chondrichthyes nervous system

), How bull sharks survive in freshwater [website]. 393434). Ampullae of Lorenzini - Wikipedia In the local market, scaleless species' skins are used for drumheads, while scaly species' skins are made into shagreen, Cell of Nervous System and Nerve Impulse Conduction for NEET, GERD Symptoms Important Concepts and Tips for NEET, Chinkara Important Concepts and Tips for NEET, Endocytosis - Important Concepts and Tips for NEET, Hibiscus - Important Concepts and Tips for NEET, Regulation of Kidney Function Important Concepts and Tips for NEET, NEET Biology Important Topics and Chapter Weightage, Find Best Teacher for Online Tuition on Vedantu. Encyclopedia of Animal Cognition and Behavior pp 111Cite as. The word Holocephali means complete head. Sensing temperature without ion channels. Journal of Experimental Biology, 207(20), 34633476. A digestive system consists of an esophagus extending from the pharynx to the stomach and a gut from the stomach to the anus. This is needed to decipher the world around and maintain homeostatic properties. Hart, N. S. (2020). Together, the olfactory lobes and the telencephalon comprise the forebrain of osteichthyes fish. The structure and formation of myelin in their nervous systems are nearly identical to that of tetrapods, which has led evolutionary biologists to believe that Chondrichthyes were a cornerstone group in the evolutionary timeline of myelin development. https://doi.org/10.1111/jfb.14068. 349402). [5] They have several sensory organs which provide information to be processed. The hind brain contains the cerebellum and brain stem. Many larger, pelagic species, such as the mackerel sharks (Lamnidae) and the thresher sharks (Alopiidae), no longer possess them. 325368). This is what allows them to sense the things around them. Academic Press. Journal of Experimental Biology, 207(20), 34633476. Fun fact: Sharks can use their ampullae to navigate the globe by tracking earths electromagnetic field. Jena: Bd V. Fisher. Integrative Zoology, 4(1), 312. In addition to sharks and rays, nearly everything that swims is prey for both animals. (2010). (Lond. Cell and Tissue Research, 228(1), 139148. https://doi.org/10.1007/s11160-010-9162-x. The nervous system in fishes can be divided into two parts: the central nervous system and the peripheral nervous system. The localization and analysis of the responses to vibration from the isolated elasmobranch labyrinth: A contribution to the problem of the evolution of hearing in vertebrates. Long gestation (development of offspring) and take a long time to reach maturity. Many believe the jaw developed first as a way to increase respiratory efficiency eating was a secondary function! Laboratrio de Ictiologia Sistemtica, Departamento de Zoologia, Instituto de Cincias Biolgicas, Campus Universitrio Darcy Ribeiro, Universidade de Braslia, Braslia, DF, Brazil, Laboratrio de Fauna e Unidades de Conservao, Departamento de Engenharia Florestal, Faculdade de Tecnologia, Universidade de Braslia, Braslia, DF, Brazil, Laboratrio de Anatomia Comparada de Vertebrados, Departamento de Cincias Fisiolgicas, Instituto de Cincias Biolgicas, Universidade de Braslia, Braslia, Brazil, Laboratory of Vertebrate Comparative Anatomy, Department of Zoology, University of Braslia, Braslia, Brazil, Laboratory of Ichthyology, Department of Zoology, University of So Paulo, So Paulo, Brazil, You can also search for this author in Academic Press. Meredith, T. L., Kajiura, S. M., & Hansen, A. Chondrichthyes' sensory systems are part of the nervous system responsible for receiving external and internal stimuli and translating them into nerve impulses that are transmitted to the central In J. The lateral line system of nerves provides osteichthyes with a sense of hearing, in the form of vibrations in the water, which can help osteichthyes avoid predators and detect prey. In J. (1983). A DiI-tracing study of the neural connections of the pineal organ in two elasmobranchs (Scyliorhinus canicula and Raja montagui) suggests a pineal projection to the midbrain GnRH-immunoreactive nucleus. Systematic Ichthyology Laboratory, Department of Zoology, University of Braslia, Braslia, Brazil, Fauna and Protected Areas Laboratory, Department of Forest Engineering, University of Braslia, Braslia, Brazil, Laboratory of Vertebrate Comparative Anatomy, Department of Zoology, University of Braslia, Braslia, Brazil, Laboratory of Ichthyology, Department of Zoology, University of So Paulo, So Paulo, Brazil, You can also search for this author in In either in