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
