Protochordates and The Origin of Craniates Flashcards
Also known as enterocoelomates because their coelom develops through enterocoely
deuterostomes
proposed a taxonomic classification of deuterostomes
Ernst Haeckel (1874)
Four extant phyla of deuterostomes
Xenoturbellida
Echinodermata
Hemichordata
Chordata
Invertebrate extant phyla of deuterostomes
Xenoturbellida
Echinodermata
coelom forms when the mesoderm splits, doe
protostomes
the coelom forms when the mesoderm pinches off through the process of enterocoely, merges with coelom
deuterostomes
Closest relatives of vertebrates along with the hagfish
Provide clues to the invertebrate origin of animals with backbones
Protochordates
Protochordates are composed of subphylums:
Hemichordata
Urochordata
Cephalochordata
Phylum
Unique calcium carbonate skeleton
Secondary radial symmetry in adults
Bilateral symmetry in early life stage
Phylum Echinodermata
Commonly known as acorn worms
Vermiform bottom dwellers found in shallow mud water
Fragile and can reach up to 5 feet in length
can be in freshwater
Phylum Hemichordata
Proposed classification of Hemichordata in 1870 by Gregenbaur
Enteropneusta
Proposed classification of Hemichordata in 1874 by Haeckel
Phylum Chordata
Proposed classification of Hemichordata in 1884 by Bateson
Subphylum Hemichordata
Subphylum Hemichordata example
acorn worm
Bateson’s considerations placing Phylum Hemichordata under Phylum Chordata
Collar nerve cord is dorsally located with lumen
Have slits that open to the exterior in lateral walls of the foregut
Have a stomochord, short diverticulum of the foregut
findings ultimately showed that it is not homologous to the chordate notochord
short diverticulum of the foregut
stomochord
Class
Wormlike acorn worms
Mucus-covered body
Active proboscis collects food in mucous strands
Cilia carry particles to groove at the edge of the collar, then to the mouth
Thrust proboscis into mud and ingest mud to extract the organic matter
Sexes are separate
Fertilization is external
At least one species undergoes asexual reproduction
Class Enteropneusta
connects protocoel with a proboscis pore to the outside in Class Enteropneusta
Buccal diverticulum
________ of body musculature forces excess water out through the gill slits in Class Enteropneusta
Contraction
Roll of gill pores is part of _________ that connects with series of gill slits in sides of pharynx in Class Enteropneusta
branchial system
Primarily ciliary-mucus feeders using U-shaped gill slits
Class Enteropneusta
Class Enteropneusta has a vessel that expands into a sinus and heart vesicle above the buccal diverticulum
Middorsal vessel
Blood enters network of blood sinuses called _______ and then through an extensive system of sinuses to the gut and body wall in Class Enteropneusta
glomeruli
in Class Enteropneusta, consists mostly of a
subepithelial plexus
in Class Enteropneusta, formed by an invagination of ectoderm (hollow in some species)
Dorsal nerve cord (neurocord)
in Class Enteropneusta, a ________ larva develops similar to that of echinoderm larva
ciliated tornaria
Basic plan similar to that of Enteropneusta
Small animals, usually 1 to 7 mm in length
Many individuals may live together in collagenous tubes (zooids are not connected)
Ciliated grooves on tentacles and arms collect food
Both dioecious and monoecious species
Asexual reproduction is by budding
Class Pterobranchia
Body divided into three regions in Class Pterobranchia
proboscis, collar and trunk
Similarties between hemichordates and echinoderms
Bilaterally symmetrical larvae
Similar in certain developmental processes, in muscle proteins, etc.
