INDEX
Question number Page number
Question 1: discuss the distinctive characteristics that set chordates apart from all other phyla
Page 3
Question 2.1:
Describe the events that takes place during metamorphosis of solitary ascidians
Page 4
Question 2.2:
Discuss the feeding method of larvaceans
Page 5
Question 3: discuss each of the following aspects of
Hemichordates
Phylogeny body organisation
Page 6
Question 4 write explanatory notes on each of the following
4.1) Adaptation of sharks which promote buoyancy in water
4.2) Osmoregulation in freshwater and marine bony fishes
Page 7
Page 8
Question 5 discuss the different types of snake venom and their effect on pray
Page 10
Bibliography Page 11
Question 1
Discuss the distinctive characteristics that set chordates appart from all other phyla: (Hickman et al 1994)
The animals most familiar to most people belong to the great phylum chordate. Humans themselves are members and share one of the common characteristics from which the phylum derives its name, the notochord.
1) Notochord
 A structure to prevent body shortening.
 All chordates have as their primary internal longitudinal skeletal element the notochord, a stiff but flexible rod that runs the length of the bilaterally symmetrical animal just ventral to the nerve cord.
 The notochord develops in every chordate embryo and is retained in many adults.
2) Dorsal tubular nerve cord
 A structure to coordinate movement.
 In the chordates the cord is dorsal to the alimentary canal and is formed as a tube.
 The anterior end of this tube in vertebrates becomes enlarged to form the brain.
 The hollow cord is produced by the infolding of ectodermal cells on the dorsal side of the body above the notochord.
.
3) Pharyngeal gill slits
 Pharyngeal gill slits are perforated slitlike openings that lead from the pharyngeal cavity to the outside.  They are formed by the invagination (infolding of one part within another part of a structure; a folding that creates a pocket) of the outside ectoderm and the evagination (the protrusion of some part or organ from its normal posistion) of the endodermal lining of the pharynx.
4) Postanal tail
 A structure added to the body behind the end of the digestive tract.
 It has evolved specifically for propulsion in water.
5) Advances chordates show over other phyla:
a. Living endoskeleton
b. Pharynx and efficient respiration.
c. Advanced nervous system.
Question 2
Ascidians, or sea squirts, are by far the most common and are the best known. Ascidians may be solitary, colonial or compound. Each of the solitary and colonial forms has its own test, but among the compound form many individuals may share the same test. In some of these compound ascidians each member has its own incurrent siphon, but the excurrent opening is common to the group.
2.1) Describe the event which takes place during metamorphosis of solitary ascidians
(Karaiskou et al 2015)
1) After a rapid embryogenesis, the nonfeeding larvea swim for a few hours and then metamorphose into a juvenile that is sessile filter feeders.
2) During the swimming period, larvae prepare for the onset of metamorphosis, which usually begin with adhesion.
3) Ascidian larae have a set of protrusions named adhesive pipillae at their anterior-most part of there body.
4) Once adhesion occurs, the larvae initiate metamorphic events:
a. Secretion of adhesives by the pipillae or epidermis of the trunk, this is a prerequisite event for the metamorphosis because it is required for attachement to substrate.
b. Reversion and retraction of pipillae
c. Regression of the tail.
d. Loss of the outer cuticle layer of the larval tunic.
e. Retraction of the sensory vesicles.
f. Phagocytosis of visceral ganglion, sensory organs and cells of the axial complex.
g. Emigration of blood cells or pigmented cells, occurs through the epidermis into the tunic. h. Rotation of visceral organs through an arc, expansion of the brancial basket, and elongation of the oozooids of juvenile.
Conclusion
Metamorphosis, the process of an organism undergoing physical transformation, it refers to the profound changes at the morphological, physiological, biochemical, behavioral and ecological levels that happen in a coordinateed way during a brief period folloeing the postembryonic development stage. This developmental transistion phase is characterised by variuos cellular mechanisms that are not unique to metamorphosis, such as contraction, cell migration, spesific tissues growth and differisation or cell death.
If ascidians initiate metamorphosis before they arrive to theire final destination, they can no longer move to a better location because they become tail-less during metamorphosis. This untimely metamorphosis could force ascidians to live in a nonappropriate environment for their survival, which could result in inefficient growth and reproduction. To avoid this risk, ascidian larvae may have developed the regulation to start metamorphosis strictly after adhesion.
2.2) Discuss the feeding method of larvaceans
 Larvaceans are filter feeders.
 The larvaceans produces a test (kind of skeleton) known as a house of protein and cellulose that surrounds the animal and which contains a complicated arrangement of filters that allow food in the surrounding water to be brought in and concentrated prior to feeding.
 The larvaceans continuously moves its tail with a sinusoidal movement, to create a flow of water through the filters and the thinner of them are connected to its mouth by a straw-like tube.
 They secrete many nets from an ovoid house to catch small phytoplankton or bacteria.
