Chordata

Amphioxus

Amphioxus

small fishlike translucent animal that exhibits the five distinctive hallmarks of Phylum Chordata

dorsal nerve cord, notocord, pharyngeal pouches, endostyle, postnatal tail

5 distinctive characteristics of chordates at some life stage

distinct head and sense organs

what does amphioxus lack compared to other vertebrates?

agnatha and gnathostomata

how are vertebrates grouped

paraphyletic

what kind of group are reptiles?

Pisces

jawed vertebrates with appendages (if any) as fins

Tetrapoda

jawed vertebrates with appendages (if any) as limbs

birds

what does the monophyletic taxa reptila include?

Notochord

-Rod like flexible structure extending the length of the body

-Hydrostatic organ with fluid in cells or compartments between cells

muscles

what attatches to the notochord?

vertebrae

what replaces the notochord in many vertebrates?

dorsal to digestive tract

where is the nerve cord located?

infolding of ectodermal cells

how is the nerve cord produced?

pharyngeal cavity, outside

Pharyngeal slits lead from _______ to the __________.

ectoderm, endoderm

Pharyngeal slits formed by the inpocketing of the _____ and the invagination of ________ of pharynx

filtration

function of pharyngeal slits

Eustachian tube, middle ear cavity, tonsils, and parathyroid glands

structures that develop from pharygeal pouches

thyroid gland

derived form endostyle

endostyle

Usually found on the pharyngeal floor and secretes mucus to trap small food particles coming in from the mouth

postanal tail

provides motility for larval tunicates and Amphioxus during their free-swimming stages

tunicates

-Urochordates or “tail chordates

- Found in all seas and at all depths.

- Most are sessile as adults.

larval

what stage of tunicate bears chordate hallmarks?

nutrients, not gasses

what does the cephalochordata circulatory system transport

external

what type of fertilization in cephalochordata?

larger and more active

vertebrates are _____ than protochordates

cartilage, bone

Vertebrate endoskeleton probably composed initially of ____ and later of _____

neural crest

-a population of ectodermal cells lying along length of the embryonic neural tube

-Contributes to formation of many different structures like most of the cranium, pharyngeal skeleton, tooth dentine, some cranial nerves, ganglia, and Schwann cells

-regulate development of adjacent tissue

ectodermal placodes

-plate-like ectodermal thickenings on either side of neural tube.

-Give rise to olfactory epithelium, lens of eye, inner ear epithelium

hox genes

-genes that control the body plan of chordate embryos

-make sure body structures develop in correct place

more complex animals

where are more copies of the hox genes found

ostracoderms

armored jawless fishes, which were the earliest known vertebrate fossils found in the late Cambrian deposits

paired fins

what did the earliest vertebrates lack?

conodonts

strange microscopic tooth-like fossils used to date paleozoic marine sediments

monophyletic

what type of group is gnathostomes (jawed)

paraphyletic

what type of group is agnathans (no jaws)

predation on large and active food

what is the benefit of jaws?

1st gill arch

what developed into a jaw?

notochord

what is the first part of the endoskeleton to appear in the chordate embryo?

enlarged anterior end of the nerve cord

what forms the chordate brain?

incurrent, excurrent

In ascidians, _________ or oral siphon marks anterior side while ___________ or atrial siphon marks dorsal side

mucous net secreted from endostyle

how do ascidians feed?

mantle

what lines the outer tunic of ascidians

hermaphroditic with single ovary and single testis

sea squirt reproductive structures

pharyngeal slits and endostyle

chordate features retained in adult sea squirts

lancelets or amphioxus

slender, laterally compressed, translucent animals that are about 3 to 7 cm long

ileocolic ring

areas where food can be concentrated in amphioxus

pumped by ventral aorta through brachial arteries to pharyngeal bars to paired dorsal aortas which form single dorsal aorta

how does blood flow through cephalochordata circulatory system?

nutrient transport, lacks erythrocytes/hemoglobin for respiration

what is the main function of cephalochordate blood, why?

ocelli

fuctions as cephalochordata photoreceptor

in atrium through the atriopore

how are cepholochordate gametes released?

body wall

where does cephalochordate gas exchange occur?

modifications of skeletal structures and muscles

increased vertebrate speed and mobility

higher

how does the metabolic rate of vertebrates compare with other organisms

V to W shaped

how did the myomere shape change from ancestral to modern chordates

structural strength and better muscle attatchment

benefits of bone (over cartilage)

for mineral storage and homeostasis (calcium and phosphorus)

why may bones have evolved

electroreceptors

detect electrical currents when prey is near

lateral line receptors

receptors for vibration

pectoral and pelvic

paired fins in gnathostomes for stable swimming

homologous

jaw musculature is ________ to the musculature that originally supported gills