Phylum Hemichordata & Chordata

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PoriferaPorifera PlatyhelminthesPlatyhelminthes MolluscaMollusca ArthropodaArthropoda

HemichordataHemichordataCnidariaCnidaria NemerteaNemertea AnnelidaAnnelida

EchinodermataEchinodermataChordataChordataLophophoresLophophores

ProtozoansProtozoans

Chordate Relatives• Common ancestry revealed by dorsal nerve tube

and pharyngeal gill slits• Gill slits form (throat pocketings) at some time

during development; used for feeding or gas exchange

Phylum Hemichordata• Three body regions

– Proboscis– Collar– Trunk

• Deuterostome• Gill slits• Open circulatory

system• Dorsal and ventral

nerve cord

Phylum Hemichordata

• 85 species of acorn or tongue worms

• Ciliated mucus-covered proboscis, resembles acorn or tongue

• Burrow in sediment and feed on sediment or filter feed

• Elongated trunk with pharyngeal openings

2012 New Hemichordate Worm found

• found about 1.5 miles (2.5 kilometers) beneath the surface of the Atlantic Ocean

• has large lips on either side of its head region that reminded researchers of the floppy-eared Stars Wars character

• full scientific name is Yoda purpurata, or "purple Yoda."

Discovered a new type of acorn worm, scientists have. Named it after Yoda, they

did.

• Researchers found the worm during the ECOMAR research program, which uses a remotely operated submersible to search for new animals along the seafloor at the Mid-Atlantic Ridge between Iceland and the Azores.

• Scientists are interested in these deep sea species, because they are close to the evolutionary link between vertebrates and invertebrates.

• In other words, the force is strong with them.

Phylum Chordata

• Three subphyla unified by having a notochord at some point in life cycle and metameric tail

– Notochord = densely packed muscle fibrils enclosed by sheath in rod shape; provides skeletal support

– Metameric tail = repetition of similar segments; extends beyond anus

Phylum Chordata Characteristics

• Notochord• Gill slits or pharyngeal

pouches• Dorsal hollow nerve

cord• Postanal tail• Segmented muscles• Deuterostome

Chordates

Phylum Chordata

Evolutionary Adaptations of Chordates

• From filter feeding ancestors to active predators– Mobility– Oxygen capture– Digestion– Circulation– Nervous system

Skeletal Changes

• Skeleton becomes stronger to work with bigger muscles

• Allows more rapid movement

Oxygen Capture

• Gill slit and muscular pharynx will move more water over gills

– More oxygen is extracted from water

Circulation

• Stronger heart to circulate blood faster

Digestion

• Digest more food

– Muscularized gut

– Digestive glands

• Liver

• Pancreas

Nervous System

• More complex for better– Motor control of

body to capture food

– Sensory detection of the animals environment

– Integration centers (brain)

Brain With Three Parts

ForebrainMidbrainHindbrain

Chordate SubphylaChordate Subphyla• Phylum.Phylum. ChordataChordata

– Subphylum.Subphylum. UrochordataUrochordata

– Subphylum.Subphylum. CephalochordataCephalochordata

– Subphylum.Subphylum. VertebrataVertebrata

• Phylum.Phylum. ChordataChordata

– Subphylum.Subphylum. UrochordataUrochordata

– Subphylum.Subphylum. CephalochordataCephalochordata

– Subphylum.Subphylum. VertebrataVertebrata

Subphylum Urochordata• 3000 species of tunicates or sea squirts• Earliest derivative of chordate line• Adults bear no resemblance to other chordates, but

larval features indicate nerve cord and notochord• These disappear during metamorphosis• Only chordate feature remaining = gill slits (filter

feed)

Subphylum Urochordata• Soft-bodied marine filter feeders• Wide variety of sizes, shapes, and colonial structure• All have outer covering (tunic) containing tunicin

(cellulose-like) and in/ex-current siphons

Sea Squirts

Subphylum Cephalochordata• Small group of 23 species of

lancelets or amphioxus• Fish-like and free swimming,

also burrow in sand with only head protruding

• Unique feeding apparatus for suspension feeding (buccal cirri/gill slits)

• Resemble vertebrates more; may represent living descendants of vertebrates

Subphylum Cephalochordata

• Amphioxus• Notochord length of

body• Dorsal hollow nerve

cord• Gill slits• Segmented muscles

Amphioxus

Subphylum Vertebrata• Around 49,000 species

of vertebrates• Significant not in size

or age of group, but its morphological diversity, structural complexity, and trophic dominance

