(Lond. Some chondrichthyans guard their eggs after birth, but there is no parental care. 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. Environmental Biology of Fishes, 60(13), 4775. https://doi.org/10.1007/s004410000328. Visual Neuroscience, 26(4), 397. https://doi.org/10.1017/S0952523809990150. Morphometric and ultrastructural comparison of the olfactory system in elasmobranchs: The significance of structurefunction relationships based on phylogeny and ecology. Part of Springer Nature. Originally, the pectoral and pelvic girdles, which do not contain any dermal elements, did not connect. Skates, stingrays, guitarfishes, and angel sharks frequently reverse the direction of flow through the spiracles, apparently to clear them of foreign matter. https://doi.org/10.1002/jmor.1068. Head morphology and pore distribution of carcharhinid and sphyrnid sharks. Environmental Biology of Fishes, 28(14), 3375. Humans depend on fishes for nutrition and micronutrients, which play a very important role in their diet as they control most diseases. Nature, 421(6922), 495495. Growth is also measured by the statistical analysis of the length in systematically collected samples, by the space between concentric circles on the centra of the vertebrae, and by periodic measurements of specimens kept in aquariums. A., Casper, B. M., Mann, D. A., & Demski, L. S. (2012). Cartilage is the flexible substance found that gives human noses and ears their shape! Other bony fish, such as the freshwater elephant fish (Family Mormyridae), have exceptionally large brains in comparison to overall body size. (1995). Journal of Morphology, 274, 447455. Classification of Pisces. The skeleton is cartilaginous. Sharks, skates, and rays all of these fishes have cartilaginous Skeleton because the density of the cartilage is very less which helps the sharks to move faster in the water without the use of more energy and keeps them afloat. https://doi.org/10.1159/000100036. Pisces (with fins) and Tetrapoda (with bare limbs). A digestive system consists of an esophagus extending from the pharynx to the stomach and a gut from the stomach to the anus. Ampullae of Lorenzini (singular Ampulla) are electroreceptors, sense organs able to detect electric fields.They form a network of mucus-filled pores in the skin of cartilaginous fish (sharks, rays, and chimaeras) and of basal actinopterygians (bony fishes) such as reedfish, sturgeon, and lungfish.They are associated with and evolved from the mechanosensory lateral line organs of early vertebrates. We've learned that they have a branching system of peripheral nerves that help them sense their environment, as well as motor nerves that help them move. The class is divided into two subclasses: Elasmobranchii (sharks, rays, skates, and sawfish) and Holocephali (chimaeras, sometimes called ghost sharks, which are sometimes separated into their own class). Phylogenetic systematics of extant chimaeroid fishes (Holocephali, Chimaeroidei). 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. It contains lymphoid and hemopoietic tissue. The relation of inner ear structure to the feeding behavior in sharks and rays. Write down the characteristics of Cartilaginous Fish. https://doi.org/10.1023/A:1007647924559. Kajiura, S. M., Cornett, A. D., & Yopak, K. E. (2010). Skates: Little skate, Small deep-water skate, Andaman leg skate, etc. The Journal of Physiology. In Seminars in Cell & Developmental Biology. 7.6 Respiratory system 7.7 Excretory system 7.8 Nervous system - sense organs, structure of ommatidium 7.9 Reproductive system. Lisney, T. J., & Collin, S. P. (2007). In J. C. Carrier, J. Visual Neuroscience, 26(4), 397. https://doi.org/10.1017/S0952523809990150. A., Castell, M. E., Aguilera, P. A., Pereira, C., Nogueira, J., Rodrguez-Cattaneo, A., & Lezcano, C. (2008). Intestines are short, but have folds arranged in a spiral (increasing surface area). Just like humans and most vertebrates, bony fish have a nervous system comprised of a central brain and spinal cord, as well as many branching nerves. Having skeletons predominantly composed of cartilage is characteristic of cartilaginous fish, while having skeletons mostly composed of bone is characteristic of bony fish. Like the nervous systems of other organisms, fish detect stimuli with sensory nerves that bring signals to the central nervous system. Manta Ray. 