Anatomy of Amphioxus Flashcards
Vertical longitudinal plane passing from head to tail through the center of the body from dorsal to ventral surfaces
Median Plane
Any vertical longitudinal plane through the body- that is, the median plane or any plane parallel to it, sometimes designated as parasagittal
Sagittal Plane
Any horizontal longitudinal section through the body- that is, all planes at right angles to the median plane and parallel to the dorsal and ventral surfaces
Horizontal or frontal Plane
Section cuts vertically across the body at right angles to the sagittal and horizontal planes
Transverse or cross-plane
Line in the median sagittal plane extending from head to tail
Longitudinal or anteroposterior axis
Any line in the median and sagittal plane extending from dorsal to ventral surfaces
Sagittal or dorsoventral axis
Any line in the transverse plane running from side to side
Transverse or mediolateral
Three axes of bilateral symmetry
Longitudinal, transverse, and sagittal
Plane which passes through the longitudinal and Sagittal axes
Median Sagittal Plane
Regular repetition of body parts along the anteroposterior axis
Metamerism or Segmentation
Each division is termed a (3 divisions)
Metamere, segment, somite
Animal is said to exhibit both external and internal segmentation;
Internal metamerism is present
The segmentation of the animal body into nearly- like segments is spoken of as
Homonomous
The majority of segmented animals in which the various segments differ from each other to a greater or less extent
Heteronous
Is a primitive and generalized state in which the various segments are more or less independent and capable of performing all necessary functions
Homonomous segmentation
The segmented groups of animals are (3)
Annelids, anthropods, chordates
Metamerism in the chordate line began in the hemichordates , where gonads show evidence of serial repetition
Pseudometamerism
An intrinsic similarity indicative of a common evolutionary origin
Homology
Animals closely related by descent may differ greatly in general appearance after a long sojourn in different environments, such as seals and cats
Divergence
They have a notochord which is a dorsal nerve cord and gill slits
phylum Chordata
Phylum Chordata comprises of 4 subphyla
- Hemichordata (acorn worms)
- Urochordata (tunicates)
- Cephalochordata (amphioxus)
- Vertebrata
Cephachordates consists of 2 genera
Branchiostoma and Asymmetron
Means sharps both ends is a member of the genus
Branchiostoma
Small animal, only about 2-3 inches in length, that can be found lying along sandy seashores in temparate zones
Amphioxus
What differs in amphioxus and other fishes
Lack of skull, vertebrae, brain, heart, and kidneys
The epithelium covering is but a single cell in thickness covered in what tissue?
Connective tissue is gelatinous
The muscle masses, the myomeres are separated by?
Myosepta
Extends the entire length of the body
Median dorsal fin
An expanded continuation of the median dorsal at the posterior end of the body
Caudal Fin
An anterior continuation of the caudal fin extending to the atriopore
Ventral Fin
The opening of an internal cavity, the atrium, located just in front of the ventral fin
Atriopore
The snout like anterior end of the body that projects over the oral hood
Rostrum
22 still tentacle-like structures projecting from the free edge of the oral hood. They are thought to contain sensory elements that might be used for taste
Buccal Cirri
The longitudinal series of about sixty angularly shaped muscle segments, known also as myotomeres
Myomeres
The connective tissue partitions separating the myomeres
Myosepta
The row of rectangular bulging masses located beneath the ventral ends of the myomeres
Gonads
A pair of integumentary folds that extend along the ventrolateral surfaces from the anterior pharyngeal region almost to the atriopore
Metapleural folds
A funnel shaped membrane located at the ventral part of the anterior end of the body; it helps to direct the water vortex, created by the wheel organ , into the mouth
Oral hood
Funnel shaped cavity enclosed by the oral hood
Vestibule
The internal connective tissue rods that are present as supporting elements in both the dorsal and ventral dins. They are absent from the caudal fin
Fin rays
The supporting rod that extends almost the entire length of the body
Notochord
The elongated cylindrical mass of nervous tissue that lies above the notochord, it is almost as long as the notochors
Nerve cord
A linear series of pigment cells lying along the ventral wall of the nerve cord. They may possibly serve as photoreceptors
Ocelli
A mass of pigment cells located at the anterior end of the nerve cord. Its sensory function has not been established
Eyespot
A series of finger-like projections, lined with cilia, that lies on the the inner lateral and dorsal walls of the oral hoods.
