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ZoologyChordataAgnatha
Phylum Chordata
Bellringer
Name the two invertebrate chordate subphyla. Give examples of members of each.
Monday
Tuesday
Why are sharks, rays, skates, and chimaeras all classified in the class Chondrichythes?
Wednesday
What do members of Chondrichthyes use to control their buoyancy?
What is another term for an "ectotherm"?
What is the difference between an endotherm and an ectotherm?
Thursday
Describe the key characteristics that distinguish cartilaginous fish
Friday
Chordates
What are Chordates?
All chordates have
- notochord
- dorsal, hollow nerve cord
- pharyngeal pouches
- postanal tail
Invertebrate Chordates
- No backbone
Invertebrate Chordates
Subphylum
Cephalochordata
Subphylum Cephalochordata
- Retain notocord,dorsal nerve cord, pharyngeal pouches, and postanal tail as adults
- Filter feeders: atriopores
- segmented
Subphylum
Urochordata
Subphylum Urochordata
- Commonly called tunicates/ sea squirts
- Filter feeders: excurrent siphon
- hermaphroditic
- do not retain notochord, dorsal nerve cord, or postanal tail
Review
1. Members of the Phylum __________ have a dorsal hollow nerve cord.
2. During development, the pharyngeal pouches will become ___________
3. All chordates belong to the animal kingdom. (T or F )
4. All chordates are vertebrates. (T or F )
5. You are more closely related to a sea squirt than to an earthworm.
5. What are two animals that are chordates, but not vertebrates?
6. An animal with a backbone is called a _________.
Agnatha
Kingdom Animalia
Phylum Chordata
Subphylum Verbrata
Superclass Agnatha
Agnatha
- means without jaws
- ~500 million years ago
- no identifiable stomach, instead have an elongated intestine
- pineal eye
Class Myxini
- Commonly called hagfishes
- scavangers:
- Using two toothed, keratinized plates on the tongue that fold together in a pincer like action, the hagfish rasps away bits of flesh from its prey
- For extra leverage, the hagfish often ties a knot in its tail, and then passes it forward along the body until it is pressed securely against the side of its prey.
- produce a coat of thick mucus to protect themselves.
Class Cephalaspidomorphi
Class Cephlaspidomorphi
- Commonly called lampreys
- parasitic and nonparasitic species
- parasitic species have a sucking, rasping (tearing) mouth which allows them to grip a living critter so they can bore a hole and suck the blood.
- non-parasitic species do not eat as adults and only live off the stored food they ate when they were babies
Conclusion
Agnatha species lack of jaws has made this class an easy prey for other jawed fish.
Evolution of jaws may not be what you think: It is thought that a mutation made the first gill arch (the cartilage rods that supported the gills) more flexible which allowed them to pump water over their gills
Chondrichthyes
- Cartilage fish
- Includes sharks, rays, skates, and chimeras
Chondrichthyes
Basics
The Basics
- There are just under 1000 living species
- have streamlined bodies, built for predation
- lack a swim bladder, will sink if not swimming forward
- ●buoyancy controlled by a large oil-filled liver that reduces their density
- ●skin entirely covered by placoid scales, small tooth-like structures with an abrasive feel.
- Skeleton made entirely of cartilage, no bones
- two chambered heart
Placoid Scales
Part of the reason why sharks and other cartilaginous fish can replace any lost teeth is that these teeth are really nothing more than modified skin scales.
Respiration
Nervous System
Lateral Line System: help detect pressure changes in the surrounding water.
Ampullae of Lorenzini :for detecting electric fields.
5-7 gills
force water over these gills either by pumping with their jaws and throat, or by swimming
spiracles: allow water to flow over the gills even when the shark is occupied with eating.
Reproduction
Reproduction is sexual with internal fertilization
Oviparous: lay eggs
Ovoviviparous: eggs hatch inside the mother
Viviparous: develop with umbilical chord, live birth
Subclass Elasmobranchii
Sharks, skates, rays
Subclass Elasmobranchii
- well-developed jaws
- highly developed sense organs
- powerful swimming ability
- streamlined shape
- enabled them to thrive as marine predators for more than 350 million years, as other groups have come and gone
Shark
- A typical shark is about 2m long,
- range in size from 25 cm long up to perhaps 18m in length.
- thousands of teeth arranged in several rows
- Each tooth in a shark can be rapidly replaced as it becomes worn or damaged.
- Teeth arranged on a spiral or whorl shaped cartilaginous band in which replacement teeth are always developing behind the functional tooth.
- The type of teeth specialized for prey it eats.
- crustaceans, mollusks: dense arrays of flattened teeth designed for crushing.
- Fish feeders: long pointed needle-like teeth for gripping.
