By Dr J Floor Anthoni (2007)
The echinoderms have prickly skins. On this
page you can identify the intertidal echinoderms found on the rocky shore
and in tide pools: sea urchins, starfish and sea cucumbers. None of these
can live out of the water for prolonged times but inside rock pools they
have excellent survival skills.
Echinoderms The echinoderms are the sea urchins, starfish
and sea cucumbers. They have a hard exoskeleton and usually sharp spines.
The most distinctive feature of echinoderms is an elaborate water pumping
(hydraulic) system which operates their many tubefeet and spines. Echinoderms
have no part that can be called a head.
f036909: the green urchin (Evechinus chloroticus)
[kina] derives its name from its green test (shell) even though it may
look brown to red on the outside. It is a voracious grazer but on the rocky
shore it is usually found hiding under stones. The animals found here are
usually small and young, and move to the deep as they grow larger.
f019029: with its many tube feet, a sea urchin attaches firmly
to the rock. It has tubefeet between its spines too, and with these it
can catch seaweed that is floating by. Sea urchins are commonly seen holding
seaweed on their backs for later use, or stones, perhaps for protection
against wavewash and being sand-blasted.
0609167: the largest star on the rocky shore is the prickly
eleven-armed star (Coscinasterias calamaria) [pekapeka, papatangaroa].
It is a hungry predator, eating a wide range of prey from shells to sea
urchins. Its main predator is the triton conch (Charonia capax)
which pins one of its arms down. The star then voluntarily severs its arm
in order to escape. Lost arms regrow fully.THis one already lost one arm.
f019020: this splitting star is also an eleven-armed star
and is thought to be Coscinasterias muricata. It has the habit of
staying small by splitting itself in half and then regrowing the missing
arms, even though it may not end up with eleven arms.
f037020: closeup of 7 arms regrowing on a splitting star.
f036135: the sturdy reef star (Stichaster australis)
[pekapeka, patangaroa] is found mainly on the West Coast and along the
South Island where it survives the low tide. It has eleven arms that are
not prone to splitting. It is a fierce predator.
the seven-armed prickly star (Astrostole scabra) [tangaroa
wae whitu] is not found in the intertidal. It is the largest sea star in
NZ, with arms extending to 75cm. It is also a fierce predator of other
echinoderms: sea urchins and starfish.
the orange splitting star (Allostichaster insignis)
(150mm) is bright orange with usually 3 large and 3 smaller arms as it
splits when reproducing asexually. Mainly South Island.
the four-n-four star (Allostichaster polyplax) has
two sets of four arms, is brownish with orange tubefeet. Mainly South Island.
the brooch star (Diplodontias dilatatus)(Asterodon
dilatatus) (70mm) is a stiff star with an outline of rectangular
plates. It is variable in colour but always creamy white below. South from
f037016: the common cushion star (Patiriella regularis)
[kapu parahua] is an extraordinary animal because it has such a varied
diet as predator, scavenger, grazer and detritus feeder. It can do so by
extending its stomach over its food and digesting it outside its body.
It normally has five arms but the animal shown here has six, and it also
has two madrepore plates (whitish dots). Two species of Patiriella
have so far been identified.
f992830: two cushion stars competing for the same dead triplefin
on an aquarium window. The big one claims most of the quarry by covering
it as well as it can. It has its (green) stomach all over most of the fish.
All the while, the little star is muscling in on the head of the fish,
extending its (green) stomach as far as it can. They may remain in this
position for a week until they give up or the food is wholly digested.
f050221: the elevated cushionstar (Stegnaster inflatus)
[kapu parahua rahi] is also called ambush star because of the way it catches
its food. It looks like the common cushion star but is very colourful (white
yellow orange red purple blue green) in all kinds of spotted combinations.
Its top surface feels slimy while its bottom surface feels raspy with spines
centred towards the middle. In this manner prey will end up centred under
f036107: here the ambush star (Stegnaster inflatus)
has its trap set by standing high on the tips of its arms, creating a 'safe'
shelter underneath its body. But the moment its belly is tickled, the trap
springs as it closes the side flaps amazingly quickly. The victim is then
digested in the hermetically sealed space under its belly. It is amazingly
effective in catching snails of all kind, shrimps and even seahorses and
Ocnus brevidentis, a small white seacucumber of up
to 2cm can sometimes be found under submerged rocks and between kelp holdfasts.
Trochodota dendyi is a finger-long sea cucmber that
burrows up to 20cm deep into sand. It is found inside estuaries.
0703004: an ambush star (Stegnaster inflatus) has
trapped a large common prawn (Palaemon affinis) and has extruded
its stomach entirely around it. Within 8 days it will have digested the
whole shrimp, including its shell.
f018916: a young sea cucumber (Australostichopus mollis)
looks prickly but is in fact quite soft to the touch. It is not commonly
found in rock pools as it prefers calmer water. Sea cucumbers eat detritus
and are numerous where raw sewage enters the sea. Its main predator is
the large cask shell Tonna cerevisina, not found in the intertidal,
as it needs deep sand for burrowing.
Brittle stars Brittle stars have long slender arms with which they
walk. They can move quite rapidly after having been exposed. As their name
suggests, they are rather 'brittle', easily breaking an arm or two. They
do so voluntarily when threatened. The severed arm wriggles to call attention
away from the star, fleeing for its safety. Lost arms can be regrown completely.
When handling a brittle star, be very gentle and hold the star by its centre
disc, rather than by its arms.
Brittle stars are quite amazing because they are able
to catch plankton and fine plankton detritus with mucus, which is transported
by their tube feet from the ends of their arms to their mouths in the middle.
Brittle stars are also called sand stars.
f019023: the mottled brittlestar (Ophionereis fasciata)
[weki huna] does not move by means of its tubefeet but walks on its arms
quickly to safety. It is seldom found in the open, but lives underneath
stones or inside cavities from where it extends its arms. It feeds on plankton
and detritus. Food sticks to mucus and is then transported to the central
mouth by many almost invisible tubefeet.
f019034: an oar star (Ophiopteris antipodum) has flat
spines that loook like rowing-oars. Although it looks deceptively more
solid than the mottled brittlestar, it nonetheless easily breaks its arms
off. It is the fastest moving brittle star.
f018909: the red-checkered brittle star (Ophiocoma bollonsi?,
amphiura rosea?) [weki riki]has very long legs.
f04053: detail of the disc of a red-checkered sand star.
f018914: orange heart sand star (?) is rarely found
as it prefers deeper water. The brown patches are colonies of bryozoa.
The dark holes are date shell burrows.
f019027: an orange brittle star is firmly lodged behind a
pebble under a large boulder, from where it extends its arms to catch food.
f027427: two snake stars in a dispute, on open terrain. The
snake star (Pectinura maculata) [weki] is a most unusual brittlestar.
It has long, rounded arms which do not break off easily and it gives live
birth! In an aquarium it takes food from one's hand by coiling the tip
of an arm around it and bringing the tip of its arm to its mouth. The snake
star is rarely found in rock pools as it prefers deeper water where it
lives under big stones.