By Dr J Floor Anthoni (2007)
Amongst the intertidal rocky shore crustaceans
we find crabs, shrimps and barnacles. The shrimps like to live in the water,
some crabs can live out of the water and barnacles can live out of the
water for long periods of time. Because of this, barnacles are amongst
the most prolific creatures on the intertidal rocky shore.
Crustaceans Crustaceans belong to the Arthropods who
have external skeletons and jointed legs. The Arthropods include
ants, bees, spiders, scorpions but also many marine creatures like shrimps,
lobsters, crayfish, barnacles, sea lice and many more. Unlike land Arthropods,
crustaceans have gills and two pairs of antennae. Because crustaceans live
inside a box (their external skeleton), they are unable to grow unless
they escape from the box first. This they do by moulting. The box is split
between chest and tail and the animal extracts itself from its feelers,
eyes, legs, gills and tail. A cast moult looks every bit like the original
shrimps, lobsters and crayfish These have five pairs of legs and two pairs of feelers.
Underneath their tails they have another five pairs of swimming legs or
swimmerettes. Females use these to hold their eggs with.
f013929: the common shrimp (Palaemon affinis) or rockpool
shrimp [tarawera] is a most amazing native species as it swims gracefully
forward and backward using its pleopods (swimmerettes). Females
hold their eggs between these swimming legs. This shrimp has 4 little nippers
and 4 long antennas that give it advance warning of any attack. Although
the common shrimp is found in rock pools, it is much more common in sheltered
f050433: the painted prawn (Alope spinifrons) does
not swim around but crawls in between quick backward bursts of speed. The
patterns on its body seem dull brown but they consist of bright blue and
red colours. It usually lives in small groups underneath boulders.
0609164: small snapping shrimps, perhaps Alpheus novaezealandiae,
[kowhitiwhiti moana] a native species. Snapping shrimps have one big claw
with which they make loud snapping sounds.
f003505: although the red rocklobster (Jasus edwardsii)
[koura moana] or crayfish is seldom found in the intertidal, its external
skeleton or moult is often washed up into a rockpool. The crayfish shown
here is 'empty' as the animal has left its moult to grow a bigger one.
Inbetween the foliage of seaweeds lives a well camouflaged
small weed prawn (Hippolyte bifidirostris) with tiny blue specks
(35mm), and the larger chameleon prawn (Hippolyte multicolorata)
(60mm) which changes colour at will or according to what it eats.
Valvifera The infra order Valvifera consists of millipede
looking crustaceans with ten body plates and 8 pairs of legs.
Idotea stricta: a tubular shaped 'stick insect'
or sea centipede [weri moana], brown to green in colour often found on
Barnacles Barnacles begin their lives as a shrimp-like creature
which settles down in a suitable place. It then cements its head to the
rock and begins catching prey and cementing a huge limestone skeleton of
four or six plates. Miraculously it is able to grow this house bigger and
bigger. Barnacles close their houses with a hatch consisting of two or
The four intertidal barnacle species: 1. column barnacle
columna, 2. brown barnacle Chamaesipho brunnea, 3. modest
or sheet or beaked barnacle Austrominius modestus, was (Elminius
modestus), 4. plicate barnacle Epopella plicata (Elminius plicatus).
The brown barnacle lives highest up the shore, followed by the columnar
barnacle, plicate barnacles and sheet (modest) barnacles.
A barnacle is a crustacean, living upside down in a house
of 4 or 6 plates in such a way that it can grow these plates bigger. Instead
of having legs for walking, its legs have adapted to catching plankton,
as they are studded with bristles. It has long catching legs and shorter
ones to sweep these clean.
The Chamaesipho barnacles have 6 column plates
whereas the Elimius barnacles have 4. Below the intertidal more
kinds of barnacle ar found, including the large Balanus species.
f009514: the sheet barnacle, beaked barnacle or modest barnacle
(Elminius modestus)(Austrominius modestus) [tio piripiri]
can cover the rock in a dense sheet of adjoining individuals, no larger
than 5mm. Here the sheet of barnacles has almost encapsulated a snakeskin
0608217: the brown surf barnacle (Chamaesipho brunnea)
is usually found intermixed with the sheet barnacle in loose formations.
Its lid consists of four parts, separated by one straight line and a wobbly
one, as if it is smiling. the sides of the column widen towards where it
0612059: closeup of the sheet barnacle Elminius/Austrominius
modestus, also called the beaked barnacle. Short with a wide base.
