Phylum Echinodermata Clear Concept

Phylum Echinodermata Clear Concept

1. Welcome to the Presentation of Phylum : ECHINODERMATA Presented by : Group D Illutsrated by:

2. Introduction   The echinoderms are exclusively marine enterocoelous coelomata , triploblastic animals having pentamerous radial symmetry derived from a original bilateral symmetry without definite head or brain with an endoskeleton of calcareous plates or spicules embedded in the skin with a peculiar water vascular system of coelomic origin, pushing out of the body surface, numerous small delicate projections the podia or tube feet, with an ectodermal nervous system without nephridia and with gonads opening directly to the interior by special ducts. The name “ Echinodermata ” literally means “spines or prickly skinned” and refers to the conspicuous spines possessed by their skin. This name was at first used by “Jacob Klein” for echinods . The Greeks applied the name echinas to the hedgehog as well as the sea urchin; both having a prickly appearance. It was “ Leukart ” who first established Echinodermata as a distinct group of animal kingdom.

3. General Characteristics - The echinoderms are exclusively marine and are among the most common and widely distributed of marine animals. - They occur in all seas from the intertidal zone to the great depths. - Radially symmetrical and nearly always pentamerous . - Body is triploblastic , coelomate with distinct oral and aboral surfaces and without definite head and segmentation. - They are moderate to considerable size but none are microscopic. - Body shape rounded to cylindrical or star-like with simple arms radiating from a central disc or branched feathery arms arise from a central body.

4. - Surface of the body is rarely smooth, typically it is covered by five symmetrically space radiating grooves called ambulacra with five alternating inter-radii or inter ambulacra. - Body wall consists of an outer epidermis, a middle dermis and an inner lining of peritoneum. - Endoskeleton consists of closely fitted plates forming a shell usually called theca or test or may be composed of separate small ossicles . - Presence of water vascular or ambulacral system is the most characteristic feature. It consists of tubes filled with a watery fluid.

5. - Alimentary tract is usually coiled tube extending from the mouth located on the oral surface to the annus on the oral or aboral surface. - Circulatory or haemal or blood lacunar system is typically present. - Excretory system is wanting. - Nervous system is primitive, consisting of networks concentrated into the radial ganglionated nerve cords. - Sense organs are poorly developed. - Sexes are usually separated ( dioecious ) with few exceptions. Gonads are simple with or without simple ducts.

6. - Reproduction is usually sexual; few reproduce asexually or by regeneration. - Fertilization is external, while few echinoderms are viviparous. - Development is indeterminate including characteristic larvae which undergo metamorphosis into the radially symmetrical adults.

7. - Radially symmetrical and nearly always pentamerous . - Body is triploblastic , coelomate with distinct oral and aboral surfaces and without definite head and segmentation. - Surface of the body is rarely smooth, typically it is covered by five symmetrically space radiating grooves called ambulacra with five alternating inter-radii or inter ambulacra. - Endoskeleton consists of closely fitted plates forming a shell usually called theca or test or may be composed of separate small ossicles . - Presence of water vascular or ambulacral system is the most characteristic feature. It consists of tubes filled with a watery fluid. Identifying Characters of Echinodermata

8. - Alimentary tract is usually coiled tube extending from the mouth located on the oral surface to the annus on the oral or aboral surface. - Excretory system is wanting. - Nervous system is primitive, consisting of networks concentrated into the radial ganglionated nerve cords. - Sense organs are poorly developed. - Sexes are usually separated ( dioecious ) with few exceptions. Gonads are simple with or without simple ducts.