In addition to the dorsal nerve cord, there is another one on the ventral surface, as in invertebrates
Deuterostomous development
Sequence analysis of the gene encoding the small subunit of rRNA supports a deuterostome clade by which taxa
Echinodermata
Hemichordata
Chordata
should be classified close both to echinoderms and protochordates but in a separate taxon
Hemichordates
Marine chordates
Notochord is found in the locomotive tail of the free-living larval stage
Enclosed in tunics
Filter feeders
Subphylum Urochordata
Subphylum Urochordata 3 classes
Ascidiacea
Larvacea
Thaliacea
Urochordata class
Sea squirts are the best known urochordate
Can either be solitary or colonial
Larvae are tiny and have a fleeting existence lasting for a few minutes to a few days and do not feed
Presence of uninucleated striated muscles
Class Ascidiacea
Urochordata class
Nervous system consists of dorsal hollow nerve cord, several ganglia and nerves
Definitive blood cells and a functional heart does not differentiate until metamorphosis
Adhesive papillae attaches the larva to a permanent substrate
Class Ascidiacea
used for statoreception in Class Ascidiacea
Otoliths
used for photoreception Class Ascidiacea
Ocellus
Class Ascidiacea water pathway
Respiratory water mouth pharynx gills atrium atriopore
Class
Notochord is resorbed and becomes source of nutrients during metamorphosis
Nervous system location is altered and rearrangement of viscera takes place
Water flows through slits into atrial cavity and out through excurrent siphon
Class Ascidiacea
Class
Called sea squirts because they discharge a jet of water when disturbed
Class Ascidiacea
______ becomes the incurrent siphon (anterior)
Class Ascidiacea
Larval mouth
______ becomes the excurrent siphon (dorsal)
Class Ascidiacea
atriopore
Class Ascidiacea
Water entering the incurrent siphon passes through a ciliated perforated
pharynx with an elaborate basketwork
Class Ascidiacea
Feeding depends on the formation of a mucous net that is secrete by the ____
endostyle
Class Ascidiacea
on gill bars of pharynx pull mucus into a sheet
Particles trapped in sheet are worked into a rope and carried back to the esophagus and stomach
Polyp becomes a filter feeder because of this
Cilia
circulatory system of Class Ascidiacea
Heart drives blood first in one direction, then in reverse
gland that samples incoming water and may have an endocrine function
Subneural gland
with a single ovary and a single testes and fertilization is external in Class Ascidiacea
Hermaphroditic
Adult sea squirts retain 2 of 5 chordate features
Pharyngeal slits
Endostlye
Tadpole larvae have all 5 chordate characteristics
true
class
Planktons on surface water or deep sea
With a long body and a long flat locomotive tail supported by a notochord
Retain larval form yet is sexually mature
Resemble the larval stages of other urochordates
Class Larvacea
class
Surrounded by a thick, delicate hollow sphere of mucus interlaced with passages for water entry produced by the larva
Phytoplankton and bacteria trapped on a feeding filter inside the sphere are drawn into the branchial basket through pulsating movement
Class Larvacea
Class Larvacea
When ______become clogged with wastes, they are left behind and a new sphere is built
feeding filter
Colony may be linear or it may consists of a floating water-filled sac
Incurrent aperture projects into the sea and excurrent aperture empties into the saccular chamber
Colonies move with water current
Only one order has a free-living larval stage and has a very short-life span
Class Thaliacea
class Thaliacea has No notochord to be described
true
the correct morphological development or evolution
Pedomorphosis preceding Peramorphosis
Any outcome arising from evolutionary changes in developmental rates (see heterochrony) that involves the addition of new stages to the end of the ancestral development sequence.
