What Animal Phylum Is The Sister Taxa Of Chordates

Chordata

Chordata is defined equally the virtually recent mutual ancestor of tunicates and cephalochordates, and all of that ancestor's descendants.

From: Encyclopedia of Biodiversity , 2001

Vertebrates, Overview

Carl Gans , Christopher J. Bell , in Encyclopedia of Biodiversity (2d Edition), 2001

Chordata

Chordata is defined equally the almost recent common ancestor of tunicates and cephalochordates, and all of that antecedent's descendants. Chordates share a common, generalized body plan and can be diagnosed by four features shared by members of all the major groups: a notochord, pharyngeal slits, a hollow dorsal nerve tube, and a postanal tail (an extension of the body posterior to the anus). The notochord is a strong, flexible rod running dorsal to the coelom along the length of the body below the primal nervous system. In many vertebrates, the notochord is almost completely replaced past blocks of bone forming vertebrae. Pharyngeal slits are lateral openings from the pharynx (an organ situated behind the mouth that constitutes part of the digestive tract). These features are found in all chordates at some point during their lifetime, only they are not retained as fully functional units throughout life in all chordates.

The tunicates (urochordates) are a grouping of basal chordates represented by approximately 3000 species. They are entirely marine. Some tunicates spend their entire life every bit pelagic organisms, floating in the water cavalcade. One grouping of tunicates, the ocean squirts, undergo a dramatic metamorphosis from a planktonic larval form to a sessile developed (attached to a substrate); a notochord is present in the tail of the larval stage but is resorbed in the adult during metamorphosis. The pharynx enlarges in the adult and expands to grade a barrel-shaped branchial basket through which a constant flow of water passes equally the animal filter-feeds.

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Cambrian explosion

Nelson R. Cabej , in Epigenetic Mechanisms of the Cambrian Explosion, 2020

Cambrian fossils

Panarthropoda is a superphylum that comprises phyla Arthropoda, Onychophora, and Tardigrada, with the latest group's position however uncertain. Panarthropoda are widely represented in the Cambrian beast. A lobopod may have been the ancestor of tardigrades and a lobopod with appendage articulations like the Lower Cambrian, Fuxianhuia protensa isp. Hou, 1987 (Fig. 4.viii) may have been ancestor of euarthropods and onychophorans (Xianguang and Bergstrom, 1997).

There is a substantial fossil record of arthropods and the full number of the extant arthropod species, most of them insects, amounts to several millions. The earliest euarthropod trace fossil records are dated around 537 Ma (an earlier origin of euarthropods seems to be disproven past the lack of such trace fossils in Ediacaran Lagerstätten), but many believe they cannot be older than 550 Ma (Daley et al., 2018). Crown group arthropods appear at the base of the Atdabanian, ∼ 530–524 Ma, and the earliest fossil of the group may exist Rusophycus, commonly associated with trilobites, which appears before trilobites, earlier at the Tommotian (Budd and Jensen, 2017).

The fossil record has shown that early Cambrian radiodontan arthropods possessed big compound eyes (Cong et al., 2016) (Fig. 4.8).

Panarthropoda are characterized by appearance of the ventral nerve cord and the key nervous arrangement in Euarthropoda, Tardigrada, and Chengjiangocaris kunmingensis. They evolved segmental ganglia, whereas the latter developed regularly spaced nervus roots similarly to the VNC of Onychophora, whose postcephalic CNS is lateralized and lacks segmental ganglia (Yang et al. (2016) (Fig. 4.9).

†, fossil taxa; ?, uncertain graphic symbol polarity within total-group Euarthropoda; asn, anterior segmental nerve; cn, longitudinal connectives; co, commissure; dln, dorsolateral longitudinal nervus; ico, interpedal median commissure; irc, incomplete band commissure; pn, peripheral nerve; psn, posterior segmental nerve; rc, band commissure. Reconstruction of VNC in Onychophora adapted from Dewel et al. (1993). Distribution of serotonin in the trunk of Metaperipatus blainvillei (Onychophora, Peripatopsidae): implications for the evolution of the nervous system in Arthropoda. J. Comp. Neurol. 507(2), 1196–1208.

About 540 Ma, Cambrian panarthropods evolved 4 main encephalon types, and a groovy diversity of complex behaviors (Fig. 4.10), only they evolved no novel ground patterns e'er since (Strausfeld et al., 2016). The central nervous system of the Cambrian arthropods is largely conserved in extant arthropoda.

