Phylum Chordata

Subphylum Vertebrata

3 Major characteristics of the phylum Chordata:

1. A Dorsal Nerve Cord

2. Gills (pharyngeal slits)

3. A Notochord

Subphylum Vertebrata

5 Characteristics of Vertebrates:

1. Have a Backbone (vertebral column, spine)

2. The vertebrae enclosed and protect the nerve cord

3. They have a complex brain – nervous system

4. Bilaterally symmetrical body plan

5. Presence of an endoskeleton

Subphylum Vertebrata

• Fishes were the 1st vertebrates to evolve from an invertebrate (probably the chordate). They appeared more than 500 million years ago. Therefore, they are the oldest and simplest of all the vertebrates

• They are the most abundant vertebrates in species and individuals. There are ~ 22,000 species of fishes that make up ~ ½ of ALL vertebrates

Marine Fishes

• Fishes feed on most types of marine plants and animals. Many other animals feed on them as well. Therefore, they play a key role in the Marine Ecosystem.

• Humans have many uses for fishes:– They provide a vital source of protein

– They can be ground up and used as fertilizer or chicken feed

– They can be used to make leather, glue, vitamins, as well as many other products

– They provide a sport for sports fisherman

– They can also be kept as pets

Marine Fishes

• All fishes are ectothermic, so their body temperature is dependent on their surroundings

• They have a 2-chambered heart and breathe through gills

• Reproduce sexually through internal or external fertilization depending on the species

• MOST have Paired Fins

Marine Fishes

• MOST have scales

• All fishes have highly developed sensory systems. Cartilaginous and bony fishes have an adaptation called the lateral line system – it is a line of fluid-filled canals that run along the sides of a fish. The lateral line system allows a fish to detect movement and vibrations in the water so that they can swim in the dark or through complex coral reefs.

Marine Fishes

3 MAJOR CLASSES OF FISHES:

1. Class Agnatha – Jawless Fishes

2. Class Chrondichthyes – Cartilaginous Fishes

3. Class Osteichthyes – Bony Fishes

Marine Fishes

Subphylum Vertebrata

Fishes

Larvae of a jawless fish

*Cranium

*Vertebrae

Skeletal elements of a jawless fish

Subphylum Vertebrata

Subphylum Vertebrata

Jawless Fishes

Jawless Fishes

• They are the most primitive fishes alive today

• They lack jaws so they feed by suction with the aid of a round, muscular mouth and rows of teeth

• Body is cylindrical and elongate (like eels)

• They lack the paired fins and scales that most fishes have

Jawless Fishes – ancient diversity

Hagfish

Lamprey

Jawless Fishes – modern diversity

Jawless fish: Hagfish

Jawless Fishes: Hagfish

• Also known as slime eels

• Feed mostly on dead or dying fishes

• Occasionally bore into their prey and eat them from the inside out

• They dig tunnels in the muddy bottom sea floor as a place to live

• 20 known species

• Skin is used in manufacturing of leather goods, and for bait

Click for Video

Jawless fish: Lamprey

Jawless Fishes: Lampreys

• Found in temperate (mild) regions

• Primarily freshwater fishes, some move to the sea as adults

• They attach to other fish and suck their blood or feed on bottom invertebrates

• There are ~ 30 species

Click for Video

lampreys

Jawless Fishes – modern diversity

Jawed Vertebrates

*Jaws

*Paired fins

Fossil placoderm

Class Chondrichthyes

Cartilaginous fishes

Cartilaginous Fishes• Include sharks, rays, skates, and ratfishes• Have a skeleton made of cartilage – a material

lighter and more flexible than bone• Have moveable jaws that contain well-developed

teeth• Mouth is usually ventral • Have paired lateral fins – efficent for swimming• Have rough, sand-paper skin because of the

presence of tiny scales, placoid scales (which are similar in composition to teeth

Class Chondrichthyes

Paired fins

Placoid scales

Class Chondrichthyes

Shark Characteristics:• Well adapted for fast swimming and hunting

• Described as “living fossils” because they are similar to species that swam the seas 100 million years ago

– Have changed very little over time

• Have a caudal fin (tail fin) that is well developed and powerful

• Have 2 dorsal fins

• They have paired pectoral fins that are large and pointed in most species

• Most sharks swim continuously, forcing water through the mouth, over the gills, and out through the gill slits– Not all sharks need to swim continuously

