Echinoderms Flashcards
Why are echinoderms called echinoderms
Because most possess spiny skin
Unique characteristics of Echinodermata
- spiny skin
- pentamerous: radially symmetrically body with 5 pointed arms
- calcareous ossicles make up endoskeleton
- lack cephalization
- water vascular system
- connective tissue is changeable/flexible
Larval stages of echinoderms are
Free living and bilaterally symmetrical
Water vascular system
- complex series of fluid filled canals derived from a pair of coelomic compartments which service numerous flexible feeding and locomotor appendages called tube feet
- canals lead to thin-walled tubular structures called tube feet
Tube feet have ____ on the ends
Suckers
Madreporite
A sieve plate that links the WVS to the external marine water
Polian vesicles and tiedemanns bodies:
Accessory fluid-storage structures which filter fluid from the water vascular s system into the main body cavity known as perivisceral coelom, maintaining body turgidity and fluidity
All echinoderms live in _____ habitats
Marine
Examples of Echinoderms
Sea lilies, feather stars, brittle stars, sea stars, sand dollars, sea biscuits, sea cucumbers and sea urchins
Body development plan of echinoderms
Deuterostomes
-first opening during embryonic development is the formation of the anus, and then the mouth
-Triploblastic with coelomic cavity
Echinoderm endoskeleton
- internal skeleton
- consists of calcium carbonate and magnesium carbonate
Echinoderms lack _____ and ______ ends, instead, most adults body surfaces are designated as being ______ or ______
Anterior
Posterior
Oral (with mouth)
Aboral (not with mouth)
Coelomocytes
Cells produced by the axial organ, present in body fluids and coelomic fluids
-function in identifying and phagocytosis foreign materials, including bacteria; making pigments and collagens for connective tissues; digestion of food particles; transport of oxygen and nutritional materials and in wound healing
Echinoderms have _________ capacity; like annelids, they have the ability to regenerate a missing body part
Regenerative
Mutable connective tissue/ catch tissue
High ability to alter the stiffness, fluidity and shape of connective tissues from solid to fluid; controlled by nerve impulses
In echinoderms
Specialized _______ are absent among adult echinoderms, although a _______ occurs in larvae
Excretory organs
Cilia-driven nephridial system
Echinoderms lack or have no true ____
Heart
Bio toxins
Most echinoderms are known to be toxic or venomous, although few are deadly to humans
Echinoderms lack a ________; instead it is composed of
Centralized nervous system
Nervous system is composed of three diffuse nerve networks
Have an ectoneural system that receives sensory input from the epidermis
Echinoderms lack _______ and _______; instead they have
Respiratory and excretory
Thin walls of their tube feet allow oxygen to diffuse in an wastes to diffuse out
What type of circulatory system do echinoderms have
Open
Echinoderms have a well developed _______ and a complete ______
Coelom
Digestive system
How do echinoderms communicate with
eachother
Pheromones
Detect chemicals with sensory cells on their body surface
Eyes of echinoderms
Possess simple eyes (ocelli) that can sense light
Functions of tube feet
- Attachment to substrates via a combination of ionic interaction (suction) and activity of the duo-gland
- Gaseous exchange and body circulation
- Excretion: primary site for excretion through simple diffusion
- Chemo reception for light reception: tube feet have genes which code for vision in vertebrates
- Locomotion
Locomotion of echinoderms
- movement by the tube feet is controlled by contraction of moulds muscles
- tube feed lack circular muscles and so cannot extend themselves
- locomotion requires the coordination of protraction and retraction of up to 2000 tube feet
- fluid is pumped into the tube foot by contraction of the ampulla, causing them to extend outward. As the feet extend, they attach their suckers to new locations, farther away from precious attachment
- results in slow but powerful form of movement
Asexual reproduction of echinoderms
-fragmentation: divisions of the body into 2+ parts and the regeneration of missing parts
- adult asteroids and ophiuroids central disc separates into 2 pieces and each regrows arms
- few holothurians adult body routinely breaks in half transversely, and each regrows
-requires that certain body parts of the organism are present in the lost prices
Sexual reproductive form and structures of echinoderms
- are diecious
- bear multiple gonads (except holothurians and crinoids)
- asteroids have at least one pair of gonads extend into each arm
- concentricycloids bears 10 gonads in coelomic cavity
- ophiuroids have many gonads empty into each bursa
- echinoderms have 5 gonads
- holothuriands have single gonad
Fertilization in echinoderms
- fertilization in most echinoderms includes eggs and spermatozoa (shed in water) =external fertilization
- except in concentricycloids which have ducts leading out from the male testes which are used as copulatory organs for internal fertilization
Development of echinoderms can be ____ or ____
Direct
Indirect
Indirect echinoderm development
- egg, planktonic larval stages and juvenile form
- fertilized egg divides many times to produce a hollow ciliated ball of cells (blastula); cleavage is total, indeterminate and radical
- blastula invaginated at one end to form a primitive gut and the cells continue to divide to form a double-layered embryo (gastrula) which develops into a basic larval form called a dipleurula larva, which has bilateral symmetry.
