LECTURE 16 - Chordata Flashcards
1
Q
(IN CHORDATA) What are Tunicata?
A
- Tunicates are large marine animals, sessile or pelagic, feeding by a branchial basket enclosed in a capacious bag
2
Q
What families radiate from Tunicata?
A
- Ascidiacea (sessile attached tunicates)
- Thaliacea (pelagic tunicates)
- Larvacea (pelagic neotenous tunicates)
3
Q
How do Tunicates develop?
A
- Tunicates have indirect development through a unique type of larva
- Many tunicates have a tadpole-like larva that feeds in the plankton
- It eventually attaches mouth-first to a hard substrate and metamorphoses into the adult form
4
Q
(IN TUNICATA) What are Ascidiacea?
A
- A leathery tunic forms the body wall, encloses the branchial basket, the atrium and the viscera
- The branchial basket is the pharynx, perforated by numerous gill slits
- Waters enters through an incurrent (branchial) siphon, powered by cilia
- Mucus secreted by the endostyle coats the walls of the branchial basket and captures food particles, which pass into the gut
- The water stream then flows into the atrium and exists through the excurrent (atrial) siphon
- Colonial sessile tunicates
- The mangrove tunicate is a colonial ascidian comprised of individual zooids connected through a series of root-like stolons at the base of the colony
- These stolons provide blood to zooids, linking them to one another, and serve as attachment points between the colony and substratum
- Each zooid is surrounded by a tunic opening to the water column via an orange siphon
5
Q
What is immune recognition in colonial ascideans?
A
- The colonies compete for space by destroying competitors whom thy diagnose as non-kin
6
Q
(IN TUNICATA) What are Thaliacea?
A
- Pelagic tunicates
- Doliolids: solitary jet-propelled jellies
- Salps: Colonial chains
- Pyrosomes: colonial cones
7
Q
(IN TUNICATA - IN THALIACEA) What are Doliolids?
A
- Doliolids are small free-floating filter feeders
- They force water to flow through their bodies to gather plankton
- This can also be used for “jet” propulsion and can move quite quickly
- They grow to around 1 or 2 cm in length
- They are barrel-shaped with two wide siphons, one at the front and the other at the back end, and eight or nine circular muscle strands reminiscent of barrel bands
- They have a complicated life cycle consisting of sexual and asexual generations
8
Q
(IN TUNICATA - IN THALIACEA) What are Salps?
A
- Salps are barrel-shaped, free-floating tunicates
- They move by contracting their bodies, which causes water to pump through their gelatinous bodies
- They strain the pumped water through their internal feeding filters, feeding on phytoplankton
- They have a complex life cycle, showing alternation of generations
- The larvae are quite different from the adults, but both are mostly-transparent, tubular, gelatinous animals that are typically between 1 cm and 10 cm long
9
Q
(IN TUNICATA - IN THALIACEA) What are Pyrosomes?
A
- Pyrosomes are free-floating colonial tunicates that usually live with plankton in the upper layers of the open ocean in warm seas, although some may found in deep water
- They form cylindrical or cone-shaped colonies made up of hundreds to thousands of zooids
- Colonies range in size from less than one centimetre to several metres in length
- Each zooid is only a few millimetres in size, but is contained in a common jelly-like tunic that joins all of the individuals
- Each zooid draws in water from the outside and expels the filtered water to the inside of the cylinder of the colony, driving it forwards
10
Q
(IN TUNICATA) What are Larvacea?
A
- The adult larvacean has the appearance of a larva but develops reproductive structures and gametes (neoteny)
- Gametes are released through a gonopore and fertilization is external
- Larvaceans are small animals that live in the upper waters of the ocean worldwide
- The undulating tail creates a feeding current that draw water into the feeding structure or “house”
- The animal in the centre of the house gathers the collected food by driving it to the pharynx using ciliary action; excess water exits via pharyngeal slits
- When the house becomes clogged, it is discarded
11
Q
What is the notochord?
A
- The NOTOCHORD is a flexible, rod-like structure derived from mesoderm
- The first part of the endoskeleton to appear in an embryo
- Provides skeletal support throughout most of the length of a chordate
- Place for muscle attachment
- In vertebrates, the notochord is replaced by the vertebral column (but it still appears as an embryonic structure, serving as a scaffold for the growing of the embryo); remains of the notochord may persist between the vertebrae, forming the gelatinous pads in the intervertebral disks
12
Q
Describe locomotion with a notochord.
A
- The NOTOCHORD is an elastic cartilaginous rod that resists axial compression but allows lateral flexion
- It prevents the collapse of the body during muscle contraction and transforms the alternate contraction and extension of the axial musculature on either side of the body into a sculling movement that propels the animal forward
13
Q
What is the post-anal tail?
A
- The POST-ANAL TAIL amplifies the sculling motion generated by the notochord and increases the force of propulsion by presenting a broad surface to the water
- The POST-ANAL TAIL provides motility in larval tunicates and lancelets
- It is variable in length and extends to the anus
- Evolved for propulsion in water in aquatic species
- It has a variety of functions in vertebrates
14
Q
What is the dorsal hollow nerve cord?
