Echinodermata Phylum PDF

Phylum- Echinodermata Prof. M.P.K.S.K. de Silva Department of Zoology Echinodermata Greek meaning spiny skin  About 6000 species  entirely marine group  no freshwater or land animals  Found in all marine waters except the Arctic  live near the shore not more than 100 me...

Phylum- Echinodermata Prof. M.P.K.S.K. de Silva Department of Zoology Echinodermata Greek meaning spiny skin  About 6000 species  entirely marine group  no freshwater or land animals  Found in all marine waters except the Arctic  live near the shore not more than 100 meters ….or  Deep water echinoderms at depths up to 1000 to 5000 meters  More echinoderms are present in the warmer conditions Phylum Echinodermata  Many echinoderms remain concealed during the day  they mainly feed during the night.  can withstand a very large range of temperature.  distribution mostly due to temperature. social behavior in echinoderms.  Echinoderms tend to live in large numbers.  This has also been shown to have been true in the past from the fossil records.  the availability of food is greater in some areas which attracts more echinoderms.  Can exert a greater defense against predators.  constitutes the only major group of deuterostome invertebrates  Closely related to the Phylum Chordata because  they both have Deuterostome development  and an endoskeleton Key features of Echinodermata Body not metameric adult with radial, pentamerous symmetry characterised by five or more radiating areas Radial symmetry in modern echinoderms has been derived secondarily from a bilaterally symmetrical ancestral form body differentiated into oral and aboral SURFACES  No head or brain Skeletal structure  Endoskeleton of dermal calcareous ossicles; covered by an epidermis  calcareous ossicles articulate with one another as in the starfish and brittle stars,  or may be fused together to form a rigid test, as in the sea urchins  Coelom extensive  Form the perivisceral cavity and the cavity of the water-vascular system  water-vascular system (ambulacral, system) extends from the body surface as a series of tentacle-like projections (podia or tube feet). Features Unique to the Taxonomic Group  1) Echinoderms have a calcitic skeleton that is composed of many ossicles.  These ossicles act as an exoskeleton, although they are truly an endoskeleton since they're produced by mesenchymal cells.   2)Presence of a water vascular system  This system is used for locomotion, respiration and feeding.  3) pentaradial body organization in adults  Echinoderm's level of symmetry changes from the larvae stage to the adult stage.  When they are larvae they have bilateral symmetry and as adults they have radial symmetry  Presence of water vascular system  No parasitic species  No circulatory,  excretory, or  respiratory systems  Gas exchange occurs through skin gills & diffusion into the tube feet  Coelomic fluid bathes organs & distributes food & oxygen  Digestive system usually complete; anus absent in ophuroids.  Have a nerve ring surrounding the mouth that branch into nerve cords down each arm Other Body Systems  few specialised sensory organs  Eyespots on the tips of each arm detect light  Tube feet respond to touch Reproduction  Separate sexes  Two gonads (ovaries or testes) in each arm produce eggs or sperm  Have external fertilization  Females produce up to 200,000,000 eggs per season  Fertilized eggs hatch into a larva which settles to the bottom after 2 years  & changes into adult  Asexually reproduce by regenerating arms  They are the first invertebrates where the female broods the tiny stars. Echinoderm water vascular system  The water vascular system is an internal closed system of reservoirs and ducts containing a watery fluid.  Water is drawn mainly from the surrounding seawater, sucked in through a perforated plate, the madreporite.  Water enters through sieve plate or madreporite on aboral surface into a short, straight stone canal  Stone canal connects to a circular canal around the mouth called the ring canal  Five radial canals extend down each arm & are connected to the ring canal Arm of an Echinodermate WATER VASCULAR SYSTEM WATER VASCULAR SYSTEM  From the radial water canals, branches extend into the tube feet which may be used for locomotion and food capture  The holothurians differ, in that the madreporite is internal and coelomic*  in the crinoids, the madreporite may be replaced by minute scattered openings called hydropores.  Network of canals creating hydrostatic pressure to help the starfish move Tube feet  Radial canals carry water to hundreds of paired tube feet  Bulb-like sacs or ampulla on the upper end of each tube foot  Each tube foot is connected to the radial canal and also to a balloon-like ampula.  The muscular ampula works like a squeeze bulb, forcing water into the tube foot, causing it to straighten and extend.  Ampula contract & create suction  Rows of tube feet on oral surface (underside) are found in ambulcaral grooves under each arm  This results the tube foot to  move,  attach, or  open bivalves (feeding) Body wall appendages- 04 types  Tube feet  Spines  Pedicellariae  papulae Tube feet  Short, tubular, external projections of the body  Tip of the podium forms a sucker  Found on ambulacral areas and grooves  Multiple functions  Locomotion  Tactile  Feeding  Burrowing  respiration the pedicellariae  present on the surface of the asteroids and echinoids  absent in ophiuroids, crinoids and holothurians  pincer-like structures  Composed of a head and a stalk Pedicellariae  Head consist of number of articulating blades (2-3)  Movable stalk  Some sessile pedicelareae too Different types of pedicellariae  Scissor type  Forcep type  Gemniferous- globular blades (jaws)  Tridactyle- has teeth on the blades  Trifoliate-leaf like blades  Ophiocephalus-snake head like jaws  Urchin pedicellaria are three-jawed pincer claws  whereas those of Asteroids have two jaws  Pedicellaria seem to have two main functions  - to discourage small larva from settling on the surface of an echinoderm  for defense against predators.  In response to an attack from a soft- bodied predator will move their spines aside  and expose pedicellaria to pinch the predator.  Usually, this will discourage the soft- skinned predator.  a hard-skinned predator, such as a large cancer crab, is relatively unaffected by pedicellaria.  In cases of attack from these predators, the urchin will direct its spines (which can be aimed outward in any direction), toward the predator. Spines  Calcareous protrubances  Form surface armature  Covered by epithellium and supported by number of muscles  Some are poisonus  Some have glands that secrete mucous Functions  Locomotion  Digging  Burrowing  Protection  Found in all Echinodermates except Holothuroidea Papulae  Thin evaginations of the body  Used in respiration Feeding habits  Some echinoderms such as starfish are predators  some such as sand dollars feed on detritus  some such as sea urchins scrape algae from the rocks.  Echinoderms are essentially going to feed on anything that is too slow to escape.  Echinoderms also prey on mollusks cause severe destruction on many oyster beds.  Some starfish are also causing damage to the coral reef by feeding on the polyps Protection  several ways that echinoderms protect themselves  have spines on their exoskeleton and sometimes even poisonous organs that can be harmful to animals and humans.  chemical secretions make other animals to respond by leaving them alone.  Eg. a sticky mass secreted from their anus causes predators to become trapped.  Echinoderms also produce a toxin called holothurin that may be lethal Predators of Echinodermates  Echinoderms do not have many predators due to their spiny exoskeleton and the lack of much flesh  Some of their predators are fishes, crabs, sharks, crows and other larger animals in the ocean.  The predator must be strong enough to break their exoskeleton. Importance of Echinodermates  In many countries echinoderms are a source of food and are used in soups.  Some echinoderms, such has the holothurians, produce a toxin called holothurin, which can kill fish by poisoning waters.  The eggs and spermatozoa of the echinoderm are very easy to collect and therefore they have been used to conduct research in developmental biology. Classification- Includes 5 classes:  Crinoidea - sea lilies & feather stars  Asteriodea – starfish  Ophiuroidea - basket stars & brittle stars  Echinoidea - sea urchins & sand dollars  Holothuroidea - sea cucumbers