Peramorphosis
process of development in which an organism retains juvenile characteristics into adulthood,
Pedomorphosis
Generally called amphioxus (sharp at both ends) or lancelet (little spear)
Marine forms in sandy beaches
Filter feeders by burrowing in the sand, making a U-turn and having the oral hood protruded
Hollow nerve cord lies above the notochord
Pairs of spinal nerve roots emerge at each trunk segment
Anterior nerve cord is not enlarged, yet is homologous to vertebrate brain
Sexes are separate
Gametes are set free in the atrium and pass out through atriopore
Fertilization is external
Larvae soon hatch and gradually assume the shape of adults
Subphylum Cephalochordata
Subphylum Cephalochordata Genera:
Branchiostoma and Asymmetron
has the five distinctive characteristics of chordates in simple form
Amphioxus
in Amphioxus, Water enters the mouth directly driven by cilia in the _______
buccal cavity and pharynx
in Amphioxus, Water passes through pharyngeal slits where food is trapped in mucus secreted by the
endostyle
in Amphioxus, Food is moved through gut via cilia concentrated in areas called the
ileocolic ring
in Amphioxus, Food particles separated from mucus are passed into _______ where they are phagocytized
in Amphioxus,
in Amphioxus, Filtered water leaves body by an
atriopore
Closed circulatory system is complex but lacks a heart in Amphioxus
true
how does blood flow in amphioxus
Blood is pumped by peristaltic contractions in ventral aorta, passes upward through branchial arteries in pharyngeal bars to paired dorsal aortas
Blood moves by microcirculation through tissues and returns to ventral aorta
Blood lacks ________ and mainly transports nutrients in amphioxus
erythrocytes and hemoglobin
Sense organs are simple, including an unpaired _______ that functions as a photoreceptor in amphioxus
ocellus
Subphylum Cephalochordata
is a diverticulum resembling the vertebrate pancreas in secreting digestive enzyme
Cecum
Subphylum
possesses features that suggest the vertebrate plan
Trunk muscles resemble vertebrate patterns
Posses basic circulatory plan of vertebrates
Cephalochordata
Differences of Cephalochordata From Vertebrates
Almost no cephalization and no paired sense organs
No vertebral column
Has pharyngeal slits in large numbers
Brain lacks major craniate subdivisions
Segmented musculature extends to the anterior tip of the head
One-layered external integument
No muscular heart
Coelom is found in adult forms only
Similarities of Cephalochordata From Vertebrates
Big five
Segmented or metameric musculature
Two layered skin
Blood flow direction in arterial and venous channels
Homologous homeobox gene clusters
have been found in very old rocks, indeed, predating the origin of the vertebrates
Fossil cephalochordates
earliest known cephalochordate found in South China (Early Cambrian)
Yunnanozoon
cephalochordate fossil found in BC, Canada (Middle Cambrian)
Pikaia
eel-like; earliest known chordata fossil somewhat similar to Pikaia
Cathaymyrus
A Vertebrate Larva
Ammocoete Larva
Shows evidence that vertebrates share a common ancestor with protochordates
Notochord that commence from the midbrain and continues to the end of the body (no vertebral column)
Ammocoete Larva
Dorsal hollow nerve cord develops as of the amphioxus but with a tripartite brain
Seven pair of gill slits open to the exterior for respiration
Skin is multilayered
Body wall musculature provides locomotion
Filter feeders
Ammocoete Larva
Hypobranchial groove in ammocoetes sink and becomes the
subpharyngeal gland
Ammocoetes and amphioxus difference in diverticulums
Ammocoetes have a solid liver diverticulum which the amphioxus has a saccular diverticulum at the same location but are not analogous
Food particles are trapped in mucus produced by the ________which is homologous to the hypobranchial groove of amphioxus
endostyle
Larva that has a:
Circulatory system with heart (sinus venosus, atrium and ventricle) and RBC
Sense organs are present such as otic vesicles (precursor of membranous labyrinth but not for hearing), olfactory sac (chemoreception associated with feeding) and pineal and parapineal organs (act as photoreceptors)
Paired lateral eyes eventually form but are rudimentary
Ammocoete Larva
which collect body fluid for processing and excretion in Ammocoete Larva
funnel-like nephrostomes
in Ammocoete Larva, Fluids are expressed into the coelom via
glomeruli
in ammocotes, _increase in number as larvae elongates and lead to ducts which empties to the exterior near the anus
Tubules
Gonad is paired early in larval life and becomes unpaired later in ammocoetes
true
Bottom-dwelling organisms from the Late Cambrian
Sucked up organic material from the sediment like vacuum cleaners
Most ancient agnathan or jawless fish
Extinct by the Devonian because they could not compete with other jawed fishes
Ostracoderms
Cartilaginous internal skeleton
Dorsoventrally flattened
Cartilaginous internal skeleton
Dorsoventrally flattened
Dorsal eyes
Armored head
Ostracoderms
