STUDY OF STAR FISH
3.1 Asterias rubens
3.2 Digestive System
3.3 Food and Feeding Mechanism
3.4 Water Vascular (Ambulacral) System
3.5 Reproductive System
3:6 Autotomy and Regeneration
3.1 Asterias rubens:
Starfish belongs to a large group of marine animals called echinoderms. They can be found in all oceans of the world. Largest populations of starfish live in the Indian and Pacific oceans. Starfish (also known as sea stars) are usually located in the shallow water. There are more than 1500 species of starfish and not single one can survive in the freshwater.
Common genera of starfish or sea star are Asterias, Luidia, Pentaceros, Solaster, Asterina etc. Genus Asterias includes about 1,500 species of which most common is Asterias rubens. Starfish are marine invertebrates. They typically have a central disc and five arms, though some species have more than this. The aboral or upper surface may be smooth, granular or spiny, and is covered with overlapping plates. Many species are brightly coloured in various shades of red or orange, while others are blue, grey or brown. Starfish have tube feet operated by a hydraulic system and a mouth at the centre of the oral or lower surface. They are opportunistic feeders and are mostly predators on benthic invertebrates. They have complex life cycles and can reproduce both sexually and asexually. Most can regenerate damaged parts or lost arms and they can shed arms as a means of defence. Starfish is a voracious predator of coral throughout the Indo-Pacific region, and the northern Pacific.
Systematic Position:
Phylum : Echinodermata
Subphylum : Eleutherozoa
Class : Asteroidea
Subclass : Euasteroidca
Order : Forcipulata
Genus : Asterias
Order : Forcipulata
Genus : Asterias
Species : rubens
Habits and Habitat:
The starfish are free-living marine animal and occur on sandy or muddy bottoms or crawl about over rocks and shells. They are well represented in almost all seas from tide-marks to deep waters. They move slowly on hard substratum or adhere firmly to it with the help of their characteristic locomotory tube feet or podia. Starfish are carnivorous, feeding mainly on crustaceans, polychaetes and molluscs. It is bottom dwelling hence known as benthonic animal. Asterias is strongly positive to light. Some species are negative to light. Starfish in general, exhibit remarkable powers of autotomy and regeneration. Some species of Asterias also exhibit biological relationship like parasitism and commensalism.
External Features:
Shape, size and colour: Body of starfish is pentamerous radial symmetry and flattens in the oral and aboral surface. Body consists of an indistinct central disc, from which radiate out five elongated and tapering, symmetrical arranged projections called arms or rays. The axes of arms called radii and the regions of the central disc between the arms are called interradii. In some genera, number of arms may be more than five; for example, there are more than 40 arms in Heliaster and 7-14 arms in Solaster. The averages Size of starfish is from 10 to 20 inches in diameter. Colouration is variable including shades of brown, yellow, orange, pink and purple. There may also show combination of colours.
Oral or lower or actinal surface: Flat lower surface of the body which is kept towards the substratum. The oral or ventral surface bears following structures
1. Mouth: - Central disc of oral surface bears a centrally located opening called as the actinostome or mouth. It is a pentagonal aperture with five angles, each directed towards an arm. The mouth is surrounded by a soft and delicate membrane called peristomial membrane or peristome, and is guarded by five groups of oral spines or mouth papillae.
2. Ambulacral Grooves: From each angle of mouth extends out five narrow grooves called ambulacral grooves. Each groove shows two rows of short tubular retractile projections called tube feet or podia. Each groove guarded on each side by two or three rows of movable calcareous spines, which are capable of closing over the groove.
3. Podia or Tube feet: Each ambulacral groove contain two rows of short, soft, thin walled, tubular structure called tube feet or podia that end in sucker. Tube feet consist of three parts, ampulla, podium and sucker. Sucker work as suction for the firm attachment on the surface to which it is applied. Tube feet are characteristic organs of echinoderms.