Trilobites are derived arthropods and they may have appeared first at the Ediacaran-Cambrian boundary, but the earliest trilobite trunk fossils are dated 521 Ma (earlier soft-bodied trilobites left no traces), from Siberia (Profallotaspis jakutensis and Profallotaspis tyusserica), Morocco (Hupetina antiqua), Espana (Lunagraulos tamamensis), and Laurentia (Fritzaspis generalis) followed, inside a few million years, by finds into other areas of the earth (Daley et al., 2018). Some other trilobite-like arthropod, Arthroaspis bergstroemi, is discovered in Sirius Passet, Groenland (Stein et al., 2013). The first trilobite radiation event occurred betwixt 520 and 513 Ma (Lin et al., 2006) (Fig. iv.11) and the group of trilobites existed 20–seventy million years before they were extinct (Lieberman, 2008). Trilobite-like fossils like genus Parvancorina (Lin et al., 2006), are institute toward the end of Ediacaran in a few Lagerstätten in Burgess Shale, Australia, and South China.

The head of trilobites evolved of various combinations of torso segments. Recently fossil evidence shows that the extinct trilobite Schmidtiellus reetae Bergström, 1973, possessed sophisticated eyes of apposition blazon, like those of extant bees or dragonflies (Schoenemann et al., 2017) (Fig. 4.12).

Molluscs. The fossil record of the lower Cambrian includes clades of the phylum Mollusca, comprising seven extant classes. The crown group Mollusca had already evolved in the beginning of the Tommotian, more than 530 Ma, only no consensus exists about their stem grouping lineage (Budd and Jensen, 2017). As well the controversial Ediacaran Kimberella, among the clades that left fossils in the early on Cambrian are gastropods, bivalves, and rostroconchs, likewise as helcionellid molluscs, which announced as the earliest gastropods (Landing et al., 2002). Many believe stalk grouping molluscs evolved in the terminal Ediacaran (∼542 Ma) only fossils of mollusc species, along the brachiopods, appear first in the Fortunian ∼537 Ma (Zhuravlev and Wood, 2018). Helcionellids, the small mollusc fossils, ordinarily seen as molluscs, appear first at the very get-go of the Cambrian over 540 Ma (Steiner et al., 2007) until 530 Ma.

Another group of sclerite-begetting metazoans of the lower Cambrian are halkieriids, a crown group molluscs, amongst which the better studied, Halkieria evangelista, from the Sirius Passet fauna of Due north Greenland (Conway Morris, 1998), together with Wiwaxia and Odontogriphus belong to the stem group of the superphylum Lophotrochozoa (Butterfield, 2006).

Fossils of phylum Brachiopoda announced in the terminal Ediacaran (∼542 Ma). This phylum is widely represented in the Cambrian fossil record. Its representatives are among the first skeletal organisms of the Lower Cambrian. Brachiopod fossils are found around the world and in a big number of centers of diversification (Ushatinskaya, 2008). The evolutionary relationship of this group with the extinct lower Cambrian chancelloriids and the extant Lophotrochozoan phyla - molluscs, annelids and brachiopods is not resolved.

Annelids. Annelids are another big phylum of the superphylum Lophotrochozoans comprising more than 9000 species (Zhang, 2011). The oldest fossils of the phylum Annelida belong to the class Polychaeta institute in early Cambrian mudstones (520 1000000 years old) from the Sirius Passet deposit of North Greenland (Parry, 2014) (Fig. 4.13). Phragmochaeta canicularis gen. et sp. nov. is an early on Atdabanian (∼530 Ma) fossil, equanimous of about 20 segments, from the Lower Cambrian Sirius Passet (Greenland) that is interpreted equally a polychaete annelid (Conway Morris and Skin, 2008). Another likely late Early Cambrian annelid fossil is that of Myoscolex ateles Glaessner, 1979, found in Australia (Dzik, 2004).

Hemichordates: Hemichordate fossils grow first with the lower Cambrian (Bengtson, 2004). In hemichordates, the branchial slits that earlier were used for filter feeding evolved into pharyngeal slits and into gill slits in fish. A heart Cambrian Burgess Shale fossil, Oesia disjuncta, previously compared to annelids and tunicates, now is considered a intermission feeder hemichordate (enteropneust) that dwelled inside tubes of the green algae Margarita (Nanglu et al., 2016).

The Yunnanozoan fossils found in the Chengjiang fossil Lagerstätte, S China, are interpreted as the earliest hemichordate fossils and are considered equally a link between the invertebrates and vertebrates Shu et al., 1996a,b; Chen et al. (1999).

Phylum Chordata comprises three subphyla: subphylum Cephalochordata (Acrania or lancelets), subphylum Tunicata (earlier Urochordata) and subphylum Vertebrata (Fig. 4.fourteen). Urochordata and Vertebrata are sis groups, merely urochordates take lost segmentation (Nielsen, 2012, p. 348). Their common Bauplan is characterized by

1.: segmented body with paired articulated legs,
ii.: the presence of the notochord, formed from the roof of the archenteron,
3.: the neural tube, formed from the ectoderm in contact with the notochord,
4.: longitudinal muscles running along the notochord (Nielsen, 2012b, p. 349).

A crucial issue in the evolution of the subphylum Vertebrata compared to its sister groups, cephalochordates and tunicates, is the emergence of the neural crest, which was essential for the exceptional increase in the structural and functional complication of vertebrates (Fig. iv.15).