• They have many rows of sharp, triangular teeth. If a tooth is lost or broken it is replaced by another, which slowly shifts forward from the row behind it (like a conveyer belt)

Shark Characteristics:

Shark Diversity

Shark Diversity – there are many variations to the shark body

megamouth shark

Megachasma pelagios

Pygmy shark

Squaliolus laticaudus

Rhincodon typus

Whale shark

Mitsukurina owstoni

Goblin shark

Shark Diversity

• Olfactory organs can detect chemicals diluted 1/10 billionth their original concentration

• Lateral line senses low frequency vibrations of prey over large distances

• Excellent vision, even in dim water, used at close range

• At close range, sharks are guided to prey by electric fields surrounding all animals

Shark Senses

Ampullae of Lorenzini

Ampullae of Lorenzini

Ampullae of Lorenzini

Shark Conservation

Manta birostris

Skates and rays

Skates and Rays Characteristics:• ~ 470 extant species

• Have dorsoventrally-flattened bodies and for the most part live on the bottom of the sea (which means they are referred to as demersal)

• Some rays look like sharks and some sharks look like rays in appearance. However, only rays, skates and related fishes have their gill slits on the ventral side of the body rather than on the side as in sharks (ex Angel Shark and the Shark Ray)

Skates and Rays Characteristics:

• Their pectoral fins are also flat and greatly expanded

• Many stingrays have a whip-like tail usually equipped with stinging spines for defense

• Poison glands produce venom that can cause serious wounds to anyone who steps or falls on them, some may even result in death

Electric Rays can deliver shocks up to 200 volts by use of specialized organs

located on each side of the head

Narcine brasiliensis

Skates and Rays Characteristics:

• Eagle, Manta, and devil rays are the few rays that don’t spend most of their time on the ocean bottom

• Skates are similar to rays in appearance and feeding habits, however they lack a whip-like tail and stinging spine

Netflix River Monsters Death Ray Video

Hydrolagus colliei

Ratfishes or chimaeras

Ratfishes Characteristics:

• ~ 25 species

• Are mainly deep-fishes

• Their gill slits are covered by a flap of skin

• Some have a long rat-like tail

• They feed on crustaceans and mollusks

Class Osteichthyes

bony fishes – 24,000 living species

Class Osteichthyes – are the majority of the fishes

Bony skeleton

Complex and adaptable

Mouth – is located at the anterior endTeeth are usually fused to the jawbones

Class Osteichthyes

Scales – are thin, flexible, and overlapping; develop from bone

Fins and tail

Fins usually consist of thin membranes that are suported by bony spines, or fin rays.

- Some are flexible and used for propulsion and manueverability

Operculum – is a flap of bony plates and tissue that protects the gills

Swim Bladder – is a gas-filled sac just above the stomach and intestine, allows for the heavy bony skeleton

Buoyancy

Fish diversity

BIOLOGY OF FISHES

Ichthyology is the scientific study of fishes

Body Shape:

• Body shape is derived from a fish’s lifestyle – Sharks and marlin have a

streamlined body for fast swimming

– Rays and skates are flat on the top and bottom for life on the ocean floor

– Eels have an elongate body because they often live in narrow spaces

• Body shape can also help fishes camouflage themselves. They can be shaped to resemble sea grasses, rocks, and corals

Body form and niche

Flounder

Body form and niche

seahorse

Body form and niche

Porcupine fish

Body form and niche

jawfish

Coloration

Coloration:• Bony fishes can use color for camouflage

• The colored pigments are found in special cells located in the skin called chromatophores

• The varying amounts of different in chromatophores results in fishes of many colors

• Some can change color based on mood or reproductive condition

• Warning coloration is when fishes that are dangerous, poisonous, or taste bad reveal it to others by use of bright colors

• Cryptic Coloration is when fishes blend with the environment to deceive predators and prey

• Discriptive coloration is when fishes have the presence of stripes, bars, or spots that help break up the outline of its body

Locomotion:• Fish swim to obtain food, escape predators, and find mates.

• Most swim in a side to side rhythmic motion by use of bands of muscles or myomeres

• Fishes that don’t swim in the standard side to side motion use their fins to maneuver around in the water.