Function: They are mainly used for locomotion and capturing of food. They are also help in respiration.
4. Eyes and Tentacles: Tip of each arm bears a small median, non-retractile and hollow projection, called terminal tentacle. It acts as a tactile and olfactory organ. At its base occurs a bright red light sensitive eye spot contains several ocelli.
Aboral surface: It is the upper convex dorsal surface is called abactinal surface bears following structures
1. Tubercles or Spines: The entire aboral surface bears by short stout immovable blunt calcareous irregular arranged spines.
2. Dermal branchiae or Papulae: It bears a large number of pores are present between the ossicles of boy wall. Through each pore projects out a very small soft, minute, finger like, hallow retractile process called dermal branchiae or papulae. Each Dermal branchiae or Papulae is a hallow process of the body wall containing extension of the coelom. It is respiratory and excretory in function
3. Madreporite: The aboral surface of starfish bears distinct, flat, circular area and conspicuous button like structure called madreporite. It is located eccentrically on the aboral surface. It is present in an interradius between two arms, these two arms are called the bivium and the remaining three arms are called trivium. Madreporite is a sieve like plate, with numerous narrow and radiating grooves bearing pores which lead into water-vascular system inside the body.
4. Anus: A minute circular aperture, the anus is situated close to the centre on the aboral surface of central disc. Echinoderms are the only animals that have an anus in a dorsal position.
Pedicellariae: The pedicellariae of starfish are minute, whitish like structures, found on both oral and aboral surfaces of the body, in association with spines. Pedicellariae are modified spines and microscopic jaw like bodies. Pedicellariae may be stalked or sessile. But only stalked type occurs in Asterias. Each consists of a short fleshy and a movable stalk, bearing two articulating calcareous blades or valves, resting upon and articulating with a third calcareous plate, the basal or basilar piece. Such pedicellariae consisting of three calcareous plates are termed forcipulate. Opposite surfaces of two valves are serrated. Valves open and close with the help of one pair of abductor and two pairs of adductor muscles, respectively. According to disposition of valves, two types of pedicellariae occur in Asterias.
1. Straight type: In this type of pedicellariae the two valves are straight and when closed, these meet together along their entire length like a forceps. Valves open and close with the help of two pair of adductor muscles and one pairs of abductor muscle, respectively.
2. Crossed type: In this type of pedicellariae the two valves cross each other like a pair of scissors. Straight type occurs largely among the dermal branchiae, whereas the crossed type occurs in cluster at the bases of the spines. Valves open and close with the help of three pair of adductor muscles and one pairs of abductor muscles, respectively.
Function: The pedicellariae help in the capture and removal of debris and minute organisms, which may settle on the body surface and interfere with respiration by covering the dermal branchiae and tube feet. In some starfishes, the pedicellariae may help in capturing of small prey.
3.2 Digestive System: Consist of alimentary canal and associated digestive gland.
A) Alimentary canal: Starfish possesses a complete digestive tract located in the central disc. It lies along the oral aboral axis and is quite short due to flattening of the body along that axis. Alimentary canal differentiated into mouth, oesophagus, stomach intestine and anus.
1. Mouth: It is a small pentagonal aperture surrounded by a delicate peristomial membrane called peristome, situated on the oral surface in the centre of central disc. It is surrounded by sphincter muscles and radial muscles. It has great capacity of expansion and retraction.
