f048809: the mottled sand star (Luidia varia) is a large star with seven arms, living for long periods under the sand. This common sand star is shown here but may not occcur at the Poor Knights.

f048810: the comb star (Astropecten polyacanthus) lives almost its entire life burrowed under the sand where it can sometimes be inferred from a slight five-armed depression. Finding one means that many are around.

f012806: the hat urchin () does not burrow in the sand but catches sand particles and other objects with its top side tube feet.

f019422: close-up of a hat urchin. Divers can distinguish two varieties, the high hat and the low hat, but these are probably the same species.

f012807: the underside of the hat urchin shows small spines, all directed towards its middle such that any struggling prey will be pushed towards the centre where its mouth is.

f019423: the cleaned top of a hat urchin shows that is both sideways symmetric (top left to bottom right) as well as five-sided symmetric.

f009908: the mystery prize goes to the giant heart urchin (Brissus gigas), previously thought to be rare until Dr Anthoni discovered how and where it lives [1]. Here is a dead shell of one that died prematurely, near the rubble of its deep burrow.

f009909: the giant heart urchin (Brissus gigas) can grow to a size of 1.5kg, and is both two-sided as well as five-sided symmetric. The reason it was not found is that it burrows to a depth of 30cm from where it is difficult to detect, even though it leaves large markings on an undisturbed sea bottom.

f032808: the top of the giant hear urchin shows all spines combed backward, with short tubefeet in between. Living entirely underground, this urchin causes a continuous collapse of the sand around it, to form a funnel through which detritus falls. Tubefeet then move it further towards its mouth.

f032809: the bottom shows a 'foot' of forward-combed spines towards its mouth where a tiny commensal clam is seen. These tiny clams move like Amazonian jungle grip-tail monkeys through the forest of spines. The urchin also consumes sand grains which exit from its rear end in a continuous stream.

[1] Anthoni, J F (1993): Hauraki Gulf Marine Survey an investigation of the kelp mass mortalities of 1993.

f012815: sea lettuce growing just out of reach of the grazing green sea urchins in wave-washed water that could knock the urchins off the rock, sending them to the deep.

f022410: a male Sandager's wrasse peeping through one of the holes in Trev's Rock, grazed by strong purple urchins.

f030621: where purple urchins survive, they are able to push the green urchins out, as shown here.

f036909: the common green urchin (Evechinus chloroticus) has short spines, low friction profile and a good grip, and is therefore able to live higher up the wall.

f030424: the purple urchin (Centrostephanus rodgersi) looks black from a distance, but in close-up is indeed purple. It has a high friction profile and loose grip, and prefers to stay lower on the wall, or inside hollows.

f016430: the brown urchin () has longer spines still, and is found in even more shelter. It is an uncommon visitor from warmer seas.

f033121: the white-spined urchin (Tripneustes gratilla) has zillions of tubefeet, also on top, and is often found in the canopy of the flexible weed.

f020710: a young diadema needle urchin (Diadema palmeri) found on the colourful rock face near the sand by night. The young ones have white sectors.

f020137: a mature diadema urchin by night. Notice how it has lost its white sectors.

f009709: a serpent star (Ophidiaster macknighti) is variable in colour from yellow to brown.

f025022: the knightaster (Knightaster bakeri) is always pale, usually more flattened than the serpent star, and has tapering arms ending in small white tips. It is also much smaller. (I don't think this photo is the right one)

f025019: a diver finds a firebrick star (Asterodiscides truncatus) on a vertical rock face of the western entrance to Rikoriko.

f025232: close-up of the back of a firebrick star (Asterodiscides truncatus) shows that its spines are spherical, feeling smooth to the touch.

f051820: the seven-armed star (Astrostole scabra) is NZ's largest sea star. It predates on sea urchins and molluscs, but it too is predated on by the trumpet whelk (Charonia sp.), as the star shown here misses an arm already.

f029623: feather stars (Crinoids) are found in very protected places,  yet close to the current. Their arms are long and flexible, branched like feathers. Their tiny tubefeet can hardly be seen by the naked eye. They catch plankton of all kind.

f018916: the NZ sea cucumber (Stichopus mollis) looks prickly but feels soft to rubbery. It is more common in sheltered coastal bays polluted by sewage. It is not large, 10-20cm overall length. It feeds on detritus.