Chordates

A chordate 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

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 Muscle segments Tail Anus Pharyngeal pouches Mouth Hollow nerve cord Notochord

Nonvertebrate Chordates 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”

Nonvertebrate Chordates (continued) Lancelets – small, fish- like 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

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 Muscle Kidney Vertebra Stomach Pyloric cecum Swim bladder Esophagus Spinal cord Gills Brain Urinary bladder Anus Reproductive organ Intestine Pancreas Liver Gallbladder Heart Operculum Mouth

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 Bulbus Arteriosus Ventricle Sinus Venosus Body muscle circulation Digestive system circulation Gills Heart Brain and head circulation Oxygen-poor blood from the veins collects in the sinus venosus. Blood enters the atrium and flows to the ventricle. The ventricle pumps blood into the 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 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 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