BIOL 1604 Lecture Notes - Lecture 19: Altricial, Cervical Vertebrae, Reptile

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27 Feb 2017
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Phylum Chordata
Chordates share features with some invertebrates
Bilateral symmetry
Deuterostomes
Coelom
Tube within a body plan. Anteroposterior axis
Metamerisim (segmentation inconspicuous in many species)
Cephalization
Digestive system complete
Epidermis
Phylum Chordata characteristics
Notochord
o Semirigid body of fluid filled cells enclosed by a fibrous sheath
o In most, extends the length of the body and is ventral to central nervous system
Support
Allows for lateral bending
Muscle attachment
Dorsal hollow nerve cord
o Single, dorsal to the digestive tract and notochord
o The anterior end forms the brain in vertebrates
o Responsible at least in part for chordate success
Pharyngeal slits or pouches
o Openings that lead from the pharyngeal cavity to the outside
o Inpocketing of the outside ectoderm (pharyngeal grooves)
o Outpocketing of the endodermal lining of the pharynx (pharyngeal pouches)
o Protochordates: filter feeding apparatus
o Aquatic vertebrates: give rise to the gills
o Tetrapodes: give rise to different structures
Endostyle for filter feeding or thyroid gland
o Only recently recognized as chordate characteristic
o Endostyle: secretes mucus
o Thyroid gland: endocrine (hormones)
Postanal tail
o Probably evolved for propulsion in water
o Vestige in humans coccyx
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Subphylum Urochordata (tunicates or sea squirts)
Tunic or test surrounds the animal and contains cellulose
Marine. Most sessile as adults
Solitary, colonial, or compound
Free living larva bears all the chordate hallmarks
Adults: have only pharyngeal slits and endostyle
Circulatory system: ventral heart and two vessels
Nerve ganglion and a few nerves
Incurrent and excurrent siphons
Suspension/filter feeders
Development
o Hermaphroditic
In general, gametes carried out through the excurrent siphon and released
into the water
o Metamorphosis: the notochord and the tail disappear
Subphylum Cephalochordata (lancelets)
Laterally compressed
Shallow marine and brackish waters
Closed circulatory system
Ocellus (photoreceptor)
Suspension feeders
o Water leaves the body by an atriopore
o Pharyngeal slits with mucus
o Intracellular digestion in the hepatic cecum
Dioecious
Sperm released into the water
Larva similar to the adult
Subphylum vertebrata
Distinctive endoskeleton (the notochord is replavced by cartilage or bone)
Craniata: cranium enclosing the brain, olfactory organs, eyes, and inner ear
Smooth, skeletal, and cardiac muscle tissue present. Segmented myomeres in fishes and
amphibians
Muscularized digestive tract
Three lobed brain
Ventral heart with chambers, red blood cells
Paired glomerular kidneys and ducks
Endocrine systems. Gland often diverse and abundant
Well developed paired sensory glands
Epidermis and dermis
Scales, hair, feathers developed from epidermis
Keratinized or bony structures often present in integument
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Most with 2 pairs of appendages supported by limb girdles
Free living (but few ectoparasitic fish)
Dioecious except some fish
Mostly sexual reproduction. Asexual reproduction by parthogenesis in some fishes,
amphibians, and lizards.
o Musculoskeletal modifications
Notochord replaced by a series of cartilaginous or bony vertebra
Endoskeleton permits large body sizes
Neural spines: more area for attachment
Cartilague: fast growth and flexibility
Bone: stronger muscle attachment
Large!
Physiological upgrade
o Increased metabolic rates
o Accessory digestive glands, liver and pancreas more food ingested
o Erythrocytes with hemoglobin enhanced transportation of gases, nutrients, etc.
Brain and sensory systems
o Triparate brain protected and paired sense organs including eyes with lenses,
pressure receptors, inner ears for equilibrium, and sound reception, chemical
receptors, olfactory organs, electroreceptors, lateral line receptors
Fish:
Agnatha: lack jaws (hagfishes, lampreys)
Gnathostomata: have jaws (all other vertebrates)
Anamniota: vertebrates whose eggs lack amnion (fishes and amphibians)
Amniota: embryos develop within an amnion membrane forming a fluid-filled sac (reptiles,
birds, mammals)
Pisces: vertebrates with appendages, if any, in the form of fins
Tetrapoda: four-limbed vertebrates (including taxa that have lost limbs such as caecillians)
Jawless
Ostracoderms (extinct)
Hagfish
Lampreys
Jawed: cartilaginous and bony fishes (hinged
Chondrichthyes
Osteichthyes
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