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Vertebrates (Fishes)

Phylogenetic Relationships:

Fishes:

Sub-Phylum Craniates.

  • Skull Surrounded the brain
  • Having sense organs such as OLPHACTORY ORGANS
  • Eyes
  • Inner ears
Classification of Fishes
    Fishes are divided into 2 infra phylums

(1)    Infra phylum hyperoteroti

Infra-phylum hyperoteroti includes the Hag fishes.

(2)    Infra-phylum Vertebrata:

Infraphylum Vertebrata is further divided into 2 groups on the basis of the presence and absence of hinged jaws.

(i)    Jawless vertebrates

(ii)    Jawed vertebrates

#    Traditionally taxonomy:

  •     Traditionally taxonomic grouping combines hagfishes, lampreys, and extinct assemblages called ostracoderms.
  • Ostracoderms are extinct, having hard body covering.
  • Then, hag-fishes, lampreys, and extinct assemblages were placed in a single group that’s called Agatha, on the behalf of the absence of jaws.

Modern cladistic analysis:

  • Lampreys show more characteristics than cartilaginous and bony fishes and on this behalf, they place lampreys into vertebrates.
  • In addition; jaws fishes with bony endoskeleton have been classified into a single class Osteichthyes.
  • This grouping is paraphyletic because the common ancestors of this group are also the ancestor of tetrapods (amphibians, birds, reptiles, mammals) sharing characters such as bony skeleton, swim bladder, and other characters.

The most recent classification system:

  • has dropped Osteichthyes as a class name and elevated former-sub class sarcopterygian and Actinopterygii to class level status.
  • One of the major reasons is because tetrapods are descendants of the sarcopterygian, they should also be included within this group.
  • According to the zoologist, the most primitive craniates' evolution indicates that the hag-fishes are the most primitive living craniate.

Survey of fishes

(1)    Infra Phylum Hyperotretii

(2)    Infra Phylum Vertebrata

        1.    Infra phylum Hyperotreti

Class myxini:

  • They are about 20-species and about 4-genera.
  • Example: Hag fishes
  • Their head is supported by a cartilaginous bar and their brain are enclosed in a fibrous sheet.
  • They lack vertebrates and retain the notochord or the axial support.
  • Having 4 pairs of sensory tentacles –surrounding the mouth
  • Having ventrolateral slime glands.
  • Habitat:
  • Hag fishes are found in cold water and marine habitat.
  • They usually feed on soft-bodied invertebrates and scavenge dead and dying fishes.
    Fig: Hag Fishes

2.    Infraphylum Vertebrata:

  • Characterized by vertebrates that surround a nerve chord and serve as primary axial support. Basically, vertebrates are the member of the super-class

Infra-phylum Vertebrata is divided into 2-super-classes.

(1)    Superclass petromyzontomorphi

(2)    Suoer Class Ganathostomata

1.    Superclass Petromyzontomorphi:

  • They are large sucker-like mouths.
  • Re-inforced by cartilage
  • Gills are attached with spine-shape

Superclass petromyzontomorphi have 1 class.

Class Petromyzontida:

  • Having a sucking mouth with teeth and a rasping tongue
  • Having 7-pairs of pharyngeal slits and blind olfactory sacs.
  • Example: Lamprey.

2.    Super class ganathostomata:

  • These have hinged jaws and pair appendages
  • The vertebral column may have replaced the notochord and also has 3 –semicircular canals.

Superclass Gnathostomata has the following classes

(i)    Class chondrichthyes

(ii)    Class Actinopterygii

(i)    Class Chondrichthyes:

  • Having cartilaginous skeleton
  • Lack opercula and swim or lungs

Class Chondrichthyes have 2-sub classes:

(a)    Subclass-Elasmobranchii

(b)    Subclass- Holocephali

(a)    Subclass-Elasmobranchii:

  • Having cartilaginous skeleton
  • They may be particularly classified on the behalf of placoid scales or non-scales

Examples: Sharks, skates, rays

    (b)    Subclass Holocephali:

  • The operculum covers the pharyngeal slits
  • They lack scales
  • Teeth modified into crushing plates

Example: Ratfish

(ii)    Class Actinopterygii:

  • Paired fins supported by dermal rays
  • Blind olfactory sacs
  • Pneumatic sacs functions as a swim bladder

Examples: ray fined fish

(iii)         Class Sarcopterygii:

  • Paired fishes supported by muscular lobs
  • Pneumatic sacs functions as lungs
  • Artia and ventricles are at least partly divided

Example: lungs fishes and all tetrapods.

(2)    Infra-Phylum Vertebrata

Class-Petromyzontida

  • Aganathans:
  • Aganathans is the class of petromyzontida.