The evolution of chordates is an integral office of the Cambrian explosion although Cambrian chordate fossils are scanty (Chen and Li, 1997). The primeval Cambrian fossil identified and widely accustomed as a basal chordate is genus Pikaia represented past a single species Pikaia gracilens (Conway Morris and Whittington, 1979) dated to the Centre Cambrian (Fig. 4.xvi).

Cambrian fossils of P. gracilens are described equally basal to chordates. It had a notochord and about 100 myomeres, resembling chordate myomeres, and notochord. Pikaia was not a fast swimmer because its monomers contained only slow twitch muscle fibers. It is considered as "the near stem-ward of the chordates with links to the phylogenetically controversial yunnanozoans" (Conway Morris and Caron, 2012).

Later on, another chordate fossil, Cathaymyrus diadexus, about 10 million years older than Pikaia, was discovered in South China Lagerstätte (Shu et al., 1996a,b). Chordate fossils and fifty-fifty agnathan fishes are part of the Chengjiang Cambrian fauna in South Red china found in deposits of 545–490 Ma, merely chordate fossils evolved every bit early equally ∼555, if not before (Shu et al., 1999).

Commonly tunicates are considered to be the closest relatives to vertebrates. They conserve the notochord simply during larval development but lose information technology as adults, after metamorphosis. All the tunicate fossils described as such so far are controversial. The just one that is widely accepted and bears a hitting resemblance to modern ascidians is a tunicate species, identified as Shankouclava shankouense from the Lower Cambrian Maotianshan Shale, South China, dated abut 520 meg years ago (Chen et al., 2003) (Fig. 4.17).

Lower Cambrian fossils of Haikouella lanceolata and a few other similar fossils of Chengjiang Lagerstätte of Yunnan province (Due south China) are identified as jawless chordate fish (agnathans) related to the extant hagfish and lampreys. Of the aforementioned Chengjiang origin are fossils of two other chordate taxa Haikouichthys and Zhangjianichthys (Conway Morris, 2008).

Based on the similarities between the ciliary bands of the echinoderm and enteropneust larvae and the neural tube of amphioxus likewise as in the patterns of gene expression in the anterior protostomian CNS and in the brain of vertebrate embryos, biologists (Arendt et al., 2008; Nielsen, 2013d) hypothesize that an inversion of the nerve cord and dorso-ventral organization occurred in the chordate CNS, which evolved via the circumoral ciliary band of a dipleurula, a hypothetical ancestral form of bilaterian echinoderms and chordates. Hence, the dorsal side of chordates is thought to exist homologous to the ventral side of protostomes and enteropneusts. Similarly, the vertebrate eyes are considered to exist homologous to the ciliary frontal eye of amphioxus (Nielsen, 2012c).

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Geologic Time, History of Biodiversity in

James W. Valentine , in Encyclopedia of Biodiversity (Second Edition), 2001

Standing Diversity of Marine Chordates

The phylum Chordata includes an invertebrate class, the Cephalochordata, that is known from the Early on Cambrian and is represented today past amphioxus, ( Branchiostoma spp.), but this class is not known to ever have been various. In that location are primitive groups inside the grade Vertebrata, such equally lampreys and hagfish, that in fact lack vertebral columns. A group of marine vertebrates at near this level of organization, known as the Conodonta from toothlike feeding structures, appeared during the Middle Cambrian and left a meaning Paleozoic fossil record. Conodonta became extinct during the Triassic. Nonconodont jawless fishes (Agnatha) appeared in the late Upper Cambrian and radiated into four distinctive, disparate clades during the Silurian; many agnathans had bony armor that has provided about of their fossil record, merely the agnathans seem not to accept been rich in species. They were joined by jawed fishes by Devonian fourth dimension. The jawed forms radiated to produce several disparate types—arthrodires and placoderms, with bony head shields and plated armor, and several chondrichthian groups (sharks and rays), which were the richest of fish clades in Late Paleozoic seas. Also arising at least by Early Devonian time was a clade, the osteichthyes or bony fishes, which was of secondary importance during the Paleozoic but came to be the almost richly diverse vertebrates in the sea during the Mesozoic and quite dominate marine vertebrate faunas today. Thus the history of marine fishes can be summed up equally outset modestly in the Cambrian and finally achieving pregnant disparity during Silurian and perhaps Early on Devonian radiations that established most major groups, which then waxed and waned in richness, with bony fishes finally coming to dominance. Reptiles entered the ocean during the earliest Mesozoic and mammals early in the Cenozoic, but neither group became very rich in marine species.

