Chordate Characteristics and Tunicates

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Questions and Answers

What function does the postnatal tail serve in larval tunicates and amphioxus?

Stores nutrients

Provides motility for free swimming (correct)

Facilitates digestion

Regulates temperature

What evolutionary advantage do fins provide fish in relation to their postnatal tail?

Enhanced spawning capabilities

Improved propulsion efficiency (correct)

Better camouflage

Increased buoyancy

What is the main characteristic of adult tunicates?

They are primarily free-swimming.

They maintain their larval features.

They lack a protective tunic.

They are sessile. (correct)

Which feature is present in Class Ascidiacea during its adult stage?

Pharyngeal slits and endostyle Signup and view all the answers

In which process do ingested food particles get trapped in tunicates?

Trapping on a mucous net Signup and view all the answers

How does the heart of tunicates function differently compared to typical vertebrates?

It alternates direction of blood flow. Signup and view all the answers

What is the composition of the protective tunic that surrounds tunicates?

Cellulose and other non-living materials Signup and view all the answers

At what stage is the postnatal tail always found in chordates?

At some embryonic stage Signup and view all the answers

What type of blood does the right side of the heart receive?

Deoxygenated blood Signup and view all the answers

Which group of animals has a completely separate left and right ventricle?

Mammals and birds Signup and view all the answers

What is the main advantage of a high-pressure cardiovascular system in active terrestrial organisms?

It enables blood to be pumped uphill to overcome gravity. Signup and view all the answers

Which nitrogenous waste is excreted by birds and many reptiles?

Uric acid Signup and view all the answers

Why is ammonia not considered adaptive for vertebrates in dry terrestrial habitats?

It requires too much water to be excreted safely. Signup and view all the answers

What characteristic defines Amniotes as a monophyletic group?

They share a common ancestor and all descendants. Signup and view all the answers

What significant evolutionary feature developed in amniotes that aids in terrestrial reproduction?

Amniotic egg. Signup and view all the answers

Which of the following skull features is associated with diapsids?

Two openings behind the orbit. Signup and view all the answers

What is the functional significance of the skull openings in amniotes?

They house large muscles for jaw movement. Signup and view all the answers

Which membrane is responsible for cushioning the embryo in the amniotic egg?

Amnion. Signup and view all the answers

Which group are Amniotes most closely related to?

Anthracosaurs. Signup and view all the answers

How did the jaw musculature changes from aquatic to terrestrial feeding impact amniote evolution?

It facilitated more grinding of food with posterior teeth. Signup and view all the answers

What two functions does the allantois serve in the amniotic egg?

Waste storage and respiration. Signup and view all the answers

What adaptation allows the Coelacanth to live despite its descent from freshwater ancestors?

Liver with squalene for buoyancy Signup and view all the answers

Which feature primarily enables bony fish to efficiently control their buoyancy?

Swim bladder for flotation Signup and view all the answers

How do freshwater fishes maintain osmotic balance in their environment?

They pump out excess water through kidneys Signup and view all the answers

What is the primary mode of reproduction among most fish species?

Dioecious with external fertilization Signup and view all the answers

Which group of fishes utilizes Weberian ossicles to enhance their auditory capabilities?

Ostariophysi Signup and view all the answers

What physiological challenge does the evolutionary transition from water to land pose for vertebrates?

Maintaining osmotic balance Signup and view all the answers

What role do myomeres play in fish locomotion?

Propelling the fish through water Signup and view all the answers

Salmon demonstrate which type of migratory behavior?

Anadromous migration Signup and view all the answers

What is a key characteristic of ratfishes?

They have large flat plates instead of distinct teeth. Signup and view all the answers

Which of the following statements is true about the swim bladder?

It originated from lungs in primitive fishes. Signup and view all the answers

Which group of fishes includes the majority of living fishes and all tetrapods?

Osteichthyes Signup and view all the answers

Which adaptation minimizes the head movement (yaw) in many fish during swimming?

Streamlined body shape Signup and view all the answers

What adaptation helps bony fishes draw water across their gills?

Operculum Signup and view all the answers

Which respiratory adaptation allows lungfish to survive during drought conditions?

Ability to breathe air through lungs Signup and view all the answers

What process replaces cartilage with endochondral bone during development in bony fishes?

Endochondral ossification Signup and view all the answers

What distinguishes sequential hermaphrodites from other reproductive types in fish?

Ability to change sex during their lifetime Signup and view all the answers

What is the primary reason marine fish need to drink seawater?

To maintain water balance Signup and view all the answers

Which of the following is a feature of Class Actinopterygii?