Feeding:• Sharks are carnivores, but unlike most carnivores many feed

on prey larger than they are

• There are 3 species of sharks that are filter-feeders. They are the whale shark, basking shark, and the megamouth shark. They filter the water with their gill rakers, which are slender projections on the inner surface of the gill. The spaces between the gill rakers determines the size of food they capture. They feed on small fishes, squids, or plankton.

• The protrusible jaws of bony fishes allow them to be flexible in feeding habits than sharks.

• Most have well-developed teeth for catching, grasping, and holding their prey, which is usually swallowed whole

Jaw protrusionFeeding

Jaws

Filter feeding

anchovies & sardines

Filter feeding

Gill rakers

Feeding:• Deep-water fishes often have huge mouths and teeth

• Many bony fishes are non-specialists, so they will capture a variety of prey

• Fishes that mainly feed on seaweeds and other plants are known as grazers

• Some filter plankton with their gill rakers. These fishes are very small in comparison to the filter feeding sharks. (like the examples of sardines and anchovies in the previous slides) These fishes live in massive schools. Plankton feeders are the most abundant fishes in the ocean

Digestion:• Flow of food through the digestive tract:

– Mouth to Pharynx to Esophagus to Stomach to Intestine to Anus

• Chemical digestion usually begins in the stomach

• Bony fishes typically have slender blind tubes at the anterior portion of the intestine called the pyloric caecae, which secrete digestive enzymes

• The pancreas also secretes digestive enzymes

• The liver is also important in digestion because it secretes bile which is needed to breakdown fats. The liver is particularly large and oil-rich in sharks; it can make up to 20% of their body weight.

Digestion:• The intestine of

cartilaginous fishes contains a spiraling portion called the spiral valve, which increases the surface area of the intestine

• The intestine absorbs nutrients and passes them into the circulatory system to be spread out to the rest of the body. Any undigested material exits through the anus

Circulatory System:• All fishes have a 2-chambered heart located below the gills

• Closed Circulatory System

Deoxygenated blood comes into the heart from the body. Gas exchange occurs in the gills and oxygenated blood is

then carried back to the body by blood vessels called arteries. The arteries branch out into thin-walled capillaries

then come together and flow into the veins that then carry deoxygenated blood back to the heart

Circulatory System:

Respiratory System:

• Fishes take in oxygen dissolved in water and release carbon dioxide through paired gills. The gills are located in the pharynx.

• Since gas exchange occurs at the gills and a fish gets its oxygen from water the fish must make sure that water is flowing over the gills all the time. In other words they irrigate the gills.

• Every gill has its own chamber, and each gill chamber opens to the outside by a separate gill slit. The first pair of gill slits of cartilaginous fishes is modified into spiracles, a pair of round openings just behind the eyes. The spiracles allow the fish to take in water even when the mouth is buried in the ocean bottom.

Respiratory System:

• The gills on each side of bony fishes share a common gill chamber, which opens to the outside through a single opening. This way is more efficient at getting water to the gills.

• In gas exchange oxygen is diffused from the water into the capillaries located in the gills. This can occur because the oxygen level in the blood at the lungs is typically very low due to the fact that the blood has already traveled to the rest of the body.

Regulation of the internal environment:

• Marine fishes actually have blood that is less salty than seawater therefore, they lose water by osmosis. They need to replenish lost water or they will dehydrate, therefore they osmoregulate. They do this by swallowing seawater. The salt from the seawater is excreted by the kidneys.

Nervous System and Sensory Organs:• Most fishes have a highly developed sense of smell. They use this

to detect food, mates, and predators

• Fishes have special sensory cells located in olfactory sacs on both sides of the head. Each sac opens to the outside through nostrils.

• Fishes detect other chemical stimuli with taste buds located in the mouth.

• Bony fishes rely on vision more so than cartilaginous fishes. They have to move closer or farther away to focus.

• Fishes have a sense organ called the lateral line that allows them to detect vibrations in the water

• The ampulla of lorenzi in cartilaginous fishes is a sense organ in the head that can detect weak electrical fields, which helps locate prey

• They have inner ears that perceive sound waves and can also be used in equilibrium

Vision

Taste

Olfaction

Lateral Line

Lateral Line

Lateral Line

nerves

Lateral Line