Vertebrates & Phylum Chordata

• Vertebrates have an endoskeleton with a backbone, providing support for the dorsal nerve cord and muscle attachment.
• They possess a distinct skull, indicating cephalization.
• Vertebrates can be found in marine, freshwater, and terrestrial habitats.
• Flight has evolved amongst vertebrates.
• Vertebrates exhibit bilateral symmetry and are segmented, but the segmentation is often inconspicuous.
• They are triploblastic, characterized by a well-developed coelom.
• Vertebrates are distinguished by closed circulation and chambered hearts.
• Most vertebrates are free-living, while a few species exhibit ectoparasitism.
• They are deuterostomes, grouped within Echinodermata and Chordata.
• Sexual reproduction is the primary mode of reproduction among vertebrates.

Phylum Chordata

• All chordates share four key characteristics: a notochord, a nerve cord, pharyngeal gill slits, and a post-anal tail.
• The nerve cord is a tube running dorsally to the digestive tract, giving rise to the spinal cord and brain.
• The notochord is flexible, extends the length of the body, and functions as a hydrostatic organ that aids in skeletal support
• Muscles attach to the notochord and facilitate undulatory movements without shortening.
• The notochord is replaced by a vertebral column in most adult chordates.
• Pharyngeal slits filter food and support gills and jaws and form components of ears and tonsils of tetrapods.
• The post-anal tail is responsible for locomotion in aquatic species and balance, courting, and communication in tetrapods

Subphylum Urochordata

• Urochordates, also referred to as tunicates or tail-chordates, comprise roughly 3000 species.
• They are mostly sessile as adults and live in the sea.
• Urochordates have a non-living tunic containing cellulose surrounding the animal.
• Only the larval form displays all chordate characteristics in some groups.
• Through metamorphosis, adults lose the notochord and tail; the nerve cord reduces to a single ganglion.
• Classes within Urochordata include: Ascidiacea, Appendicularia, and Thaliacea.
• Acidians, or sea squirts, are the most well known and common members of the subphylum.
• While sessile, sea squirts have incurrent and excurrent siphons on their body.
• Water containing food particles enters through the incurrent siphon, is processed, and is expelled through the excurrent siphon.
• Undigestable waste is discharged into the anus
• Urochordata are hermaphroditic and achieve external fertilization, and this subphylum also exhibits regeneration.

Subphylum Cephalochordata

• Cephalochordates, known as lancets, are compressed slender animals averaging 3-7 cm that live in sandy coastal sediments.
• Lancets received their name from their bladelike shape.
• They have a slightly swollen tip on their anterior dorsal nerve cord instead of a true brain.
• Lancets possess colorless blood circulating through a ventral vessel.
• Their body structure resembles that of tunicates but features a smaller atrium and mouth.
• Larval lancets feed on plankton; adults bury themselves in the sand to filter feed.
• Water is pumped out through the atriopore separate from digestive waste.
• Segmented muscles are responsible for their undulation.
• Tentacles serve as sensors for these creatures.
• Cephalochordata sexes are separate, and gametes are released into the atrium subsequently passing through the atripore for external fertilization.

Subphylum Vertebrata:

• Vertebrata, also known as Craniata, is a large and diverse group
• Vertebrate endoskeletons support indeterminate growth.
• A stiff vertebral column spans their bodies, coupled with a hollow, central nervous system (or spinal cord.)
• They have a mouth at the anterior end and an anus before the posterior end and display a present tail posterior to the anus during at least one development stage.
• A chambered heart characterizes vertebrata, from sizes of 7.7mm to 33 meters
• Vertebrates represent approximately 4% of all animal species.