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T-box Genes in Development and Affliction

A. Di Gregorio , in Electric current Topics in Developmental Biology, 2017

one Introduction

The phylum Chordata comprises animals characterized by the presence of the notochord, an axial structure of mesodermal origin necessary for their development (e.yard., Stemple, 2005). Most chordates develop a vertebral column during their early life, and therefore are grouped in the subphylum Vertebrata, which includes humans. Animals that develop a notochord only not a vertebral column, defined equally invertebrate chordates, are grouped into ii subphyla of marine organisms, Cephalochordata and Urochordata (or tunicates). The main representative of extant cephalochordates is amphioxus, commonly known every bit lancelet, while tunicates are grouped into iii principal classes, Ascidiacea (ascidians), Thaliacea (thaliaceans), and Larvacea (larvaceans or appendicularians). Reverse to what had been believed for several decades, contempo molecular phylogenies have suggested that tunicates are more closely related to vertebrates than cephalochordates (Delsuc, Brinkmann, Chourrout, & Philippe, 2006). Nevertheless, afterwards tunicates branched off from the primary chordate lineage, ~ 500 1000000 years ago, their genomes take undergone several rearrangements, which have led to clade-specific gene duplications and gene losses, and consistent adaptations and divergence.

Among tunicates, ascidians are the largest and most-studied form. Numerous ascidian genomes are publicly available in a searchable format, and several studies have been carried out on evolutionarily conserved gene families. In particular, solitary ascidians of the genera Ciona and Halocynthia are widely used for studies of factor expression, regulation, and function (e.g., Kourakis & Smith, 2015; Lemaire, 2009). One of the chief reasons for the continued involvement in these model organisms is the similarity of their embryonic body plan to that of vertebrates (Fig. aneA and B ). In addition to sharing the notochord with developing vertebrates, ascidian embryos also display a dorsal tubular nervous arrangement, ventrally located endodermal derivatives, and a uncomplicated "brain," comprising the sensory vesicle and visceral ganglion, able to receive and process sensory inputs and to coordinate the swimming movements of paraxially located, nonsegmental muscle cells (e.g., Passamaneck & Di Gregorio, 2005). Recent studies have identified ascidian structures related to neurogenic placodes (Abitua et al., 2015; Manni et al., 2004) as well as migratory cells that share central molecular markers and the ability to differentiate into various prison cell types with vertebrate neural crest cells (Jeffery et al., 2008; Stolfi, Ryan, Meinertzhagen, & Christiaen, 2015). Ascidian larvae are unable to feed themselves, hence they swim for an interval ranging between several minutes and a few days, depending upon their species, then settle to begin metamorphosis. At metamorphosis, the body plan is massively rearranged; both notochord and embryonic muscle are eliminated, while part of the cells of the sensory vesicle and inductive nervus cord human action as primordial stem cells in the formation of the adult neural circuitous (NC, Fig. one) (Horie et al., 2011). The newly formed trunk programme contains a different prepare of chordate features, such equally pharyngeal gill slits (PGS, Fig. 1), a thyroid-like structure, called endostyle (En, Fig. i), and a tubular heart (Ht, Fig. 1) (Karaiskou, Swalla, Sasakura, & Chambon, 2015).

Comparative genomic studies suggest that tunicates have undergone cistron losses that take affected various ancestral gene families every bit well every bit individual genes present in nonchordate invertebrates (Berná & Alvarez-Valin, 2014). For example, tailless, a cistron encoding a nuclear receptor, and genes controlling the cyclic rhythms, are missing in Ciona simply are present in Drosophila (Dehal et al., 2002). In particular, a complete gear up of Hox genes was likely present in a common chordate ancestor, as suggested past the presence of a complete Hox cluster in the amphioxus Branchiostoma floridae (Garcia-Fernández & Holland, 1994), while a few Hox genes are absent-minded in Ciona (Spagnuolo et al., 2003). A similar scenario can be envisioned for members of another evolutionarily conserved family of transcription factors, the T-box family unit. Brachyury-related and Tbx7/viii-related genes have been identified in amoebas, and in sponges the T-box cistron family expands to include Tbr1-, Tbx1-, and Tbx2-related genes (Holstien et al., 2010; Papaioannou, 2014; Sebé-Pedrós, de Mendoza, Lang, Degnan, & Ruiz-Trillo, 2011). The genome of Branchiostoma floridae contains representatives of all the T-box genes subfamilies found in vertebrates, including a Tbx4/5 ortholog that seems to have been lost from the ascidian genomes (Paps, Holland, & Shimeld, 2012; Ruvinsky, Silverish, & Gibson-Brownish, 2000). On the other hand, in improver to factor losses, ascidian genomes as well brandish lineage-specific factor duplications, as in the case of the multiple Tbx6-related genes plant in Ciona (order Phlebobranchia) (Takatori et al., 2004) and Halocynthia (guild Stolidobranchia) (Stolfi, Sasakura, et al., 2015).

In sum, the favorable phylogenetic position, the simplified yet conserved body plan organization, and the presence of representative T-box genes return ascidians informative model organisms and a valuable reference for comparative studies of T-box genes. This review mainly focuses on the T-box genes identified in the ascidian Ciona intestinalis, their expression patterns and the mechanisms controlling their expression, and on cognate genes identified thus far from other ascidian species. The developmental roles of these genes and their positions within the simplified cistron regulatory networks of ascidians are summarized and compared to those of their vertebrate counterparts.