• Three novelties bind all vertebrates

Subphylum Vertebrata1. Neural crest tissue = specialized kind of

ectoderm that gives rise to nervous system, retina, gill cartilage, and pigment cells

2. Enlargement of anterior end of neural tube to form the brain

3. Endoskeleton = backbone composed of vertebrae (bony/cartilaginous segments replace notochord during development), cranium (bony/cartilaginous housing for brain), paired pectoral and pelvic appendages

Subphylum Vertebrata Characteristics

• All are bilaterally symmetrical with regional differentiation• Head region = houses sensory organs, brain, anterior

opening to digestive tract• Trunk region = body cavities that house viscera• Tail or caudal region = lacks viscera, but has muscles and

skeleton (function in locomotion, reduced, or specialized)

Subphylum Vertebrata• Metamerism (serial repetition of body parts)

limited to trunk muscles, skeleton (vertebrae and ribs), and the nerves associated with trunk

• All have gills at some point in life cycle (breathing organs or transient developmental structures)

• Closed circulatory system = arteries move blood to periphery from multi-chambered heart, veins move blood from periphery to heart, capillaries

• Myomeres associated with endoskeleton

Vertebrate Classes

Vertebrate Diversity

• Major evolutionary innovations among vertebrate groups fall into four categories:

1. Musculoskeletal system2. Nervous system3. Respiratory/circulation systems4. Nature of the egg

Musculoskeletal system

• Most primitive in jawless vertebrates (hagfish, lampreys), have reduced braincase and cartilaginous gill-arch supports

• Hagfish = only notochord• Lamprey = notochord strengthened by

addition of small arches of cartilage in anterior trunk segments and small blocks of cartilage posteriorly--These are evolutionary precursors to vertebrae!

Musculoskeletal system• All other vertebrates:

– replacement of notochord with bony* vertebrae--articulate, protective housing for nerve cord

– development of pectoral/pelvic appendages (from fins to limbs)

Musculoskeletal system

• appearance of jaws associated with braincase

*cartilage in sharks/rays-descended from bony ancestors

Nervous System• Increased structural complexity allowed an

elaborate nervous system to evolve

• Cephalization: elaboration of the anterior end of spinal cord to form hollow brain and sensory organs (protected by skull)

• Peripheral nervous system: paired nerves in every body segment (relay brain’s messages to periphery)

Nervous System• Autonomic nervous system: function

automatically without voluntary control by brain– Sympathetic: increases activity, slow

digestion– Parasympathetic: decreases activity,

stimulate digestion– This complementary system best

developed in mammals so they can maintain metabolic activity while still able to respond to external conditions

Respiration• Respiration:

– Vertebrates require more oxygen than inverts, birds/mammals = highest demands (endothermic)

– Soft skin, moist environment (eel, amphibian) = gas exchange across skin in addition to respiratory organ

– Gills or lungs = derived from the pharynx

– Water pumped across gills, get gas exchange

– Air breathed into lung, gas exchange across epithelial lining

Respiration• Birds also have air sacs extending from

lungs into many parts of body

• Mammals have diaphragm to forcefully pull air in/expel air out

Circulation• Allied with respiratory system: transports

oxygen, nutrients, and water to cells and removes wastes/carbon dioxide

• All systems closed: heart, arteries, veins, capillaries

Circulation

• In gilled, 2-chamber heart: one atrium, one ventricle, blood enters heart via veins, leaves via aortic arches in gills (gas exchange), blood proceeds to rest of body

Circulation

• In amphibians, aortic arches are reduced and modified into vessels in order to pass blood from lungs to 3-chambered heart (atrium separated by septum, one ventricle)

Circulation• In snakes and lizards, ventricle also has

septum (incomplete 4-chambers)

Circulation• In birds and mammals, complete

separation of oxygenated/deoxygenated blood, 4-chambered heart, efficient system with no mixing gives greater blood volume and higher blood pressure (needed for metabolic requirements)

Excretion

• Kidneys = separate food/water from excess salt/waste in blood

The Egg

• Eggs enclosed by plasma membrane internally and vitelline membrane externally

• Fish and amphibian eggs pass down oviduct where chitinous chorion or gelatinous protein-polysaccharide material added (anamniote egg = no amniotic membrane)

• External fertilization; moist climate to prevent desiccation

The Egg

• Evolution of amniote egg: equipped with extra membrane layers of protection (amnion, yolk sac, chorion, allantois) as well as a leathery/calcareous shell

• In reptiles and mammals (monotremes); fertilization internal; subject to predation

• Marsupials and placental mammals retain young internally (helps young develop to an advanced stage before born)

The End