- most asteroids have larval form next called brachiolaria with 3 additional arms used for attaching to sea floor
- echinoids and ophiuroids have complex advanced larvae closely similar in type
- few days to several weeks in a free-swimming form, the echinoderm larvae undergo a complex transformation (metamorphosis) that results in the juvenile echinoderm
Direct development in echinoderms
- involved large eggs with abundant yolk transforming into juvenile echinoderms without passing through larval stage
- parental care or blood protection ranges from actual retention of young inside the body of the female until born as juveniles to retention of the young on the outer surface of the body
-brood protection is best developed among Antarctic, Arctic’s and deep sea echinoderms, in which young may be help around the mouth or on the underside of the parents body (starfish and cucumbers)
Class crinoidea include
Sea lilies and feather stars
Class stelleroidea subclasses
Subclasses
- Ophiuoidea (brittle stars)
- asteroidea (sea stars)
Subphylum echinozoa classes
Classes
- Echinoidea (sea urchins, sand dollars)
- Holothuroidea (sea cucumbers)
Class Crinoidea characteristics
- major part of the body is supported above the substrate either by a long stalk or series of grasping claws (cirri)
- suspension feeders by presence of an oral surface on the upper half of the body
- no ampullae associated with tube feet
- lack medreporite
2 groups of Crinoidea
Stalked crinoids (sea lilies) all deep water
Non stalked, motile crinoids (feather stars)
Stalked crinoids (sea lilies)
- stalk is flexible and composed of a series of cancerous discs (Columnals) stacked one on top of the other and held together by connective tissue
- have digestive system which is tubular, consisting of a mouth, intestine, and terminal anus and is confused entirely to a calyx/ tegmen complex (cup shaped structure)
- calyx is covered by a lid-forming membrane (the tegmen) that bears the mouth
Class Stelleroidea characteristics
- possess 5 arms generally or multiples of 5’s extending from the central disk, commonly referred to as a star
- contains all other arms echinoderms apart from crinoids
- lack stalks but possess arms arrayed in star-like shape around a flattened body
Subclass Ophiuoidea characteristics
- arms with ossicles in linear series linked with connective tissue and muscles
- oral surface possess 5 pairs of invaginations (bursar slits), which may function for gaseous exchange and as a brood chamber
- 5 long arms from small central disc
- digestive system confined to central disc, possessing single opening with a mouth and no anus
- body disc have an oral surface which is often covered with a thin layer of minutes, calcareous scales, while aboral surface bears a number of calcareous plates (shields)
- have bursa
Subclass Ophiuroidea movement
- motile, free living
- move in snake-like manner made by arms during locomotion
Bursae
One feature that distinguishes ophiuroids from all other echinoderms is the presence of a slit-shaped in folding on the oral surface along the arm margins, adjacent to the arm shields. These 10 invaginations are known as bursar and they project well into the coelomic space in the central disc
-function in reproduction, gas exchange, waste elimination, brood chambers where embryos develop
Feeding or subclass Ophiuroidea
Are predators, scavengers, deposit feeders or filter feeders
Hide under rocks during days but emerge to feed at night
Subclass Asteroidea characteristics
- gonads and a part of the digestive tract continue into each arm
- star shaped body like Ophiuroids
- arms not distinct from the central body disc and do not play an active role in locomotion
- tube feet with suckers to move slowly
- tube feet lie in distinct ambulacral grooves on the oral surface
Asteroid feeding habit
Predators and scavengers
-prey on large invertebrates, bivalves, smaller preys
Asteroids feeding
- during feeding on large prey, cardiac stomach of some protrudes out of the body disc through the mouth and placed in contact with the preys soft tissues
- mouth directed downward, opens into a short esophagus and passes upward into a lower stomach called a cardiac stomach where food is digested