A
- The NERVE CORD is a hollow tube dorsal to the notochord
- It originates as a plate of ectoderm that rolls into a tube dorsal to the notochord and develops into the central nervous system
- The brain develops at the anterior end of the nerve cord in vertebrates
- Protected by the vertebral column in vertebrates
15
Q
What are gill slits?
A
- GILL SLITS are opening in the wall of the pharynx that allow a current of water to pass from the mouth to the atrium (a space between the body wall and the pharyngeal wall), and subsequently to the outside
- They are formed when pharyngeal grooves (clefts) and pharyngeal pouches meet to form an opening
- They originally evolved for filter feeding, and have been co-opted for respiration in fish
- In terrestrial vertebrates, the embryonic gill slits develop into Eustachian tube, middle ear cavity, tonsils, and parathyroid glands
16
Q
What is the endostyle?
A
- The ENDOSTYLE in the pharyngeal floor secretes mucus that traps food particles
- Mucus is an aqueous suspension of the glycoprotein mucin which adheres to small particles and enables them to be swept along by cilia
- It is found in most metazoans and can preform a range of functions including protection and can perform a range of functions including protection, locomotion, lubrication, predator deterrence and food capture
- In vertebrates, the embryonic endostyle develops into the thyroid gland
- The endostyle in the pharyngeal floor secretes mucus that traps food particles
- Found in lamprey larvae and protochordates
- Secretes iodinated proteins
- Homologous to the iodinated-hormone-secreting thyroid gland in adult lampreys and other vertebrates
17
Q
What is the generalized chordate body plan?
A
- Notochord
- Myomeres
- Post-anal tail
- Dorsal hollow nerve chord
- Pharyngeal slits (ancestral trait of deuterostomes)
- Endostyle
18
Q
What is the perfect model of a simple generalized chordate?
A
- Amphioxus (LOOK AT ANATOMY SLIDE)
19
Q
How do Amphioxus feed?
A
- Amphioxus is usually half-buried in the substrate, head protruding
- It feeds on small particles (1 - 100 um) which are trapped in a mucus net strung from the branchial bars (supports of the gill slits)
- Larger particles are rejected by the oral cirri (‘tentacles’)
- The water current is generated by cilia on the branchial bars, passes through the mouth, into the pharynx, through the gill slits, into the atrium, and exits through the atriopore
20
Q
How do Amphioxus reproduce?
A
- The gonads are serially repeated structures that occupy the ventral mid-region of the body
- Sexes are separate, but there are no copulatory structures nor even a gonoduct
- Gametes are released into the atrium and leave through the atriopore
- Fertilization is external
21
Q
Describe the development of Amphioxus.
A
- The early stages of development are similar to other deuterostomes such as echinoderms
- It leads to a characteristic neurula larva in which the notochord induces the overlying ectoderm to form a neural plate, which rolls up to form a hollow dorsal nerve cord
- After neurulation, the development resembles vertebrates
22
Q
What is a Pikaia?
A
- A cephalochordate from the Burgess Shale, 505 MYA
23
Q
What is adaptation responsible for?
A
It is responsible for spectacular biodiversity
24
Q
What do chordates include?
A
- The chordates include
- Two non-vertebrate subphyla: the Urochordata an the Cephalochordata
- All of the vertebrates: fish, amphibians, reptiles, mammals and birds
25
Q
What are the SHARED characters in all Chordates?
A
- Notochord
- Post-anal tail
- Endostyle
- Pharyngeal slits
26
Q
What are the COMMON characters of all Chordates?
A
- Ventral heart
- Reduced segmentation
- Segmented musculature
27
Q
What is segmented musculature?
A
- The axial musculature consists of serially repeated V- or W-shaped blocks of muscle (myomeres)
- Each block is attached to a vertebra
28
Q
(IN CHORDATA) What are Urochordates?
A
- Another name for Tunicates
- ~3000 species
- Marine
- As larvae:
- Planktonic
- Resemble tadpoles
- As adults:
- 1mm - 60 cm
- Solitary or colonial
- Benthic and sessile or pelagic
- Filter-feeders
29
Q
Describe Urochordate’s life history
A
- Planktonic larvae
- Larva settles on its head
- Pharynx enlarges
- Head and tail degenerate
- No notochord in adults
30
Q
Describe the Urochordate larvae
A
- Urochordate larvae have all shared chordate characteristics as larvae
31
Q
(IN CHORDATA) What are Vertebrata?
A
- ~52,000 species (fishes, amphibians, reptiles, birds, mammals)
- Vertebral column replaces the notochord to protect the spinal cord
- Well-developed cranium protecting brain (enlarged anterior end of nerve cord)
- Neural crest develops from neural tube
- Internal organs: liver, kidneys, endocrine glands, heart and closed circulatory system
- Endoskeleton of cartilage or bone
- Paired lateral appendages (fins, limbs)
32
Q
(IN CHORDATA - IN VERTEBRATA) What are Craniata?
A
- Craniates are chordates that have a head (cranium) and share some common characteristics: skull, brain, eyes, other sensory organs
- The development of a head allowed for a new way of feeding: ACTIVE PREDATION
33
Q
What are the origins of vertebrates?
A
- The earliest known vertebrates fossils belong to two 530 million year old fish-like animals
