The Chordates

Kingdom - Animalia Phylum - Chordates Subphylum – 1- Vertebrata Invertebrates 2- Cephalochordata 3- Urochordata

What is a Chordate? 1 - Dorsal, nerve cord 2 - Notochord - Thin flexible rod, that supports the body Retain - Invertebrate Solidifies – vertebrate 3 - Pharyngeal pouches - gill slits 4 - Muscular tail ** Need not be present during the entire life cycle.

Muscular, Post – Anal Tail Chordates have a tail posterior to the anus In many species, the tail is greatly reduced during embryonic development The tail contains skeletal elements and muscle They provide a source of locomotion for fish and some other forms of marine life. Many land animals use their tails to brush away flies and other biting insects. Some species, use their tails for balance; and some, have what is known as prehensile tails, which are adapted to allow them to grasp tree branches.

Invertebrate Chordates Two classes Urochordates - Tunicates (sea squirt) Cephalochordate - Lancelets ** Do not have backbones.

Urochordates Are all marine, and are enclosed in a tough cellulose-like tunic (hence the common name tunicate). The most primitive ancestors of the Subphylum Invertebrata. Most of the body of the adult is occupied by a very large pharynx with numerous gill slits that act as a sieve for food. Water taken into the incurrent siphon enters the pharynx and passes out through the gill slits, leaving food particles trapped in the pharynx. A groove in the pharynx called the endostyle secretes mucus that traps the particles and conveys them into the digestive tract.

Tunicates differ strongly in appearance between the adult and larva Adults are sessile (and sometimes colonial), and must obtain food by siphoning sea water through its body and trapping food particles. Larvae are tadpole-like and free-living, and have gill slits, dorsal nerve cord, and notochord. The larval stage lasts only a few days, and ends when the larva attaches to a substrate and metamorphoses into an adult.

Tunicate

Cephalochordata This class includes the several species of lancelets, small, fishlike, filter-feeding animals found in shallow water. A lancelet has a long body, pointed at both ends, with a large notochord that extends almost from tip to tip and is present throughout life. At one end is a mouth surrounded by prominent bristles and leading into a pharynx. The pharynx has gill slits, an endostyle similar to that of a sea squirt, and an atrium surrounding the pharynx. Water enters the mouth and leaves through the gill slits, and food is trapped in the pharynx.

Lancelet

Vertebrate Chordates The evolution of vertebrates involved invasions of sea, land, and air. Vertebrates (subphylum Vertebrata) are chordates with a spinal column. The name vertebrate comes from the individual bony or cartilaginous segments called vertebrae that make up the spine.

Vertebral column or backbone. Backbone replaces the notochord. Dorsal nerve cord is the spinal cord. Bilateral symmetry Complete digestive system Closed blood system with a ventral heart, arteries, veins Segmented muscles Paired appendages Separate sexes They have an endoskeleton (bone or cartilage)

Head Vertebrates have a distinct and well differentiated head; The brain is fully encased within a protective box, the skull or cranium, made of bone or cartilage. For this reason, the vertebrates are sometimes called the craniate chordates.

Classes Agnatha – jawless fish (30,000 species) Chondrichthyes – cartilage fish Osteichthyes – bony fish Amphibia – amphibians (4,035 species) Reptilia – reptiles (8,240 species) Aves - birds (9,956 species) Mammalia – mammals (5,416 species)