- pyloric caeca is above lower stomach and helps in secretion of digestive enzymes, absorption of nutrients and storage for assimilated foods
- have anus but lies on the aboral side nearly one line with mouth
Subclass Asteroidea defence
- can sever or autotomize some of their arms when threatened or in danger, similar to crinoids and Ophiuroidea
- similar mechanism to their ability to rapidly liquify of mutable connective tissue
- severed arms are left with the predator while the animal escapes
Concentricycloids unique characteristics
(Sea daisies)
- tube feet arranged in a circular pattern along the animals periphery and are connected to the double ringed water vascular system
- circular and flat shaped
- lack arms
- no pentamerous radial symmetry
- spacious coelom and a water vascular system but it resembles a 2 concentric water vascular rings
- tube feet serviced by individual ampullae and a cancerous endoskeleton of distinct ossicles
- body covered with marginal spines and skeletal plates
Class Echinoidea characteristics
- most adults have Aristotle lantern that can protrude from mouth for grazing and chewing
- podia of tube feet pores pass through the ambulacral plates
- ossicles joined to form a ring test
- lack arms
- skeletal plates bear many moveable spines and 3 jawed peducellariae
Common members of class Echinoidea
Sean’s dollars, sea urchins
Sea urchins is a model species of the class Echinoidea, characterized by large numbers of ________
Long, rigid, calcium carbonate spines
Most sea urchins are _____ and wandering
Free living
Some may burrow into rocks
Spines of class Echinoidea function as
Gathering and manipulating food, locomotion, protection and defence and in bracing the animal when it wedges into crevices
Some members of Class Echinoidea possess _____ which are extruded through the spines or spine associated structures
Toxin
Echinoids may be _____ or _____
Regular or irregular
Regular urchins have an almost perfect, spherical symmetry (sea urchins)
Irregular echinoids (sand dollars and heart urchins) display various degrees of bilateral symmetry, which may be associated with a lifestyle of burrowing through sand, gravel or mud
Echinoids lack a true _______
Stomach
Esophagus leads into a very long, convoluted intestine where the food is both digested and absorbed
Sea urchin shape
Regular echinoids are hemispherical in shape, round on top and flat on the lower surface
-spines are very long and brightly coloured
Urchin movement
Move by pushing against the substratum with the spines and extending the tube feet in the direction of movement. If turned over they can revert themselves by means of the tube feet on the aboral surface
Sea urchin mouths
- mouth located in the center of the under surface and surrounded by the thickened region bearing five pairs of short, heavy tube feet and sometimes five pairs of bushy gills
- within the mouth is an elaborate five sided jaw structure called aristotles lantern that can be partially extruded from the mouth to grind up calcareous exoskeletons of animals and plants
Anus of urchins
Anus located at the center of the aboral surface and surrounded by a thin-walled area without skeletal plates
Class Holothuroidea characteristics
(Sea cucumbers)
- soft-bodied
- bilaterally symmetrical
- Vermiform creatures with distinct anterior and posterior ends with podia generally confused to distinct ambulacral strips
- possess calcareous ossicles which are microscopic and embedded into the body wall
- size varies from a few centimetres to 1 meter in length
- cephalization not pronounced
- lack arms but have tentacles which can be protracted from the mouth to capture food
- possess both circular and longitudinal muscles
Habitat of class Holothuroidea
Burrows in sand or mud
Feeding of class Holothuroidea
Deposit feeders, ingesting sediment and extracting the organic component
Respiratory system of class Holothuroidea
Composed of respiratory tree; which extend from the cloaca into the coelomic cavity
Surface dwelling species of sea cucumber possess ________ with _______ used for _____
Ambulacral tube feet
Suckers
Locomotion and attachment, similar to echinoids and asteroids
Suckers may be used for Ectoparasitism of fish
