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65 results for “Horseshoe Crabs”
Figure 4. A in Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura
Figure 4. A, Pasternakevia podolica Selden & Drygant, 1987 from the late Silurian (Ludlow) of Zalissia, Ukraine. Specimen ISEA I - F/MP/3/1499/08, isolated opsithosoma with articulated microtergite of somite VII (arrowed). Image courtesy of Ewa Krzemin´ ska. Scale bar = 10 mm. B, undescribed chasmataspidid from the Lower Devonian (Emsian) of Siberia, Russia. Specimen PIN 5116-6, disarticulated buckler with microtergite of somite VII (arrowed) still firmly attached to its anterior margin. Image courtesy of Dave Marshall. Scale bar = 2 mm.
Figure 8 in Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura
Figure 8. Summary cladogram of the internal relationships of Prosomapoda. Arachnids, eurypterids, and chasmataspidids form a clade, here termed Dekatriata. Xiphosurans are paraphyletic with respect to Dekatriata, with xiphosurids forming a monophyletic clade of their own. All taxa outside the two labels are synziphosurines, which would here be polyphyletic. For the full consensus tree see the Supporting information.
Figure 3. A, Bunodes lunula d in Revised systematics of Palaeozoic 'horseshoe crabs' and the myth of monophyletic Xiphosura
Figure 3. A, Bunodes lunula d'Eichwald, 1854 from the late Silurian (Ludlow) of Oesel, Estonia. Specimen ELM G1:262:2, clearly showing the partially reduced pre-opercula tergite of somite VII (arrowed) between the downturned carapace and the hypertrophied tergite of somite VIII. Scale bar = 10 mm. B, 'Eurypterus' stoermeri Novojilov, 1959, a chasmataspidid from the early Devonian (Lochkovian) of Siberia, Russia. Specimen PIN 1138-1, exhibiting the microtergite of somite VII (arrowed) positioned between the carapace and the buckler. The microtergite curves anteriorly towards its lateral edges, and is particularly noticeable on the left-hand side. The occurrence of ridges associated with the lateral eye on the carapace is also labelled. Image courtesy of Dave Marshall. Scale bar = 2 mm.
Horseshoe crab body size cline
<p><strong>Aim</strong></p> <p>Adult body size often exhibits patterns across large-scale environmental gradients, creating ecogeographic clines. However, the form of body size clines varies across taxonomic groups, with linear and non-linear patterns in body size observed in nature. Non-linear body size clines have received less study, and questions remain about how environmental gradients interact to produce non-linear clines. We examined the body size of the American horseshoe crab (<em>Limulus</em> <em>polyphemus</em>), a widely distributed marine arthropod, and evaluated the hypothesis that temperature and active season length can interact multiplicatively to result in a dome-shaped distribution.</p> <p><strong>Location</strong></p> <p>Fourteen states in the United States of America and three Mexican states, representing the entire geographic range of the species.</p> <p><strong>Methods</strong></p> <p>We compiled environmental data and body size measurements from more than 49,000 individual horseshoe crabs. For each location, we extracted from the literature or calculated from raw data the mean male prosoma width and the mean female prosoma width. We applied a General Additive Modeling (GAM) approach to characterize the body size cline, test a hypothesis regarding temperature and season length, and explore evidence for the influence of additional environmental factors.</p> <p><strong>Results</strong></p> <p>Model results indicate temperature and season length could act multiplicatively to produce dome-shaped clines, and these findings align with and quantify previous anecdotal reports of a strong dome-shaped body size cline across latitude for horseshoe crabs.</p> <p><strong>Main conclusions</strong></p> <p>Active season length appears to become relatively more influential on horseshoe crab body size in the northern part of their range, while temperature effects per se appear to dominate in southern latitudes. For horseshoe crabs, the pattern of size variation is consistent with the predictions of Optimal Resource Allocation models, but more study is needed to elucidate mechanistic underpinnings. Considering climate change projections, results from our study suggest future shifts in horseshoe crab body sizes.</p>
The different fates of two Asian horseshoe crab species with different dispersal abilities
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Horseshoe crab body size cline
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Data from: Between-population differences in multi-stressor tolerance during embryo development in the American horseshoe crab, Limulus polyphemus
