in the form of cuticular pores that are absent in juveniles but present in adults. This study represents the first scanning electron micrographs of tardigrade embryos, demonstrating the utility of this technique for studying embryogenesis in tardigrades. This work further adds an external morphological perspective to the developmental data already available for H. dujardini, facilitating future comparisons to related panarthropod taxa. J. Morphol. 278:563-573, 2017. © 2017 Wiley Periodicals, Inc.

Application of Environmental Management on the Farming Practice of Mud Crab Scylla Serrata at Coastal Area of Ujung Alang, Cilacap, Indonesia: Efforts toward Sustainable Aquaculture

One of the biota associated strongly to the presence of mangrove forests as their habitat is the mangrove crab, Scylla serrata. Mangrove crab farming done in coastal areas the village of Ujung Alang, Cilacap was aimed to enlargement of the size of the juvenile (60g/ind.) to the commercial size (200g /ind.). Mutilation was done to determine the effect of the removal of part of locomotors and molting process. The experiment included 10 crabs without mutilation as a control (C); 10 crabs by removing the 3 left walking legs (T1); 10 crabs by removing the 3 right walking legs (T2); and 10 crabs by removing the 3 pairs of walking legs (T3). Monosex farming was done using a box made of polyethylene as a shelter. Based on observations during the 8 weeks, T3 treatment gave the highest score in body weight and carapace width and length. The first molting (M1) occurred for the crab-treated T3 has the best percentage of molting (100%) compared to other treatments. The observation area of crab farming, the natural habitat of mangrove forests or in the control area found as many as 82 species of macrobenthos of 44 families and of the 4 classes that include gastropods (60 species), polychaetes (14 species), bivalves (6 species), and crustaceans (2 species). Based on biotic and abiotic factors, the area of aquaculture and mangrove areas did not show significant differences, indicating the farming practices Scylla serrata in the shelter system is environmentally save.

The Hox genes Ultrabithorax and abdominal-A specify three different types of abdominalappendage in the springtail Orchesella cincta (Collembola)

BackgroundIn Drosophila and many other insects, the Hox genes Ultrabithorax (Ubx) and abdominal-A (abd-A) suppress limb formation on most or all segments of the abdomen. However, a number of basal hexapod lineages retain multiple appendages on the abdomen. In the collembolans or springtails, three abdominal segments develop specialized organs that originate from paired appendage primordia which fuse at the midline: the first abdominal segment bears the collophore (ventral tube), involved in osmoregulation; the fourth segment bears the furca, the leaping organ, and the third segment bears the retinaculum, which retains the furca at rest. Ubx and abd-A are known to be expressed in the springtail abdomen, but what role they play in specifying these distinct abdominal appendages is not known. This is largely because no genetic model has been established in collembolans or any other non-insect hexapod.ResultsWe have developed a convenient method for laboratory culture of the collembolan Orchesella cincta on defined media, a method for in-situ hybridization to embryos and a procedure for gene knockdown by parental injection of double-stranded RNA (RNAi). We show that Orchesella Ubx transcripts are detectable in the first to third abdominal segments, and abd-A transcripts in the second to fourth segments. Knockdown of Oc-Ubx leads to the homeotic transformation of the collophore into a pair of walking legs (a more anterior identity) but the retinaculum into a furca (a more posterior identity). Knockdown of Oc-abd-A leads to the transformation of the retinaculum into a collophore and of the furca into legs (both anterior transformations). Simultaneous silencing of both Oc-Ubx and Oc-abd-A transformed all three of these appendages into paired legs, but did not cause appendages to develop on the second, or on the most posterior abdominal segments.ConclusionsWe conclude that, in Orchesella, Oc-Ubx alone specifies the collophore on the first and Oc-abd-A alone specifies the furca on the fourth abdominal segment. Oc-Ubx and Oc-abd-A function together, apparently combinatorially, to specify the retinaculum on the third segment. The efficiency of RNAi in Orchesella makes this an attractive model for further genetic studies of development and physiology in basal hexapods.Electronic supplementary materialThe online version of this article (doi:10.1186/2041-9139-5-2) contains supplementary material, which is available to authorized users.