0612060: closeup of the sheet barnacle Elminius modestus.
The four plates of its column can now be seen. Also blue-banded periwinkles
0608218: in the columnar barnacle (Chamaesipho columna)
the lid is seated deeper inside the column, while its sides do not widen
much towards its base. Also the 'smily' line is less pronounced than in
the brown barnacle, and is simpler while also more erratic in shape. Columnar
barnacles often fuse tightly together. In this photo the columnar barnacles
are surrounded by flea mussels and sheet barnacles.
f009622: the plicate barnacle (Epopella plicata) likes
more shelter than the previous barnacles. It has a folded (plicated) column
with four outer plates and is very sharp on top. Coastal NZ, not found
on outer islands.
the large pink barnacle (Balanus decorus) [tiotio]
(40mm tall) has alternate pink and white plates. It lives in deeper water
and is widely spread.
f048927: the flat barnacle (Tetraclitella purpurascens)
is found only submerged. It tapers widely towards its base and its opening
is very small and triangular; its trapdoor is similarly shaped. This barnacle
can indeed be very flat at times.
f048932: this conical submerged barnacle (Aaptolasma nolearia?)
has its hairy legs out, catching plankton. The fan of legs moves like a
hand, clutching imaginary particles, then withdrawing the hand momentarily.
Where the current is fierce, the hairy hand is just stretched out and pulled
Goose barnacles [werewere] are occasionally found on the
rocky shore. They prefer to live submerged. Some are found attached to
flotsam. There are many species but all have a flexible stalk and a barnacle-shaped
animal on top. Some have long stalks, others short. Some allow themselves
to be grown over by other species, becoming unrecognisable in the process.
Calantica spinosa [werewere tukaha] is a 40mm
gooseneck barnacle with small embedded spines in its stalk.
Calantica villosa isa 40mm gooseneck barnacle
with small spindle-shaped scales and plates that may have a felt-like texture.
deep-sea stalked barnacle (Smilium zancleanum)
[werewere huna] found only in deep water such as on telephony cables.
eared stalked barnacle or whale barnacle (Conchoderma
auritum) [maungunga ika moana] found on humpack whales.
striped stalked barnacle (Conchoderma virgatum)
[maungaunga] found only on bottoms of ships and flotsam but sometimes attached
to the bodies of fish.
Crabs Crabs are crustaceans with flattened bodies and legs
adapted for scurrying sideways, sometimes at high speed. As they grow,
they shed their exoskeletons, which can often be found in rock pools.
f015513: the moult of a purple shore crab (Leptograpsus
variegatus) [papaka nui]. Although formidably strong and fast, the
purple shore crab scuttles away often long before being seen. It lives
mainly out of the water in rock cracks, foraging at the low tide by night.
Its legs are flattened and it has equally sized nippers.
f219109: the smooth shore crab (Leptograpsus/Cyclograpsus
lavauxi) is found high above high tide, near the land vegetation line.
It lives in moist and cool places. Only 2cm wide, this crab looks a polished
smooth grey or brown, speckled or marbled, with light coloured nippers.
It is shy and difficult to catch. The one shown here lives in a rotten
wharf beam. 28mm carapace.
f033505: the red rock crab (Plagusia/Gainusia chabrus,
P. capense) [papaka ura] lives entirely under water although it may
come out to forage on seaweeds that are out of the water. Its skin is covered
in fine hairs. It is mainly a plant eater but also scavenges.
f050408: a young red rock crab is brown. These animals grow
very fast, to adult size within one year.
f032507: the blackfinger crab (Ozius truncatus) is
quite formidable but placid and can easily be handled. It lives near the
high tide level under boulders, but is not found in the South Island.
It can grow old often feeding on black neritas.
f032427: the bighand crab (Heterozius rotundifrons)
or pebble crab, looks very much like a pebble, as it also keeps entirely
still when discovered and handled. Its right-hand claw is larger and in
males very much larger.
f033306: a mature male blue pebble crab (Heterozius rotundifrons)
found in a mangrove forest.
