Hemichordata and Invertebrate
Chordates
Phylum
Hemichordata
Characteristics of Hemichordata:All live marine environments.
Bilaterally
symmetrical.
Body divided into three
sections, a proboscis, a collar
and a trunk.
Body cavity a true
coelom divided into
three cavities.
Dorsal, sometimes
tubular, nerve cord.
Complete digestive
tract, feeds on fine
particles in the water.
Class Enteropneusta
Marine worms
Ciliated epidermis and glands
cover acorn worms
Burrow in sandy and
muddy substrates
Common name ‘acorn worms’
Maintenance Functions
Ventral Mouth
Lateral Pharyngeal slits,few to several hundred
Cilia and mucus assist
acorn worms in feeding
Ciliary tracts converge
near the mouth and
form a mucoid string
that enters the mouth
Enteropneusta
extends its posterior
end out of the burrow
during defecation.
Eww!!!
Nervous system
• Ectodermal in origin
• Lies at the base of
the ciliated epidermis
• Consist of dorsal and
ventral nerve tracts
• No major ganglia
• Sensory receptors
are unspecialized
Respiration
• Simple diffusion of
metabolic waste
• Cilia associated with
Pharyngeal slits
circulate water into
mouth and out of body
• Gas exchange as
water passes through
pharyngeal slits
Circulatory system
• Colorless blood moves nutrients
and wastes
• Dorsal and ventral contractile
vessel
• Blood moves anteriorly in dorsal
• Posteriorly in ventral vessel
• Branches from theses vessels
lead to open sinuses (Partially open
circulatory system)
• Anterior flowing blood moves
through glomerulus (excretory
organ)
• Waste filtered into proboscis
coelom and out through pores
Reproduction and Development
Dioecious!!
External Fertilization
pheromones
Evolutionary ties b/w hemichordatres
and echinoderms
Ciliated larvae
Class Pterobranchia
pteron- wing
branchia- gill
Deep marine water
Some live in shallow waters
Body divided
into three
regions
Size 0.1 - 5mm
Individuals
called
zooids
Most live in secreted tubes in asexually
produced colonies
Maintenance Functions
Filter feeders
Cilia on tentacles trap and transport
Food to mouth
Respiration and excretory
exchange by diffusion
Reproduction and Development
Asexual budding is common and responsible
for colony formation
Also some posses one or two gonads
Most species are dioecious
External fertilization
Planula-like larva (cnidarian)
Settles to a substrate, forms cocoon and
metamorphoses into an adult
Phylum Chordata
Characteristic of the chordates
Deuterostome embryo development
Notochord, phayngeal slits or pouches,
dorsal tubular nerve cord, and postanal tail
Coelomate animals
Bilateral symmetry
Endoskeleton
Two major groups: nonvertebrate chordates
and vertebrates
Subphylum Urochordata
• Uro, tail and chorda, cord
• Class ascidians
– Tunicates or sea squirts
•
•
•
•
Solitaire or colonial
Sessile adults
Attach to solid substrates
two siphons that permit
seawater to circulate
through the body
• Oral siphon also the
mouth
• Atrial siphon
Body wall
• Tunic- gown
• Connective tissue
like covering
• Tough secreted by
the epidermis
• Composed of
proteins
Salts, cellulose
• Stolons extensions
of tunic help root
Maintenance Functions
• Longitudinal and circular
muscles below the body
wall epithelium
• Nervous system largely
confined to body wall
• Forms nerve plexus with a
single ganglion between
oral and atrial opening
• Sensitive to mechanical
and chemical stimuli
around siphon but no
complex sensory organs
Reproduction and Development
• Tadpole larva
• Attaches to substrate by
adhesive papillae
located below the mouth
• During development
internal structures rotate
1800 bending the
digestive tract into a Ushape
Reproduction and Development
• Monoecious
• Self fertilization and cross fertilization
Subphylum Cephalochordata
• Elongated laterally flattened
nearly transparent
• Lancelets
• Size up to 5 cm tadpole like
animals
• All four chordate
characteristics persist
throughout life
• Shallow waters
• genera Branchiostoma
(Amphioxus)
Reproduction and Development
• Dioecious
• Gonads shed gametes
into the atrium
• Leave the body through
the atriopore
• External fertilization
• Bilaterally symmetrical
larva
• Larva free swimming
• Larva Settle to substrate
then metamorph into
adults
Maintenance Function
• Filter feeders
• Buried in sandy
substrate
• Mouth pointed
upward
• Cilia on lateral surfaces of gill sweep water into
mouth
• Food sorted in the cirri
•Edible particles move along cilia to the gut
• No true heart
• Contractile waves in
the walls of major
vessels propel
blood
• Blood contains
amoeboid cells and
bathes tissues in
open spaces
• Excretory tubules are modified coelomic
cells closely associated with blood vessels.
• Coelom reduced- restricted to canals near the
gill bars, endostyle and the gonads