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Data from: Chromosome-level genome assembly of the coastal horseshoe crab (Tachypleus gigas)
<p class="CxSpFirst"><span>Horseshoe crabs, represented by only four extant species, have existed for around 500 million years. However, their existence is now under threat because of anthropogenic activities. The availability of genomic resources for these species will be valuable in planning appropriate conservation measures. Whole-genome sequences are currently available for three species. In this study, we have generated a chromosome‐level genome assembly of the fourth species, the Asian coastal horseshoe crab <i>Tachypleus gigas</i> (genome size 2.0 Gb). The genome assembly has a scaffold N50 value of 140 Mb with approximately 97% of the assembly mapped to 14 scaffolds representing 14 chromosomes of <i>T. gigas</i>. In addition, </span>we have generated the complete mitochondrial genome sequence and deep-coverage transcriptome assemblies for four tissues.<i> </i>A total of 26,159 protein-coding genes were predicted in the genome. The<i> T. gigas</i> genome contains five Hox clusters similar to the mangrove horseshoe crab <i>Carcinoscorpius</i><i> rotundicauda</i>, suggesting that the common ancestor of horseshoe crabs already possessed five Hox clusters. Phylogenomic and divergence time analysis suggested that the American and Asian horseshoe crab lineages shared a common ancestor around the Silurian period (~436 Ma). Comparison of the <i>T. gigas </i>genome with those of other horseshoe crab species with chromosome-level assemblies provided insights into the chromosomal rearrangement events that occurred during the emergence of these species. The genomic resources of <i>T. gigas</i> will be useful for understanding their genetic diversity and population structure and would help in designing strategies for managing and conserving their stocks across Asia.</p>
Data from: Chromosomal level reference genome of Tachypleus tridentatus provides insights into evolution and adaptation of horseshoe crabs
Horseshoe crabs including Tachypleus tridentatus are a group of marine arthropods living fossil species which have existed on the earth for 500 million years. However, the genetic mechanisms underlying their unique adaptive ability are still unclear. Here, we assembled the first chromosome-level T. tridentatus genome, and proofed that this genome is of very high quality with contig N50 1.69 Mb. By comparison with other arthropods, some gene families of T. tridentatus experienced significant expansion, whichare related to several signaling pathways, endonuclease activity, and metabolic processes. Based on the comparative analysis of genomics and 27 transcriptomes from 9 tissues, we found that the expanded Dscam genes usually locate at the key hub positions of immune network. Furthermore, the Dscam genes showed higher levels of expression in the yellow connective tissue, the birthplace of blood cells with strong differentiation capability, than the other 8 tissues. Besides, Dscam genes are positively correlated with the expression of the core immunity gene, clotting factor B, which is implicated in the coagulation cascade reaction. The effective and unusual immune ability endowed by the expansion and expression of Dscam genes in horseshoe crabs may be a factor that makes horseshoe crabs having a strong environmental adaptability with ~500 million years. The high-quality chromosome-level genome of a horseshoe crab and unique genomic features reported in this study provide important data resources for future studies on the evolutionary history of marine ecological systems.
FIGURE 7. Marine vertebrates from the Strelovec Formation. A in Revisiting horseshoe crab fossils from the Middle Triassic (Anisian) Strelovec Formation Konservat-Lagerstätte of Slovenia
FIGURE 7. Marine vertebrates from the Strelovec Formation. A: Placopleurus sp. PMSL T-899. B: Sangiorgioichthys sp. PMSL T-900. C: Marcopoloichthys sp. preserving ocular structures. PMSL T-1745. D: Eosemionotus sp. PMSL T- 1262. E Saurichthys sp. with stomach contents containing Eosemionotus sp. A and E reflected to align with other images. Image credit: Jure Žalohar.
FIGURE 5. Molluscs and brachiopods from the Strelovec Formation. A in Revisiting horseshoe crab fossils from the Middle Triassic (Anisian) Strelovec Formation Konservat-Lagerstätte of Slovenia
FIGURE 5. Molluscs and brachiopods from the Strelovec Formation. A: An ammonoid. PMSL T-1805. B: Lingulid brachiopod. PMSL T-865. C: Modiolus sp. PMSL T-836. D: Worthenia sp. PMSL T-1772. A coated in ammonium chloride sublimate. All converted to greyscale. Image credit: A: Tomaž Hitij; B, C, D: Jure Žalohar.