Expression patterns ofWntgenes in the venom claws of centipedes

The venom claws of centipedes, also known as forcipules, represent an evolutionary novelty that must have arisen in the centipede stem species, as they are not found in any other myriapods. The developmental-genetic changes that are involved in the origin of novelties are of considerable interest. It has previously been shown that centipede forcipules have a unique Hox code. However, this is a combinatorial code: no single Hox gene has a forcipule-specific expression. Here, we focus on Wnt genes. Two genes of this family show forcipule-specific expression in the "model centipede" Strigamia maritima: Wnt7 and Wnt11. For Wnt7, this forcipular expression zone seems to be a new one, which has arisen in evolution subsequently to other expression zones of the same gene. However, for Wnt11, the forcipule-specific expression probably arose by reduction of a more general pattern that originally included most or all of the limbs of an ancestral myriapod. Thus the developmental-genetic basis of the evolutionary change that turned the first pair of walking legs into venom claws is complex, involving different types of change in expression pattern. This sort of complexity is likely to be the case regarding evolutionary changes in morphology in general. Whether the origins of those features that can be considered as novelties are different in terms of their developmental-genetic basis from more routine evolutionary changes remains an open question.

Symely, a seldom occurring developmental anomaly in the spider Tegenaria atrica

This article presents the results of teratological studies on the spider Tegenaria atrica. Temperatures alternating between 14°C and 32°C every 12 h were applied as a teratogenic factor in the early stage of embryogenesis. This treatment resulted in specimens with various developmental malformations, including symely of the walking legs. Symely, which is one of the anomalies that results from disturbances during the formation of metameres to the germ band, usually affects the third and fourth pair of walking legs. Fusion of legs from the same pair entails changes in the symmetry of the whole body, particularly in the structure of prosoma and its position in relation to the opisthosoma. These changes are the cause of the exceptionally high mortality among embryos.

A ten-legged sea spider (Arthropoda: Pycnogonida) from the Lower Devonian Hunsrück Slate (Germany)

AbstractA new sea spider (Arthropoda: Pycnogonida) from the Lower Devonian Hunsrück Slate (Germany) is described asPentapantopus vogteligen. et sp. nov. This is the fifth pycnogonid species known from this exceptional fossil Lagerstätte. The most conspicuous character of the new species is the presence of five pairs of walking legs. This character, in concert with a reduced abdomen, indicates a phylogenetic position ofP. vogteliamong the crown group pycnogonids.P. vogteliextends the knowledge of fossil pycnogonid body plans and underlines the significance of the Hunsrück Slate, as this locality shows the highest diversity of sea spiders for the entire fossil record so far.

The delineation of the fourth walking leg segment is temporally linked to posterior segmentation in the mite Archegozetes longisetosus (Acari: Oribatida, Trhypochthoniidae)

Acari (mites and ticks) lack external segmentation, with the only indication of segmentation being the appendages of the prosoma (chelicerae, pedipalps, and four pairs of walking legs). Acari also have a mode of development in which the formation of the fourth walking leg is suppressed until the nymphal stages, following a hexapodal larva. To determine the number of segments in the posterior body region (opisthosoma) of mites, and to also determine when the fourth walking leg segment is delineated during embryogenesis, we followed the development of segmentation in the oribatid mite Archegozetes longisetosus using time-lapse and scanning electron microscopy, as well as in situ hybridizations of the A. longisetosus orthologues of the segmentation genes engrailed and hedgehog. Our data show that A. longisetosus patterns only two opisthosomal segments, indicating a large degree of segmental fusion or loss. Also, we show that the formation of the fourth walking leg segment is temporally tied to opisthosomal segmentation, the first such observation in any arachnid.

Comparative studies on the structure and development of the venom‐delivery system of centipedes, and a hypothesis on the origin of this evolutionary novelty

The venom-injecting forcipules of centipedes represent an evolutionary novelty that appeared in the centipede stem lineage more than 400 Ma. No other lineage of arthropods (or indeed of animals) has evolved claws for injecting venom from a pair of walking legs. However, little is known of the development, ultrastructure, or detailed function of centipede forcipules. Here, we provide comparative structural information on the venom duct apparatus that is the main functional system within each forcipule, based on scanning electron microscopy and transmission electron microscopy studies. We also give comparative developmental information, using DAPI staining, on embryonic forcipules from the four main centipede orders, including Scutigeromorpha. The photographs of Scutigera embryos we present are the first to be published for any species belonging to this order. The structure of the venom apparatus within each forcipule represents a discrete element of the novelty, whose origin requires a special explanation. This is in contrast to the novel external shape of the forcipules, which can be arrived at gradually by a series of changes from the starting point of a standard walking leg. Drawing on a proposed structural homology between venom glands and epidermal glands, we present a hypothesis of how the venom gland and duct may have arisen in evolution.