2. Oesophagus: Mouth opens into a short and wide oesophagus. It extends vertically to open into the stomach.
3. Stomach: It is a spacious sac occupying most of the interior of the central disc. It is differentiated into two distinct parts, a larger oral part or cardiac stomach and a smaller aboral part or pyloric stomach.
a) Cardiac stomach: It is a large saclike structure occupying the greater part of the central disc. Its wall is thin muscular and highly folded having five lobed sacs. Entire cardiac stomach can be everted through mouth at the time of feeding. This is brought about by contraction of the body muscles and consequent pressure of coelomic fluid. Retraction is brought about by five pairs of retractor muscles, which connect the cardiac stomach with ambulacral ridges of five arms. Cardiac stomach is glandular and secretes mucus.
b) Pyloric stomach: It is a small, flat pentagonal sac opening aborally into intestine. Each angles of the pentagonal pyloric stomach is drawn out into ducts which extends the corresponding arm and branches to form a form a pair of large appendages called as pyloric caeca or hepatic caeca or digestive glands or gastric glands. Thus, there are five pairs of pyloric, caeca, one pair in each arm extending right up to its tip.
4. Intestine: It is a short, five-sided tube extending vertically to aboral surface, where it opens out by an anus. It gives out two or three small, branched and brownish appendages called the intestinal or rectal caeca. Intestinal caeca secrete a brownish fluid, probably excretory in nature.
5. Anus: The intestine opens on the aboral side by small opening on the central disc called anus.
B) Pyloric caeca or Digestive glands: Each arm of sea star contains a pair of digestive glands or pyloric caeca extending up to its tip and each is suspended from the aboral body wall by a pair of longitudinal mesenteries. Each pyloric caecum has a hollow longitudinal axis, from which arise two series of short, lateral, hollow branches, each terminating into several small bladder-like pouches or lobules of greenish or brownish colour. The hollow axes of the two pyloric caeca of an arm open into a common pyloric duct that leads into pyloric stomach. Epithelial lining of pyloric caeca consists of four types of flagellated columnar cells
I) Secretory or granular cells: These cells secrete juice containing proteolytic, amylolytic and lipolytic enzymes that digest proteins, starch and fats. The function of pyloric caeca is like the pancreas of vertebrates.
II) Mucous cells which secrete mucus.
III) Storage cells which store and reserve food as lipids, glycogen and protein- polysaccharide complex.
IV) Current producing cells which bear longer flagella that maintain a steady flow of enzymes towards the stomach along the aboral side and of digested food into pyloric caeca along the oral side.
3. 3 FOOD and Feeding:
Food: Sea star is a carnivorous animal and feeds voraciously on clams, oysters, mussels, snails, crabs, barnacles, worms, and even sea urchins and other smaller starfish. At times it also feeds on small fishes and injured and dead animals.
Feeding: Asterias (sea star) ingests and digests food in a fascinating manner. The Prey is captured by starfish in a very interesting manner. It creeps over the prey and holding it with help of tube feet and arms. Asterias arches its body over the prey, assuming a characteristic umbrella like posture. By the contraction of body muscles the coelomic fluid exerts pressure on the stomach and cardiac stomach is everted through the mouth and wrapped round prey. The enzyme secreted by pyloric caeca and enzymes poured out on to the prey and when digestion is complete and stomach is withdrawn in the body with the digested food. The small sized prey is directly ingested through mouth into stomach. It may be interesting to note how a sea star devours clams and other bivalves. It conveniently creeps over the clam, arches its body over it and firmly attaches its tube feet to two shell valves in such a way that the ventral margin of the clam comes to lie in front of its mouth. It then tries to pull apart the two valves held tightly together by the powerful adductor muscles. A few tube feet at the tips of arms are also attached to the substratum to aid in the process. Pull is steadily maintained till the adductor muscles of clam arc exhausted and give way. Adductor muscles cannot, as a rule, remain in a continuous state of contraction for a long time. When the valves finally gape, cardiac stomach of sea star is everted into the mantle cavity of the clam to devour it
Physiology of Digestion:
Digestion in Asterias is extracellular as well as intracellular. The pyloric caeca glandular cells secrete juice containing proteolytic, amylolytic and lipolytic enzymes that digest proteins; the amylolytic enzymes convert starch and fats. The proteolytic enzymes convert proteins into diffusible peptones, starch into maltose and lipolytic enzymes convert fats into fatty acids and glycerol. Digested food is absorbed mainly by pyloric caeca and distributed to various parts of the body by coelomic fluid. The cilia of the cardiac and pyloric stomach set up strong currents that carry the digested food into the stomach and then pyloric caeca. When the digestion is partially completed, Asterias withdraws its stomach along with the digested food by means of its retractor muscles and closes its mouth by contraction of sphincter muscle. It then moves away discarding empty shell. Remaining digestion of food occurs in pyloric stomach and pyloric caeca. Undigested material which mainly eliminated through the mouth and very little matter passes out of the anus.