 A gland located near the pharynx secretes mucus to make these nets. The oiliary current brings the food and the mucus flow guides food into a ciliated pharynx and stomach.  This high efficiency allows them to feed on much smaller nanoplankton.
Conclusion
Filter feeding is a method of feeding in which tiny food particles are strained from surrounding water by various mechanisms. It is a primitive but immensely successful and widely employed mechanism.
They absorb nurients directly from their external environment. Filter feeders can play an important role in clarifying water and are therefor considerd ecosystem engineers.
Question 3
The Hemichordata are animals that were formerly considered a subphylum of chordates, based on their possession of gill slits and rudimentary notochord, however it is now generally agreed that the so-called hemichordate notochord is really a stomachord and not homologous with the chordate notochord, so the hemichordate are given the rank of a separate Phylum
Discuss each of the following aspects of hemicordates (Ramel 1992)
3.1) Phylogeny
Hemichordates share characteristics with both echinoderms and chordates.
 Gill slits; primarily for filter feeding and secondly for breathing.
 Short dorsal somewhat hollow nerve chord in the collar zone foreshadows the nerve chord of chordates.
 Early embryogenesis is remarkably like echinoderms and early tornaria larva is almost identical to the bipinnaria larva of asteroids.
 The similarity between the hydraulic action of the coelomic pouches and that of the water vascular system in echinoderms and the similarity in plan of the sub-epithelial nerve plexus of the two groups are further evidence of their relationship.
 Within the phylum the class pterobranchia is considered more primitive than the class enteropneusta shows affinities with ectiprocta, branchiopoda because of is lophophore and sessile habbits.
 Pterobranchs may be similar to the common ancestor of both hemichordates and echinoderms. The position in the animal kingdom: (Hickman 1994)
 Hemichordates belong to the deuterastome branch of the animal kingdom and are enterocoelous coelmates with radial cleavage.
 Hemichordates show some of both echinoderm and chordate characteristics.
 Chordate plan and structure is suggested by gill slits and a restricted dorsal tubular nerve chord.  Similarity to the echinoderms is shown in larval characteristics.
3.2) Body organisation
1) Soft bodied; wormlike or short and compact with stalk for attachement.
2) Body divided into proboscis, collar, and trunk, coelimic pouch single in proboscis, but paired in other two; buccal diverticulum in posterior part of proboscis.
3) Entertopneusta free moving and of burrowing habits; pterobranch sessile, mostly colonial, living in secreted tubes.
4) Circulatory system of dorsal and ventral vessels and dorsal heart.
5) Respitory system of gill slits connecting to the pharynx with outside as in chordates
6) No nephridia; a single glomerulus connected to blood vessels may have excretory function.
7) A subepidermal nerve plexus thickend to form dorsal and ventral nerve cords, with a ring connective in the collar; dorsal nerve cord in some.
8) Sexes seperate in Enteropneusta; with gonads projecting into body cavity; in some pterobranches reproduction may be sexual or a sexual by budding. (Hickman 1984)
A tibular dorsal nerve chord in the collar zone may represent an early stage of the condition in chordates; a diffused net of nerve cells is similar to the uncentralized, sub epithelial plexus of echinoderms. The gill slits in the pharynx which are also characteristics of chordates are used primarily for filter feeding and only secondary for breathing and are thus comparable to those in protochordates. Conclusion
Hemichordates are vermiform bottom dwellers, living usually in shallow waters. Some are colonial and live in secreted tubes. Most are sedentary or sessile. Their distribution is fairly worldwide, but their secretive habits and fragile bodies make collecting them difficult.
Question 4
All fishes are slightly heavier than water because their skeleton and other tissues contain heavy elements that are present only in trace amounts in natural waters. To keep from sinking, sharks must always keep moving forward in the water because they have no swim bladders. The swim bladder serves as the most effective floating device in bony fishes
Adaptation of sharks which promote buoyancy in water
1. Their sizeable livers filled with an oil that contains squalene
 The sharks liver makes up 25-30% of the entire body mass of the animal
 The compound squalene, found inside the liver, has a low density and a specific gravity of
0.855, making it the optimal material to assist the shark in maintaining bouyancy, because it is lighter than water.
2. Their fins
 Dynamic lift is achieved by using their pectoral fin, the fins that are found on their belly, to create a lift beneath them. o This is similar to what a bird does with its wings.
 It implies that the shark needs to keep swimming in order for this to work o This also means thet they can only swim forward.
 Caudial fin, or tail, is also used exstensively for the maintainig of buoyancy it thrusts the shark in a forward direction, keeping it moving rapidly.
3. Their cartilaginous skeleton
 The complete exclusion of bone makes the shark lighter and more agile, preventing it from sinking. o This is significant in larger species. o Mechanism enabling buoyancy can be controlled when the shark goes into either tonic immobility or thanatosis to escape from predators as they appear dead. (Gibson
2014)
Conclusion
The shark is built for hunting prey and swimming in both fast and slow spurts. Its ability to remain buoyant is of utmost importance for is survival and hunting habits. Streamlined body with a heteroscercal tail, cartilaginous skeleton; five to ten gills with seperate openings all help in the promotion of buoyancy in sharks.