their mouth or along whisker-like Springer, Cham. On this Wikipedia the language links are at the top of the page across from the article title. Originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. (2021). In Seminars in Cell & Developmental Biology. Each clasper has a groove for guidance of sperm. Mother produces up to 50 pups in each of two uteruses. Gardiner, J. M., Hueter, R. E., Maruska, K. P., Sisneros, J. https://doi.org/10.1023/A:1007647924559. Montgomery, J. C., Windsor, S., & Bassett, D. (2009). Regardless of brain size, osteichthyes' brains all follow a basic plan. 349402). Schluessel, V., Bennett, M. B., Bleckmann, H., Blomberg, S., & Collin, S. P. (2008). These select Elasmobranchii have the ability to withstand both salt and fresh water. Didier, D. A. The Respiratory System Part 1: Structures and Mechanisms of Breathing; The Respiratory System Part 2: Regulation of Breathing . Maruska, K. P. (2001). Compagno, L. J. A spiracle is a small hole found behind each eye. In J. C. Carrier, J. Morphology of the mechanosensory lateral line system in elasmobranch fishes: Ecological and behavioral considerations. A., Castell, M. E., Aguilera, P. A., Pereira, C., Nogueira, J., Rodrguez-Cattaneo, A., & Lezcano, C. (2008). Schluessel, V., Bennett, M. B., Bleckmann, H., Blomberg, S., & Collin, S. P. (2008). Chondrichthyes' sensory systems are part of the nervous system responsible for receiving external and internal stimuli and translating them into nerve impulses that are transmitted to the. Journal of Morphology, 269(11), 13651386. Journal of Physiology-Paris, 102(46), 256271. In the majority of ovoviviparous sharks and rays, organically rich uterine secretions provide supplemental nourishment, which is absorbed by the yolk sac and in many cases by appendages borne on its stalk. Lisney, T. J. A fish in the group Osteichthyes has a number of peripheral nerve adaptations that allow it to delicately sense the watery environment in which it lives. They contain a central nervous system containing a brain and spinal cord and a peripheral nervous system containing the various nerves throughout the body. The nervous system of bony fishes contains homologous (or similar) structures to that of humans. Cell and Tissue Research, 228(1), 139148. The digestive system is well-developed. Vertebrates comparative anatomy, function, evolution, 7th edn. This means that fish are capable of feeling stimuli related to pain. Explain how a shark is able to maintain buoyancy. The next time you see a fish swimming in a fish tank, go off on a fishing trip, or visit an aquarium, think about the truly remarkable adaptations of the nervous system of the bony fish - the Osteichthyes. Understand bony fish nervous systems and see a labeled diagram of a fish brain. https://doi.org/10.1159/000100036. The Circulatory System Part 1: Evolution and Blood! There are so many misconceptions about this class of vertebrates; education is the first step to protecting sharks which in turn will help protect food webs and biodiversity in our oceans. Lateral Line System - an overview | ScienceDirect Topics Within the infraphylum Gnathostomata, cartilaginous fishes are distinct from all other jawed vertebrates. The central nervous system of osteichthyes is comprised of a brain and a spinal cord, just like our own central nervous system. There are also rare viviparous species. Eye growth in sharks: Ecological implications for changes in retinal topography and visual resolution. That electrical signal goes through fluid filled pores and strike nerves to signal the brain. Kempster, R. M., McCarthy, I. D., & Collin, S. P. (2012). 11051112). Vision in sharks and rays: Opsin diversity and colour vision. The lateral line appears as a line that runs down the length of the body. Osteichthyes Respiratory System | Study.com Environmental Biology of Fishes, 28(14), 3375. What are they homologous to? [12] Recent studies vindicate this, as Doliodus had a mosaic of chondrichthyan and acanthodian traits. Chondrichthyans have tooth-like scales called dermal denticles or placoid scales. Sensory adaptations to the environment: Electroreceptors as a case study. https://doi.org/10.1007/BF00751027. Google Scholar. The Chondrichthyes are the basalmost extant branch of Gnathostomata and comprehend a monophyletic group of fishes with fossils and extant representatives distributed in 65 families with 1282 valid species. To unlock this lesson you must be a Study.com Member. People living in coastal regions of many developing countries rely heavily on them for income and