Module 6

Question 1

Echinodermata characteristics

Answer 1

pentaradial symmetry
ambulacra
calcareous endoskeletons
papulae/dermal branchiae
pedicellaria
nerve net
specialised sensory organs
water vascular system
ampullae and tube feet

Question 2

Pentaradial symmetry

Answer 2

they have five or more radii, also known as ambulacra
- echinoderm larvae show bilateral symmetry
- early fossils show that ancient species were bilateral, suggesting that the pentaradial symmetry is derived in modern species

Question 3

Ambulacra

Answer 3

refers to the lines of symmetry in the echinoderm body plan
- ambulacral areas host the tube feet and water vascular system
- the inter-ambulacral areas are the spaces between the ambulacra and host the reproductive organs
- ambulacra lines are not evident on the aboral (upper) surface, but can be found from the oral to aboral side in sea stars

Question 4

Calcareous endoskeletons

Answer 4

all echinoderms have a series of calcareous skeletal components covered by an epidermis
- these can be in large plates as found in the tests of sea urchins or small ossicles as found in sea cucumbers
- helps to provide rigidity, structure, and protection to the echinoderm body

Question 5

Papulae; dermal branchia

Answer 5

aid in respiration and excretion in tandem with the respiration and excretion that occurs across tube feet and the water vascular system

Question 6

Pedicellaria

Answer 6

can be found in groups of echinoderms and are tiny jaw-like structures that help to keep the body free of debris and parasites, protect the papulae and occasionally help with food capture

Question 7

Nerve net

Answer 7

circum-oral ring and radial nerves

Question 8

Specialised sensory organs

Answer 8

• tactile: tube feet/podia and tentacles
• chemo and photoreceptors
• statocysts - balance and orientation

Question 9

Water vascular system

Answer 9

hydraulic system formed by a bunch of canals and tubes and is unique to echinoderms
- used for locomotion and feeding, as well as respiration and excretion
- madreporite: opening place in the aboral surface that draws in water and pumps it around the ring canal along radial canals down each ambulacral groove

Question 10

Ampullae and tube feet

Answer 10

host suckers that are used to grip onto surfaces and food and is filled by water

Question 11

Classes of echinodermata

Answer 11

Asteroidea
Ophiuroidea
Crinoidea
Echinoidea
Holothuroidea

Question 12

Asteroidea

Answer 12

Sea stars
- exist with their oral side down and aboral side facing up
- the asteroid mouth and stomach are found no the underside of the animal along with the ambulacral grooves that host the tube feet for locomotion
- the aboral side hosts one or more madreporites and interambulacral openings called gonopores for reproduction
- predatory: feed on bivalves, crustaceans, other echinoderms, corals, worms, and fishes
- extracellular digestion - echinoderms eject their stomach to digest most of their meal on the outside of their bodies
- stomachs have 2 regions - the lower oral (cardiac) stomach
- the upper internal (pyloric) stomach, which connects the pyloric caeca (digestive glands in each arm) for further digestion

Question 13

Ophiuroidea

Answer 13

Brittle stars
- highly photosensitive
- most species are suspension feeders that feed on detritus from the water and sediment using their arms
- the madreporite is on the oral side
- brittle stars tend to crawl using their arms → they do not have the pedicellariae or papulae, and their tube feet do not have suckers or ampullae
- the ambulacral grooves are not closed → this means their arms do not contain organs
- brittle stars have stomach pouches and gonads that are confined to the central discs
- have no anus, meaning waste is cast back out of the mouth
- have bursae → these open towards thee oral surface and aid with gonad development and water circulation for gas exchange
- this feature suggests development of an internal respiratory system

Question 14

Echinoidea

Answer 14

Sea urchins
- have pronounced dermal ossicles called tests and spines
- have a range of pedicellariae and spines, some of which have toxins
- oral side down and aboral side up
- the ambulacral grooves of sea urchins extend upwards from the oral right around to the aboral side
- two main forms → regular and irregular urchins
- regular urchins: round-ish and exhibit pentaradial symmetry
- rrregular urchins: have uniquely shaped tests and include the sand dollars and heart urchins. They are also secondarily bilateral with the mouth and anus shifted to suit life buried in the soft sediment

