Fishes

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Fishes Invertebrate Chordates

• The Chordate Heritage
• A. Chordates are deuterostomes. Page 447
• (bilateral animal in which the anus forms from
  the first indentation in the embryo and the
  second indentation forms the mouth this is just
  the opposite situation in the protostomes)
• EX Protostome-- Mollusks, Annelids, and
  Arthropods

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Fishes Invertebrate Chordates

• CONTD
• EX Deuterostomes Echinoderms and
  Chordates
• The phylum Chordata consists of a majority of
  species that are vertebrates (with a backbone)
  and a minority are invertebrate chordates.

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Fishes Invertebrate Chordates

• 2. All chordates, at some time in their lives,
  have four distinctive features
• a. A notochord is a long rod of stiffened
  tissue that supports the body later it
  changes to bony units in vertebrates.
• b. A dorsal, tubular nerve cord lies above the
  
• notochord and gut. The nervous
  system of
• the chordate develops from this
  dorsal tube.
• The anterior end of this tube
  increases in mass and becomes a
  modified brain.

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Fishes Invertebrate Chordates

• c. A muscular pharynx with gill slits is
  positioned at the entrance to the digestive
  tract. It functions in feeding, respiration or
  both.
• d. A tail, or rudiment thereof, exists near the
  anus.

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Fishes Invertebrate Chordates

• Contd Chordates
• There are 2,100 species of chrodates, which
  include Urochordates and Cephalochordates, these
  are invertebrates no backbones. However,
  there are over 48,000 species of chordates that
  do have backbones these are the Vertebrates. A
  backbone of cartilage or bone and a brain encased
  in a chamber of cartilage or bone.

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Fishes Invertebrate Chordates

• Urochordates
• 1. Tunicates, or sea squirts (p 446), are
  marine organisms covered with a
  gelatinous tunic.
• a. The larval stage resembles a
  tadpole and has a notochord in the tail.

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Fishes Invertebrate Chordates

• Contd Urochordates
• b. Metamorphosis to the adult results in a
  loss of the notochord and tail, a
  regression of the nerve cord, and an
  expansion of the pharynx for filter
  feeding. So, Tunicates are filter feeders.
  They are also classified as having NO
  COELOM a body cavity with a protective
  tissue lining and enclosing the
  organs to hold them in place.

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Fishes Invertebrate Chordates

• The adult is a sessile filter-feeder,
  maintaining a constant flow of water through the
  gill slits into the body to bring in food
  particles and oxygen and carry away wastes.
• Water in Water Out
• Oral opening Atrial opening

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Fishes Invertebrate Chordates

• Cephalochordates
• Lancelets are small, fishlike animals with
  tapered bodies.
• a. They lie buried in the sand filtering food
  from the stream of water passing
  through the pharynx.
• b. Muscles are arranged in a segmented pattern
  on both sides of the notochord circulation is
  closed (but no red cells) respiration is
  directly across the body wall.

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Fishes Invertebrate Chordates

• Contd Cephalochordates
• c. Their brain forms at the anterior end
• of the nerve cord.

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Fishes Invertebrate Chordates

• 2. Lancelets display all of the vertebrate
  characteristics throughout their lives.
• i.e. One or more cells constructed of the same
  kind of atoms and molecules according to the laws
  of energy exhibit a metabolism where they
  acquire, and use energy and materials to survive
  and reproduce sense and make controlled
  responses to their internal/external
  environments have heritable instructions encoded
  in DNA to do what? have characteristics that
  define a population of organisms that can change
  thru generations

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Fishes Invertebrate Chordates

• Early Craniates
• All fishes, amphibians, reptiles, birds and
  mammals alive today are craniates.
• 1. Among the earliest jawless fishes
  (agnathans) were the ostracoderms.
• a. They were covered with hardened external
  plates but did not have a well developed
  endoskeleton. Page 447

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Fishes Invertebrate Chordates

• Contd Early Craniates
• b. They lived on the ocean bottom
• where they were filter feeders. They
  eventually vanished because they could not
  adapt, possibly because they had no jaws.

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Fishes Invertebrate Chordates

• 2. Placoderms arose and were the first
  fishes with jaws and paired fins.
• a. In these fishes, bony elements
• reinforced the notochord and
• pairs of fins stablized the body.
• b. Gill openings in the head became
• enlarged and fitted with teeth
• they functioned as jaws.

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Fishes Invertebrate Chordates

• c. Initially, chordate feeling was
• limited to filtering, sucking and
• rasping food when predatory
• fish started biting tearing off
• flesh. A radical change ensued.
• d. As the Paleozoic drew to a close,
• placoderms were replaced by cart-
• ilaginous and bony fishes.

