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