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Ascidians of the Red Sea: In Peril and Invasive

Noa Shenkar , ... Gal Vered , in Reference Module in World Systems and Ecology Sciences, 2022

Abstruse

Ascidians (Phylum: Chordata, Class: Ascidiacea), or sea squirts, will seldom attract the attending of an enthusiastic diver in the tropical coral-reefs. In highly diverse reefs such as those in the Red Bounding main the ascidians often hibernate in shaded areas on natural substrates, underneath corals and stones, and it requires a defended exploration of the substrate in order to spot them. Ascidians are nonetheless highly diverse and colorful, possessing fascinating traits and endless possibilities for scientific exploration. The ascidian fauna of the Red Body of water is characterized with a high percentage of unique species, yet, the inflow of not-ethnic species to urbanized areas has been recently documented. Marine pollution poses additional threats to the ethnic creature, which is currently non included in any specific conservation planning. Hither nosotros provide a general overview of Cherry Sea ascidians, including current trends in their research, in order to encourage further scientific studies on this overlooked group of unique invertebrates dispersed in various tropical environments.

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Subphylum Urochordata (Tunicata)

Fatma El-Bawab , in Invertebrate Embryology and Reproduction, 2020

Abstract

Subphylum Urochordata from Phylum Chordata includes Form Ascidiacea, which is divided into Enterogona, e.chiliad. Ciona, and Pleurogona, e.thou. Styela. This work deals more than with Pleurogona. The compound ascidians increase in size and reproduce agametically by budding and the bud is chosen the blastozooid. The near primitive type of budding appears in species of Clavelina. In some families, budding begins at the larval stage, a few hours after settling. Ascidians besides reproduce gametically, and they are without exception hermaphroditic (Berrill, 1950). Some species undergo the phenomenon of protandry (Millar, 1952). The development of the gonads (gametogenesis) during the whole convenance flavor was studied and described in detail, histologically and histochemically, in South. plicata, S. partita, and C. intestinalis collected from Alexandria waters. The process of deutoplasmogenesis (vitellogenesis) was the focus and information technology was evidenced that information technology is almost the same in the three species and, furthermore, the same as in the crab Portunus pelagicus.

After spawning, the egg undergoes maturation; during this process ooplasmic segregation occurs, and an heady shift in egg cytoplasm regions is initiated by sperm entry. In Styela and Boltenia eggs, information technology is a very fine process since they have coloured myoplasms. The second phase of embryogenesis is the cleavage. Ascidian cleavage is characterized by brusque synchronous cell cycles. They are characterized by bilateral holoblastic cleavage, a pattern found primarily in tunicates. Consummate development leads to an elongated microscopic larva, called an appendicularia or more than commonly a tadpole larva.

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Amino Acids, Peptides and Proteins

Nicolas Andreotti , ... Jean-Marc Sabatier , in Comprehensive Natural Products II, 2010

5.10.three Peptides from Serpent Venoms

The snakes (Phylum Chordata, Class Sauropsida, Order Squamata) currently represent approximately 2500 indexed species amongst which 400 are venomous. They are divided into four formal categories depending on their jaws, and subdivided into many families and subfamilies. ²¹ The most toxic or lethal families of snakes are Elapidae (e.thou., cobras, coral snakes, and kraits) and Viperidae (vipers and pit vipers) ( Figure 3 ). These snakes possess very potent venoms in their glands that are mixtures of compounds exhibiting enzymatic or nonenzymatic activities. Basically, snake venoms comprise a variety of Ser proteases, organic compounds (due east.one thousand., purins), ²² phospholipase inhibitors, and toxins with different pharmacological deportment (i.eastward., ion channel modulators (eastward.yard., myotoxins), cardiotoxins, inhibitors of acetylcholinesterase or fasciculins). Amidst toxin effects hemolysis was described (e.chiliad., disintegrins, sarafotoxins, natriuretic peptides, and Crisp toxins), anticoagulation, hypotension (e.g., inhibitors of voltage-dependent Ca²⁺ channels), inhibition of platelet aggregation (east.1000., disintegrin peptides and C-type lectin-similar proteins) and blockage of neurotransmission (e.m., toxins acting on voltage-gated Na⁺ (Nav) or voltage-gated Grand⁺ (Kv) channels, muscarinic toxins, waglerins, and bradykinin-potentiating peptides). ²³ Therefore, the nature of products characterized from snake venom is coherent with the selected strategies of prey immobilization (i.e., hypotension, paralysis, and digestion). It is worth mentioning that, autonomously from noncharacterized compounds, the precise functional roles of some 'characterized' molecules present in venom are actually poorly understood and remain to exist addressed. Examples are provided with the angiogenesis-stimulating vascular endothelial growth factors (VEGFs) (from snake species Vipera and Bothrops) whose verbal functions are unknown although it has been suggested that they might heighten venom distribution past increasing vascular permeability afterwards a snake bite.