- large mammals: pointed lower teeth and triangular serrated upper teeth for cutting
- Plankton feeders : have small non-functional teeth.
- Sharks use a series of methods to detect prey related to distance.
- Chemoreception is used to detect prey from a distance and sharks appear to be able to detect odors as dilute a 1 part in 10 billion.
- Vibrations can also be detected from a distance using the lateral line system.
- Once a shark gets relatively close, vision takes over.
- Sharks have very good vision at low light intensities. If a familiar prey item is located an attack may occur quickly.
- If the prey is unfamiliar (e.g. a person), the shark may circle to gather more information.
- Such a shark may bump the potential prey with its rostrum presumably to gather extra sensory information.
Rays & Skates
Rays & Skates
• Rays and skates glide through the sea with flapping motions of their large wing-like pectoral fins
• Rays and skates are diverse in their feeding habitats
• Some are bottom-dwellers others are filter-feeders
• When not feeding or swimming, they cover themselves with sand and spend hours resting on the ocean floor.
Chimeras
Subclass Holocephali
- Chimaeras live in temperate ocean floors down to 8,500 feet deep, with few occurring at depths shallower than 660 feet
- They have elongated, soft bodies, with a bulky head and a single gill-opening
- They grow up to about 5 feet that includes their lengthy tail
- Examples include: ghost sharks, ratfish, spookfish
- Have a U-shaped stomach (Not as complex as humans)
- Stomach leads to the intestine which is called the spiral valve.
- Intestines are short, but have folds arranged in a spiral (increasing surface area).
- This leads to a cloaca – an opening for the urinary, digestive, and reproductive systems (one hole for all!)
- Sharks/relatives also have an enlarged liver (up to 20% of the weight of the fish) that produces lots of oil. The principle component of shark liver oil is called squalene.
A Little Review
Osteichthyes
- Bony fish
- Largest class of vertebrates
- Lungs or swim bladder
- Scales
- Two types
- lobe-finned
- ray-finned
Subclass Actinopterygii
- ray-finned fish
- less robust bones: Fins are webs of skin supported by bony spines or “rays”
- 96% of bony fish
- Salmon, eels, angler fish, seahorses, cod, halibut
Subclass
Actinopterygii
Subclass Sarcopterygii
Subclass Sarcopterygii
- lobe-finned fish
- paddle-like fins: Fins are fleshy and joined to the body by a bone (able to support weight); more robust bones.
- direct ancestor of all other chordates: Limbed animals are thought to have evolved from lobe-finned fishes
- Only 7 species are living today
- Coelacanth -> thought extinct, rediscovered in 1938
- Lungfish -> Have lungs and gills
General Anatomy
- Have a jaw and skeleton of bone with operculum
- bones made of collagen and calcium.
- Paired fins
- Homocercal tail: last vertebra adjoins modified bony elements (symmetrical)
- Swim bladder
Swim Bladder
Swim Bladder
- Large air sac within the fish
- Acts as a buoyancy organ
- Increases in size when the fish wants to go up and decreases in size when the fish wants to go down.
- Neutrally buoyant fishes can hover in the water and swim with much less energy.
Physiology
- Fish have a single circulatory pattern, wherein the blood passes through the heart only once during each complete circuit.
- heart consists of an atrium, a ventricle, a thin-walled structure known as sinus venosus, and a tube called bulbus arteriosus.
- blood contains plasma (the fluid portion) and blood cells
- red blood cells or the erythrocytes contain hemoglobin
- white blood cells
- thrombocytes: perform functions that are equivalent to the role of platelets
Circulatory
- Similar to chondrichthyes, however no enlarged liver.
- Have a U-shaped stomach
- Have pyloric ceca which increases gut area and aids in digestion by secreting digestive enzymes.
- No true cloaca (Separate opening for digestive system)
Digestion
http://web.utk.edu/~rstrange/wfs550/html-con-pages/v-digest-sys.html
- External and internal fertilization (depends on species)
- Ovoparous (egg laying), Viviparous (live bearing), ovoviviparous (Aplacental yolk sac viviparous) all seen in bony fish.
- Some are hermaphrodites (both male and female reproductive organs at same time, or can change)
Reproduction
- The central nervous system is compromised of a brain and spinal cord.
- At the nose end of the fish lie olfactory lobes, which provide sense of smell.
- A fish's spinal cord transmits motor messages to its peripheral nerves, and sends sensory messages back to the brain, the various nerves of the peripheral nervous system branch throughout the body.
Nervous
- Some wastes diffuse through the gills into the water, while others are removed by the kidneys. Wastes leave through the anus.
- Marine fish - gills excrete salt to compensate for salt taken in when drinking sea water.
- Freshwater fish - gills absorb salt to compensate for salts lost in urine