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. 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 some deepwater sharks, the column is reduced.[1]. Meredith, T. L., & Kajiura, S. M. (2010). Lowenstein, O., & Roberts, T. D. M. (1951). To unlock this lesson you must be a Study.com Member. Springer, Cham. [4], Like all other jawed vertebrates, members of Chondrichthyes have an adaptive immune system.[5]. Eye growth in sharks: Ecological implications for changes in retinal topography and visual resolution. Made of dentine surrounded by enamel. Environmental Biology of Fishes, 61(2), 125133. 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. CrossRef Google Scholar Gruber SH (1977) The visual system of sharks; adaptations and capability. In females, the cloaca serves both as a reproductive organ and as an excretory organ. Electroreception in marine fishes: Chondrichthyans. Kempster, R. M., McCarthy, I. D., & Collin, S. P. (2012). Springer, Cham. Jaws developed over time from the gill arches, which support the gills, of jawless fish. Sensory adaptations to the environment: Electroreceptors as a case study. Hart, N. S. (2020). Journal of Morphology, 269(11), 13651386. Their skull contains a brain, which connects at the base of the skull to a spinal cord. https://doi.org/10.1016/j.jphysparis.2008.10.005. We have grown leaps and bounds to be the best Online Tuition Website in India with immensely talented Vedantu Master Teachers, from the most reputed institutions. Think of a fish, any fish at all (well, with the exception of a shark, a skate, or a ray). One last resource (not testable) a 2006 documentary about shark finning called Sharkwater has been uploaded in its entirety by the creator. Include what previous structure the jaw is thought to have evolved from. This aids in finding prey, navigation, and sensing temperature. (Homologous . Google Scholar. https://doi.org/10.1242/jeb.01140. Often has a parasite on its eye, causing it to be nearly blind. https://doi.org/10.1016/j.semcdb.2020.03.012. These signals help a fish to maintain homeostasis, which is the state of having a consistent internal environment. 349402). 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. The nervous system is composed of the nerves, spinal cord, and brain. 2005). A response is generated, and a signal is brought to specific structures through motor neurons, such as somatic motor neurons, which deliver messages to muscles, or visceral neurons, which deliver messages to visceral organs. The hindbrain contains the cerebellum, the part of the brain that controls movement and balance in humans. I would definitely recommend Study.com to my colleagues. Sharks/relatives produce less offspring than other fish, but they are larger and typical survive longer. 11051112). Boca Raton: CRC Press. Why do Sharks consider Cartilaginous Fishes? Journal of Physiology-Paris, 102(46), 256271. https://doi.org/10.1002/jmor.20106. Is the longest-lived vertebrate animal known at 392 120 years! BHL Collections: Observationes in anatomiam chondropterygiorum praecipue Squali et Rajae generum : quas venia . 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. These terms can be used across animals to describe reproductive method! (1995). Subjects: Anatomy Araripe Plateau Brazil Cear (State) Chondrichthyes Cretaceous Egertonodus basanus Fishes, Fossil Neuroanatomy Paleontology Phylogeny Sharks Sharks, Fossil Skull . Ovoviviparous (Aplacental yolk sac viviparous). Some fishes have specialized nervous systems that stimulate organs capable of generating electric fields. Kempster, R. M., McCarthy, I. D., & Collin, S. P. (2012). They are also produced in the Leydig's organ, which is only found in certain cartilaginous fishes. Journal of Physiology-Paris, 102(46), 256271. - Facts, Uses, Properties & Formula, Conditioned Inhibition: Definition, Process & Example, Traumatic Brain Injury (TBI): Diagnosis, Rehab & Recovery, Depression & Long-Term Effects of Traumatic Brain Injury, Working Scholars Bringing Tuition-Free College to the Community, Pituitary Gland, Thalamus, Hypothalamus, Pineal Body, Saccus Vasculosus, Relays messages and helps maintain homeostasis, Superficial White Zone, Central Zone, Deep