Transcript Chordates
Chordates Chordates • A chordate (Phylum Chordata) is an animal that has, for at least some stage of its life, a dorsal, hollow nerve cord; a notochord; pharyngeal pouches; and a tail that extends beyond the anus • Some chordates possess all these characteristics as adults; others, only as embryos • Most chordates are vertebrates Chordates (continued) • Notochord – long flexible supporting rod at some stage of development – usually during the embryonic stage/supports the nerve cord • Hollow dorsal nerve cord – runs dorsally above the notochord • Pharyngeal slits/pouches – paired structures located in throat region, disappear in higher vertebrates as they develop Notochord Muscle segments Tail Hollow nerve cord Anus Mouth Pharyngeal pouches Nonvertebrate Chordates • Lancelets – small, fishlike creatures – Contain all four characteristics but lack a backbone – No jaws or appendages – Primitive heart, closed circulatory system – Long pharyngeal region, many gill slits, filter feeders Nonvertebrate Chordates (continued) • Tunicates – Sea Squirts – Mogula sp. – The larvae contain all four characteristics; adults lack the tail and notochord and are sessile filter feeders – Marine chordates – Body covering called “tunic” Fishes • Aquatic vertebrates that are characterized by paired scales, fins, and pharyngeal gills • Jawless fishes – primitive • Cartilaginous fishes • Bony fishes – most advanced – 97% of species Anatomy of a Fish Kidney Pyloric cecum Stomach Vertebra Muscle Esophagus Swim bladder Brain Spinal Gills cord Mouth Operculum Urinary bladder Heart Anus Reproductive organ Pancreas Intestine Gallbladder Liver Feeding in Fish • All types – generalists (carp) to specialists (piranha) • Swallow food, don’t chew Respiration in Fish • Gills for gas exchange – most fish • Modified swim bladder for use in oxygen poor water and gills (lungfish) Circulation in Fish • Two chambered heart with an atrium and a ventricle. The ventricle forces oxygen poor blood to the gills. Have a single loop circulatory system Gills Brain and head circulation Body muscle circulation Digestive system circulation Heart Sinus Venosus Oxygen-poor blood from the veins collects in the sinus venosus. Ventricle The ventricle pumps blood into the bulbus arteriosus. Blood enters the atrium and flows to the ventricle. Bulbus Arteriosus The bulbus arteriosus moves blood into the ventral aorta and toward the gills. Excretion in Fish • Nitrogenous wastes through gills or kidneys or both • Kidneys counter osmosis (salmon) Response in Fish • Fairly well-developed nervous system • Well developed brain containing: olfactory bulb – smell, optic lobes – sight, cerebellum – coordination of movement, medulla – organ function • Lateral line system, taste, sight Movement in Fish • Use swim bladder for bouyancy and paired fins to control movement Reproduction in Fish • Most have external fertilization, but sharks have internal fertilization • Separate males and females – some species change males to females or females to males, few are both • Oviparous – lay eggs • Ovoviviparous – young developed from eggs inside female • Viviparous – live bearing, young nourished by mother Groups of Fishes • Three major Classes of Fish: – Class Agnatha – Class Chondrichthes – Class Osteichthes Class Agnatha – Jawless Fishes • Veracious feeders, not vertebrates • Some are parasitic • Lampreys – larvae are filter feeders and adults are parasitic – attach to fishes, rasp with tongue and suck fluids • Hagfish – use toothed tongue to scrape hole in dead fish and crawl in – most primitive, six hearts and open circulatory system Examples of Class Agnatha Class Chondrichthes – Cartilaginous fishes – Sharks and Skates • Skeletons are made of cartilage, tooth-like scales on skin • 3,000 teeth, 6-20 rows, 20,000 teeth in a lifetime • Sharks are dominant predators (bony jaws) • Most eat fish, some filter feed, some scavenge, few man eaters • Rays and skates, flattened sharks, most harmless, flat and glide Examples of Class Chondrichthes Class Osteichthes – Bony fishes • Flexible backbones vary among species. The more rigid a backbone, the faster a fish swims using its strong tail • 40% of all vertebrates, most advanced • Three subclasses: – Lungfish – have lungs and gills – Lobe-finned – 1 specie – Coelacanth – genus Latimeria – thought to be extinct 70 million years ago, but was discovered off Africa in 1938, 1.5 meters long, closest thing to ancestor to all land vertebrates – Ray-finned – fins are fan shaped • Most are ray-finned Examples of Class Osteichthes Origin of Fish • Fossils indicate jawless fish lived in the Ordovician period (500 million years ago) • After 100 – 150 million years, jawed fish first appeared • Armored (scaled fish), are common ancestors