Protandric simultaneous hermaphroditism in Parhippolyte misticia (Clark, 1989) (Caridea: Hippolytidae): implications for the evolution of mixed sexual systems in shrimp

The sexual system of the shrimp Parhippolyte misticia (Clark, 1989), inhabiting the rocky subtidal at Okinawa, Japan and Kimbe Bay, Papua New Guinea, was examined. Dissections suggested that the population consisted of male phase (MP) and functional simultaneous euhermaphrodite (EH) individuals. MPs have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well-developed male portion containing sperm, but an undeveloped female portion. EHs lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well-developed ovaries containing mature oocytes and testes with sperm. When EHs were maintained in pairs, both shrimp molted and spawned eggs which attached below the pleon and developed as embryos, demonstrating that EHs can reproduce as males and inseminate other EHs acting as females. These results demonstrate that P. misticia is a protandric simultaneous hermaphrodite, as reported before for other shrimp of the genera Lysmata and Exhippolysmata. Also, these results suggest that protandric simultaneous hermaphroditism might have evolved more than once independently in shrimp from the diverse and species-rich Infraorder Caridea. Future research aimed at disentangling the phylogenetic relationship of Parhippolyte, Lysmata, Exhippolysmata and other closely related genera (Calliasmata, Lysmatella, Barbouria) and describing the sociobiology of additional representatives from the genera above is needed to understand the evolutionary history of sexual systems in caridean shrimp.

Protandric simultaneous hermaphroditism in the shrimps Lysmata bahia and Lysmata intermedia

Abstract. The sexual system of two peppermint shrimps, Lysmata bahia and Lysmata intermedia, inhabiting intertidal fossil coral terraces at Bocas del Toro, on the Caribbean coast of Panama, was examined. Dissections suggested that the population of each species consisted of functional males and functional simultaneous hermaphrodites. Males have cincinulli and appendices masculinae on the first and second pair of pleopods, respectively, gonopores located at the coxae of the third pair of walking legs, and ovotestes with a well‐developed male portion full of sperm, but an undeveloped female portion. Hermaphrodites lacked appendices masculinae and cincinulli. However, they have male gonopores and ovotestes with well‐developed ovaries full of mature oocytes and testes with sperm. When hermaphrodites were maintained in pairs, both molted and spawned eggs (to beneath abdomen) that continued developing after 3 d, demonstrating that hermaphrodites can reproduce as males and inseminate other hermaphrodites acting as females. The possibility of self‐fertilization or parthenogenetic reproduction was tested and disregarded, because hermaphrodites reared in isolation spawned oocytes that failed to develop, disappearing from the abdomen after 2 d. Males reared in pairs mature as hermaphrodites in <50 d, showing the ability of males to mature as hermaphrodites. These results demonstrate that L. bahia and L. intermedia are protandric simultaneous hermaphrodites, as reported for all species of this genus whose sexual system has been examined. However, the studied species featured a lifestyle, termed “tropical‐low abundance,” here not recognized previously for the genus; they occur in low abundances in tropical environments, they do not develop symbiotic associations with sessile invertebrates, and they are not conspicuously colored. Information on the sexual systems and lifestyles of more species needs to be examined before these observations can be placed into a comparative context within the genus.

A new species of Cyphophthalmi (Arachnida, Opiliones, Sironidae) from Eastern Slovenia

A new species of Cyphophthalmi belonging to the Laurasian family Sironidae is described and illustrated on the basis of external anatomy and genitalia. Siro crassus sp. n., known from leaf litter from two beech forest localities in Eastern Slovenia, is a relatively large (2.2–2.6 mm in length), long-legged epigean species, in which the patella of leg IV surpasses the end of the body. The new species resembles the European Siro rubens Latreille, 1804 and S. valleorum Chemini, 1990 in the projecting female rear end, but differs from these species, among other features, in having ornamented metatarsi on all four pairs of walking legs.