9. Asterius rubens

10. Gorgonocephalus

11. Cucumaria miniata

12. Classsification : Classification of Echinodermata is not universally taken yet. But at present, two format of classification can be seen. One of them is given by G.Ulbaughs (1967). This format is based on the basis of external features of living and extinct species. Other one is given by A.B. Smith (1984). In this format, Phylum Echinodermata is divided into two sub-phylum. Now we’ll discuss about this classification________ Sub-phylum: Eleutherozoa

13. Class:Asteroidea Characteristics: - Starfishes or sea stars. - Arms five or more and not sharply marked off from the central disc. - Tube feet in orally placed ambulacral grooves; with suckers. - Annus and madreporite aboral . - Pedicellariae present. - Free-living, slow creeping, predaceous and scavengerous .

14. Characteristics: Fossil Pelazoic Sea stars. Platasterias latiradiata is the only living species.

15. Characteristics: They are living sea stars.

16. Characteristics: - Brittle stars and allies. - Body star like with arms sharply marked off from the central disc. - Pedicellariae absent. - Stomach sac like; no annus . - Ambulacral grooves absent or covered by ossicles ; tube feet without suckers. - Madreporite oral. Example: Ophiura , Gorgonocephalus , Asteronyx .

17. Characteristics: - A single row of plates in each inter ambulacral area. - Without typical lantern. - Madreporite radial. Example: Single extinct Ordovician genus Bothriocidaris .

18. Characteristics: - Body globular pentamerous , with two rows of inter- ambulacral plates in existing members. - Mouth central. - Aristotle’s lantern well developed. - Annus central on aboral surface with well developed apical plates. - Madreporite oral. Example: Palaeodiscus,Melonechinus,Diadema,Echinus .

19. Characteristics: - Body oval or circular, flattened oral- aborally . - Mouth oral or displaced anteriorly on oral surface. - Annus marginal, outside the apical system of plates. - Tube feet generally not locomotor . Example: Echinoneus,Cassidulus,Echinocyamus , Spatangus .

20. Characteristics: - Sea cucumbers. - No arms and no spines. - Body elongate on oral- aboral axis, body wall leathery. - Mouth anterior surrounded by tentacles. - Ambulacral grooves concealed; tube feet with suckers. - Usually with respiratory tree for respiration. Example: Cucumaria , Holothuria , Molpadia , Synapta .

21. Sub-Phylum: Pelmatozoa Greek word “ pelmatos ” means stalk and Greek word “ zoois ” means animal. That’s mean Pelmatozoa stands for “stalked animal”. Their characteristics are stalked and sedentary. Class:Crinoidea Characteristics: - Sea lilies. - Body attached during part or whole of life by an aboral stalk. - Mouth and annus on oral surface. - Arms with pinnules . - Tube feet without suckers; no madreporite , spines and pedicellariae . - Ciliated ambulacral grooves on oral surface. Example: Antedon , Neometra .

22. General Morphology of Star Fish or Sea Star There are too many varieties of species consist in phylum Echinodermata . Among them Class Anthozoa is rich of species. Metridium marginatum , known as sea-star or star fish under this class, here’s some description about this. Classification: Phylum: Echinodermata Sub-phylum: Eleutherozoa Class: Asteroidea Order: Euasteroidea Family: Forcipulata Genus: Asterius Species: Asterius rubens

23. Shape : The echinoderms present at a great diversity of organization. The original biradial symmetry is often obscured by a well developed radial symmetry. The most striking characteristic of the group is their pentamerous radial symmetry, i.e. body can be divided into five parts arranged around a central axis. The radially arranged parts are called antimeres , with the mouth at centre. Star fishes have a flattened body which is pentagonal or produced into five, six or even more tapering arms. Bristle stars have a small rounded central disc with five distinct, slender, jointed and flexible arms. Sea urchins are hemispherical while sand dollars are disc like with a cup like central disc bearing five branched arms. Size: Some fossil and dollars measure only 6mm in diameter, whereas a fossil crinoid had a stem about 22 meters long. However, the living echinoderms are of moderate size. The largest star fish, Pycnopodia helianthoides is about 30 cm. across. The shell of the largest urchins Echinosome hoplacantha has a diameter of 30 cm. One sea cucumber, Synapta maculata , measures about 2 meters in length and 5cm in diameter.