FIGURE 1 in Revisiting horseshoe crab fossils from the Middle Triassic (Anisian) Strelovec Formation Konservat-Lagerstätte of Slovenia
FIGURE 1. Locations of Sloveniolimulus rudkini specimens and the geological context of the Strelovec Formation. A: Map of Europe. Box shows close up in B. B: Map of Slovenia. Box shows close up in C. C: Close up of specimen localities. Red star indicates holotype locality. Blue star indicates location of new material from the Kalška gora Mountain. D: Stratigraphic position of Strelovec Formation.
Figure 1. The sampling sites for capturing C in Influence of environmental variability on the body condition of the mangrove horseshoe crab Carcinoscorpius rotundicauda from Banyuasin Estuarine, South Sumatra, Indonesia
Figure 1. The sampling sites for capturing C. rotundicauda in Banyuasin Estuary Waters. The sampling was conducted together with local fishermen using a trammel net.
Data from: Phylogenetic relationship among horseshoe crab species: effect of substitution models on phylogenetic analyses
The horseshoe crabs, known as living fossils, have maintained their morphology almost unchanged for the past 150 million years. The little morphological differentiation among horseshoe crab lineages has resulted in substantial controversy concerning the phylogenetic relationship among the extant species of horseshoe crabs, especially among the three species in the Indo-Pacific region. Previous studies suggest that the three species constitute a phylogenetically unresolvable trichotomy, the result of a cladogenetic process leading to the formation of all three Indo-Pacific species in a short geological time. Data from two mitochondrial genes (for 16S ribosomal rRNA and cytochrome oxidase subunit I) and one nuclear gene (for coagulogen) in the four species of horseshoe crabs and outgroup species were used in a phylogenetic analysis with various substitution models. All three genes yield the same tree topology, with Tachypleus-gigas and Carcinoscorpius-rotundicauda grouped together as a monophyletic taxon. This topology is significantly better than all the alternatives when evaluated with the RELL (resampling estimated log-likelihood) method.
Data from: Ancestral whole genome duplication in the marine chelicerate horseshoe crabs
Whole-genome duplication (WGD) results in new genomic resources that can be exploited by evolution for rewiring genetic regulatory networks in organisms. In metazoans, WGD occurred before the last common ancestor of vertebrates, and has been postulated as a major evolutionary force that contributed to their speciation and diversification of morphological structures. Here, we have sequenced genomes from three of the four extant species of horseshoe crabs—Carcinoscorpius rotundicauda, Limulus polyphemus and Tachypleus tridentatus. Phylogenetic and sequence analyses of their Hox and other homeobox genes, which encode crucial transcription factors and have been used as indicators of WGD in animals, strongly suggests that WGD happened before the last common ancestor of these marine chelicerates >135 million years ago. Signatures of subfunctionalisation of paralogues of Hox genes are revealed in the appendages of two species of horseshoe crabs. Further, residual homeobox pseudogenes are observed in the three lineages. The existence of WGD in the horseshoe crabs, noted for relative morphological stasis over geological time, suggests that genomic diversity need not always be reflected phenotypically, in contrast to the suggested situation in vertebrates. This study provides evidence of ancient WGD in the ecdysozoan lineage, and reveals new opportunities for studying genomic and regulatory evolution after WGD in the Metazoa.
Data from: Chromosome-level genome assembly of the coastal horseshoe crab (Tachypleus gigas)
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Data from: Phylogenetic relationship among horseshoe crab species: effect of substitution models on phylogenetic analyses
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Data from: Chromosomal level reference genome of Tachypleus tridentatus provides insights into evolution and adaptation of horseshoe crabs
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Data from: Ancestral whole genome duplication in the marine chelicerate horseshoe crabs
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Data from: Opsin repertoire and expression patterns in horseshoe crabs: evidence from the genome of Limulus polyphemus (Arthropoda: Chelicerata)
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