Chordates

how does the size of Chordata compare to other groups?

fourth largest group on Earth

three broad groups of chordates

cephalochordates, urochordates, vertebrates

chordate phylogeny

Eumetazoa, Bilateria, Deuterostomia, Chordata

what is distinctive about Eumetazoa?

true tissues

what is distinctive about Bilateria

bilateral symmetry (Echinoderms are exception)

what is distinctive about Deuterostomia?

anus develops from blastopore

five characteristics all chordates have in at least one part of their life cycle

notochord, pharyngeal slits, endostyle, dorsal hollow nerve cord, postanal tail

notochord description

thin, flexible rod dorsa to coelom

primary function of notochord

to permit swimming motion

when do humans have a notochord

only during embryonic stages

what does the notochord serve as a template for in human embryos?

the vertebral column

three species that has a notochord in adult stages

Amphioxus, hagfish, lamprey

layers of notochord

superficial layer of dense and tough connective tissue, collagenous sheath, core composed of cells with large fluid-filed vacuoles

what is the rigidity of the notochord a function of?

the hydrostatic pressure of the fluid-filled vacuoles

what happens to the notochord if the fluid from the core is released?

the notochord collapses

why is “gill slits” a misnomer for pharyngeal slits?

they play no role in respiration, gills don’t develop from them

what organ and system are pharyngeal slits part of?

pharynx, digestive system

adult species that has pharyngeal slits

Amphioxus

what do pharyngeal slits become in humans?

lower jaw, portion of inner ear, auditory tube

endostyle description

endocrine gland involved in iodine metabolism

what does the endostyle develop into in adults?

thyroid gland

dorsal hollow nerve cord description

nerve cord found along the back, usually in a hollow tube

how is the chordate nerve cord different from that of the invertebrates?

invert nerve cord is ventral, chordate nerve cord is dorsal

what does dorsal hollow nerve cord form from?

endoderm

what disease occurs from incomplete development of the dorsal hollow nerve cord?

spina bifida

how is chordate tail different from invertebrate tail?

most invert anuses terminate at the most posterior location, in chordates the anus terminates prior to tail (postanal tail)

what does the postanal tail reduce to in humans?

the coccyx/tail bone - significantly reduced postanal tail

how many extant species of cephalochordates

32

three genera of cephalochordates

Asymmetron, Branchiostoma, Epigonichthys

cephalochordate common name

lancelet

four characteristics of Asymmetron

60 mm long, asymmetrical, gonads on right, tropical

four characteristics of Branchiostoma

55 mm long, symmetrical, gonads on both sides, temperate

four characteristics of Epigonichthys

60 mm long, asymmetrical, gonads on right, tropical and temperate

two discovered fossils of cephalochordates

Pikaia (60 mm) and Yunnanozoon (1 cm)

cephalochordate feeding strategy

bury in sand, filter feed

three key organs in cephalochordate feeding

wheel organ, pharyngeal slits, hepatic cecum

wheel organ function

creates water current

pharyngeal slits function in cephalochordates

trap food particles in mucous

hepatic cecum functions

digestion and filters out toxins

urochordate representative

tunicates/sea squirts

how many species of tunicates

3000

location of tunicates

most species are sessile, but some (salps) are free-floating and aggregate into large colonies

path of food in urochordates

food pulled in through the oral/branchial siphon by cilia lining slits in the branchial/pharyngeal basket, water filters out the atrial siphon (digestive system terminates)

four key organs of urochordates

brain/ganglion, stomach/intestines, heart, basic circulatory system

which chordate characteristics are missing from adult stage of urochordates?

all but endostyle - notochord, dorsal hollow nerve cord, pharyngeal slits, postanal tail

which chordate characteristics do tunicate larva have?

all five - endostyle, pharyngeal slits, dorsal hollow nerve cord, postanal tail, notochord

urochordate reproduction style

sexual reproduction is most common, asexual reproduction is possible