CHAPTER 23 Chordates Integrated Principles of Zoology, 17th edition ©McGraw-Hill Education. All rights reserved. Authorized only for instructor use in the classroom. No reproduction or further distribution permitted without the prior written consent of McGraw-Hill Education. Figure 23.2 23-2 ©McGraw-Hill Education. Figure 23.2 Cladogram of living members of phylum Chordata. Figure 23.3 Figure 23.3 Phylogenetic tree of the chordates. 23-3 ©McGraw-Hill Education. Phylum Chordata • Phylum Characteristics – Bilateral symmetry – 5 unique features present at some point • • • • • Notochord Pharyngeal slits or pouches Dorsal tubular nerve chord Endostyle or Thyroid gland Postanal tail Five Chordate Hallmarks • Notochord – Rod like flexible structure extending the length of the body – Found in ventral surface of neural tube – Composed of mesoderm – Key site of muscle attachment – Pliable to allow undulation movement 23-5 ©McGraw-Hill Education. Five Chordate Hallmarks • Dorsal Tubular Nerve Cord – The cord is dorsal to digestive tract and the anterior end enlarges to form the brain 23-6 ©McGraw-Hill Education. Five Chordate Hallmarks • Pharyngeal Pouches and Slits – only seen during embryonic stages – Develop into gills in water-breathers – In terrestrial tetrapods, the pharyngeal pouches give rise to a variety of structures: Eustachian tube, middle ear cavity, tonsils, and parathyroid glands 23-7 ©McGraw-Hill Education. Five Chordate Hallmarks • Endostyle or Thyroid Gland – The endostyle was not recognized as a chordate characteristic until recently – Endostyle releases mucus to capture food – Chordates: binds iodine and produces hormones 23-8 ©McGraw-Hill Education. Five Chordate Hallmarks • Postanal tail » Developed for propulsion in water » Modified into caudal fin » Many tetrapods have well-developed tails for balance » Coccyx: trace remnant of tail in humans 23-9 ©McGraw-Hill Education. Phylum Chordata • Subphylum Urochordata (Gr. uro, tail + L. chorda, cord)—Tunicates © John A. Anderson/ShutterStock, Inc. Phylum Chordata • Subphylum Urochordata Characteristics – Solitaire or colonial – Sessile adults – About 1600 species of tunicates identified; found in all seas and at all depths – Attach to solid substrates – two siphons that permit seawater to circulate through the body – Oral (incurrent) siphon also the mouth – Atrial (excurrent) siphon water being expelled Figure 23.6 Figure 23.6 Metamorphosis of a solitary ascidian from a free-swimming larval stage. 23-12 ©McGraw-Hill Education. Figure 23.4 Figure 23.4 Structure of a common tunicate, Ciona sp. 23-13 ©McGraw-Hill Education. Reproduction and Development • Monoecious • Self fertilization and cross fertilization ©McGraw-Hill Education. Phylum Chordata: Subphyla Characteristics • Subphylum Cephalochordata (Gr. kephalo, head + L. chorda, cord)—Lancelets • Elongated laterally flattened nearly transparent • Size up to 5 cm tadpole like animals • About 29 species of Amphioxus are described with 5 occurring in North American coastal waters • All five chordate characteristics persist throughout life • Live in Shallow waters • genera Branchiostoma (Amphioxus) • Filter-feeders that burrow into sand with anterior end out Phylum Chordata • Subphylum Cephalochordata Characteristics: – Notochord extends from head to tail – Oral Hood: anterior end of body • Cirri: finger-like projections that keep particles out of mouth and help in feeding Subphylum Cephalochordata Phylum Chordata • Subphylum Cephalochordata Characteristics: – Feeding • Endostyle: binds iodine and produces mucus that traps food as it passes into atrium • Food-bearing mucus passes into short esophagus • Gut extends as elongated intestine opening just at anus just before caudal fin • Hepatic Cecum: lipid and glycogen storage Phylum Chordata • Subphylum Cephalochordata Characteristics: – Circulatory system: • Closed Circulation similar to primitive fish • No heart; ventral aorta pumps blood through branchial arteries to dorsal aortas to body back to veins • Mainly carries nutrients – Gas exchange: • Mainly occurs across skin – Excretion: • Protonephridia accumulate nitrogen waste and take to atrium via nephridioduct Phylum Chordata • Subphylum Cephalochordata Characteristics: – Reproduction • Dioecious but can’t tell male from female • From 25 to 38 pairs of gonads along atrial wall • Spawning: release egg and sperm by rupturing atrial wall • Free-swimming bilateral larvae eventually settle into sand and metamorphose into adults Phylum Chordata • Paedomorphosis retention by an organism of juvenile or even larval traits in the adult form. Phylum Chordata • Subphylum Vertebrata (Craniata) – Common Characteristics • Well developed coelom segmented into: –Pericardial cavity: containing the heart –Pleuroperitoneal cavity: containing lungs and abdominal organs • Body covering (skin): stratified epithelium from ectoderm with inner connective tissue from mesoderm; numerous variation Phylum Chordata • Subphylum Vertebrata – Common Characteristics • Bone or cartilage endoskeleton with vertebral column and a head skeleton • Appendicular skeleton with two pairs of appendages supported by girdles (pectoral and pelvic) • Digestive tract of muscles ventral to vertebral column Phylum Chordata • Subphylum Vertebrata – Common Characteristics • Circulatory system of ventral, multichambered heart attached to arteries, veins, and capillaries; blood contains variety of cells suspended in plasma • Excretory system with pair of tubular kidneys featuring waste-draining ducts • Endocrine system of glands without ducts located randomly • Large three-lobed brain; 10 to 12 cranial nerves and paired sense organs Neural Crest • Neural crest cells are a temporary group of cells that arise from the embryonic ectoderm cell layer, and in turn give rise to a diverse cell lineage—including melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia. Neural Spines 23-27 ©McGraw-Hill Education. Musculoskeletal Modifications Physiology Upgrade 23-28 ©McGraw-Hill Education. New Head, Brain, and Sensory Systems 23-29 ©McGraw-Hill Education. The Earliest Vertebrates – Ostracoderms were armored jawless fishes, which were the earliest known vertebrate fossils found in the late Cambrian deposits – These show many vertebrate characteristics like heart, pair eyes, ear capsules, and rudimentary vertebrae – Earliest Ostracoderms had armor with bone in dermis but lacked paired fins that later fishes used for stability 23-30 ©McGraw-Hill Education. Placoderms and Acanthodians – One of the earliest jawed vertebrates are called Placoderms that appeared in the early Silurian and were heavily armored and many were grotesque • Had diamond shaped scales and large plates of bone but went extinct and left on descendants – Acanthodians are another jawed bony group that underwent a great diversification into bony fishes that dominate waters today 23-31 ©McGraw-Hill Education. Gnathostomes • All jawed vertebrates are called Gnathostomes whether living or extinct – Gnathostomes constitute a monophyletic group since the presence of jaws is a derived character state shared by all jawed fishes and tetrapods – Agnathans, defined by the absence of jaws, is paraphyletic since many vertebrate ancestor groups lack jaws – Having jaws was one of the most important events in vertebrate evolution as this allowed predation on large and active food 23-32 ©McGraw-Hill Education. Evolution of Jaws – Evidence indicates jaws arose from the modification of 1st two cartilaginous gill arches • The gill arches and jaws form from upper and lower bars that bend forward and are hinged in the middle • Both gill arches and jaws are derived from neural crest cells rather than from mesoderm • Jaw musculature is homologous to the musculature that originally supported gills 23-33 ©McGraw-Hill Education.