3.4 Water Vascular or Ambulacral System:
It is a unique feature of the anatomy of all the echinoderms which helps mainly in locomotion. It is modified from the coelom, from which it separates during of the animal. Thus, it is the modified part of the coelom and consists of a system canals lined with ciliated epithelium and filled with sea water, containing amoeboid corpuscles. Its original function is concerned with obtaining food and it plays a vital role in the· locomotion of the animal. The water vascular system of starfish consists of madreporite, stone canal, ring canal, radial canal, Tiedemann’s bodies, polian vesicles, lateral canals and tube feet.
1. Madreporite: The water vascular system starts from the madreporite, which is a hard, rounded and calcareous plate like structure situated on the aboral surface of the central disc of the body. The madreporite is situated in an interradial position i.e. between the bases of two arms of bivium. Its surface bears numerous fines, straight 'or wavy radiating grooves or furrows, having at their bottom minute ciliated pores. Each furrow contains as many as 200 to 250 pores, which lead into very short and fine tubes called the pore canals. Each pores leads into pore canal and pore canal unite to form larger collecting canal which leads into ampulla of stone canal.
2. Stone Canal: Stone canal is a 'S' shaped tube opening on the oral side into a ring canal around the mouth. Its wall is supported by series calcareous rings hence called 'stone canal. The lumen of the stone canal is lined by v tall flagellated or ciliated cells which draw the water current into canal. On one side its wall projects into its cavity as a ridge that bifurcates into lamellae rolled .spirally. The ridge and its lamellae occupy a greater part of the lumen the stone canal. Stone canal along with an axial organ is enclosed in a coelomic sac called axial sinus. The stone canal, axial organ and axial sinus these three together form the axial complex.
3. Ring Canal: It is wide, somewhat pentagonal ring forming round the oesophagus. Angles of pentagon lie in the radial canal.
4. Tiedemann's Bodies: These are also known as racemose gland. Inner side of ring canal gives off inter-radially a pair of small vesicles called Tiedemann's bodies. These are small yellowish, irregular or rounded glandular sacs opening into ring canal on its inner side. There are only 9 Tiedemann's bodies, the 10th being absent and its position is taken by stone canal. Each Tiedemann's body consists of a bounding peritoneum enclosing a stroma of connective tissue and muscle fibres containing numerous radiating tubules. Electron microscope has revealed that each cell of the radiating tubules bears a flagellum in midst of microvilli like processes. Exact function of Tiedemann's bodies is still not clearly understood. However, some workers consider them as filtering devices, some look upon them as enzyme-forming bodies and others as lymphatic glands, probably manufacturing phagocytic amoebocytes which are released into water-vascular system.
5. Polian Vesicles: Polian vesicles are large, thin walled, pear shaped sac. Asterias the ring canal gives off in each inter radius 2 to 4 Polian vesicles. They are contractile structures which store water. Polian vesicles perform many functions. They are supposed to regulate the pressure in water vascular system. Polian vesicles also manufacture amoeboid cells. Each vesicle is lined by a flattened epithelium, followed by a well developed circular muscle layer and stratum of connective tissue containing longitudinal muscles. In most sea stars but not in Asterias present variable number of polian vesicles.
6. Radial Canals: Along each radius, the ring canal gives out a radial canal which extends up to the tip of the corresponding arm and terminates as the lumen of a small terminal median tentacle, bearing an eye at its base.