Early Vertebrates

• The earliest jawless, fish-like vertebrates emerged during the Cambrian period and were grouped under Agnatha considered vertebrate ancestors.
• Myllokunmingia and haikouichthys, earliest known vertebrates, were first discovered in China.
• These were small, fish-like beings, complete with a notochord, primitive cranium, and gill slits.
• They lacked jaws, paired fins, and true vertebrae but had cartilaginous skeletal elements.
• Pteraspidomorphs first radiated in the Ordovician period and became the first jawless fish aided in possessing bony head shields for defense.
• Ostracoderms radiated in the Silurian period, developing bony armor though remaining jawless.
• Placoderms radiated in the Devonian period as true jawed vertebrates thus allowing them more efficient means of predation.
• These vertebrates possessed dominant bony plates as coverings and were dominant predators in marine environments.

Superclass Agnatha

• Jawless fish that includes about 119 species: Myxini (hagfishes) and Petromyzontida (lampreys).
• They lack jaws, internal ossification and scales, but have paired fins, with pore-like gills and eel-like bodies.
• Cartilage constitutes their skeleton and reproduce sexually, and are oviparous with a two-chambered heart
• Tend to be common predators with Hagfishes (Myxini) not possessing vertebrae, are soft-skinned with covered eyes that are blind.
• Marine bottom waters are a common habitat, but they have reproductive patterns are only relatively know.
• They use yolk eggs, not developing in larval stages.
• Lampreys (Petromyzontida) are parasitic with naked s-kins and commonly develop eyes in bodies commonly found marine during adulthood which ultimately spawns during freshwater
• They swim the bodies with undulation known for targeting for attacking salmonid fish, utilizing the attached suctorial mouth

Class Chondrichthyes

• Cartilaginous skeletons distinguish this group of fish
• Bones are absent as skeletons are extensively calcified with jaws (present in polyphydont teeth) with large stomachs ( not found in chimaeras).
• With well developed brains, the liver is large and filled with oil.
• They use senses of smell, vibration (using lateral lines), electroreception and well developed vision as well, separate from internal fertilizers
• Sexes are separate.
• Internal fertilization w/ claspers
• They can be oviparous or ovoviviparous (no larval stage), with elevated concentrations of urea in paired with the presence with 5-7 gills without the existence of swim bladders or lungs
• This class are split into to classes, sharks, rays, and holocephalic chimaeras .
• Sharks encompass about 45% of Elasmobranchs, these typically hunt with 5-7fill splits with accompanying lateral lines.
• rays have a dorsoventrally flattened body and enlarged pectoral fins and gill openings located on its head underbelly,
• In comparison, Skate is known for for thicker ,shorter with row of spike

Class Osteichthyes

• Distinguished as bony fishes in the vertebrae phylum, characterized composed completely from bones ( internal structure This class is also categorized by containing ( 300,000 living species).
• Bony fishes have fin with operculum attached bony plates, with an operculum over their gills and swimm bladders with dual fins which lead primary to most common fertilization through methods
• Their body structures also support oviparity, ovoviviparity and viviparity
• Actinopterygii is responsible for supporting and stiffening rays of bone as well as fins that lacks muscle
• This in turn provides a means of of ganoid, ctenoid, or cycloid of skin which scales from dermatol
• They are commonly teleost
• Actinoptevygii includes mudkiooer that modern f in fresh waters through scale, swim bladder and fins .
• In comparison, Sarcopterygii has lobes with fleshy , pairing pectoral fins used for respiration (in coelcanthys)

Class amphibia

• The oldest extant vertebrates, adapted for life on land, but still rely on fresh water to live a a life.
• They display developed pigment to adjust to legs , cutaneous, pulmonary respiration with heart systems.
• Ampihbia also consists feet that used for to use claws or webbing alongside external fertilization.
• Subcategory Caecilians, are also present as borrowing animals with vertebra that are fed by animals
• Salamanders typically prey smaller animal’ with aquatic based territories with external eggs
• Anura a very common species of Amonia uses tadpole.

Class Reptilia:

• A member a,minota clade are characterized by membrane adaptations .
• Amniotes showcase anapsid dispsid , and synaspids in skull.
• adaptation in respiration occur because, desiccation resisant skin that uses four membranes which includes choleric amniotic and yolk sac.