24. Coloration: Echinoderms adapted various types of color, such as yellow, orange, brown & purple. The body has two surfaces. The upper convex & darker side is called the aboral & abactinal surface. The lower surface is flat, less pigmented & is called the oral actinal surface.

25. Habit & Habitat: Asterias are exclusively marine, bottom dwelling or benthic animal, inhabiting various types of bottom mainly in the littoral zone where they crawl about or may remain quiescent at times. Asterias forbesi is found equally on hard, rocky, sandy or soft bottom, while other species of Asterias are generally solitary but under certain ecological conditions. Such as to avoid direct sunlight or excessive drying, many individuals may gather at some place for the purpose of protection. Most of them are nocturnal, remain quiet in day time and become active during night. They move by crawling on the bottom mostly at a rather slow rate. All sea stars are carnivorous and feed voraciously and almost any available slow moving or sessile animals, chiefly on polychaetes , crustaceans, mollusks, and other echinoderms. Many species of Asterias exhibits various types of biological relationships such as parasitism and commensalism etc. Sea stars have remarkable power of autonomy and regeneration.

26. Food & Feeding Mechanism: Sea star is a voracious carnivore. It prefers to prey on sedentary marine animals like clams, oysters, mussels, snails, crabs, barnacles, worms, and even sea urchins and other smaller star fish. At times it also feeds on small fishes and injured and dead animals.

27. Sea star ingests and digests food in a fascinating manner. Prey is captured and held in position by the arms and tube feet. 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 are exhausted and give way. Adductor muscles cannot, as a rule, remain in a continuous state of contraction for long time. When the valves finally gape, cardiac stomach of sea star is everted into the mantle cavity of the clam to devour it.

28. Body Structure: Oral Surface: The side of the body, which in natural condition remains towards the substratum and contain the mouth or oral opening is called oral or actinal surface. The oral surface bears the following structures.

29. ( i ) Mouth: On the oral surface, in the centre of the pentagonal central disc is an aperture, the actinosome 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. The peristomial membrane or peristome and is guarded by five groups of oral spines or mouth papillae. (ii) Ambulacral Grooves: From each angle of the mouth radiates a narrow groove called the ambulacral groove which runs all along the middle of oral surface of each arm. (iii) Tube Feet or Podia: Each ambulacral groove contains four rows of locomotory organs, food capturing, respiratory and sensory organs called tube feet or podia. The tube feet are soft. Thin walled, tubular, retractile structures provided with terminal discs or suckers.

30. (iv) Ambulacral Spine: Each ambulacral grooves is bordered and guarded laterally by two or three rows of movable calcareous ambulacral spines which are capable of closing over the groove. (v) Sense Organs: Sense organs include five unpaired terminal tentacles and five unpaired eye spots. The lip of each arm bears a small median, non retractile and hollow projection. The terminal tentacles act as a tactile and olfactory organ. At the base of each tentacle occurs a bright red photo-sensitive eye spot made up of several ocelli .

31. Aboral Surface: The side of the body, which remains directed upward or lowers the upper surface is convex & of light orange to purplish color is called aboral or abactinal surface. The aboral surface bears following structures________

32. ( i ) Annus : A minute circular aperture, called the annus . It is situated close to the centre of the central disc of aboral surface. (ii) Madreporite : At the aboral surface of the central disc occurs a flat sub-circular, asymmetrical & grooved plate called madreporiteplate . Madreporite between the basis of two of the five arms. The surface of the madreporite is marked by a number of radiating, narrow, straight or slightly wavy grooves with pores in them. (iii) Spines: The entire aboaral surface is covered with numerous short, blunt, calcareous spines or tubercles. The spines are variable in size and arranged in irregular rows running paralleled to the long axes of the arms.