employment. Despite the vertebral column protecting their brains and spinal cords, chimpanzees have developed. The localization and analysis of the responses to vibration from the isolated elasmobranch labyrinth: A contribution to the problem of the evolution of hearing in vertebrates. Chondrichthyes in the Greek language has the following meaning, chondr means Cartilage and ichthyes means Fish. In J. C. Carrier, J. Embryos of some ovoviviparous sharks, notably the porbeagle (Lamna nasus), the mako (Isurus oxyrinchus), and the sand shark (Odontaspis taurus), ingest yolks of other eggs and even other embryos within the oviduct of the mother after the contents of their own yolk sacs are exhausted. In: Vonk, J., Shackelford, T.K. Hueter, R. E., Mann, D. A., Maruska, K. P., Sisneros, J. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. Journal of Fish Biology, 95(1), 135154. Fertilization is internal. Fertilization occurs internally. Cartilaginous fish have the following characteristics: Among the Chondrichthyes are powerful jaws that are found in marine fish. Part of Springer Nature. Odds are you are thinking of a member of the group Osteichthyes. However, many of their life history traits, such as low fecundity, the production of small numbers of highly precocious young, slow growth rates, and late maturity, make them highly . A distinct heterocercal tail protrudes from the lower lobe as well as the extension of vertebrae into the upper lobe. Fish is not just crucial to the ecosystem but is also very important to us as it provides the body with many nutrients and micronutrients. Didier, D. A. Responses are generated and sent to specific structures via motor neurons. Montgomery, J. C., Windsor, S., & Bassett, D. (2009). More on Hammerhead Sharks [Video discovery], Ampullae of Lorenzini additional information [Website]. [17][18] Shenacanthus vermiformis, which lived 436 million years ago, had thoracic armour plates resembling those of placoderms.[19]. [3] They have several sensory organs which provide information to be processed. Humans depend on fishes for nutrition and micronutrients, which play a very important role in their diet as they control most diseases. Sensory physiology and behavior of elasmobranchs. 8. The class Chondrichthyes is divided into two subclasses: the Elasmobranchii (sharks, skates, and rays) and the Holocephali (elephant sharks and chimaeras). The traditional groups include Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves, and Mammalia. Animals that possess jaws are known as gnathostomes, meaning "jawed mouth.". Pectoral morphology in Doliodus: Bridging the acanthodian-chondrichthyan divide. https://doi.org/10.1016/j.semcdb.2020.03.012. 1254). Grogan E, Lund R (2009) Two new iniopterygians (Chondrichthyes) from the Mississippian (Serpukhovian) Bear Gulch Limestone of Montana with evidence of a new form of chondrichthyan neurocranium. Chondrichthyes' sensory systems are part of the nervous system responsible for receiving external and internal stimuli and translating them into nerve impulses that are transmitted to the central nervous system where they are processed. The modern bony fishes, class Osteichthyes, appeared in the late Silurian or early Devonian, about 416 million years ago. Osteichthyes have a remarkable set of evolutionary tools to help them navigate their environment, detect predators and prey, and defend themselves in a diverse undersea world. The relation of inner ear structure to the feeding behavior in sharks and rays. Many modern fish fall within this group, though they are distantly related to their cousins the cartilaginous fish, or Chondrichthyes (con-DRICK-thees), which include sharks, skates, and rays. Chondrichthyes nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves [5] . The lack of air bladders means they need to swim constantly to avoid sinking. However, this is only a general rule and many species differ. Besides the elongated upper lobe, the tail consists of two shorter lobes. Morphology of the mechanosensory lateral line system in elasmobranch fishes: Ecological and behavioral considerations. These are fertilized internally, for which the males are equipped with two copulatory organs called claspers along the inner edges of the pelvic fins. 2017 for more information), the extant chondrichthyans are divided into two groups, the Elasmobranchii (sharks, rays, and their kin) and the Holocephali (chimaeras and their kin), and can be recognized by the presence of some apomorphic characteristics, such as prismatic calcification of the cartilaginous