White Zone, Periventricular Gray Zone, Needed to maintain equilibrium and relay messages. (Note: It is rated PG but there are some graphic scenes involving shark finning), Sharkwater (2006)[Vimeo] Running time 1 hour 30 minutes. Lisney, T. J., & Collin, S. P. (2007). Gardiner, J. M., Hueter, R. E., Maruska, K. P., Sisneros, J. A. Musick, & M. R. Heithaus (Eds. Dogfish, Whale shark, Angel shark, Ground Shark, etc. Fertilization occurs internally. The record is extensive, but most fossils are teeth, and the body forms of numerous species are not known, or at best poorly understood. Habitat: Majority of the Elasmobranchii live in saltwater ocean; however, an estimated 43 species including skates, smooth dogfishes, river sharks, pajama catsharks, and sandfishes, stingrays, sawfishes, and bull shark and many more are known to feed or reproduce in freshwater rivers. https://doi.org/10.1007/s11160-010-9162-x. Journal of Morphology, 269(11), 13651386. Journal of Fish Biology, 95(1), 92134. Die Parietalorgane. (1990). There are around 1,000 species in this class of fish. Active electroreception in Gymnotus omari: Imaging, object discrimination, and early processing of actively generated signals. Newton, K. C., Gill, A. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. (2009). (Fun fact: Bull Sharks can live in both fresh and salt water and have been known spotted 4000km up the Amazon river, in Ganges river, the Mississippi, and in Lake Nicaragua! It has even been suggested[by whom?] ), Biology of sharks and their relatives (pp. In Greek, elasmo means Plate and branchia means gill, hence we can tell that long and broad flattened gills are the characteristics of these fishes. Head morphology and pore distribution of carcharhinid and sphyrnid sharks. The first pup to be able eats all of the other pups. Maisey, J. G., Miller, R., Pradel, A., Denton, J. S., Bronson, A., & Janvier, P. (2017). They dont reach sexual maturity until 156 22 years! The Greenland shark (Somniosus microcephalus), which attains 6.5 metres (21 feet) or more (although rarely taken larger than about 4 metres [13 feet]), grows only about 7.5 mm (about 0.3 inch) per year. (1990). Acta Zool 90:134-151. They can be contrasted with the Osteichthyes or bony fishes, which have skeletons primarily composed of bone tissue. 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. In A. Oppel (Ed. 304 lessons Cartilaginous fish are considered to have evolved from acanthodians.The discovery of Entelognathus and several examinations of acanthodian characteristics indicate that bony fish evolved directly from placoderm like ancestors, while acanthodians represent a paraphyletic assemblage leading to Chondrichthyes. Die Parietalorgane. Chondrichthyes are jawed vertebrates with paired fins, paired nares, scales, and a heart with its chambers in series. Google Scholar. Protected by the shell and nourished by the abundant yolk, the embryo of an oviparous species develops for 18 to 59 weeks before hatching. 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 . The mid brain plays an important role in deciphering visual information. 393434). It interprets signals collected from sensory nerves and formulates responses. Growth of a few shark species has been measured or estimated by the differences in length at the times of tagging and recapturing specimens. Chondrichthyes digestive system: The stomach, pharynx, mouth, intestines, and cloaca make up the digestive system. Chondrichthyes Nervous system. But where are nerves found throughout the body? In: Vonk, J., Shackelford, T. (eds) Encyclopedia of Animal Cognition and Behavior. https://doi.org/10.1016/j.semcdb.2020.03.012. 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 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. Maruska, K. P., & Tricas, T. C. (2004). 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. Montgomery, J. C., Windsor, S., & Bassett, D. (2009). The Greek root 'ostei-' means 'bone'. A spiracle is a small hole found behind each eye. (2013). https://doi.org/10.1111/jfb.14068. 