The structural features of ophidian toxins allow to distinguish between 3 master groups: (1) 'iii-finger' toxins (e.m., voltage-gated Caⁱⁱ⁺ (Cav1) channel blockers such as calciseptine), ^24,25 (ii) peptides homologous to Kunitz Ser protease inhibitors (Cav1 aqueduct modulators such as calcicludine, ^26,27 and Kv1.X channel blockers such as dendrotoxins ^28–30 ), and (3) myotoxins of the crotamine type (Nav channel modulators such as crotamine). ³¹ It is noteworthy that, snake Kv1.iii aqueduct-acting Natrin, ³² which belongs to cysteine-rich secretory poly peptide (Well-baked) toxins, possesses a cysteine-rich domain resembling the three-dimensional structures of ii sea anemone toxins, ShK and BgK, both acting on the same ion aqueduct subtype. The '3-finger' toxins, which are widely represented in venoms of mambas, kraits, cobras, and body of water snakes, are folded according to the β-canvas structures with loops. These toxins are reticulated by iv or five disulfide bridges, with four of them beingness conserved in this structural grouping. Therefore, 'three-finger' toxins exhibit iii β-stranded loops, which extend from a central core containing the four conserved disulfide bridges. It is worthy of notation that the 'iii-finger' architectural motif is not limited to elapid or hydrophid toxins. Snake toxins from other structural groups are, independent of their pharmacological target(s), folded by more than complex combinations of β-sheets and α and/or 3₁₀ helices. ¹

At the level of medical applications, at that place are several snake venom peptides or derivatives (not active on ion channels) that are candidate drugs or were actually developed into constructive drugs in humans. These products are particularly invaluable in the treatment of cardiovascular diseases, such as the following anticoagulants or thrombolytic compounds ³³ : integrilin/barbourin (acute coronary syndrome and angioplasty), captopril (hypertension, renal syndromes such as scleroderma and diabetic nephropathy, congestive heart failure), echistatin/aggrastat, ancrod/viprinex (acute ischemic stroke), crotavirin (infectious endocarditis), fibrolase (peripheral arterial occlusions), natriuretic-similar peptides (congestive heart failure), and dendoaspin/mambin. Other snake peptides with antitumor activities might be developed as potential chemotherapeutic agents in oncology, ^34,35 such equally contortrostatin (prevention of metastasis) and jerdonin. Finally, a therapeutic potential in analgesia has also been reported for some snake toxins/peptides with strong analgesic properties, ³⁶ such as cobrotoxin, crotamine, and hannalgesin.

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Methods in Cell Biology

Kazuo Inaba , Katsutoshi Mizuno , in Methods in Cell Biology, 2009

B Tunicates

Marine invertebrates, ascidians (Chordata), are sessile and filter feeders. They are hermaphroditic and each individual possesses both ovary and testis. Ciona, a family fellow member of the Enterogona, is one of the solitary ascidians. Both sperm duct and oviduct are attached along the intestine in parallel and it is easy to collect gametes by simple dissection. We draw here the method to collect sperm from C. intertinalis or Ciona savygni. Sexually mature animals unremarkably contain significant amounts of sperm in the sperm duct, but keeping animals collected from the wild under abiding light to forestall natural spawning is constructive for accumulating more sperm in the sperm duct. Later on opening the tunic, the trunk wall on the atrial siphon side is further cutting open and both sperm duct and oviduct are exposed. Sperm are extracted by piercing the sperm duct with a 25-gauge needle, followed past gently squeezing them out. The sperm are collected using a micropipette with a tip (Fig. 1B). As the sperm duct and oviduct are fastened forth the intestine in parallel, much attention should be paid to ensure that the oviduct is not cleaved, every bit information technology is best to collect sperm without contamination from eggs. Alternatively, the eggs can be washed out in accelerate past cutting the oviduct followed by rinsing with seawater. The volume of sperm obtained depends on both the body size of Ciona and on the extent of sexual maturation, only unremarkably 0.02–0.2 ml of sperm tin can be obtained from one individual.

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Evolutionary Developmental Biology

Jan Stundl , ... Marianne E. Bronner , in Current Topics in Developmental Biology, 2021

iii Neural crest- and placode-like cells in non-vertebrate chordates

Vertebrates vest to the phylum Chordata, which is characterized by a dorsal hollow nerve string, notochord, pharyngeal gill slits and post-anal tail. In addition to vertebrates, chordates comprise two other not-vertebrate subphyla, Cephalochordata (commonly known equally amphioxus, or lancelet) and Tunicata (too known as Urochordata; including larvaceans, thaliaceans, and ascidians). Based on morphological similarities, amphioxus was classically considered to be the closest living relative of vertebrates. However, phylogenomic studies inverse this concept, showing that the sister grouping of vertebrates are actually tunicates ( Delsuc et al., 2018; Delsuc, Brinkmann, Chourrout, & Philippe, 2006; Delsuc, Tsagkogeorga, Lartillot, & Philippe, 2008; Putnam et al., 2008; Telford, Budd, & Philippe, 2015). This phylogenetic relationship was farther supported by the presence of neural crest- and placode-like rudiments in the larval stages of tunicates (east.grand., Abitua et al., 2012, 2015; Cao et al., 2019; Horie et al., 2018; Stolfi et al., 2015), which are absent in amphioxus. Therefore, for a closer understanding of the evolution of NPB-cell populations and their ancestry in vertebrates, it is essential to examine how these domains are established in non-vertebrate chordates.