05062222: the pie-crust crab (Metacarcinus novaezelandiae)
[ngahorohoro] is active mainly by night. It is a large but docile crab
that can easily be handled. It is found mainly in the South Island. Juveniles
appear mottled grey-green. The frontal margin of its carapace is crimped
like a pie crust.
f050405: the common rock crab or black marbled crab (Hemigrapsus
edwardsii) [rerere] normally has a smooth skin, but this one was fouled
by algae. Its main colour is purple, with beige patches.
f050407: the same crab as shown on left.
f018935: a young female triangle crab (Eurynolambrus australis).
Young crabs are not yet brightly coloured, and females always have small
nippers. Triangle crabs can live only fully submerged, and they are found
f050520: a male triangle crab has much larger nippers than
the female and its tail is much thinner too, as in all crab species.
f050518: a mature male triangle crab (Eurynolambrus australis)
f018834: the NZ bristle crab (Pilumnus novaezelandiae)
[papaka] or hairy crab.
f050321: a hairy crab (Pilumnus lumpinus) [papaka
huruhuru] (up to 5cm) found under stones at low tide. Its back is covered
in dense, short, greyish brownish hairs.
Half crabs Half crabs deserve their name from the fact that they
miss a pair of legs. In many a rudimentary pair can be seen. Half crabs
have large claws even though the main source of their food is zooplankton
and detritus. They catch these fine particles with a pair of mandibles
equipped with a fine sieve. By waving these sieves through the water, within
the protection of their big nippers, they catch their food.
f018605: a mature porcelain crab (Petrolisthes elongatus)
[kawekawe] beginning to show its bright porcelain blue colours. These crabs
miss one pair of walking legs. They feed by sieving plankton from the water.
They can still swim by flapping their tails. Young porcelain crabs are
grey to brown. They can live out of the water for some time.
f018919: several species of half crab exist, like this tiny
purple one (Petrolisthes novaezelandiae?).
Spider crabs Spider crabs are not flattened like the 'ordinary' crabs,
but they have more rounded pear-shaped bodies. Instead of walking sideways,
they walk forward. The most common and endeared spider crabs of the rocky
shore are the camouflage or decorator crabs or masking crabs. They decorate
their backs with snipped-off fragments of local seaweeds, in order to blend
in with their environment. For seaweeds to stay alive, they must see the
sunlight, and for this reason camouflage crabs are often found in the open
where they can easily be stepped on.
f032309: hairy decorator crab (Notomithrax ursus)
or hairy seaweed crab is small with fine nippers. It is a precious find
and can easily be handled.
f032311: frontal view of the hairy seaweed crab shows how
well it is camouflaged.
the lesser seaweed crab (Notomithrax minor) is the
smallest of the three found in the intertidal.
f039232: the Peron's seaweed crab (Notomithrax peroni)
[papaka huna] is much larger than the lesser seaweed crab and has much
larger nippers too, particularly the males. It is much less common in the
intertidal zone as it prefers to live in calmer waters.
Pillbox crabs are usually found on the sand and mudflats
but may also be encountered under stones on the rocky shore.
Halicarcinus cookii (13mm) [waerau] has an angular
carapace with variable colour from yellow/green to orange and black. Legs
are commonly banded and smooth.
Halicarcinus innominatus [waerau] (19mm) has an oval
carapace and long forelegs. It is usually brown with patterns that extend
onto its smooth legs. Common with the greenlipped mussel
Halicarcinus varius [waerau] (10mm) has a pear-shaped
carapace, its upper half covered in small hairs. Males have hairy nippers.
Its colour varies from white/green to yellow. found in sheltered areas
on brown seaweeds or under stones.
Hermit crabs Hermit crabs have coiled tails that are thin-shelled
and vulnerable. They have adapted to living inside coiled shells of snails.
When they grow they have to leave their shell, shed their moult and find
a bigger shell which they plan with care.
f050437: a young NZ hermit crab (Pagurus novizelandiae)
[papaka moke, kaunga] is almost entirely white.
f037015:a mature NZ hermit crab (Pagurus novizelandiae)
[papaka moke, kaunga] has blue nippers with rows of tubercles, and smooth
f039509: the plankton hermit (Paguristes setosus)
has fine long hairs on its antennas, with which it catches plankton. It
does so by waving them left and right, and then 'licking' them with its
hairy mandibles. It also feeds from detritus by stirring the sand and catching
dislodged particles with its antennas.
f018925: orange hermit crab (Diacanthurus spinulimanus?)
with bristly legs and blocked antennas is usually found in deeper water.
It is not very common.