Page 295 - (DK) Ocean - The Definitive Visual Guide

ARTHROPODS 293

SUBPHYLUM CHELICERATA SUBPHYLUM CHELICERATA the other five are for walking and for HUMAN IMPACT
grasping and tearing food. Five pairs
Giant Sea Spider American of flattened abdominal appendages are MEDICAL
used for swimming and scuttling along
Horseshoe Crab RESEARCH
Colossendeis australis the bottom and also carry pagelike
LENGTH 10 in ( 25 cm) “book gills,” through which oxygen is
Limulus polyphemus
(leg-span) absorbed. Its long, rigid tail is used for If the American Horseshoe Crab
LENGTH Up to 24 in is injured, some of its blood cells
WEIGHT Not recorded steering and for righting itself. Hinged
(60 cm) form a clot, which kills harmful
HABITAT Bottom to the body, it can act as a lever.
dweller WEIGHT Up to 11 lb (5 kg) The reproductive cycle is closely negative bacteria. In order to
HABITAT Sandy or linked to spring high tides, when adults exploit this property for human
muddy bays to 100 ft
DISTRIBUTION Antarctic shelf and slope gather in large numbers on sandy benefit, crabs are collected from
(30 m)
beaches to breed. Females lay up to shallow waters on the Atlantic
Unlike most sea spiders, which have DISTRIBUTION Western Atlantic and Gulf Coast from 80,000 eggs in a depression near the coast of North America during
southern Maine to the Yucatán Peninsula
a leg-span of less than 1 in (2.5 cm), high-tide mark, providing a vital food the summer months. Researchers
the giant sea spider has a huge source for birds and other marine then remove about 20 percent
leg-span of about 10 in (25 cm). It Despite its name, the American creatures. The eggs are laid in batches of the blood from each crab.
has a large proboscis through which horseshoe crab is more closely related mostly when the moon is in its full From this they extract a protein
it sucks its food, but its body is so to spiders than to crabs. It is mainly or new phases. that is used to detect bacterial
small that the sex organs and parts active at night and scavenges anything The eggs hatch into tailless contamination in drugs and
of its digestive system are situated in it can find, including small worms, “trilobite larvae,” so called because medical devices that will be
the tops of the legs. Sea spiders are bivalves, and algae. Its horseshoe- they look a bit like fossil trilobites. in contact with blood. Taking
somewhat unusual among arthropods shaped, greenish-brown outer shell, or Carried down the shore at high tide, blood from the crabs is sometimes
in that some exhibit parental care, the carapace, is for protection, and adults the larvae swim around actively but fatal to them but most recover
males having a modified pair of legs have few predators. It has six pairs of also burrow into the sediment for after they have been returned
to carry the eggs until they hatch. thoracic appendages: the first pair safety. After a few days, they molt to the sea.
(called chelicerae), is used for feeding; and become juveniles.

SUBPHYLUM CRUSTACEA
Water Flea

Evadne nordmanni
LENGTH 1 / 32 in (1 mm)
WEIGHT Not recorded
HABITAT Open waters,
to depths of 6,500 ft
(2,000 m)
DISTRIBUTION Temperate and cool waters worldwide
Most water fleas live in freshwater
but this species and just a few others
live as plankton in the ocean. It
feeds on tiny bacteria, protists, and
organic debris and is eaten by larger
planktonic animals. It has a single
conspicuous eye and feathery
swimming appendages that are
modified antennae. Females brood
unfertilised eggs that hatch into
more females. Sexual reproduction
also occurs.

large eye

feathery
swimming
appendage OCEAN LIFE