•*Arthropods make up the
largest phylum with over a million species. They are jointed legged found in
every habitat. Crustaceans are the dominant class of marine Arthropods such as
lobster, shrimp and barnacles. The bodies are divided into a cephalothorax and
•*The success of
Arthropods is due to their segmentation, and jointed external covering, which
allows for great mobility and strength. Growth is accompanied by shedding or
molting of the exoskeleton because otherwise growth would be impossible and
therefore imposes limitations in terms of size and growth.
•*The success of
crustaceans in the sea is bought about by the gills, walking legs, swimming
legs, and feeding appendages. Water striders and tide pool insects are the
representatives of insecta and the arachnids are the sea spider (Class
Pycnogonida) and horseshoe crabs (Limulus).
•*Now in addition to crabs
and lobsters, crustaceans make up a major component of plankton. Crustaceans bear
5 pairs of appendages, two pairs of antennae, mouth parts. One major line of
crustaceans have evolved with large walking animals. Extensions of the body
wall at the base of the legs are used for gills.
•*The blood contains
hemocyanin, a copper based respiratory pigment like hemoglobin. Sexes are
separate and they develop through a series of larval stages increasing size and
numbers of segments with their associated limbs.
•*The simplest larva stage
is the nauplius larva, with three pairs of appendages.. 1st and 2nd pair of
antennae and mandibles and often swims and suspension feeds (different
functions of appendages in larva than adult.)..larger larva develop from the
nauplius according to the type of crustaceans. Some do bypass the nauplius by
developing within the egg.
•*Small crustaceans are
everywhere, plankton, bottom, among sediments, in and on other animals and
plants. These are the bugs, flies and mosquitoes of the sea.
•*Copepods The class Copepoda
includes minute sea inhabitants which provide a major source of food for fish,
mollusks, crustaceans and other animals as major components of the plankton.
Some are parasitic, infesting invertebrates or vertebrates (fish lice) and the
free living are small and capable of rapid population turnover.
•*The large first antennae
may be used for quick escape but more commonly are act as parachutes against
sinking. They can filter feed on phytoplankton but can't survive on this alone
all year round because of low phytoplankton levels, and sometimes seize large
prey items like other members of the zooplankton.
•Barnacles are sedimentary
marine crustaceans permanently attached to the substratum. For protection barnacles
have carried calcification of the cuticle to an extreme and have a shell
resembling that of a mollusk. The shell is derived from the cuticle of the
barnacle head and enclosed the rest of the body.
•*Class Cirripedia, feed
with six pairs of thoracic legs (cirri) which can protrude though the shell
plates to filter food suspended in the seawater.. They can filter fine
material, including phytoplankton and even bacteria. They are hermaphrodites
and carry out cross fertilization between neighbors.
•*There are 6 nauplius
stages increasing size which swim and filter phytoplankton over a period of a
month or so before giving rise to a non-feeding larva--the cypris larva.
•*This is the sediment
stage of the life cycle , able to drift and swim in the plankton before
choosing a settlement site in response to environmental factor which the larva
detects by an array of sense organs.
•* Barnacles colonize a
variety of substrata including living animals such as crabs, whales turtles,
sea snakes and with this moving host, the barnacle does not need to use energy
in beating its cirri.
•*Beach fleas and other
Amphipods the most familiar being the beach fleas or sand hoppers found on
sandy shores. The Amphipods are mostly marine and scavengers of detritus able
to creep using the thoracic periopods (legs) and swim with the abdominal ones.
•*They can feed by
scraping sand grains or filtering phytoplankton. The head and tail curve
downwards and they commonly are found among debris washed ashore. Whale lice
belong to this group of 5,000 species.
•Isopods are found in many
of the same environments as Amphipods and can be recognized by their flattened
top to bottom form. Fish lice belong to this group.
giant isopod is the largest known member of the isopod family. It is a
carnivorous crustacean that spends its time scavenging the deep ocean floor.
Food is extremely scarce at these great depths, so the isopod has adapted to
eat what ever happens to fall to the ocean floor from above. It will also feed
on some of the small invertebrates that live at these depths.
isopods are known to reach a size of over 16 inches in length and are one of
the largest members of the crustacean family. These animals are very
prehistoric in appearance. When threatened, the can roll themselves into a
tight ball where they are protected by their strong, armor-plated shells.
have complex mouths that contain many components that work together to pierce,
shred, and disembowel live or dead prey. Giant isopods are all over the world
at depths of over 2000 feet.
•The planktonic krill and
decapods (shrimps lobsters, crabs) are classified in the suborder Eucarida.
they have a well developed carapace, fertilized eggs are carried beneath the
•*Krill have primitive
features . All are marine, eggs hatch as nauplii, most have luminescent organs,
usually on the eyes, at the base of the 7th thoracic limbs and underside of the
abdomen. They are probably used for communication in swarming and reproduction.
•*Krill are pelagic and
filter feed when phytoplankton conditions are suitable but otherwise prey on
larger planktonic organisms. Phytoplankton rich seawater enters the tips of the
legs and is strained as it passes between the leg bases.
•Whale krill reach 2 in.
long and dominate the zooplankton of the Antarctic Ocean and is the chief food
of many baleen whales.
•*In decopod, the first 3
pairs of thoracic appendages are adapted as auxiliary mouthparts leaving 5 pairs
of legs (decopods) (and the 1st pair of these can be claws). Decopods have been
divided into swimmers (natantains) and crawlers (reptantains) essentially,
shrimps and prawns ///and lobsters, crayfish and crabs.