33. (iv) Papulae or Gills: Between the ossicles of integument are present a large number ofminute dermal pores. Through each dermal pore projects out a very small, delicate, tubular conical finger like, thin walled, membranous & retractile projection called the dermal branchia or gill or papillae. (v) Pedicellariae : Besides the spines & gills, entire aboral surface is covered by manywhitish modified spines like tiny pincers or jaws called pedicellariae . The oral surface also bears pedicellariae . Each pedicellariae consists of a long or short, flexible stalk having no internal calcareous support.

34. Water Vascular System The water vascular system is a modified part of coelom & it consists of a system of sea water filled canals having certain corpuscles. It plays most vital role in the locomotion of the animal. It comprises________ ( i ) Madreporite (ii) Stone Canal (iii) Ring Canal (iv) Tiedemann’s Bodies (v) Polian vesicles (vi) Radial Canal (vii) Tube feet

35. Here’s some description____________ (a) Madreporite : The madreporite is rounded calcareous plates occurring on the aboral surface of the central disc in inter radial position. Its surface bears a number of radiating, narrow, straight or wavy minute pores at its bottom. (b) Stone Canal: The ampulla opens into an s-shaped stone canal. The stone canal extends downwards & opens into a ring canal, around the more the walls of stone canal is supported by a series of calcareous ring. (c) Ring Canal: The ring canal or water ring is located to the inner of the peristomial ring of ossicles and directly above to the hyponeural ring sinus. It is wide & pentagonal or five sided.

36. (d) Tiedemann’s Bodies: The ring canal gives out inter- radially nine, small, yellowish, irregular or rounded glandular bodies called racemose or tiedemann’s bodies from its inner margins. The tiedemann’s bodies rest upon the peristomial ring of ossicles . (e) Polian vesicles: The ring canal gives off on its inner side in the inter radial position one, two or four little, pear-shaped, thin walled, contractile bladders or reservoirs with long necks called polian vesicles. (f) Radial Canal: Along each radius, the ring canal gives out a radial canal which extends up to the tip of the corresponding arm. Radial canal ics below the ambulacral ossicles and terminates as lumen of the terminal tentacle.

37. (g) Lateral Canal: In each arm, the radial canal gives out two series of short, narrow, transverse branches called lateral or podial canals. Each lateral canal is attached to the base of tube feet & is provided with a valve to prevent backward flow of fluid into the radian canal. (h) Tube feet: There are four rows of tube feet in each ambulacral groove. A tube feet or podium is a hollow, elastic, thin walled, closed cylinder or sac-like structure having an upper sac-like ampulla , a middle tubular podium & a lower disc like sucker.

38. Locomotion of Echinoderms: Locomotion is performed with the help of water-vascular system which sets up a hydraulic pressure. By the action of cilia lining the ambulacral canals, sea water enters through madreporite and fills up all canals of the system including the tube feet. Body is moved by the stepping action of tube feet which are alternately adhered to and released from the substratum. One or two arms, in the desired direction of movement, are raised from the substratum. Simultaneously the ampullae of tube feet to these arms contract by the action of their circular muscles. This increases the hydraulic pressure within the tube feet, which consequently elongate, extend forward and adhere firmly to the substratum by vacuum action of their suckers. Adhesion is further strengthening by mucus secreted by the tips of the tube feet. Then, by muscular activity, tube feet assume a vertical posture, dragging the body forward. Tube feet then shorten by contracting their longitudinal muscles and forcing some water back into their ampullae . Consequently, the suckers release their hold on the substratum.

39. During locomotion, one or two arms serve as leading arms, and all the tube feet extend in the same direction in a coordinated manner. However, the tube feet may not work in unison. As a result, the star moves forward steadily but slowly, at a speed of about 15 cm per minute. Sea stars can also climb up the rock by the combined action of their tube feet. I f a sea star is accidentally turned upside down; it can correct its posture by folding or arching its arms. In folding action, tips of one or two arms twist to bring their tube feet in contact with the substratum, thus permitting the whole body to fold over and right itself. In arching the upturned body is first raised on its arm tips and then rolled over.

