Echinodermata -1and 2.pdf
Document Details
Uploaded by InvaluableUkiyoE
Tags
Full Transcript
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