Page 296 - (DK) Ocean - The Definitive Visual Guide

294 ANIMAL LIFE

SUBPHYLUM CRUSTACEA SUBPHYLUM CRUSTACEA
Cyclopoid Copepod Gooseneck Barnacle

Oithona similis Pollicipes polymerus
LENGTH LENGTH
3
1 / 54– / 32 in (0.5–2.5 mm)
Up to 3 in (8 cm)
HABITAT HABITAT
Surface waters to a Intertidal zone of rocky
depth of 500 ft (150 m) shores
DISTRIBUTION Atlantic, Mediterranean, Southern DISTRIBUTION Eastern Pacific coast of North
Ocean, southern Indian and Pacific oceans America, from Canada to Baja California, Mexico

Copepods make up a large percentage So called because of its resemblance
of zooplankton, and this is one of the to a goose neck and head, the
most abundant, widespread species. gooseneck barnacle forms dense
As the name suggests, cyclopoid colonies in crevices on rocky shores
copepods have a single, central eye, with strong waves. Barnacles anchor
which is light sensitive. They have a themselves to rocks by a tough,
tiny, oval body that tapers to a thin flexible stalk (peduncle), which also
tail. Most have six body segments contains the gonads. This is actually
and six pairs of swimming limbs. their “head” end. Once the barnacle has
Tiny food particles are filtered from attached itself to an object it secretes
the water using specialised mouthparts. a series of pale plates at the end of
Females can be recognized when its stalk, forming a shell around its
carrying egg sacs attached to featherlike legs, which comb through
their abdomens. the water for food. The legs face away
As part of the zooplankton, from the sea, enabling the barnacle to
copepods of this genus are a vital feed by filtering out particles of detritus
element of oceanic food chains. They from returning tidal water as it funnels
feed on marine algae and bacteria and past them through cracks in the rocks.
in turn are an important source of These barnacles become sexually
protein for many ocean-dwelling mature at about five years of age and
animals. Every night cyclopoid may live for up to 20 years. The larval
copepods migrate from a depth of stage is free-living but depends on sea
about 500 ft (150 m) to the surface currents for its transport and survival.
layers of the ocean to feed. This daily Colonies of gooseneck barnacle are
journey, which is undertaken by many susceptible to the damaging effects of
marine creatures, is one of the largest oil pollution and they recover only
mass movements of animals on Earth. slowly from disturbance.

Like all adult barnacles, the adult at the top of the cone open, allowing
SUBPHYLUM CRUSTACEA PEOPLE
acorn barnacle remains fixed in one the acorn barnacle to feed. It does this
Acorn Barnacle place once it has anchored itself to a when the tide is in by waving its CHARLES DARWIN
site. The free-swimming juveniles pass modified legs, called cirri, in the water
through several larval stages before
Semibalanus balanoides to filter out food. When the tide is Before the British naturalist
LENGTH molting into a form that can detect out, the plates are closed to prevent Charles Darwin (1809–1882)
1
Up to / 2 in (1.5 cm) both other acorn barnacles and the barnacle from drying out. Acorn proposed his revolutionary theory
diameter suitable anchoring sites. Once a larva barnacles are hermaphrodites that
HABITAT fixes itself to a rock, using cement possess both male and female sexual of evolution in The Origin of
Intertidal zone of rocky Species (1859), he spent eight years
shores produced by glands in its antennae, it organs, but they function as either a studying barnacles. Realizing the
molts again. It then secretes six gray male or a female. They do not shed impact his ideas on evolution
DISTRIBUTION Northwest and northeast Atlantic, calcareous plates, forming a protective their eggs and sperm into the water; would have on existing scientific
Pacific coast of North America cone that looks rather like a miniature instead they use extendable penises, to and religious thinking, he delayed
volcano. Four smaller, movable plates transfer sperm to receptive neighbors. writing and instead produced
four monographs on the
classification and biology
of barnacles. This work earned
him the Royal
Society’s Royal
Medal in 1853,
validating his
reputation as
a biologist.

OCEAN LIFE