Vertebrate Zoo L2: The Diversity of Craniates and Characteristics of the group
- Created by: ValentineDevil
- Created on: 24-01-19 20:42
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- The Diversity of Craniates and Characteristics of the group
- Diagnostic features of craniates
- Skull (Craniata)
- An elaborate skull is a feature shared by lampreys and jawed vertebrates (the hagfish skull is simpler in construction)
- Neurocranium is the innermost component (immediately surrounds brain and sense organs)
- Originates as cartilage around the brain and sense organs- second oldest component of the skull
- Consists of 4 components
- Bones of occipital region
- Bones of temporal region
- Bones of sphenoid region
- Bones of the ethmoid region
- Present in embryos of all craniates, and represents the adult condition in hagfish, lampreys and cartilaginous fish
- Neurocranium of an adult shark is a single element, called a basal plate, deriving from fused cartilages.
- Pairs of capsules attached, which support and protect organs of hearing, sight and smell
- Neurocranium of an adult shark is a single element, called a basal plate, deriving from fused cartilages.
- Dermatocranium is everything but the face, and forms the external sheath around the neurocranium
- Develops from dermal bone (phylogenetically ancient constituent)
- Dermal bones formed through the deposition of bone tissue within the connective tissue
- Consists of 4 compoents
- 1. Dermal bones of cranial roof
- 2. Dermal bones of the primary palate
- 3. Dermal bones of the upper jaw
- 4. Dermal bones of the lower jaw
- Many primitive craniates had extensive body cover consisting of dermal plates, but dermatocranium is most recently evolved component of the skull
- Absent only in hagfish, lampreys and cartilagious fish
- Develops from dermal bone (phylogenetically ancient constituent)
- Splanchnocranium (AKA Viscerocranium)
- Originates from pharyngeal arches (oldest part of the skull)
- support and move gills and formation of jaw
- Present in all embryos, represents adult condition in hagfish,lampreys, cartilaginous and bony fish
- Consists of 3 components
- 1. First arch (mandibular arch)
- Two segments only, unlike others made of several segments
- Second arch (hyoid)
- Additional arches (3rd up to 6th or 7th)
- 1. First arch (mandibular arch)
- Originates from pharyngeal arches (oldest part of the skull)
- Sensory placodes
- Localised thickenings in the ectoderm of the head region of a craniate's embryo
- Olfactory epithelium lining the nasal cavities develops from an olfactory placode... eye lens from lens placode... inner ear from otic placode...
- Formation: e.g. invaginating placode then otic pit to otic vesicle
- In aquatic vertebrates, the lateral line placodes give rise to the lateral line system
- Five-part brain
- Brain of craniates develop from five vesicles of the neural tube
- Craniates share basic modalities of brain development
- Cranial nerves
- Paired cranial nerves
- III, IV and VI only in vertebrates
- Paired cranial nerves
- Nasophypophysis
- Accomodates olfactory organ and pituitary gland
- Primitively, has anterior opening, or external nostril (Anteriorly on snout (hagfish) or atop head (lamhreys)
- In hagfish, the single nostril can be large while in lampreys it is usually very small
- Lampreys and hagfish: single nostril continues as a hypophyseal duct that leads to nasal capsule (olfactory organ) situated in a median position
- Jawed vertebrates show two external nostrils, leading to two separate nasal capsule
- Position of capsules is more anterior in position, anterior or anterodorsal to the mouth
- In hagfish and lamprey, the single capsule occurs dorsal to the pharynx
- Position of capsules is more anterior in position, anterior or anterodorsal to the mouth
- Semicircular canals
- Detect angular acceleration and deceleration of the head.
- 3 in jawed verts, 2 in lampreys and 1 in hagfish
- Each canal detect motion in a singular plane- activated by circular motion
- filled with endolymph- motion of fluid informs brain about direction of movement
- Gill filaments
- Caudal fin skeletons
- supported by cartilaginous rods in a hagfish embryo
- Endoskeleton
- Cartilaginous and / or bony
- Complex digestive and circulatory systems
- Double circulation in mammals
- Increasing complexity of the heart of craniates
- Neural Crest
- Temporary group of cells unique to craniates that arise from the embryonic ectoderm cell layer, and in turn give rise to diverse structures.
- Sensory neurons
- Some skeletal and connective tissues in skull
- Some pigment-containing cells and other integumentary tissues
- Gill arches, jaws, and parts of the braincase floor
- Jawed verts: involved in formation of dermal skeleton (scales, teeth and dermal bones)
- Temporary group of cells unique to craniates that arise from the embryonic ectoderm cell layer, and in turn give rise to diverse structures.
- Skull (Craniata)
- Diagnostic features of craniates
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