Example: Lampreys

  • Common Inhabitat of the marine and freshwater environment in a temperate zone.
  • Adult lamprey prey on the other fishes
  • While at the larval stage they are filter feeders.
  • Lips: having sensory and attachment function
  • Mouth: sucker Numerous epidermal tooth also covered by tongue-like structures.
  • The lamprey has a salivary gland with anticoagulant secretion and feeds mainly on the blood of the prey.
  • Some of the lampreys are predatory brook lamprey (freshwater)
  • They are basically filter feeders.

Life history of lamprey:

Migration:

Migration occurs in following

(i)    Fishes
(ii)    Birds

  • Adult lamprey, inhibit in the ocean
  • Their basic habitat is fresh water and marine water
  • When they become old or at end of their lives they migrates sometimes hundreds of miles to a spawning bed in a freshwater stream.


    Once lamprey reach their spawning side, they began building a nest by making a small depression in the substrate

    When the nest is prepared a female usually attaches to the stone with her mouth. A male wraps his body around the female eggs are shed in small batches occur a paired of severed hours and fertilization and extended with several eggs hangs in approximately a week into ammoceta larvae.

    The larva drifts down the softer substrate, where they burying then in sand and mud and become a filter feeder ammoceta larvae grow from 7mm to about 17 cm over 3-7 years. Later development larvae metamorphosis into adults over a period of several months. The mouth becomes feeding muscular develop lamprey eventually leave the mud permanently and began journey like a predator.

(2)    Super-Class Ganathostomata:

  • Jaws of vertebrates evolve from pharyngeal architects.
  • It is extremely important event ventilations and the captured
  • Pair appendages

Gnathostomata are classified into

    Superclass Ganathostomates

Again divided into 2 Classes

(i)    Chondrichthyes (cartilaginous fishes)

(ii)    Stitches (Bony-fishes)

  • Both classes have an extinct species, having a body outer-covering placoderm.

(i)    Class-Chondrichthyes:

  • Their members are sharks, skates, rays, and rat fishes.
  • Most of the Chondrichthyes are carnivores or scavengers.
  • Most are marine
  • In addition to their biting mouthparts and paired appendages also possess placoid scale and cartilaginous endoskeleton

It has 2-sub classes

   (a) Class Elasmobranchii

(b) Class Elasmobranchii

    (a)    Class Elasmobranchii:

  • Their member is sharks, skates, and rays.
  • Having 820 species.

Sharks:

  • Their size is about the smallest 1 m + laboratory specimen then 10m called as Basking or wheel sharks)
  • The largest shark is not a predator but is a filter feeder.
  • They have a pharyngeal arch modification that strains plankton, the most feared sharks are the great white sharks and the MAKO

Skates and Rays:

  • Specialized on seafloor
  • Inhabits in shallow water
  • Mostly feed on invertebrates.
  • Lateral expansion of the pectoral fins, into wing-like appanages.
  • Having an elaborate color pattern on the dorsal surface of these animals provides effective camouflage
  • Stingrays have a tail modified into a defensive lash.
  • This group also includes the electric rays and manta rays fish

Sub-Class Holocephali:

  • Having total 30-specie
  • Example: chimeras
  • Has a large head with smallmouth surrounded by large lips
  • A narrow tapering tail has returned the common name Rat-fish.

Specific-character:

  • They have gills covered by the operculum.
  • Their teeth are modified into large plates.
  • They have no scale on their body.

Bony fishes:

  • Having at least some bones in their skeleton
  • Scales may be present
  • They have a bony operculum
  • They have lungs or swim bladder
  • Their estimated species are about 24,000
  • They belong to the class Osteichthyes.

Having further 2-classes

(i)    Sarcopetrygii

(ii)    Actinopterygii

(i)    Actinopterygii:

  • Sometimes called ray-finned fish because their fins lack mausculurable.
  • They use a swim-bladder for gas exchange.
  • Used swim bladder for gas exchange usually attached to their dorsal body ball that regulates the buoyancy.

(ii)    Sarcopterygii:

  • Having muscular lobs associated with fins.
  • Use lungs usually for gases exchange.
  • Example: Neoceratodus inhibit in the freshwater of quelling Australia
  • Protopterus and lepidoserans (Africa)

Coelanthus: 

  • Fossil record to million-year-old
  • For example lata marina (existence specie)

Tetrapods:

  • These are extinct fishes.

Group of Actinopterygii:

Chondroitin:

  • Their 25-species are remains only, their endoskeleton is cartilaginous and their ancestors have a bony endoskeleton.
  • Their living species are paddle fishes and sturgeon.
  • Chondriostrain has a tail with large upper lobs.

(Strangers)

  • They mostly live on the seas and migrate to rivers for breeding. They are larger up to 1,000 kg and bony plates cover the anterior portion of the body.

Paddle fishes:

  • They are large freshwater chondriostrain they have a large paddle-like aroctrum that is unarmed and believed to detect weak electric fields. They swim to the water with large mouths opened filtering crustaceans and small fishes. 
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