BIOL 1030 – TOPIC 16 LECTURE NOTESTopic 16: Deuterostomes: Phylum Chordata (Ch. 34)I. Phylum Chordata (chordates) [clade] – general featuresA. key traits: deuterostomes with notochord, jointed appendages, and segmentationB. four key features present at some point in life cycle of all chordates:1. dorsal, hollow nerve cord – becomes brain and/or spinal cord2. notochord - flexible, fibrous rod along back (replaced by vertebrae in advanced vertebrates)3. pharyngeal gill slits - openings in the throat region4. postanal tail – most other animals with tails near the anus have anus at end of tail5. these features may each be lost or altered in the adult6. three subphyla: Cephalochordata, Urochordata, and VertebrataII. Nonvertebrate chordatesA. Subphylum Cephalochordata (clade) – lancelets1. fishlike creatures that bury selves in mud and filter feed2. all four key chordate feature present in adults3. like vertebrates, muscles broken up into bands called myomeres (body segmentation)4. essentially no brain in adultsB. Subphylum Urochordata (clade) – sea squirts, tunicates1. barrel-shaped, sessile, filter-feeders2. many secrete and live in a tough cellulose sac (tunic) as adults3. only have pharyngeal gill slits as adults, other chordate characters only present in tadpole-like larvae4. incurrent and excurrent siphons5. no brain in adultsIII. Subphylum Vertebrata (clade)A. more properly called Craniata (read on and see if you can figure out why)B. characteristics1. head with brain and skull1 of 9BIOL 1030 – TOPIC 16 LECTURE NOTES2. vertebral column – during development in most (all but Myxini), surrounding and ultimate replacement of notochord bybony or bone-like, hollow vertebrae; also, encase brain in protective box (skull or cranium) of bone or cartilage3. neural crest ectoderm – a unique set of stem cells that form near neural tube and migrate during development, involved in forming a variety of structures4. highly developed internal organs- unique kidney and excretory system- endocrine glands (make many hormones)- specialized heart; closed circulatory system5. endoskeleton made of cartilage and/or bone- cartilage and bone are tissues with compacted collagen protein fibers- collagen matrix laid down first (provides flexibility)- for bone, calcium phosphate is then deposited (provides rigidity)- better than chitin – strong but not brittle (if you get enough calcium)C. excellent fossil record - bone makes great fossils; back to over 470 MYAD. living craniates in eight main classes1. four considered fishes (Myxini, Cephalaspidomorphi, Chondrichthyes, and Osteichthyes)2. four considered tetrapods (arose from fish; Amphibia, Reptilia, Aves, and Mammalia)3. follow the evolutionary history as the major groups are coveredIV. fishes – paraphyletic assemblage (grade)A. aquatic vertebrates that lack pentadactyl (5-fingered) limbsB. over half of all vertebrates; evolutionarily, the first vertebratesC. characteristics1. gills – water comes through mouth and goes out throat slits covered with small blood vessels (capillaries); blood flow goes opposite water flow to maximize gas exchange2. single-loop blood circulation: heartàgillsàrest of bodyàheartD. history of fishes1. first fishes (now mostly extinct): ostracoderms- bony head shields2 of 9BIOL 1030 – TOPIC 16 LECTURE NOTES- no jaws; filter feeders- internal skeletons of cartilage- abundant in Ordovician and Silurian Periods (505-408 MYA)- perhaps one living group, Class Cephalaspidomorphi, remains- jaws evolved from gill arches in some ostracoderms about 410 MYA2. gnathostomes – jawed vertebrates3. first successful group of jawed fishes: Class Acanthodii (Acanthodians; extinct clade[?]), or spiny fishes- scaly skin with small bony plates- up to 7 paired fins with strong spines- still had internal skeleton of cartilage- common in Devonian Period (408-360 MYA); now extinct4. members of Class Placodermi (placoderms; extinct clade[?]), or armored fishes, largely replaced the spiny fishes (although spiny fishes may have descended from them!)- became common during late Devonian- extinct by end of Devonian5. sharks and bony fishes evolved in the Devonian and became dominant by the end of that period6. Devonian Period called Age of Fishes because of dominance and diversity of fishes in that timeV. Superclass Agnatha (grade) – jawless fishesA. Class Myxini (clade) – hagfishes1. the hagfishes alive today are of uncertain origin, may not be properly classified2. temperate oceans3. cannot regulate body salts4. slime glands5. no vertebrae (so, craniates but not really vertebrates)B. Class Cephalaspidomorphi (clade) – lampreys1. apparently derived from one group of ostracoderms that lost plates2. vertebrae only shards of cartilage in tail (but are generally considered true vertebrates)3. larva called ammocoete – filter feeder for many years3 of 9BIOL 1030 – TOPIC 16 LECTURE NOTES4. transform into adult with oral disk with many teeth to attach to other fishes and rasp out body fluid with aid of horny tongue5. some do not feed as adults: transform, breed, and dieVI. Class Chondrichthyes (clade) – cartilaginous fishes; sharks, skates, raysA. may have evolved from a placoderm (or form a clade with placoderms)B. have lost bone and have calcified cartilage insteadC. jaw improved over that of placoderms, opens widerD. shark teeth developed from rough scales; as part of skin, are continually replacedE. built better for swimming than placoderms: more streamlined body, better finsF. sharks became dominant predators after the Devonian, have remained as such through today1. diversity plummeted during the Earth’s largest mass extinction event ~250 MYA2. number of species has slowly risen since that time; as diverse as ever now (but many are facing extinction due to human influences)3. myth - sharks are really primitive and the same as what was swimming around hundreds of millions of years ago4. fact - sharks are incredibly advanced animals that have evolved greatly since their origin approximately 360 MYAG. reproduction1. internal fertilization - males with claspers used to insert sperm into the uterus of females2. most species have live birth (a few do lay fertilized eggs)VII. Class Osteichthyes (clade) – bony fishes and their descendants (grade if you leave out tetrapods)A. may have evolved from an acanthodian (or form a clade with acanthodians)B. characteristics of bony fishes1. swim bladder- internal structure filled with