7. Lateral Canals: Each radial canal, in its corresponding arm, gives out two series of narrow lateral or podial canals, along its entire length. . The lateral canals of two series are alternately long and short in such a way that each short canal has a long canal on its outer and inner side but a short canal on its opposite side, and vice versa. Each lateral canal opens into a tube foot, the opening being provided by a valve to prevent back flow of fluid into radial canal.
8. Tube Feet: There are two double rows of tube feet in each arm, one double row in relation to each series of alternately placed long and short lateral canals. Each tube foot has the form of a closed thin-walled tube. It extends through a gap, called the ambulacral pore, which lies between two adjacent ambulacral ossicles. Each tube foot can be distinguished into three regions, a rounded sac-like ampulla, a middle tubular podium and a cup like sucker at the lower end.
Function: The tube feet are locomotory and respiratory organs of Asterias. Tube feet also help in attaching the body to the substratum and in capturing and handling the food.
3.5 Reproductive System:
Asterias is a unisexual or dioecious animal i.e. sexes are separate. But there is no sexual dimorphism. The males and females are not distinguished externally as there is no marked sexual dimorphism except in the breeding season. Testes and ovaries are morphologically similar and occupy similar position in the body. Testes and ovaries are differing in colour. The testes are usually greyish in colour and the ovaries being pinkish to orange in colour. Reproductive organs lack copulatory organs, accessory glands, and reservoirs or receptacles for storing sperms and ova. Some sea stars are hermaphrodite.
Gonads: There are five pairs of testes and five pairs of ovaries, one pair in the base of each arm, lying freely between pyloric caeca and ampullae of the tube feet. Gonads (testes and ovaries) are morphologically similar and occupy similar positions in the body. Colour variation however exists, the testes being greyish and the ovaries pinkish to orange. Gonads develop periodically and their size varies with their degree of development. When mature, they occupy a considerable portion of perivisceral space, frequently extending up to tips of arms. In the breeding season or at the time of spawning gonads are fully grown but after spawning they are reduced to minute tufts. Each gonad is a branched structure consisting of masses of small rounded follicles like bunches of minute grapes. From the point of attachment of each gonad arises a short duct called gonoduct that opens to the outside on the aboral side by minute gonophores, situated laterally on the aboral side.
There are five pairs of testes in male and five pairs of ovaries in female. Each pair of gonads lies free laterally in the base of each arm between the pyloric caeca and the ampullae. The testes and ovaries are morphologically similar and occupy similar position. They show differences when they are carefully examined microscopically. The size of the gonads varies considerably according to the season. In immature individuals gonads are small but in mature specimen they occupy considerable portion of perivisceral space and often extend up to the tips of arms. In the breeding season or at the time of spawning gonads are fully grown but after spawning they are reduced to minute tufts. Each gonad is a branched structure consisting of masses of small rounded follicles like bunches of grapes. From the point of attachment of each gonad arises a short duct called gonoduct that opens to the outside on the aboral side by minute genital pore or gonoduct at the side of the base or an arm. The gonoduct or genital duct is ciliated. There are no copulatory organs, no accessory glands, no receptacles to store ova and no reservoirs for storing sperms. Each gonad is lined by germinal epithelium containing the germ cells underlined by the connective tissue. It is enclosed in a genital sinus of coelomic nature, with a wall of muscle and connective tissue and externally covered by coelomic epithelium. The aboral sinus forms an outgrowth called genital sinus which encloses a cellular cord, called genital rachis. It is continuous with the aboral end of the axial organ called genital stolon. It is believed that the sex cells (sperms or ova) are originated at the aboral end of axial gland (genital stolon) from where they migrate to gonads. Another view regarding the formation of germ cells is that the walls of coelomic epithelium near the proximal part of axial complex form the germ cells.