Question 15

Holothuroidea

Answer 15

Sea cucumbers
- have an elongated oral-aboral axis
- their mouth and anus point sideways
- pentaradial symmetry can be found in the cross-section of a sea cucumber
- 3 ambulacral grooves are found on the sole (underside) with many tube feet for locomotion, while two ambulacra, grooves are on the dorsal (upper side) with tube feet reduced or absent
- mainly considered secondarily bilateral due to the shifted placement of their five ambulacral grooves
- respiratory tree - found at the aboral end and is used for respiration and excretion
- ability to eviscerate and regenerate
- when threatened, sea cucumbers eviscerate their internal organs to deter predators
- some sea cucumbers discharge their sticky threads to ensnare their enemies
- others can dissociate their bodies due to high amount of catch collagen in their body wall
- missing body parts or deformed features can quickly regenerate
- oral tentacles used for feeding and a long-through-gut
- use their tentacles for deposit-feeding on the seafloor or suspension-feeding from the water column: helps to clean sediment

Question 16

Reproduction in echinodermata

Answer 16

deuterostomic development

broadcast spawning:
- sexual reproduction which involves the releasing of eggs and sperm into the water column
- gametes then undergo deuterostomic development as plankton in the water through a series of larval stages
- echinoderm larvae are bilaterally symmetrical
- following these developments, echinoderm larvae settle on the seafloor and metamorphose into a juvenile

Question 17

Two main odes of development across all classes

Answer 17

Planktotrophic
Lecithotrophic

Question 18

Planktotrophic

Answer 18

larval development involves the “feeding larvae”
- these larvae have ciliated bands - a series of tiny hair like features - tat beat to make whirlpools around the larval body
- this helps them swim, reorientate and pass food particles into their mouths
- species with larvae that undergo planktotrophic development tend to have females that release many small eggs with larvae
- these spend a prolonged period of time feeding and developing in the water column

Question 19

Lecithotrophic

Answer 19

involves the “non-feeding” larvae
- females release fewer but larger eggs with a high degree of maternal provisions for the larvae to feed on
- the larvae therefore do not need to feed externally and undergo more rapid direct development with shorter larval durations

Question 20

Asexual reproduction in echinodermata

Answer 20

• some echinoderms reproduce asexually
• involves fragmentation or fission → this is where individuals split themselves in half and regenerate their missing limbs and organs to produce two viable adults
• some species undergo this mode of reproduction under particular environment conditions
• fission can also occur in the larval form of some species: they split their top and bottom to make larval clones before reaching a mature life stage

Question 21

Hermaphroditic

Answer 21

some echinoderms are hermaphroditic → both male and female
- some switch sexes during their lives while others can host both eggs and sperm at the same time with the potential to self-fertilise
- this however limits the amount of genetic information being spread between generations

Question 22

Brooding species

Answer 22

developing larvae and juveniles are kept safe in specialised brood pouches or folds on the adult body
- this strategy avoids the planktonic larval stages that are at risk of predation and currents
- most common in cold water and deep seas where there are less favourable environmental conditions

Question 23

Regeneration

Answer 23

echinoderms can add more links to the binds of collagen fibroids joined together by proteins
- can release enzymes that break down these protein links that essentially liquifies the tissues
- can turn from solid to liquid very quickly, causing a breakdown if the body wall that is followed by regeneration
- less energy is demanded than through the use of muscle tissue and allows for the adaptable forms, postures, and regeneration

Question 24

Crinoidea

Answer 24

Feather stars
- can have 5 to 100s of arms that have pinnules (side branches) and minute tube feet used for suspension feeding
- oral side is up, with their body and crown facing upwards and cirri acting as holdfasts that root onto the seafloor
- cirri are also used for locomotion (creeping and crawling) along with their arms and pinnules for swimming
- have a U-shaped gut, meaning their anus also points upwards
- have no madreporite
- the water vascular system uses existing coelomic fluid, with no direct internal-external fluid exchange