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. Nervous System Ampullae of Lorenzini Jelly filled canals that can detect electrical fields, magnetic fields, temperature, salinity, water pressure, etc. Despite the vertebral column protecting their brains and spinal cords, chimpanzees have developed. Phylogenetic and ecological factors influencing the number and distribution of electroreceptors in elasmobranchs. The peripheral nervous system contains the many nerves that extend from the brain and spinal cord and articulate with other structures in the body. Question: What does that mean for ovoviviparous organisms in terms of the evolutionary continuum? Meredith, T. L., & Kajiura, S. M. (2010). Didier, D. A. Comparative Vertebrate Physiology Long Answer Test Review! Taormina has taught advanced high school biology, is a science museum educator, and has a Master's degree in museum paleontology. Hueter, R. E., Mann, D. A., Maruska, K. P., Sisneros, J. Crampton, W. G. R. (2019). A review of the sensory biology of chimaeroid fishes (Chondrichthyes; Holocephali). Hueter, R. E., Mann, D. A., Maruska, K. P., Sisneros, J. Create your account. https://doi.org/10.1002/jmor.20106. Reviews in Fish Biology and Fisheries, 20(4), 571590. Vertebrates comparative anatomy, function, evolution, 7th edn. https://doi.org/10.1007/978-3-319-47829-6_1018-1, DOI: https://doi.org/10.1007/978-3-319-47829-6_1018-1, eBook Packages: Springer Reference Behavioral Science and PsychologyReference Module Humanities and Social Sciences, DOI: https://doi.org/10.1007/978-3-319-47829-6_1018-2, Over 10 million scientific documents at your fingertips, Not logged in Maruska, K. P., & Tricas, T. C. (2004). 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. Journal of Fish Biology, 95(1), 135154. Each clasper has a groove for guidance of sperm. Understand bony fish nervous systems and see a labeled diagram of a fish brain. Integrative Zoology, 4(1), 312. The lateral line appears as a line that runs down the length of the body. Schluessel, V., Bennett, M. B., Bleckmann, H., Blomberg, S., & Collin, S. P. (2008). Phylogenetic systematics of extant chimaeroid fishes (Holocephali, Chimaeroidei). Behavior and physiology of mechanoreception: Separating signal and noise. Chicago: SEM. However, this is only a general rule and many species differ. ), Lehrbuch der vergleichenden mikroskopischen Anatomie der Wirbeltiere (pp. The first Cartilaginous fishes evolved from Doliodus-like spiny shark ancestors. Brain Structure and Function, 220, 11271143. injured/weakened prey), Have a U-shaped stomach (Not as complex as humans), Stomach leads to the intestine which is called the. 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. Didier, D. A. Rays are worth an economical amount. Maisey, J. G. (2001). (2001). Integrative Zoology, 4(1), 312. In chondrichthyans, the nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves. The nervous system comprises of the brain and ten pairs of the cranial nerves. Kajiura, S. M., Cornett, A. D., & Yopak, K. E. (2010). Integrative Zoology, 4(1), 312. The Chondrichthyes are a group of jawed fishes with a cartilaginous skeleton. ), Biology of sharks and their relatives (pp. Describe the structure of placoid scales. Boca Raton: CRC Press. 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. https://doi.org/10.1007/BF00206272. It includes sharks and rays, skates, and sawfishes. Nutrition is crucial to children's physical and mental development. Two chambered hearts, one with an auricle and one with a ventricle, are present in these creatures. 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. Nutrients supplied by blood vessels. Sensory biology of elasmobranchs. 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. https://doi.org/10.1007/s11160-010-9162-x. However, preliminary studies believe the parasite can act as a lure for prey giving the shark a a benefit as well. https://doi.org/10.1038/421495a. Kajiura, S. M., Cornett, A. D., & Yopak, K. E. (2010). Caputi, . Journal of Fish Biology, 80(5), 20552088. ), How bull sharks survive in freshwater [website]. The nervous system in fishes can be divided into two parts: the central nervous system and the peripheral nervous system. A fish's brain is broken up into the telencephalon (which contains the cerebrum and olfactory lobes), diencephalon (which contains structures such as the pineal body, pituitary gland, thalamus, hypothalamus, and saccus vasculosus), mesencephalon (which contains the various white and gray zones), and hind brain (composed of the cerebellum and brain stem). They collect water in the mouths which is then passed through the gills. Brain, Behavior and Evolution, 69(4), 266279. Sensing temperature without ion channels. Has a high concentration of a toxin trimethylamine N-oxide which causes the meat to be toxic if not treated. Not all sharks are swimming noses: Variation in olfactory bulb size in cartilaginous fishes. Corwin, J. T. (1978). Corwin, J. T. (1978). There are two superclasses of Gnathostomata, viz. Pisces are classified into three categories: Placodermi (Aphstohyoids) Chondrichthyes; Osteichthyes; Placodermi (Aphstohyoids) All members of this class are extinct today. Mandado, M., Molist, P., Anadon, R., & Yanez, J. https://doi.org/10.1007/s004410000328. The class Chondrichthyes is divided into two subclasses: the Elasmobranchii (sharks, skates, and rays) and the Holocephali (elephant sharks and chimaeras). Brain Structure and Function, 220, 11271143. They have a complex nervous system with a brain that connects to a spinal chord. Olfactory morphology and physiology of elasmobranchs. 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. It contains the olfactory components which are responsible for deciphering signals involved with smells. They may be the remains of stem-chondrichthyans, but their classification remains uncertain. Primordial germ cells are of endodermal origin. A. Musick, & M. R. Heithaus (Eds. 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. Relative eye size in elasmobranchs. Some species of bony fish have exceptionally large olfactory lobes, particularly catfish and other predators that hunt by smell. PubMedGoogle Scholar. 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. (1995). Part of Springer Nature. 2, pp. Environmental Biology of Fishes, 61(2), 125133. Vigh-Teichmann, I., Vigh, B., Silva, M. M., & Aros, B. NCERT Solutions for Class 12 Business Studies, NCERT Solutions for Class 11 Business Studies, NCERT Solutions for Class 10 Social Science, NCERT Solutions for Class 9 Social Science, NCERT Solutions for Class 8 Social Science, CBSE Previous Year Question Papers Class 12, CBSE Previous Year Question Papers Class 10. https://doi.org/10.1206/3875.1. A distinct heterocercal tail protrudes from the lower lobe as well as the extension of vertebrae into the upper lobe. PubMed Caputi, . Discuss how osteichthyes sense their environment. Also, most chordates are dioecious, meaning that the males and females of species are different (''di . With this, fishes can detect when the water around them moves, alerting them of a passing nearby fish. [6] Capture-induced parturition is often mistaken for natural birth by recreational fishers and is rarely considered in commercial fisheries management despite being shown to occur in at least 12% of live bearing sharks and rays (88 species to date).[6]. Kajiura, S. M. (2001). (2001). Pectoral morphology in Doliodus: Bridging the acanthodian-chondrichthyan divide. https://doi.org/10.1023/A:1007647924559. Osteichthyes fish in the gymnotid group, which includes knife fish and electric eels, can produce a shocking electric current using specialized nerve endings. The egg cases of most species are more or less pillow-shaped; those of the horned sharks (Heterodontus francisci) are screw-shaped with a spiral flange. https://doi.org/10.1002/jmor.10661. 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 . 325368). https://doi.org/10.1111/j.1749-4877.2008.00130.x. 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. Osteichthyes fishes are another group of fishes, which are bony fishes. The class Chondrichthyes has two subclasses: the subclass Elasmobranchii (sharks, rays, skates, and sawfish) and the subclass Holocephali (chimaeras). At the rostral, or nose, end of the fish lie olfactory lobes, which provide the sense of smell. Its like a teacher waved a magic wand and did the work for me. Journal of Fish Biology, 80(5), 20552088. Correspondence to The Osteichthyes Respiratory System. Most of them live in the ocean. The Central Nervous System of Hagfishes Mark Ronan & R. Glenn Northcutt Chapter 464 Accesses 4 Citations Summary A brain and spinal cord constitute the central nervous system of hagfishes, the extant sister group of lampreys and gnathostomes among the craniates.