•*Now they are divided
morphologically into two sub-orders..shrimplike with many branched gills and
planktonic eggs hatching as nauplius larva (Dendrobranchiata) and Pleocyemata
which have gills lacking secondary branches and eggs carried on pleopods before
hatching as zoeae.
•*Prawns and shrimp have
no exact zoological definition and are interchangeable. The most important
shrimp families are the penaeids and sergestids. The first contain commercial
shrimp. Most pelagic shrimps are active predators feeding on crustaceans of the
zooplankton, such as krill and Copepods.
•*Bottom dwelling species
are scavengers but range from carnivores to herbivores. Sexes are distinct
although some females pass through an earlier male stage
•*Lobsters and freshwater
crayfish ...belong to a group known historically as macrurans (large tails) but
now make up 3 infra-orders , Astacidea (lobsters, freshwater crays, scampi) the
Palinura (spiny and Spanish lobsters and Thalassinidae (mud lobsters and mud
•*Lobsters and freshwater
crays walk on the substratum on the four pairs of back legs. The 1st pair is
modified as a pincer. They are carnivorous scavengers living in holes on rocky
bottoms. The American lobster can reach 2'long (48 lbs) and live for 100 years.
Fresh water crays are omnivorous about 4 inch long.
•*Squat lobsters and
hermit crabs are intermediate between lobsters and crabs. The abdomen is
variable in structure and hermit crabs probably evolved from ancestors that
lived in crevices and eventually specialized into using discarded gastropod
shells. Hermit crabs live as carnivorous scavengers on sea bottoms ranging from
bottom to sea shore and have a terrestrial existence in the tropics.
•*Some crustaceans that
look somewhat like crabs belong to the Anomura. They differ from true
crabs by having at most only three pairs of walking legs instead of four. Some
anomurans are hermit crabs which have a soft coiled abdomen protected by a
snail shell. Most hermit crabs are scavengers on dead plant or animal matter.
•*Hermit crabs are divided
into families partly on which of the two claws is bigger. Other anomurans are
the false crabs, flat and with similar sized chelipeds. The abdomen is a short
flap tucked under the thorax and there are only three pairs of walking legs.
is squat lobster? Technically, it is a Pleuroncodes planipes.
Actually it refers to a whole family of lobster which has many many species.
•The name is will known in Europe as squat
lobsters and are regularly fished and marketed from the North Sea. It is one of
the smallest of commercial lobster species and is perhaps the most abundant.
•These crabs all possess a
reduced abdomen held permanently flexed beneath the cephalothorax The reduction
of the abdomen has brought the center of gravity of the body directly over the
walking legs making locomotion very efficient and rapid. The sideways gait
•* The crab shape is
therefore the ultimate shape in efficient crustacean walking. They live beyond
the top of the shore to the deep sea to the hydrothermal vents 1.6 miles deep
and on the other hand the ghost and fiddler crabs live at the top of sandy and
muddy shores up rivers and into fresh water.
•*Most crabs burrow to
escape their predators descending back-first into the sediment . Some can swim
using the last pair of legs as paddles, run rapidly (ghost crabs) , pea crabs
live in the mantle cavity of bivalves and the female coral gall crabs become
imprisoned by surrounding coral growth with a small opening left for plankton
and the small male for reproduction
•*Most crabs are
scavengers although terrestrial ones can eat plant material.
crustaceans are important as a food source for man and as plankton for the
organisms of the sea. Crayfish--over a million pounds a year are caught and
another 2 million reared artificially.
•*Horseshoe crabs and
Sea Spiders..Chelicerated Arthropods...no jaws, no antennae
with abdominal gills and a long spikelike telson. The class contains Limulus
the horseshoe crab and fossil sea scorpions called eurypterids.
•*This genus appeared 175
million years ago and not undergone any evolutionary change since. It also
occupies a unique place in Arthropods. Like spiders it possesses chelicerae,
claws instead of chewing jaws, lacks antennae and has 6 pair of appendages.
•*Horseshoe crabs or king
crabs have a protective hinged carapace which covers the crab with a long
caudal spine protruding behind. There are compound eyes on the carapace and
median simple eyes. Beneath the carapace lie the chelicerae and 5 pairs of
walking legs (comparable in evolution to the chelicerae, pedipalps and 4pr of
walking legs in spiders.
•*They live on sandy or
muddy bottoms in the sea, plowing their way through the upper surface of the
sediment. During burrowing, the spine levers the body down while the 5th pair
of walking legs acts as shovels.
•*The carapace form helps
move through sand and the spine is used to right itself if it gets turned over.
They are scavenging carnivores and have jawlike extensions on the bases of
their walking legs used to trap and macerate prey such as clams and worms before
it passes to the mouth.
•*The last pair of legs
use the bases to crack open bivalves. The appendages at the rear are modified
and each is expanded into 150 gill lamella resembling leaves of a book and
appendage movement maintains a current over the gills. Small horse shoe crabs
can swim upside down using their gills as paddles.
•* Reproduction occurs at
night when they congregate in intertidal zones, the female laying 2-300 eggs
which get fertilized by the clasping male. Eggs hatch into larva which mature
in 3 years
•500 species about an inch
long...except giant sea spider. The abdomen is reduced to a knob. The
intestines extend into the legs as well as gonads located in legs. Between
palps and 1st pair of legs are an extra set of legs with which the male carries
the eggs. It has 4 eyes near the anterior end of the animal and has no
respiratory or excretory system.
•*Sea Spiders are
exclusively marine found in the intertidal zone and deep sea. They are able to
grip the substratum with their claws and sway from one individual to another
They feed by either sucking up the preys body tissues or cutting of pieces with
their chelicerae and eating them.
•*Colors are usually
white/transparent but red in the deep sea species. Economic importance seems to