Ray-finned fishes Signup and view all the answers

Which feature is NOT associated with fish locomotion adaptations?

Reduced body segmentation Signup and view all the answers

What is one of the challenges faced by chondrosteans?

Threats from pollution and overfishing Signup and view all the answers

How many species are currently classified under Class Sarcopterygii?

8 species Signup and view all the answers

What significant change occurred in the evolution of teleosts?

Introduction of light and flexible scales Signup and view all the answers

What type of fins do ray-finned fishes possess?

Ray fins Signup and view all the answers

Which form of respiration is primarily used by Australian lungfishes?

Gill respiration Signup and view all the answers

What is a notable feature of early neopterygians?

They gave rise to modern bony fishes. Signup and view all the answers

Which aspect distinguishes the coelacanths from other lobe-finned fishes?

They are a group with 8 living species. Signup and view all the answers

What adaptations are evident in the evolution of ray-finned fishes?

Lighter scales and increased maneuverability. Signup and view all the answers

Which of the following statements is true regarding lungfishes?

They possess lungs for gas exchange as an adaptation. Signup and view all the answers

Study Notes

Postnatal Tail

All chordates have a tail at some embryonic stage, the tail may be retained or lost depending on the organism's life stage.
The tail is an adaptation for swimming, enhancing motility in larval tunicates and amphioxus.
Fish evolved fins, further increasing swimming efficiency.
In mammals, the tail is usually present in adults, with the exception of humans, who retain only a vestigial tail (the coccyx).

Subphylum Tunicata

Includes approximately 3,000 species of marine animals.
Most are sessile as adults.
Their defining feature is a tough, non-living cellulose tunic that surrounds the animal.
They are classified into three classes: Ascidiacea, Thaliacea, and Larvacea.

Class Ascidiacea

Includes sea squirts.
The most common, diverse, and well-known group within the Tunicates.
All have a larval stage with all chordate features.
As adults, they retain only pharyngeal slits and an endostyle.
They feed by filtering water through their pharyngeal slits, trapping food particles on a mucus net secreted by the endostyle.
Their heart is unique as it pumps blood in one direction for a few beats, then pauses, reverses its action, and pumps in the opposite direction.

Class Chondrichthyes

Includes sharks, rays, and skates.
They are cartilaginous fish with no bony structures.
Unlike most vertebrates, they retain their cartilaginous endoskeleton throughout life.
They have evolved a variety of specialized adaptations for their aquatic lifestyle, such as a heterocercal tail that provides lift and propulsion, and a large, oily liver for buoyancy.

Class Holocephali

Includes chimaeras or ratfishes.
Distant relatives of sharks, they have a unique combination of shark-like and bony fish features.
Diverged from the shark lineage at least 380 million years ago.
They have 48 living species, found in deep waters around the world.
Have flat, tooth-like plates instead of distinct teeth.
Their diet includes mollusks, echinoderms, crustaceans, and fish.

Osteichthyes: Bony Fishes & Tetrapods

Represent a lineage of fishes with bony endoskeletons that emerged during the early to middle Silurian.
Contains 96% of living fishes and all living tetrapods.
Feature a bony endoskeleton (endochondral bone), lungs or a swim bladder, and several unique cranial and dental characters.
Bony fishes evolved into two primary lineages: Actinopterygii (ray-finned fishes) and Sarcopterygii (lobe-finned fishes).

Actinopterygii (Ray-Finned Fishes)

The most diverse and successful group of vertebrates.
Includes five major groups: Paleoniscids, Bichirs, Chondrosteans, Neopterygians, and Teleosts.
Teleosts represent 96% of living fishes.
They have undergone significant diversification with adaptations for diverse habitats and feeding strategies.
Key adaptations include a movable bony cover over their gills (operculum) that helps to draw water across the gills, a gas-filled swim bladder for buoyancy and gas exchange, and specialized jaw and skeletal elements for efficient feeding.

Sarcopterygii (Lobe-Finned Fishes and Tetrapods)

Includes lungfishes and coelacanths.
Lungfishes are adapted to survive in oxygen-poor environments and can breathe air through their lungs.
Coelacanths are a group of lobe-finned fishes considered extinct for millions of years until their rediscovery in 1938.
They are a remnant lineage of Devonian freshwater fishes with several unique adaptations for their aquatic life, such as fleshy fins for maneuvering and a powerful jaw.

Adaptation: Locomotion in Water

Most fishes swim at a speed of ten body lengths per second, which translates to about 10 kph.
Larger fish generally swim faster.
The trunk and tail musculature propel the fish through the water.
Myomeres (zigzag bands of muscle) contract in a wave-like motion, enabling the fish to generate thrust and control movement.