Tunicates establish a various group of marine filter feeders that have undergone remarkable evolutionary changes in body program, genome organization, and life strategies. Their chordate traits are manifested by their polliwog-like larvae, which have a dorsal hollow neural tube, a notochord, striated eye muscles, and tail. In comparison to vertebrate embryos, they have an invariant and small-scale number of cells, which makes it possible to follow the fates of unmarried cells during development (Holland 2016; Lemaire, 2011; Satoh, 2014, 2016). Ascidian neural patterning does non involve a BMP morphogen slope (Darras & Nishida, 2001; Lemaire et al., 2008) but rather the FGF/ERK, Nodal, and Delta-Notch signaling pathways (Hudson, 2016). Interestingly, the ascidian NPB is divers by a subset of the transcription factors involved in vertebrate NPB specification, such as Msx, Zic, and Pax3/7 (Imai, Levine, Satoh, & Satou, 2006; Li et al., 2017; Stolfi et al., 2015; Zhao et al., 2019).

Putative tunicate homologs of neural crest cells derived from the NPB were first described by Abitua et al. (2012). The descendant cells of the a9.49 cell lineage give rise to pigment cells of the ocellus and otolith. These cells limited NPB and neural crest "specifier" genes such as Msx, Zic, Pax3/vii, Snail, Ets, Id, and FoxD, merely they are not capable of long-range migration. In addition, misexpression of Twist, a transcription gene of import in cranial neural crest formation in frog and fish, conveys migratory abilities to the a9.49 cell lineage (Abitua et al., 2012). Another piece of evidence that tunicates accept neural crest-like cells is the bipolar tail neurons in the trunk of ascidian polliwog larvae. These ascidian neurons take a set of features similar to the vertebrate neural crest-derived mechanosensory neurons of the dorsal root ganglia, such as long-range migration to their final destinations, expression of vertebrate orthologues of Neurog, Islet, Asic, and also comparable mechanism of synapse formation (Stolfi et al., 2015).

In addition to there beingness putative neural crest prison cell homologies ascribed to tunicate cells, several studies have speculated that tunicates might also have rudiments of cranial placodes (Abitua et al., 2015; Cao et al., 2019; Horie et al., 2018; Ikeda et al., 2013; Mazet and Shimeld, 2005; Wagner and Levine, 2012). Molecular genetic bear witness of neural plate formation revealed that ascidian embryos limited vertebrate orthologues of Six1/ii, FoxC, Dmrt, Foxg and Eya in the "preplacodal-like" domain (PPLD) (Abitua et al., 2015; Horie et al., 2018; Liu and Satou, 2019; Tresser et al., 2010). The first bear witness that the ascidian PPLD gives rise to a placode-like structure, which produces ciliated principal sensory cells that might exist evolutionary related to those derived from vertebrate olfactory placodes, was provided by Abitua et al. (2015). In addition, information technology was later shown that ascidian neural crest-like cells, the bipolar tail neurons, could exist transformed into the placode-like palp sensory cells, which ascend from the "preplacodal" domain (Horie et al., 2018). Taken together, these data support the hypothesis that both neural crest and placodes accept a mutual evolutionary origin from the NPB.

In contrast to tunicates, amphioxus lacks a cell population that is obviously homologous to neural crest or placodes. However, they do clearly display an NPB-similar domain betwixt the neural plate and non-neural ectoderm, which exhibits expression of "NPB specifiers" like to those of vertebrates, including Msx, Pax3/7, Zic and Dlx (Gostling & Shimeld, 2003; The netherlands, Schubert, Kozmik, & Holland, 1999; Sharman, Shimeld, & Holland, 1999; Wada, The netherlands, Sato, Yamamoto, & Satoh, 1997; Yu et al., 2008). This suggests that the NPB specification module is at to the lowest degree partially conserved across chordates. In addition, specification of the amphioxus NPB-similar region also requires BMP-signaling activity, however at college levels (Kozmikova et al., 2013).