endoskeleton, the presence of placoid scales, and pelvic fin modified in claspers in males. As they do not have bone marrow, red blood cells are produced in the spleen and special tissue around the gonads. Academic Press. Journal of Fish Biology, 80(5), 20552088. Write down the characteristics of Cartilaginous Fish. Correspondence to Lisney, T. J., & Collin, S. P. (2007). American Museum of Natural History Novitates, 3119, 186. In O. M. Johari (Ed. The Chondrichthyes are the basalmost extant branch of Gnathostomata and comprehend a monophyletic group of fishes with fossils and extant representatives distributed in 65 families with 1282 valid species. Class Chondrichthyes " Cartilaginous Fish" Kingdom: Animalia Phylum: Chordata Sub Phylum: Verterbrata Class: Chondrichthyes Not all sharks are swimming noses: Variation in olfactory bulb size in cartilaginous fishes. 2005). Maisey, J. G., Miller, R., Pradel, A., Denton, J. S., Bronson, A., & Janvier, P. (2017). Class Osteichthyes - The Biology Classroom - University of British A., & Demski, L. S. (2004). Chondrichthyes - Wikipedia Litherland, L., Collin, S. P., & Fritsches, K. A. A. Musick, & M. R. Heithaus (Eds. In J. C. Carrier, J. https://doi.org/10.1007/s004410000328. Unit 2-3: Mechanisms of Evolution and Natural Selection, Unit 3a-1: Genetic Modification and Gene Transfer, Unit 5-3: Phylum Platyhelminthes Webquest Notes, Unit 5-4: Phylum Nematoda Webquest Notes. Boca Raton: CRC Press. Phylogenetic systematics of extant chimaeroid fishes (Holocephali, Chimaeroidei). The annual growth increments of tagged juvenile whitetip reef and Galapagos sharks, both species that become at least 2.5 metres (8 feet) long, were found to be 31 to 54 mm (1 to 2 inches) and 41 mm (about 1.5 inches), respectively. Fertilization takes place internally. All animals have a nervous system, though the overall structure may vary between species. In: Vonk, J., Shackelford, T. (eds) Encyclopedia of Animal Cognition and Behavior. Brain Structure and Function, 220, 11271143. Chondrichthyes (/kndrki.iz/; from Ancient Greek (khndros)'cartilage', and (ikhths)'fish') is a class that contains the cartilaginous fishes that have skeletons primarily composed of cartilage. Chondrichthyes Sensory Systems | SpringerLink The class Chondrichthyes has two subclasses: the subclass Elasmobranchii (sharks, rays, skates, and sawfish) and the subclass Holocephali (chimaeras). Studnicka, F. K. (1905). 29.1D: Characteristics of Vertebrates - Biology LibreTexts The notochord is gradually replaced by a vertebral column during development, except in Holocephali, where the notochord stays intact. Skates, stingrays, guitarfishes, and angel sharks frequently reverse the direction of flow through the spiracles, apparently to clear them of foreign matter. Endocrine system | Definition, Organs, Function, Structure, Diagram The lateral line has nerves that are able to pick up sensory information about water displacement. Veronica Slobodian . Christina graduated with a Master's in biology from the University of Louisiana at Lafayette. Vigh-Teichmann, I., Vigh, B., Silva, M. M., & Aros, B. https://doi.org/10.1111/jfb.13922. Phylogenetic systematics of extant chimaeroid fishes (Holocephali, Chimaeroidei). Some nerves come directly from the brain and are responsible for picking up important sensory information such as taste, smell, and sight. 17. Class Chondrichthyes Notes - SlideShare The hindbrain contains the cerebellum, the part of the brain that controls movement and balance in humans. Electroreception in marine fishes: Chondrichthyans. List of transitional fossils Chondrichthyes, Sharks of the World: An Annotated and Illustrated Catalogue of Shark Species Known to Date, "Function of the heterocercal tail in sharks: quantitative wake dynamics during steady horizontal swimming and vertical maneuvering", "Origin and evolution of the adaptive immune system: genetic events and selective pressures", "Sharks, rays and abortion: The prevalence of capture-induced parturition in elasmobranchs", "The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland", "Chondrichthyan-like scales from the Middle Ordovician of Australia", "The systematics of the Mongolepidida (Chondrichthyes) and the Ordovician origins of the clade", "Spiny chondrichthyan from the lower Silurian of South China", The oldest complete jawed vertebrates from the early Silurian of China - PubMed, "Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion", Images of many sharks, skates and rays on Morphbank, Myliobatiformes (stingrays and