Neutral Buoyancy

Fish are slightly denser than water, due to their skeletons and tissues.
Sharks rely on a heterocercal tail for lift and pectoral fins for stability to counter their sinking tendency.
A large, special lipid-filled liver (containing squalene) provides additional buoyancy to sharks.
Bony fishes evolved a gas-filled swim bladder, which provides the most efficient flotation device.
The swim bladder evolved from paired lungs in primitive Devonian bony fishes.
It is present in most bony fishes but absent in tunas, some abyssal fishes, and most bottom dwellers.
Fish control their depth by adjusting the volume of gas in their swim bladder, allowing for suspended movement with no muscular effort.

Hearing & Weberian Ossicles

Fish detect sounds as vibrations in their inner ear.
Hearing in water is challenging due to its density.
A group of fishes, the ostariophysi, possess Weberian ossicles, small bones that transmit sound vibrations from the swim bladder to the inner ear.
This adaptation enables them to hear faint sounds over a broader range.

Respiration

Sharks respire through gill slits, while bony fishes have opercular flaps.
The gills are located within the pharyngeal cavity, covered by a movable flap called the operculum.
The operculum helps move water from the mouth across the gills, creating a countercurrent exchange system that maximizes gas exchange.
Several fish groups have adaptations for breathing air, including lungfishes, eels, electric eels, and Indian climbing perch, who have adapted their respiratory systems for life outside of water for varying durations.

Osmotic Regulation:

Freshwater fish are hyperosmotic regulators, meaning they have a higher salt concentration in their blood than the surrounding water.
They maintain their internal salt balance by pumping out excess water through their kidneys and absorbing salt from the water using specialized cells.
Marine fish are hypoosmotic regulators, meaning they have a lower salt concentration in their blood than the surrounding water.
To compensate for water loss, they drink seawater and excrete excess salt through specialized cells, feces, or kidneys.

Feeding Behavior:

The majority of fish are carnivorous, consuming a wide range of organisms from zooplankton to large vertebrates.
Herbivorous fish feed on plants and macroalgae.
Suspension feeders filter water for microorganisms.
Other feeding adaptations include scavenging, detritivory, and parasitism.

Migration:

Freshwater eels migrate to the sea to spawn.
Salmon are anadromous, spawning in freshwater rivers after spending their adult lives in the sea.
They exhibit remarkable homing ability, returning to their natal rivers to reproduce.

Reproduction:

Most fish are dioecious, with external fertilization and oviparity (laying eggs).
Some fish groups have evolved viviparity (giving birth to live young).
Reproductive strategies include sequential hermaphroditism, synchronous hermaphroditism, and parthenogenesis.

Transitioning from Water to Land:

Amphibians are uniquely adapted for both aquatic and terrestrial life, with their life cycle involving a transition from an aquatic larval stage to a terrestrial adult form.
The shift from water to land in vertebrates was a gradual process involving significant evolutionary changes.
Tetrapods, which include amphibians and amniotes, originated approximately 140 million years ago.

Early Diversification of Amniotes:

Amniotes are a monophyletic group, meaning they share a common ancestor.
They arose about 315 to 330 million years ago.
The early amniotes were small and lizard-like.
Amniotes evolved three distinct patterns of holes (fenestrae) in their skulls: anapsid, diapsid, and synapsid.
These fenestrae accommodated large jaw muscles, facilitating more efficient feeding and contributing to the diversity of amniote diets.

Adaptations of Amniotes:

Amniotes evolved seven major adaptations that promoted their success in terrestrial environments:
- Amniotic egg: This unique structure protected the embryo from desiccation and provided a safe environment for its development.
- Amnion: This membrane encloses the embryo in a fluid-filled sac, providing cushioning and an aqueous environment for growth.
- Allantois: This membrane stores metabolic waste and is highly vascularized, contributing to gas exchange and waste removal.
- Chorion: This membrane is also highly vascularized and functions as an efficient respiratory organ alongside the allantois.
- High pressure cardiovascular system: This adaptation enables active terrestrial organisms to deliver oxygen and nutrients efficiently against gravity's pull, maximizing their metabolic rate.
- Water conserving nitrogen excretion: The adaptation of excreting waste as urea or uric acid reduced water loss and enabled terrestrial survival.
- Improved cutaneous respiration: Land vertebrates developed a less-permeable skin to minimize water loss in dry environments.

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Description

This quiz explores the fascinating adaptations of chordates, focusing on postnatal tails and the subphylum Tunicata. Learn about the unique features of tunicates and their classifications, including the well-known class Ascidiacea. Test your knowledge on the specifics of these marine animals and their evolutionary traits.