Interestingly, the amphioxus NPB-like progenitors transiently express the "neural crest specifier" Snail, even though no cells undergoing EMT or emigrating from the amphioxus neural tube have been detected (Langeland, Tomsa, Jackman, & Kimmel, 1998; Yu et al., 2008). Other NPB and neural crest specifiers (such as Ap2 and SoxE) are expressed in the mesoderm or non-neural ectoderm, respectively, but are missing from the neural plate border (Meulemans and Bronner-Fraser, 2002; Yasui, Zhang, Uemura, Aizawa, & Ueki, 1998; Yu, 2010; Yu, Kingdom of the netherlands, & Holland, 2002; Yu, et al., 2008). The lack of the majority of "neural crest specifiers" in the NPB and the absence of migrating cells supports the hypothesis that the total module of the neural crest gene regulatory network was complemented from other cell types to the neural tube in a common ancestor of tunicates and vertebrates (Meulemans and Bronner-Fraser, 2005; Yu, 2010).

Another hypothesis based on amphioxus information assumes that the neural crest-descendant jail cell types evolved from the neuroectodermal pigmented photosensory cells. In this scenario, the amphioxus pigmented Hesse organs (dorsal ocelli) with their constituent photoreceptors and shading pigment cells correspond a possible evolutionary homolog of vertebrate neural crest–derived sensory cells and pigment cells (Bakery and Bronner-Fraser, 1997; Ivashkin & Adameyko, 2013). Appealing as it is, this hypothesis would necessitate that the Hesse ocelli emerge from the NBP, both in development and evolution—which remains to exist shown.

In contrast to vertebrates and ascidians, amphioxus has no ectodermal domain with a specific gene expression contour homologous to the preplacodal region. Interestingly, the key placode "specifiers," Six1/2 and Eya ( Schlosser et al., 2014), are expressed in the epidermal sensory neurons situated forth the entire length of the larval body (Kozmik et al., 2007). These sensory neurons have a "placodal" expression profile, undergo epithelial-to-mesenchymal transition and migrate like vertebrate placode-derived neurons but they do not arise from the NPB (Kaltenbach, Yu, & Holland, 2009; Lu, Luo, & Yu, 2012). This would imply that either these amphioxus cells are not homologous to the placode-derived sensory neurons, or that they are homologous to placodal derivatives but that a "developmental takeover" occurred during chordate evolution (Arendt, 2008).

There is a similar situation regarding amphioxus Hatschek's pit where Six1/2 and Eya are also expressed (Kozmik et al., 2007). Traditionally, Hatschek's pit has been proposed as the amphioxus homologue of the vertebrate adenohypophyseal placode (anterior pituitary), a hypothesis supported past the similar gene expression patterns of Pitx, Pax6, Islet, Lhx3 and Trk (Benito-Gutiérrez, Nake, Llovera, Comella, & Garcia-Fernàndez, 2005; Glardon et al., 1998; Hatschek, 1881; Jackman, Langeland, & Kimmel, 2000; Patthey et al., 2014; Schlosser, 2017; Yasui et al., 2000; Wang, Zhang, Yasui, & Saiga, 2002). Still, the Hatschek's pit is formed by the left (Hatschek'south) diverticulum derived from the endodermal pouch, which then fuses with the surface ectoderm (Hatschek and Tuckey, 1893). Thus, Hatschek's pit develops from mixed endodermal and ectodermal cells and therefore has a unlike embryonic origin from the ectodermal adenohypophysis of vertebrates. In consequence, Hatschek's pit is either non homologous to the adenohypophyseal placode, or it is homologous to adenohypophyseal placode merely has changed its developmental origin during chordate evolution.

In summary, these results propose an evolutionary scenario in which the NPB specification cistron regulatory network (GRN) module was already established in the mutual chordate antecedent. The subsequent split up of this module into neural crest- and placode-specific submodules within the NPB region may have occurred in the common antecedent of tunicates and vertebrates. Despite the conserved molecular identity of amphioxus peripheral sensory neurons, including Six1/2 and Islet, these neurons do not appear to be developmentally derived from the NPB. Notwithstanding, given the prevalent origin of peripheral sensory neurons from the lateral neural border in non-chordate animals (see beneath), the sensory lineage in amphioxus may take been secondarily modified in evolution.

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Animals, Poisonous and Venomous

T. Dodd-Butera , M. Broderick , in Encyclopedia of Toxicology (Third Edition), 2014

Toxicity

Snakes are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, suborder Serpentes. At that place are 14 families, only Colubridae, Elapidae, Hydrophidae, Viperidae, Crotalinae, and Viperinae are the families and subfamilies of poisonous snakes (see Figure three).

The dose and exposure to venom vary due to the complexity of multiple components, the amount injected, and the blazon of snakebite. Approximately 20% of snakebites practise non involve injection of venom. These are known equally 'dry' bites. With envenomations in humans, effects vary from cytotoxic, neurotoxic, and hemotoxic events, which are dependent on species, seasonal, and geographic factors. Potential symptoms include tissue destruction, paralysis, and extensive haemorrhage. Victims are frequently young, and face the potential of lifelong inability, fifty-fifty when the snakebite does not result in fatality.

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Source: https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/chordata

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iii Neural crest- and placode-like cells in non-vertebrate chordates

Animals, Poisonous and Venomous

Toxicity

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