Osmoregulation in freshwater and marine bony fishes
Osmoregulation, the maintenance of constant osmotic pressure in the fluids of an organism by the control of water and salt consentration
Freshwater fishes
 Salt consentration in fresh water is much below that of the blood of freshwater fishes
 Water tends to enter their bodies osmotically and salt is lost by diffusion outward
 Although the scaled and mucus covered body surface is almost impermeable to water, water gain and salt loss do occur across thin membranes of the gill.
(Smith 1931), (Haywood 1973)
 Freshwater fishes are hyperosmotic regulators
 Freshwater fishes have defences against these problems
1. The excess water is pumped out by the mesonephric kidney which is capable of forming a very dilute urine
2. Special salt absorbing cells located in the gill epithelium actively remove salt ions, principally sodium, chloride, from the water to the blood.
3. Together with salt present in the fishes’ food replaces diffusive salt loss. These machanisms are so efficient that a freshwater fish devotes only a small part of its total energy expenditure to keeping itself in osmotic balance. (Pang et al,1977
Marine boney fishes
 Are hypo-osmotic regulators
 Having a much lower blood salt concentration than the seawater around them, they tend to lose water and gain salt (Smith 1931)
 To compensate for the loss of water they tend to drink the sea water around them
 Unwanted salt is disposed in 2 ways:
1. The major sea salt ions (sodium, chloride, potassium) are carried by the blood to the gills where they are secreted outward by salt secretory cells (Haywood 1973)
2. The remaining ions, mostly divalent ions (magnesium, sulfates and calcium) are left in the intestines and voided with the feces
 A small but significant fraction of these residual divalent salts in the intestine penetrates the intestinal mucosa and enters the bloodstrem. These ions are excreted by the kidneys by tubular secretion.
Conclusion:
Most boney fishes are restricted to either freshwater or seawater habitats. However some 10% of all fishes can pass back andforth with ease between both habitats. These fishes are also known as euryhaline fishes. Fishes that can only tolerate only very narrow ranges of slat concentration, most freshwater and marine fishes are said to be stenohaline fishes
Question 5
The tropical and subtropical countries are the homes of most species of snake, both of the venomous and nonvenomous varieties. Even in these locations one third of all snakes are venomous. The nonvenomous snakes kill their prey by constricting or by biting and swallowing of prey.
Discuss the different types of venom and their effect on prey
1. Neurotoxic
It attacks mainly on the nervous systems affecting the optic nerves (causing blindness) or the phrenic nerve of the diagram (causing paralysis of the respiration system) where the victims suffocate to death. (Thomson 2014)
Sitotoxic
Damages the tissue causing necrosis and the victim will die because of serious neurosis and blood loss.
Hemotoxic
It damages the blood vessels and causes blood to become very thin and the victim will bleed to death. It stops the blood from clotting
Miotoxic
This is a mixture between hemotoxic and neorotoxic and has both effects.
2. Hemolytic
Breaks down red blood corpuscles and blood vessels and produces extensive extravasations of blood into the tissue spaces.
Conclusion
Snake venom comes in different types. Different types of venom have different effects on prey. The potency of the venom varie according to the species of snake, size of the snake and the amount of venom injected (Chapter 18)
References
1. Hickman, C.P., Roberts, L.S. 1984. Integrated principles of zoology. Edited by D.L. Bowen.
Seventh edition. Cleveland: Times Mirror/Mosby college publishing.
2. Karaiskou,A. Swalla,B.J.,Sasakura,Y. And Cambon, J, P. (2015). Metamorphosis in solitary ascidians. Genisis, 53:34-47
3. Gibson, A. 2014. Shark information. [Online]. Available: http://www.sharkinfo.com/articles
[Cited 12 April 2015]
4. Thomson, T. 2014. Reptiles. [Online]. Available: http://www.timsreptiles.co.za [Cited 9 April
2015
5. Hammerschlag, N., A review of osmoregulation in freshwater and marine elasmobranches [online] available: http://www.oceansconservationscience.org.
6. Pang, PKT.,Griffith, RW., Atz,JW. 1977. Osmoregulation in elasmobranches. 200/17:365-
377
7. Smith, H.W.1931. The absorption and excretion on water and salts in fishes. 98:269-310
8. Haywood, G.P. 1973. Hypo osmotic regulation coupled with reduced metabolic urea: analysis of serum, osmolarity, chloride and urea, 23: 121-127
9. Haywood, G.P. 1973. Indications of sodium, chloride and water exchange accross the gills.
Berlin, 29:267-276.
10. Ruppert, E.E and Barnes, R.D. 1994. Invertebrate zoology. Sixth edision. Saunders collage publishing, fort worth
11. Ramel, G.1992. study of Hemichordates.[online] available:
http://earthlife.net/inverts/hemichordata.html