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Fishes Invertebrate Chordates

• Trends in Vertebrate Evolution (Pg 448)
• A. The single, continuous notochord was
  replaced by a column of separate, hardened
  vertebrae, bony segments, parts of which became
  modified near the head to form jaws.
• The flexible column, part of the endoskeleton
  was less cumbersome than external plates. The
  union of bony segments muscle segments enhanced
  maneuverability hard bones invited more
  forceful contractions. The result a faster,
  more agile fish.

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Fishes Invertebrate Chordates

• B. The fins of fishes were the starting
• point for the legs, arms, and wings
• seen among higher vertebrates.
• C. Gradually, there was less reliance
• on gills and more on lungs and the
• circulatory system (heart, blood
• vessels), which work in connection.

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Fishes Invertebrate Chordates

• Existing Jawless Fishes
• A. The lampreys and hagfishes are
• descendants of the early jawless
• fishes.
• 1. Both have a cylindrical, eel-
• like body with no paired fins.
• 2. A notochord and cartilaginous skeleton
• are present.

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Fishes Invertebrate Chordates

• 3. These are fresh water fish. Lampreys are
  still found in fresh water, where hagfish are
  found in marine habitats.

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Fishes Invertebrate Chordates

• B. Hagfishes are scavengers that look like
• large worms with feelers (sensory
• tentacles) around the mouth. (Cart-
• ilaginous backbone, no jaws, burrow
• into sea floor, prey on small inverte-
• brates -gt polychaetes. As a defense
• mechanism they secrete a gallon of
• sticky mucus over themselves. They
• can go without a meal for seven months.

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Fishes Invertebrate Chordates

• C. Lampreys are parasitic on other fish,
• attaching to them with an oral, sucker-
• like disk. They rasp away at flesh with
• their mouthparts. There are also non-
• parasitic species living in fresh brooks
• streams. During the early 1800s
• lampreys invaded the Great Lakes via
• Hudson River thru the canals that
• were built for commerce thereby en-
• dangering the indigenous species of
• fish.

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Fishes Invertebrate Chordates

• Existing Jawed Fishes
• Enormous numbers of fishes attest to their
  success in meeting the challenges of life in the
  water.
• 1. Their streamlined bodies allow easy
• movement through the dense medium.
• 2. Tail muscles are organized for powerful
  force.
• 3. The swim bladder provides buoyancy. This
• adjustable flotation device exchanges gases
  with blood
• inside the body.

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Fishes Invertebrate Chordates

• B. Fishes With a Skeleton of Cartilage
• 1. Cartilaginous fishes (Chondrichthyes)
• possess a streamlined body with a
• cartilaginous endoskeleton, gill slits,
• fins, and small scales on the body
• surface.

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Fishes Invertebrate Chordates

• 2. This group includes the sharks,
• skates, rays, and chimaeras.
• a. Sharks are formidable predators
• with their powerful jaws and
• teeth (replaceable).

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Fishes Invertebrate Chordates

• b. Skates and rays live on the ocean
• bottom where they feed on
• invertebrates their flattened teeth
• are used to crush the bodies of
• shelled prey. Some can jolt
• prey with electricity (200 volts)
• or sting with a venomous tail
• spine (gland).

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Fishes Invertebrate Chordates

• C. Chimaeras are almost scaleless, with
  a body resembling a rat. They
• mostly feed on mollusks . Common
• name Ratfish.

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Fishes Invertebrate Chordates

• C. Fishes With a Skeleton of Bone
• 1. Most bony fishes (Osteichthyes)
• are ray-finned fishes.
• a. The highly maneuverable
• fins are supported by rays that
• originate from the dermis.
• b. The teleosts (salmon, tuna
• catfish, perch, minnows, pikes, etc.)
• are a very successful group occupying
• the reef and open ocean habitats.

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Fishes Invertebrate Chordates

• c. Ancestors had sac-shaped out-
• pouchings from the wall of the
• esphagus, a tube to the gut. These
• then evolved into lung-like sacs
• that supplemented the gills in gas
• exchange.

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Fishes Invertebrate Chordates

• 2. The lobe-finned fishes bear fleshy
• extensions on the body.
• Coelacanths are the only living lobe-
• finned fishes. Have lung-like sacs but
• they do not serve in gas exchange.
• NEED EXAMPLE

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Fishes Invertebrate Chordates

• 3. Lungfishes have gills and one or a pair
• of lungs that are modified gut wall
• outpouchings. They dont assist in
• buoyancy, just respiration. They must
• surface to take-in air. Mostly found in
• the Southern Hemisphere Africa,
• Australia, South America. They burrow
• themselves in mud to prevent dry
• wig out until the next rainy season.

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Fishes Invertebrate Chordates

• The question from some scientist is
• Is the lungfishes ancestor, a four (4)
• legged walker, tetropod???
• (recent article)