The Animal Kingdom Chordates

Phylum Chordata Chordates Possess all the characteristics of animals farther down on the evolutionary ladder: nucleus, multi- cellular, heterotrophic. Possess tissues, bilateral symmetry, a coelom, and a deuterostome.

The Animal Kingdom Review branch points in animal evolution. 1st = presence of tissues 2nd = symmetry 3rd = type of body cavity – a coelom Acoelomate: Sponges, Cnidarians, Flatworm.s Coelomate: Nematodes, Annelids, Mollusks, Arthropods, Echinoderms 4th = embryonic development Protostomes (blastopore becomes stomach): Mollusks & Arthropods. Deuterostomes (blastopore be- comes anus): Echinoderms, Chordates

Phylum Chordata Chordata includes 3 subphyla: the urochordates, cephalochordates, & vertebrates. All share 4 anatomical structures at some point in life. A notochord (in all embryos): a rod between the digestive tube and the nerve cord; provides skeletal support (in humans – it becomes the gelatinous material between vertebral disks. A dorsal nerve cord; it develops into the brain and spinal cord Pharyngeal gill slits connect the pharynx to the outside. Slits allow water that enters the mouth to exit without continuing through the entire digestive tract. Slits have become modified for gas exchange (in aquatic vertebrates), jaw support, hearing, etc. Most chordates have a post-anal tail. In contrast, nonchordates have a digestive tract that extends nearly the whole length of the body.

Phylum Chordata Chordata includes 3 subphyla: the urochordates, cephalochordates, & vertebrates. All share 4 anatomical structures at some point in life. A notochord A dorsal nerve cord Pharyngeal gill slits A post-anal tail

Phylum Chordata Chordata includes 3 subphyla: Urochordates (called tunicates) adhere to rocks, docks, and boats.; they are suspension-feeders. Larvae have all four chordate characteristics, but adults possess only the gill slits. Adult Larva

Phylum Chordata Chordata includes 3 subphyla: Cephalochordates (called lancelets) have all four chordate characteristics persisting through adulthood. Lancets are just a few cm. They live with their posterior end buried. Also suspension feeders. Molecular evidence suggests that the vertebrates' closest relatives are the cephalochordates.

Phylum Chordata Chordata includes 3 subphyla: Vertebrates possess an endoskeleton with a backbone, and a closed circulatory system, with a chambered heart for an active lifestyle that requires a large supply of fuel. An endoskeleton can grow indefinitely, unlike an exo- skeleton that must be re- placed from time to time. Examples: fish, amphibians, reptiles, birds, mammals.

Vertebrates An overview of vertebrate diversity. At the base are hagfishes and lampreys which lack hinged jaws. All others (gnathostomes) have true jaws & paired appendages. In fishes, these paired appendages function in swimming. In tetrapods, the appen- dages become legs. Amphibians lay eggs in water or a moist environment. Others are amniotes; pro- ducing shelled, water-retain- ing eggs allows them to com- plete their life cycles on land. Ex: reptiles and birds. In mammals, offspring develop internally.

Vertebrates Vertebrates evolved in the sea 530 mya. First ones had no jaws. Hagfish are the most primitive vertebrates around today. They are scavengers that feed on worms and dead fish. Skeleton of cartilage. Lampreys are parasites that use hook-like teeth, a rasping tongue, & a sucking mouth to scape skin from fish and drink its blood. Hagfish

Vertebrates Vertebrate jaws evolved from skeletal supports of pharyngeal slits. The remaining gill slits remained for respiration. A common ancestor gave rise to sharks and bony fishes 425 to 450 million years ago.

Class Chondrichthyes Cartilage fishes Ex: sharks & rays – 850 species. Endoskeleton of cartilage Paired fins: pectoral at front, pelvic at back, dorsal on top, caudal at end (most fish). Series of gill slits on side of body.

Class Chondrichthyes Cartilage fishes Ex: sharks & rays – 850 species. Rough skin due to tooth-like scales in skin → Rows of teeth in jaws replaced from behind as the old ones are lost. No swim bladder, so they sink to bottom if not swimming. Senses: good sense of smell, can sense electric currents in water, pressure-sensitive cells on side of body (the lateral line) detects pres- sure as fish swim by, vision not too significant. Internal fertilization - pelvic fins adapted for clasping

Class Osteichthyes Bony fishes Ex: tuna, salmon – 21,000 species Endoskeleton of bone. Scales usually made of bone as well. Gills housed in one cham- ber on each side of head covered by a bony plate called the operculum.

Class Osteichthyes Bony fishes Ex: tuna, salmon – 21,000 species Have a swim bladder, so they can maintain any depth in water while standing still. Senses: color vision is important, many sense electric currents in the water, also have the lateral line. Most fertilize eggs outside the body: external fertilization - guppies, mollies, swordtails are exceptions.

Class Osteichthyes Bony fishes Ray-finned - fan-shaped fins supported by bony rays - majority of fish. Ex. trout, marlin, grouper

Class Osteichthyes Bony fishes Lobe-finned - fleshy fins supported by bones. Ex: coelocanth (deep ocean) Ex: & lungfish (functional lungs - live in stagnant area or places that dry up - must move or burrow into river bottom - the ancestor of amphibians from DNA comparison). Lungfish

Class Amphibia Amphibians - Greek: Amphi + bio = “double life” referring to life stages in water (for reproduction) & on land Evolved 350 mya during the early Carboniferous Period from lungfish.

Class Amphibia Amphibians - Greek: Amphi + bio = “double life” referring to life stages in water (for reproduction) & on land. Most have legs at right angle to body (not underneath). Gills as larvae & lungs as adults. Gas exchange thru skin as well. External fertilization in water; eggs not water-tight. All carnivorous as adults; larvae usually herbivorous.

Class Amphibia Caecilians Burrowing animals with tail but no legs, eat earth- worms & small animals.

Class Amphibia Salamanders & newts Distinct head, trunk, & tail with legs.

Class Amphibia Frogs & toads No tail as adult; hind limbs for jumping

Class Amphibia Frogs & toads Anatomy of the grassfrog

Class Amphibia Frogs & toads: evolution of the vertebrate heart A fish heart has two chambers: a ventricle & an atrium The ventricle pumps blood to the gills for O 2. Amphibians have 3 chambers: 2 atria & 1 ventricle. The ventricle pumps blood into a forked artery that sends it to the skin & lungs or to the rest of the body. The open ventricle mixes O 2 -rich and mixes O 2 -rich and O 2 -poor blood: O 2 -poor blood: not efficient. not efficient. The open ventricle mixes O 2 -rich and mixes O 2 -rich and O 2 -poor blood: O 2 -poor blood: not efficient. not efficient. Fish Frog