A NEW SYNZIPHOSURINE (CHELICERATA: XIPHOSURA) FROM THE LATE LLANDOVERY (SILURIAN) WAUKESHA LAGERSTÄTTE, WISCONSIN, USA

A new synziphosurine (Chelicerata:Xiphosura) is described from the Late Llandovery (Silurian) Konservat-Lagerstätte of Waukesha, Wisconsin, USA. Venustulus waukeshaensis n.gen. and sp. is characterized by a semicircular carapace with a slightly procurved posterior margin lacking genal spines and an opisthosoma composed of 10 freely articulating segments, divided into a preabdomen of seven segments with blunt pleurae and a postabdomen of three segments lacking pleurae. The tail spine is short and styliform. This is the earliest known unequivocal synziphosurine, extending their fossil record from the Wenlock to the Llandovery, and only the second species to be described with prosomal appendages; the presence of six pairs (a pair of chelicerae and five pairs of walking legs) contrasts with the seven in the synziphosurine Weinbergina opitzi, but is comparable to the number in modern horseshoe crabs. V. waukeshaensis n. gen. and sp. is not assigned to a family here pending a wider revision, but it bears most resemblance to the Weinberginidae.

Expression patterns of leg genes in the mouthparts of the spider Cupiennius salei (Chelicerata: Arachnida).

The leg genes extradenticle, homothorax, dachshund, and Distal-less define three antagonistic developmental domains in the legs, but not in the antenna, of Drosophila. Here we report the expression patterns of these leg genes in the prosomal appendages of the spider Cupiennius salei. The prosoma of the spider bears six pairs of appendages: a pair of cheliceres, a pair of pedipalps, and four pairs of walking legs. Three types of appendages thus can be distinguished in the spider. We show here that in the pedipalp, the leg-like second prosomal appendage, the patterns are very similar to those in the legs themselves, indicating the presence of three antagonistic developmental domains in both appendage types. In contrast, in the chelicera, the fang-like first prosomal appendage, the patterns are different and there is no evidence for antagonistic domains. Together with data from Drosophila this suggests that leg-shaped morphology of arthropod appendages requires an underlying set of antagonistic developmental domains, whereas other morphologies (e.g. antenna, chelicera) may result from the loss of such antagonistic domains.

Postembryonic development in the pycnogonid Austropallene cornigera (Family Callipallenidae)

Summary This paper describes the postembryonic development of Austropallene cornigera (Family Callipallenidae), an Antarctic pycnogonid, with emphasis on the previously undescribed larval instars. Comparisons are made where feasible with the development of Propallene longiceps (Family Callipallenidae), a related species with a similar mode of development which was described in detail by Nakamura (1981). Although the development of both species is very similar, there are differences when the instars leave the parent and begin a free-living existence and there are several differences in the development of the walking legs. The P. longiceps larvae leave the parent and begin feeding immediately after becoming a fourth instar while A. cornigera larvae remain on the adult through one more molt. During leg development, both species add a new walking leg pair at each molt, but the new limb lacks either one (P. longiceps) or two (A. cornigera) segments. At each subsequent molt, the previously added walking leg gains the missing segment(s) and the next limb pair appears, complete except for the missing segment(s). This process continues until all four pairs of walking legs have appeared and have acquired the adult number of segments.

Maturation and Spawning of the White ShrimpPenaeus schmittiBurkenroad, 1936, Under Large Scale Rearing Conditions

AbstractThis paper describes the reproductive performance ofPenueus schmittikept under controlled conditions in a maturation facility of a commercial shrimp farm. A total of 369 females and 368 males of wildP. schmittiwere used to form 9 broodstock groups. Unilateral ablation was performed on females only. Although females were not tagged, the total number of mated females (N =533) indicates that rematuration of the ovaries did occur. Only 9 mated females (1.69%) did not spawn and only 22 mated females (4.20%) of the remaining 524 cases did not produce viable spawns. These results indicate that a large number of viable spawns (94.18%) can be expected fromP. schmitti. A minimum latency period of 6 days for the ovaries to attain full development was observed twice. The highest mating frequency occurred between the 46th and 60th days after unilateral ablation, but mating frequency remained above 2% until the 90th day. The average number of nauplii/female/spawn was 78,961 (N =524) and the average fertilization rate of the eggs was 73.12% (N =297). Usually when the pair of the spermatophores is dislodged from the thelycum of the mated female, a small sperm mass still remains between the third pair of walking legs. This condition did not show any negative effect on the fertilization rate of the eggs and nauplii production. Mating behavior displayed byP. schmittiis also described and includes three distinctive phases: a) chasing, b) mating and c) post‐mating chase.