40. Larval Development: Development of a sea star includes three larval stages __ dipleurula , bipinnaria and branchiolaria . (1) Dipleurula larva or early bipinnaria : First larval stage in all echinoderms is called early bipinnaria . This larva closely resembles a hypothetical dipleurula larva. It is believed that all modern echinoderms have been derived from a dipleurula -like ancestor. Early bipinnaria is an egg-shaped and bilaterally symmetrical organism. An anterior mid-ventral ectodermal invagination , called stomodaeum , becomes continuous with the archenteron to form the larval mouth. Blastopore becomes the larval annus . Archenteron differentiates into a digestive tract made of oesophagus , stomach and intestine. Uniform ciliation of gastrula is replaced in dipleurula by two ciliary bands__ a perioral band surrounding the mouth. Larva feeds actively on unicellular algae, particularly diatoms. Food particles are collected from the water current produced by the aboral or stomodaeal cilia. As larva swims forward, with the help of perioral band of cilia, It rotates clockwise.

41. (2) Bipinnaria larva: Dipleurula soon forms on its front side a large preoral lobe, which becomes bordered by a preoral loop of cilia. Simultaneously, on each lateral side, it forms three lateral lobes which become bordered by a postoral loop of cilia. Pre and post-oral loops arise by the sliting of the perioral band of cilia. Larva thus formed is called bipinnaria . It is bilaterally symmetrical. It swims and feed freely and after some weeks transforms into the next larval stage, the branchiolaria larva. (3) Brachiolaria larva: The lobes of the bipinnaria develop into long, slender, ciliated, contractile structures called larval arms. From the preoral lobes arise three, short and non-ciliated appendages, each ending in a sucker or adhesive disc. The appendages are called bipinnarian arms or fixing processes. Larva is now called bipinnaria . It is also bilaterally symmetrical and swims and feeds actively. It gradually metamorphoses into a small sea star.

42. Larval Forms in Echinodermata : No other group of animals has such complicated metamorphosis in the course of development. Development may be direct or indirect. In direct one, the larval stages are missing while in indirect one, various types of free swimming larvae are formed. In each class, a few members, are viviparous, that is, they brood their young in a sort of brood pouch on the surface of their body. The development of larva takes place in a typical deuterostomous fashion. In most cases the characteristic free swimming larvae developed externally which are of phylogenetic significance.

43. [I] Class 1: Asteroidea (a) Bipinnaria larva: Two types of development occur in asteroids. The direct type has large, yolky eggs and a free swimming larval stage. The indirect stage has homolecithal eggs with little yolk and a free swimming larval stage. After hatching the larva develops cilia and begins a free swimming life. The larva feeds on diatoms as an alimentary canal is formed. The presence of powerful ciliary band on the stomodaeal walls help in feeding. Two lateral longitudinal locomotory ciliated bands develop which connect in front of mouth, forming a preoral loop and in front of the annus , to form a preoral loop. Preoral loop later separates or in some cases develops independently into an anterior ciliated ring around the body. Three lobe sor projections are also develop on each side of the body bordered by ciliary bands. This larva is known as bipinnaria and develops in 2 to 7 days. (b) Brachiolaria larva: Bipinnairia larva transforms into brachiolaria larva which develops three short arms at preoral lobe, known as brachiolar arms. They contain coelomic extensions and adhesive cells at their tips. An adhesive glandular area at their base acts as a sucker. Appearance of the sucker marks the beginning of metamorphosis.

44. [II] Class 2: Ophiuroidea Ophiopluteus larva: Pluteus is the free swimming larva in brittle star s which is known as ophiopluteus . It is similar to echinopluteus of echinoids with the only difference that the former has fewer arms than the later. The posterolateral arms are the longest and directed forward. After gastrulation the arms develop gradually. Posterolateral arms are form first. After 4, 10 and 18 days, anterolateral , postoral and posterodorsal arms develop, respectively. Ciliated bands accompany the arms edges. Internally the larva contains coelomic chambers and archenteron. Internal development proceeds in the same way as in other classes. While free swimming metamorphosis of the larva starts, there being no attachment stage. Tiny serpent star sinks to the bottom to begin its adult existence.

