Midterm II (Tunicates and Cephalochordates) Flashcards
Phylum Chordata
- Bilateral symmetry
- Anterioposterior axis
- Not all are vertebrates!!
- Coelom
- Tube-within-a-tube body plan
- Metamerism
- Cephalization
5 (classic) chordate characteristics
- Notochord: a whole new package! (true synapomorphy)
- Dorsal Hollow Nerve Cord (true synapomorphy)
(KNOW DIF between two!!!) - Pharyngeal Pouches and Slits
- Endostyle or Thyroid Gland
- Postnatal Tail
- Notochord
- Rodlike, semirigid tissue enclosed in a sheath
- Extends the length of body lying between the gut and the nervous system (in most cases)
- Mainly to stiffen the body
- Providing skeletal scaffolding for the attachment of swimming muscles
- AKA support!
- Always found at some embryonic stage
- 1st part of the endoskeleton to appear in the embryo (i.e., fr. mesoderm) - In non-vert. chordates and jawless vertebrates:
- persists throughout life
- In most vertebrates:
- displaced by vertebrae
- remains as discs
- Dorsal Hollow Nerve Cord
In Chordates:
- dorsal to digestive tract (ventral to digestive tract in non-chordate inverts, e.g., insects)
Anterior end = brain
Via neurulation
- i.e., Ectodermal origin
Passes through the neural arches of vertebrae (in vertebrates)
Or just runs dorsal to notochord if no vertebrae
- Pharyngeal Pouches and Slits
- From the inpocketing of ectoderm + evagination of endoderm of pharynx
- Perforated pharynx functions as filter-feeding apparatus in non-vert. chordates (lancelets and tunicates)
- Post-embryonic secondary development in some vertebrates
- e.g., auditory tube, middle ear, glands, larynx
- Fishes added a capillary network with thin gas-permeable walls
- Led to evolution of gills
- Endostyle or Thyroid Gland
- Longitudinal ciliated groove ventral to pharynx
- Some cells in endostyle secrete iodinated proteins homologous with the iodinated-hormone-secreting thyroid gland of adult lampreys and the remainder of vertebrates
- Secretes mucous for food capture in the filter-feeding non-vert. chordates
- Postnatal Tail
- Postnatal tail + plus muscular = motility for larval tunicates and amphioxus to swim
- Efficiency increased in fishes but became smaller or vestigial in later lineages
Earliest known chordates
- Pikaia
- Burgess shale, BC
- Similar to living cephalochordate
- Originally classified as a polychaete! - Metaspriggina walcotti
- latest fossil from burgess
- Notochord, gills, gill bars, paired eyes, (W-shaped) myomeres - Haikouella
- China
- Notochord, pharynx, dorsal nerve chord
- pharyngeal muscles, paired eyes, distinct brain
- NO cranium!- sister taxon to vertebrates?
Subphylum Cephalochordata
Burrow in porous mud and sand and seldom swim
Expose mouths to seawater and filter out particles
Water enters the mouth driven by cilia in the buccal cavity pharynx
- passes through pharyngeal slits where food is trapped in mucus secreted by the endostyle
Closed circulatory system (no heart)
Only moderate cephalization
- no distinct brain or cranium (i.e., not vert)
Body surface respiration
Subphylum Urochordata (AKA Tunicata)
“tail-chordates”
Around 3000 spp
In all seas and depths
Most sessile as adults, some free-living
3 classes:
- Ascidiacae (“little bag”)
- sea squirts
- (Former) Thaliacae (“luxuriant”)
- salps
- Appendicularia (“ghost larva”)
Tunic (cellulose)
Filterfeeding!
No cephalization
Two-directional heart
Are Tunicates rlly chordata?
Free-swimming larvae show al 5 classic chord. characteristics
- Only endostyle and pharyngeal slits remain in adult
Class Ascidiacae
- Compound
- Colonial
- Solitary
One of Aquaculture’s worst enemies - All common in Atlantic Canada and wreak havoc on aquaculture sites (shellfish): biofouling
(Former) Class Thaliacea
- The Salps
- free-swimming, can be solitary or colonial
- use water current for both feeding and gas exchange as well as for locomotion (form of jet propulsion)
- Feed using a mucus net
Class Appendicularia
Around 70 spp.
Larvaceans:
- pelagic, free-swimming, tiny
Show all 5 chordate characters in the adult form
Secret a mucous house to suspension feed
