Page 292 - (DK) Ocean - The Definitive Visual Guide

290 ANIMAL LIFE

Arthropods

THE ANIMALS THAT HAVE ACHIEVED the greatest diversity on
DOMAIN Eucarya
Earth are the arthropods, of which insects are by far the most
KINGDOM Animalia
numerous. However, most marine arthropods are crustaceans,
PHYLUM Arthropoda
such as crabs, shrimp, and barnacles. Crustaceans, including
SUBPHYLA 4
both adults and larval stages, form most of the ocean’s
SPECIES About 1.25 million
zooplankton—the community of tiny, drifting life forms
that support all oceanic food chains. Like land arthropods, all marine forms have
an external skeleton, segmented body, and jointed appendages, permitting some,
such as robber crabs, to live on land as well as in water. Fully marine insects are
rare but some live on seashores and coasts.

Anatomy APPENDAGES
This spotted cleaner
Although arthropods may look very different from shrimp has jointed
walking appendages.
one another, they all have an external skeleton
Two furthers pairs of
(exoskeleton), which is either thin and flexible or rigid jointed appendages,
and toughened by deposits of calcium carbonate. The which are located on
body is segmented and has a variable number of jointed its head, are modified
into sensory antennae.
appendages—some are used for walking and swimming,
while others are modified into claws and antennae or adapted
for feeding. Muscles are attached across the joints to facilitate SPIDER FEATURES
Although it is called a crab
movement. Most of the body cavity is hollow; this space, called the and has a hinged carapace,
SEASHORE INSECTS hemocoel, contains the internal organs and a fluid—hemolymph—that this horseshoe crab is a
Springtails are wingless relatives of true close relative of spiders,
insects. Marine species can be found in the is the equivalent to vertebrate blood, which is pumped around the body ticks, and mites. Like
upper regions of seashores and will spring by the heart in an open circulatory system. Most marine forms use gills them, it has piercing
into the air if disturbed. for respiration and have well-developed sense organs. mouthparts.

digestive sensory merus dactylus
heart gland stomach antenna

carpus
eye claw propodus
ischium
coxa
basis
swimmeret
forward and backward
nerve walking movement
tail fan cluster appendage point of
(telson) attachment movements up
(ganglion)
to body and down
ARTHROPOD ANATOMY ARTHROPOD LIMB
Lobsters have a protective shell carapace covering the Walking appendages, such as this crab’s leg, comprise rigid
head and thorax, large pincers, and well-developed walking sections linked with movable joints. The joints move in
appendages. The hemocoel contains the internal organs. different planes, allowing versatile movement.
FILTER-FEEDING LIMBS Feeding
At high tide, barnacles feed by
extending their long, feathery Among crustaceans, feeding is extremely varied.
appendages from their “shell”
and sweeping the water for Many crabs are scavengers that feed on dead and
plankton and detritus. decaying organic matter. They are therefore vital in
helping to recycle nutrients. Others are hunters and
have robust claws to stun (mantis shrimp) or crush
(lobsters) their prey before tearing it apart and
consuming it. Many small planktonic crustaceans,
such as copepods, are filter feeders that make effective
use of various appendages, including long antennae,
to create water currents that waft food particles toward their mouths.
Barnacles, which are attached to rocks and unable to move, feed in a
OCEAN LIFE SCAVENGING IN THE SAND parasitic (some isopods, copepods, and the barnacle Sacculina) and obtain HARD SKELETON AND JOINTED LIMBS
similar way, using their limbs to collect plankton. A few crustaceans are
all their nourishment from their host. The shoreline is an ideal place for
These tiny porcelain crabs, less than 1 in
(2.5 cm) wide, are filter feeders. They
insects, such as kelp flies, that feed by releasing enzymes onto rotting
have typical arthropod features, such
seaweed and then taking in the resultant digested material. Farther
As the tide retreats, this sand bubbler
as a hard exoskeleton covering a
inland, among the dunes, there is more vegetation, so spiders and
crab emerges to feed on the organic
segmented body, and jointed limbs.
pollen- and nectar-feeding insects start to appear.
material contained in the sand.