There are five pairs of testes in male and five pairs of ovaries in female. Each pair of gonads lies free laterally in the base of each arm between the pyloric caeca and the ampullae. The testes and ovaries are morphologically similar and occupy similar position. They show differences when they are carefully examined microscopically. The size of the gonads varies considerably according to the season. In immature individuals gonads are small but in mature specimen they occupy considerable portion of perivisceral space and often extend up to the tips of arms. In the breeding season or at the time of spawning gonads are fully grown but after spawning they are reduced to minute tufts. Each gonad is a branched structure consisting of masses of small rounded follicles like bunches of grapes. From the point of attachment of each gonad arises a short duct called gonoduct that opens to the outside on the aboral side by minute genital pore or gonoduct at the side of the base or an arm. The gonoduct or genital duct is ciliated. There are no copulatory organs, no accessory glands, no receptacles to store ova and no reservoirs for storing sperms. Each gonad is lined by germinal epithelium containing the germ cells underlined by the connective tissue. It is enclosed in a genital sinus of coelomic nature, with a wall of muscle and connective tissue and externally covered by coelomic epithelium. The aboral sinus forms an outgrowth called genital sinus which encloses a cellular cord, called genital rachis. It is continuous with the aboral end of the axial organ called genital stolon. It is believed that the sex cells (sperms or ova) are originated at the aboral end of axial gland (genital stolon) from where they migrate to gonads. Another view regarding the formation of germ cells is that the walls of coelomic epithelium near the proximal part of axial complex form the germ cells.
Ovulation: In Asterias, the breeding take place in late spring. The mature gametes (sperms and ova) are simply discharged into the surrounding sea water by male and female respectively. The maturation and shedding of ova are controlled by a secretion of neurosecretory cells in the radial nerves. Presence of ova and spermatozoa in the surrounding sea water triggers the shedding of gametes of the individuals of the opposite sex. During breeding season the axial organ serves as a chemoreceptor for substances which en the body through the madreporite which stimulate the release of gametes. A single female lays about 1.25 million eggs in one hour or about 200 million eggs a season. A male produces sperms many times the number of eggs.
Fertilization: In Asterias fertilization is external and takes place in sea water. The gametes can not survive longer in sea water, unless fertilization takes place within short time. In the process of fertilization sperms are attracted towards the egg. The sperm which comes in contact with egg membrane penetrates its membrane leaving flagellum outside. This event brings about number of physico-chemical changes in the membrane of the ovum which prevents the entry of other sperms i.e. polyspermy. Fusion of sperm and ovum nuclei occur and zygote is formed.
Development: Development is indirect. A fertilized egg is microlecithal i. e. it contains a small quantity of yolk. The zygote is a spherical structure having diameter about 0.5 mm. The development is indirect and includes free swimming larval stages. The zygote undergoes a rapid holoblastic (complete or total) equal radial intermediate cleavage. In intermediate cleavage the fate of the blastomere is not fixed. If the blastomeres at 4 cell stage are separated, then each blastomere will develop into a larva. Cleavage forms on the second day, a single layered, hollow, spherical, ciliated embryo called coeloblastula. It is about 0.2 mm in diameter, has a fluid filled cavity, the blastocoels. The coeloblastula changes into two layered ciliated gastrula by invagination at one end. The outer layer of the gastrula is called ectoderm and inner endoderm. The cavity lined by endoderm is called archenteron or primitive gut. It opens out by wide aperture called blastopore which becomes the larval anus. Two more openings appear on the surface of the larva. The stomodaeum or larval mouth appears as a tubular in growth of ectoderm on the anterior ventral side. Embryo at this stage becomes a free swimming larva.
Larval Development:
Bippinaria larva: It is characteristic of free swimming larva of starfish. After gastrulation the egg hatches into a larva which develops cilia and begins a free swimming life. The free swimming larva within two to seven days also developed three lateral lobes on each side and give rises to bippinaria larva. At the anterior end dorso-medain arms and pre-oral arms are present. On the lateral sides antero-dorsal arms, postero-dorsal arms, post- oral arms and postero-lateral arms are present. Alimentary canal consists of mouth, Oesophagus, Stomach, Intestine and anus.