Wheel organ
The cilia beat in such a way as to suggest a turning wheel, and they help to create a vortex of water that is directed towards the mouth by the oral hood
Wheel organ
The vertical membrane located just behind the base of the wheel organ, it regulates the amount of water entering the pharynx
Velum
The opening in the velum
Mouth
Short tender projections extending from the margin of the velum that rings the mouth, by bending across the mouth, they may prevent sand or particles from passing into it
Velar tentacles
The chambar, interrupted by gill slits that extends from the mouth to the intestine
Pharynx
Slender parallel oblique bar supported by branchial rods
Gill Bars
That make up the side wall of the pharynx, cross pieces (synapticulae) link the bars
Branchial rods
The large cavity surrounding the pharynx, its ventral boundary is visible as a line extending below the pharynx to the atriopore
Atrium
The digestive tube that extends from the pharynx to the anus
Intestine
The pouch that projects forwards as an outpocketing of the intestine (midgut), it extends along the right side of the posterior part of the pharynx
Hepatic diverticulum
The outer cellular layer of the body, consisting of a single layer of columnar cells, it is covered by an acellular cuticle and rests upon a thin layer of a connective tissue
Epidermis
A short projection from the dorsal midline region that is supported by the gelatinous fin rays
Dorsal Fin
Masses of muscle under the skin, separated by connective tissue partitions, the myosepta
Myomeres
The somewhat triangular structure located on the midline, slightly ventral to the dorsal fin
Nerve cord
A very narrow cavity
Neurocoel
The larger rounded structure that lies beneath the nerve cord, it is surrounded by a connective tissue sheath
Notochord
The central cavity of the oral hood, located under the front part of the notochord
Vestibule
The thickened ciliated epithelial masses of the wheel organ are found on the
Inner hood wall
A number of these, cut transversely, are present at the lower boundary of the vestibule
Buccal Cirri
These project down from ventrolateral corners of the body
Metapleural fold
This lies in the wrinkled body wall between the metapleural folds. It extends from the myomeres on one side to those on the other. When it contracts, it compresses the atrial cavity dorsal to it from the side, thus expelling its water
Transverse muscle
The narrow cavity limited laterally by gill bars that extend between the notochord and transverse muscle
Pharynx
2 types of gill bars
Primary and Secondary gill bars
The gill bars are braced by small bridges
Synapticulae
The deeply grooved structure in the floor of the pharynx
Endostyle
The cells of endostyle are (2)
Ciliated and glandular cells (Inset B)
Located on the roof of the pharynx opposite the endostyle
Epipharyngeal groove
The cavity that surrounds the pharynx laterally and ventrally
Atrium
These are located ventrolateral in most, they protrude into the atrium from the body wall, still bounded by the atrial lining
Gonads
In sections near the posterior end of the pharynx, this hollow oval shaped structure is seen on the right side of the pharynx
Hepatic diverticulum
It lies within the atrial cavity
Coelem
Present in the cross section as three sac
- Ventral coelemic cavity (lies beneath the endostyle)
- Dorsolateral
Are located on both sides of the epipharyngeal groove
Coelemic Cavities
The paired dorsal aortae may be seen between the notochord and the dorsal end of each of the paired coelemic cavities
Blood Vessels
Enclosed within the ventral coelemic
Ventral aorta
Are present close to the midpoint of the medical border of the gonads
Cardinal Veins
This is a large hollow oval structure lying ventral to the unpaired dorsal aorta
Intestine
Beneath the intestine
Subintestinal Vein
This fin is seen cross sections of the intestine at levels posterior to the atriopore, at levels anterior to the atriopore, metapleural folds will be seen in its place
This rather than dorsal or ventral fins, is present, it is narrower and higher than either
