Ani Div Lab Week 8

Chordates

general chordata characteristics

• triploblastic coelomate deuterostomes

• bilateral symmetry

• closed circulatory system

• endoskeleton

• highly cephalized

• homologous structures

• highly developed respiratory, digestive, and excretory systems

• under deuterostomia and next to echinodermata (sea stars)

• three groups under chordata —> cephalochordata, urochordata (tunicata), and vertebrata

5 key characteristics of chordates

notochord —> flexible, rod-like structure for support

pharyngeal gill slits —> perforated openings that aid in filter feeding in simpler chordates, modified into gills

dorsal (hollow) nerve chord —> spinal cord and brain

post-anal tail —> tail for locomotion

endostyle —> secretes mucus for filter feeding in lower chordates, modified into thyroid gland

all of these are present at some point in chordates

clade cephalochordata

• marine lancelets

• show all chordate characteristics clearly as adults

• burrow in the sea floor, filter feeders

lancelet structures and functions

rostrum —> food gathering

myomeres —> structural integrity and movement

dorsal nerve cord —> central nervous system

notochord —> structural support

gill bars —> ciliated, coated with mucus. used to catch suspended food particles. structural support, protection, filter feeding gas exchange.

gill slits —> openings that lead from pharynx to exterior, allow for water to exit body, filter feeding, gas exchange.

hepatic caecum (liver) —> intracellular digestion

clade urochordata —> tunicates (sea squirts)

• sessile filter feeders as adults

• have a tunic —> tough outer test

• show the chordate charactiersitcs as larvae

structures and functions of tunicate

pharynx with gill slits —> filter feeding

endostyle —> mucus secretion

incurrent and excurrent siphons —> respiration, draw water into body and expel

notochord —> structural support

post-anal tail —> locomotion

dorsal nerve cord —> CNS

atrium —> passage from siphon to the pharynx

tunic —> tough outer covering

stomach —> chemical and mechanical digestion

intestine —> nutrient absorbption

clade vertebrata

• characterized by a vertebral column and cranium

  • cranium protects the brain

  • vertebral column protects spinal chord

• have an endoskeleton of bone and/or cartilage —> its living unlike the dead exoskeleton in arthropods —> allows for growth

• muscle attachment to endoskeleton

• closed circulatory system

• digestive and excretory system well developed (kidneys)

• highly cephalized (well developed sensory organs associated with a highly differentiated brain)

• bilateral symmetry

• possess all chordate features at some point in life

• under clade chordata

• has gnathostomata under it and “agnatha” which has cyclostomata which has petromyzontida (lampreys)

lampreys —> clade petromyzontida

• parasites that attach to fish using sucker-like mouth

• have horny teeth to rasp away at flesh

• suck out body fluids with secreted anti-coagulants

• anadromous

• larvae called ammocoetes

• under clade cyslotomata which is composed of living/extant members and is monophyletic

  • lack jaws and paired appendages

• then under “agnatha” which includes living or extinct jawless fishes and is paraphyletic

anadromous vs catadromous life cycle

anadromous

• spend most of adult life at sea

• go to rivers/streams (freshwater) to reproduce

• examples include salmon and lamprey

catadromous

• spend most of adult life in freshwater

• migrate downstream to saltwater to reproduce

• example includes freshwater eel

lamprey lifecycle

• adult freshwater spawning phase

• larval (ammocoete) phase

• juvenile —> downstream migration

• parasitic juvenile phase —> attacks fish and does its parasite things

lancelet vs ammocoete

A —> ammocoete (lamprey larva)

• more defined post anal tail (bigger)

• rounded in shape

• larger and more rounded gills/pharyngeal gill slits

B —> Lancelet (cephelochordata)

• sharper and more gill slits

• sharper tail

ammocoete structures and functions

pharynx with gill slits —> Gas exchange, filter feeding

endostyle —> secretes mucus onto gills

notochord —> structural support

dorsal nerve cord —> CNS

myomeres —> muscle tissue, structural integrity and movement

lamprey structures and functions

fins —> no paired fins, locomotion

gill slits —> openings to allow water flow to gills

nostril —> chemosensory organ serving olfactory function

buccal papillae —> finger like projections surrounding buccal cavity, creates a seal and good attachment to the host

horny teeth —> multiple rows, attachment to host

pharynx —> connects mouth to esophagus, enables respiration when attached to the host

gill bars —> respiration

heart —> circulation of blood

myomeres —> muscle tissue, allows for lateral undulation

notochord —> structural support

spinal cord —> CNS

liver —> secretes bile, accessory digestive organ

Gonads —> reproduction

CNS vs PNS

Central nervous system (CNS)

• includes brain and spinal cord

• “control center”

Peripheral nervous system (PNS)

• contains nerves and ganglion that spread to rest of the body

• involuntary control

sheep brain structures and function

cerebrum —> sensory and motor

cerebellum —> balance

medulla oblongata —> control of automatic functions (breathing, swallowing, heartrate)

corpus callosum —> connects the two halves of the brain, inter-hemispheric communication

optic chiasma —> where the optic nerves cross one another

pituitary gland —> part of endocrine system, hormone secretion

hypothalamus —> controls pituitary, homeostasis

pons —> unites messages from cerebellum and cerebral cortex (brain halves)

pineal body —> involved in biorhythms (puberty)

thalamus —> sensory integration and relay to cerebrum

meninges —> protective covering