relatives), https://en.wikipedia.org/w/index.php?title=Chondrichthyes&oldid=1142043818, Short description is different from Wikidata, Articles with specifically marked weasel-worded phrases from August 2018, Creative Commons Attribution-ShareAlike License 3.0, This page was last edited on 28 February 2023, at 05:49. Rays are worth an economical amount. Class Chondricthyes - 7 Vertebrates Nerves run throughout the body and communicate with a number of structures. https://doi.org/10.1038/421495a. To see the full list of the species, click here. 2023 Springer Nature Switzerland AG. Having skeletons predominantly composed of cartilage is characteristic of cartilaginous fish, while having skeletons mostly composed of bone is characteristic of bony fish. 1254). Nature, 421(6922), 495495. 6. These are the telencephalon, diencephalon, mesencephalon, and the hind brain. Vigh-Teichmann, I., Vigh, B., Silva, M. M., & Aros, B. Kajiura, S. M. (2001). Sharks breathe chiefly by opening the mouth while expanding the mouth-throat (bucco-pharyngeal) cavity and contracting the gill pouches to close the gill slits. American Museum Novitates, 2017(3875), 115. (2001). https://doi.org/10.1007/BF00206272. Google Scholar. Osteichthyes Nervous System Anatomy & Function - Study.com These terms can be used across animals to describe reproductive method! Vertebrates are grouped based on anatomical and physiological traits. Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. In A. Oppel (Ed. Test of the mechanotactile hypothesis: Neuromast morphology and response dynamics of mechanosensory lateral line primary afferents in the stingray. They also eat plankton and other small organisms. Carrier, J. Musick, & M. Heithaus (Eds. The O diffuses into the gills as water passes over them on their way out of the organism's body. https://doi.org/10.1242/jeb.01140. 14 Questions About Aquatic Animals Answered. Chondrichthyes' sensory systems are part of the nervous system responsible for receiving external and internal stimuli and translating them into nerve impulses that are transmitted to the central nervous system where they are processed. Sensory biology of elasmobranchs. Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs. 2, pp. (2010). All fish embryologically develop two eyes, although some groups of fish are functionally blind, whereas others have keen eyesight for spotting prey and avoiding predators. They are also produced in the Leydig's organ, which is only found in certain cartilaginous fishes. In females, the cloaca serves both as a reproductive organ and as an excretory organ. Visual Neuroscience, 26(4), 397. https://doi.org/10.1017/S0952523809990150. Phylogenetic systematics of extant chimaeroid fishes (Holocephali, Chimaeroidei). In the next five years it grows about 60 mm (about 2.4 inches) more toward its maximum recorded width of 25 cm (10 inches) in males or 31 cm (12.25 inches) in females. Correspondence to A. Musick, & M. R. Heithaus (Eds. In J. C. Carrier, J. There are two superclasses of Gnathostomata, viz. Die Parietalorgane. In J. Important note: Oviparous, viviparous, ovoviviparous are not terms exclusive to sharks! Nerves are found throughout the body of fishes. Electroreception, electrogenesis and electric signal evolution. The neuroecology of cartilaginous fishes: sensory strategies for (1995). Cell and Tissue Research, 303(3), 391401. https://doi.org/10.1111/j.1095-8649.2011.03214.x. Sensory physiology and behavior of elasmobranchs. Studnicka, F. K. (1905). Pectoral morphology in Doliodus: Bridging the acanthodian-chondrichthyan divide. Behind the olfactory lobes sits the telencephalon, which is equivalent to the cerebrum in most other vertebrates. They collect water in the mouths which is then passed through the gills. Skates, which sometimes hold the lower surface of the head slightly above the bottom, may inhale some water through the mouth; mantas, which have small spiracles and live near the surface, respire chiefly through the mouth. Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology. Calcium deposits provide strength to the endoskeleton, which is composed of cartilage. The nervous system in fishes is divided into the central nervous system, containing the brain and spinal cord, and the peripheral nervous system, containing the nerves found throughout the body that originate from the brain or spinal cord. Circulatory System Part 2: The Heart and Major Vessels; Circulatory System Part 3: Blood Pressure; Circulatory System Part 4: Vessels, Capillary Fluid Exchange, Lymphatic System; Unit 7: Respiratory System. Ampullae of Lorenzini are electroreceptors which detect electrical fields given off by muscle contractions. ), 114(4), 471489. Google Scholar. Integrative Zoology, 4(1), 312. Springer, Cham. Rays are marketed for food in many countries around the world, primarily in Europe and Asia, with about 126,000 short tons (roughly 114,000,000 kilograms) being marketed for food. Rays: Electric ray, Stingray, Manta ray, etc. ), Scanning electron microscopy (Vol. Afferent signals come from muscles, sensory organs, and structures to provide information to the central nervous system. BHL Collections: Observationes in anatomiam chondropterygiorum praecipue Squali et Rajae generum : quas venia . Nature, 421(6922), 495495. They have several sensory organs which provide information to be processed. The majority of sharks and rays other than the skates are ovoviviparous (that is, the egg hatches within the mother). Jaws developed over time from the gill arches, which support the gills, of jawless fish. Caputi, . Journal of Morphology, 250(3), 236264. The peripheral nervous system contains the many nerves that extend from the brain and spinal cord and articulate with other structures in the body. There are a number of vertebrates with jaws in the Gnathostomata division. ), Biology of sharks and their relatives (pp. Fishes also have complex organs called lateral lines which generally run down the lateral surfaces of the body starting at the head and ending at or near the start of the tail. Compagno, L. J. Encyclopedia of Animal Cognition and Behavior pp 111Cite as. Journal of Fish Biology, 95(1), 92134. Births live young that lived off a yolk sac inside an egg. CrossRef Google Scholar Gruber SH (1977) The visual system of sharks; adaptations and capability. We provide you year-long structured coaching classes for CBSE and ICSE Board & JEE and NEET entrance exam preparation at affordable tuition fees, with an exclusive session for clearing doubts, ensuring that neither you nor the topics remain unattended. Has a high concentration of a toxin trimethylamine N-oxide which causes the meat to be toxic if not treated. (2013). Lisney, T. J. ), Biology of sharks and their relatives (pp. Environmental Biology of Fishes, 28(14), 3375. This also helps the animals to prey on one another. Maisey, J. G. (2001). Kajiura, S. M., Cornett, A. D., & Yopak, K. E. (2010). Boca Raton: CRC Press. that the original bony plates of all vertebrates are now gone and that the present scales are just modified teeth, even if both the teeth and body armor had a common origin a long time ago. For instance, the human brain is a complex organ with multiple parts and components. A. Musick, & M. R. Heithaus (Eds. With this, fishes can detect when the water around them moves, alerting them of a passing nearby fish. https://doi.org/10.1007/BF00751027. The Wolffian ducts in males and Mullerian ducts in females become the functional urogenital ducts. It includes Chimaeras, also known as ghost sharks. The disk of the eastern Pacific round stingray (Urolophus halleri) increases in width on the average from 75 mm (3 inches) at birth to 150 mm (6 inches) when mature (that is, at 2.6 years old). 2023 Springer Nature Switzerland AG. The old placoderms did not have teeth at all, but had sharp bony plates in their mouth. Efferent signals send impulses out of the central nervous system to elicit responses from organs, structure, and muscles. The pineal organ of Raja clavata: Opsin immunoreactivity and ultrastructure. Chondrichthyes- Introduction, Classification, Examples and Characteristics Electroreception, electrogenesis and electric signal evolution. A review of the sensory biology of chimaeroid fishes (Chondrichthyes; Holocephali). It includes sharks and rays, skates, and sawfishes. The first abundant genus of shark, Cladoselache, appeared in the oceans during the Devonian Period. General Characteristics of Chondrichthyes Their digestive systems have spiral valves and, with the exception of Holocephali, a cloaca. The fossil record of the Holocephali starts in the Devonian period. Lisney, T. J., & Collin, S. P. (2007). The males of European thornback rays (Raja clavata) are about 50 cm (20 inches) wide when they reach first maturity, about seven years after birth; females are 60 to 70 cm (24 to 28 inches) at first maturity, nine years after birth. It contains lymphoid and hemopoietic tissue. She is a current PhD student in biology at Wake Forest University, and has been teaching undergraduate students biology for the last three years.

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