Brachiolaria larva: Bippinaria larva, after a few weeks of free swimming existence, change to next larval three short addition arms are added to preoral lobe, known as brachiolar arms. The brachiolar arms are one median and two laterals. Brachiolar arms contain coelomic extensions and adhesive cells at their tips. At the base of brachiolar arms is an adhesive glandular area acting as a suckers. The appearance of suckers marks the beginning of metamorphosis. Internally the larva contains coelomic chambers and alimentary canal consists of mouth, oesophagus, stomach, intestine and anus. The brachiolaria larva attach to some object by its adhesive structures. For some time anterior region acts as a stalk, while posterior part, having alimentary canal and coelomic chamber, convert into a young starfish which detaches itself begins to lead a free life.
Metamorphosis: In about six and seven week’s time, the brachiolaria larva settles on some object with help of adhesive structures. Larval mouth, anus and ciliated bands are disappearing. New mouth and anus are formed on the left and right sides. Anterior region acts as stalk for some times, while posterior part having gut and coelomic chambers, convert into a young starfish. This young starfish attaches itself and starts leading a free life. Some species cut short the development as result of deletion of some larval stages.
3.6 Autotomy and Regeneration:
Asterias shows great power of Autotomy and regeneration. In nature, animal is liable to suffer an injury. Whenever an arm is held injured, the starfish readily beaks off its own arm. This process is termed autotomy. This ability is also found in many other invertebrates. Autotomy serves as a means of protection to the animals. The dropped arm may get regenerated. The opening left in the side of the central disc by the broken off arm is immediately closed by the contraction of the adjacent body wall musculature for the protection of internal organs. When the process of regeneration starts, the first terminal tentacle, the terminal ossicle and the ·eye are formed. The internal organs lost such as pyloric caeca, radial canal, radial nerve old etc. grow out from their stumpy remains. Experimentally, also it is proved that even if four arms of the animal are cut off, it can survive and all four arms are regenerated in due course of time. Specimens with small regenerating arms at the base of large original arm are popularly called comets. A numbers of echinoderms show the breaking apart, a normal rather than accidental phenomenon and regenerating the missing parts leading to a regular aspect of asexual reproduction.Review Questions
Long Answer Questions:
- Give an account of the habit, habitat and external features of starfish.
- What is pedicellaria? Give the different types of pedicellariae in Asterias. Add a note on their function.
- Describe the digestive system and mode of feeding and digestion in starfish.
- Describe the water vascular (ambulacral) system of starfish. Add the note on role of this system in the life of starfish.
- Describe the reproductive system of starfish and add a note on the development with different larval stages.
- Give an account of the development and life history of starfish.
Write short notes on.
a) Systematic position of Asterias
b) Madreporite
c) Types of Pedicellariae in Asterias
d) Tube feet
e) Polian vesicles
f) Bipinnaria larva
g) Regeneration and autotomy
h) Feeding in starfish
i) Metamorphosis
j) Bipinaria Larva of starfish
k) Gonads of starfish
l) Structures present on oral surface
m) Structures present on aboral surface
n) Give the functions of: Terminal tentacles, Pedicellariae, Madreporite, Tube feet, Cardiac stomach, pyloric caeca, water vascular system, gonads
o) Define / Explain
Carnivorous, Autotomy, regeneration, Asteriodiae, radial symmetry, radii, stone canal, ambulacral spine, madreporite, tube feet
Short answer questions:
i. What are radii?
ii. What do you understand by oral surface?
iii. What do you understand by aboral surface?
iv. What do you understand by bivium?
v. What do you understand by trivium?
vi. What are eye spots?
vii. What is madreporite?
viii. What are pedicellariae?
ix. What are papulae?
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