45. [III] Class 3: Echinoidea : Echinopluteus larva: Larva is formed after gastrulation . Gastrula becomes conical, one side of which flatters to form the oral surface. Stomodaeal invagination communicates with archenteron and the gut is differentiated into mouth, oesophagus , stomach and intestine. Blastopore remains as larval annus . Larva begins to form projections which develop into arms. There are six arms namely, preoral , anterolateral , anterodorsal , postoral , posterodorsal and posterolaeral .

46. [IV] Class 4: Holothuroidea (a) Auricularia larva: After gastrulation and formation of coelomic sacs and gut, the embryo becomes a free swimming larva called auricularia larva, within three days. It is transparent, pelagic about 0.5 to 1 mm in length. It swims about by a ciliated band which forms preoral loop and an anal loop. Internally, larva has a curved gut with sacciform stomach, hydrocoel and right and left stomatocoels . Some giant auricularians of unknown adults reported from Bermuda, Japan and Canary Islands measure about 15mm in length and possess a frilly flagellated band.

47. (b) Doliolaria larva: It is a transitional stage from auricularia and appears barrel-shaped and alike doliolaria of crinoids. Continuous ciliated band breaks in 3 to 5 flagellated rings. Mouth is shifted to anterior and annus to posterior pole. Metamorphosis is gradual during which it acquires 5 tentacles and 1 to 2functional podia. As such it is sometimes known as pentactula . After appearance of more podia and tentacles, sea cucumber settles to the sea bottom and leads an adult mode of life.

48. [V] Class 5: Crinoidea (a) Doliolaria larva: It hatches as a free swimming larva. Body has 4 to 5 ciliated bands with an apical sensory plate at the anterior end provided with a bunch of cilia. There is an adhesive pit over the first ciliated band, near the apical plate in the mid ventral line. Between second and third ciliated band lies the stomodaeum or vestibule. Skeleton also develops at this larval stage. After the differentiation into prospective organs, larva attaches itself and internal organs rotate at an angle of 90 degrees from ventral to posterior position. Larva forms a stalk and is now referred as cystidean or pentacrinoid larva which, after sometime metamorphoses into adult.

49. Economic Importance of Echinodermata : The economic importance of Echinoderms is considerable to man. Of all echinoderms the star fish and sea cucumber are of much economic value to man. The dried skeleton of echinoderms have been crushed and utilized as fertilizer on ground. Echinoderms are quite rich in calcium and nitrogenous content so that they are used as food and lime supply four poultry. Among the Pacific Island, South Pacific Ocean and China, sea cucumbers are used as food by man. They are boiled and dried in the sun and sold in the market. In America sea cucumber has been used especially in soup for several years.

50. The ovaries of sea urchins and the eggs of starfish are eaten, either raw or cooked by the Europeans as well as by the people of tropical regions of South America and the Mediterranean. Sea urchins are also used in research particularly as model in development biology and other sections of science. Starfish, urchins and cucumber are good scavengers. The latter are perpetually ingesting mud and sediment of the sea bottom the contained organic food, thus helping in the decomposition processed of the organic material continuously accumulating at the sea bottom. Their food includes seaweeds, small crustaceans, mollusks, tube worms, small animals matter and other small organisms and bottom debris. It has been said that an ocean without echinoderms might become a putrid cesspool. Natives of the Pacific Islands use juices from the body wall of certain sea cucumbers to poison fish in tidal pools.

51. Negative Aspects: The star fish are of particular concern to man as they destroy clams oysters and other marine mollusks that serve as human food. A star fish in aquarium devours nearly 10 oysters or clams in a day. They are universally hated by oyster and clean fisherman because of tremendous damages they do to those commercially important food animals each year.