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Arthropods

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by

Katherine Degar

on 9 April 2014

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Transcript of Arthropods

Phylum Arthropoda
Basic Info
Largest Phylum (75% of all animals)
About 1 million known species
"arthro" = joint
"pod" = leg or foot
Ex: Lobsters, shrimp, crabs, sea spiders, insects, spiders, etc.
Subphylum Crustacea
"The Crustaceans"
Small Crustaceans
large, very diverse group including shrimp, crab and lobster
Contains the following Classes: Branchiopoda, Remipedia, Cephalocarida, Maxillopoda, Ostracoda, Malacostraca
largest group of arthropods with approx. 35,000 species
specialized for water with gills
exoskeleton is hardened by CaCO3
appendages are specialized for swimming, crawling, attaching to other animals, and feeding
have 2 pair of antennae to sense surroundings
body is divided into head and trunk areas
head usually has 2 sets of antennae and 3 pairs of feeding appendages
maxillipeds, mandible, and maxillae
trunk is further divided into the thorax and abdomen
gills are located where legs attach to thorax
groups include the copepods, amphipods, isopods, decapods, etc
Decapods: the larger crustaceans
Lobster and Shrimp
Small Crustaceans
Everywhere in the ocean; the "bugs" of the sea
Decapods: The larger crustaceans
Crabs
Body Structure
segmented
bilaterally symmetrical
2 major parts:
Cephalothorax-head and chest
Abdomen
Appendages are jointed; mouthparts too
Joints allow for faster walking, swimming,
handling of food and gathering sensory
info
Have an exoskeleton called the cuticle made of chitin, proteins and waxes
Chitin-Carbohydrate secreted by underlying tissue: very tough and NON-living
These animals molt (periodic shedding) because exoskeleton is so rigid it can't grow
Molting:
Underlying tissues secrete new exoskeleton
when new is ready, old splits
arthropod takes in lots of water and air to stretch the new exoskeleton before it hardens (growing room)
Occurs less as organisms gets older
lost limbs usually regenerate thru process of molting
Locomotion:
Muscles are attached to exoskeleton
Locomotion varies:
Sessile (non-moving), ex: barnacles
Crawlers, ex: crabs
Swimmers, ex: copepods
Circulatory System and Gas Exchange:
Open system with a dorsal heart
Absorbs nutrients
No veins, capillaries or arteries (just vessels)
Organs are bathed in blood
O2 and CO2 exchange occurs in sinuses
O2 is carried by hemocyanin (not hemoglobin)
Endocrine System:
Possess an advanced endocrine system
Secretes hormones that control molting,
color change, food storage and sexual
development
Undergoes metamorphosis
Larva-->intermediate form-->adult
Nervous System:
Double ventral nerve cord w/ well developed brain
Have acute sense of smell; very sensitive to chemicals in the water
Have compound eyes and antenna; very advanced sensory organs
Eyes consist of 14,000 light sensitive units grouped in a mosaic
Have statocysts (a balance sensory receptor)
Digestive System:
One way tract (mouth to anus)
Many are parasitic
Vary in feed methods (chewing vs. filter feeders)
Some have maxillipeds (appendages close to mouth)
Stomach has chitonous teeth or ridges for grinding
Stomach has bristles for sifting
Stomach is 2-chambered and connected to digest glands that secrete digestive enzymes and absorb nutrients
Reproductive System:
Dioecious
Males usually have special appendages to transfer sperm to females to fertilize eggs
Respiratory System:
Aquatic Arthropods possess gills
Terrestrial Arthropods possess trachae and book lungs
Copepods (Class Maxillopoda)
Abundant and important
use mouthparts to filter/capture food
many are planktonic; use large antennae to stay afloat
Many are parasitc
very simple creatures
ex: Cyclops
Barnacles (Class Maxillopoda)
Filter feeders
Usually sessile--may attach to other animals
some are fouling (attach to ships) organisms
Look like mollusks (made of calcareous plates) and little volcanoes
Top plates open like windows to let filtering appendages out
Some are parasitic
usually hermaphroditic
larva are free swimming; adults cement self to something with the strongest adhesive known
Has all structures of an arthropod as an adult; just inverted and modified
Can close plates for protection
Amphipods (Class Malacostraca)
Body compressed from side to side
Most are <2cm; head and tail curve down
5 pairs of legs on thorax for walking; 3 pairs on abdomen for swimming
Appendages are specialized for function
5000+ species
some jump, some crawl, some burrow in skin, some are planktonic
Isopods (Class Malacostraca)
About same size as amphipods
Flat from top to bottom; all legs are similar to each other (iso=equal)
Ex: roly polies; similar to many in water
Marine example--fish lice
Breathe w/ gills, stay in moist places
Krill (Class Malacostraca)
Planktonic; shrimp-like
Up to 6 cm
Have a carapace (shield-like structure that covers the anterior portion)
Most are filter feeders
Lots in polar waters
Eaten by whales, penguins, humans, fish
Blue whales eat 4 TONS a day
Front legs are used to catch food
Approximately 10,000 species
Class Malacostraca
Largest crustaceans in size
Prized as food
Have 5 pairs of walking legs
1st pair are very heavy w/ pincers to obtain food/defend themselves
Have a well-developed carapace that encloses the cephalothorax
American Lobster (Homarus americanus)
Before 1800s so common at low tide could be caught with bare hands; now are scarce due to commercial lobstering
are solitary and aggressive
may be cannibalistic if confined in a trap too long
walk along the bottom waving antenna
migrate every fall; walk in a single file line maintaining contact w/ antenna, groups of ~60 lobsters march about 30 miles
Swim by flipping tail forward to propel them backwards
Scavenge at night
One claw is to crush, the other to rip
Molt 25 times in 5 years, some live to be 100!
Male impregnates a newly molted female
sperm is stored in female's body until spawning
during spawning eggs flow from opening in female over the sperm and attach to her swimmerets (appendages used for swimming)
Eggs are aerated/protected for 9-12 months before hatching
Shrimp (Penaeus)
Edible shrimp are caught commercially off SE coast
Burrow during the day using pleopods (swimmerets)
Usually are crawling around on the bottom but may swim
Some are carnivorous; others eat plankton and detritus
Very thin exoskeleton
Have special appendages near mouth to create a water current over gills
Have a long spine called a "rostrum" extending from the front of the carapace
Stay in deeper water in the fall in order to spawn
Each clutch (mass of eggs) contains about 1 million but about 80% of those are eaten by fish, jellyfish, etc
Juvenile shrimp return to estuaries to feed and grow
Reach adulthood in 4-6 months w/ about 15 molts. Usually live about 1 year
Shrimp are worth more per pound than any other seafood caught by US fishermen!
Horseshoe Crab (Limulus polyphemus)
350 million years old (sometimes called a living fossil)
Only surviving member of the subphylum Chelicerata, class Merostomata
Not a real crab; more closely related to the spider (so not a true crustacean)
Lives in shallow water on Atlantic and Gulf Coasts
Carapace is horseshoe shaped and encloses a body w/ 5 pairs of legs
1st-4th-->for walking
5th--> ends w/ a flap to push crab along sand
Tail acts like a rudder, not a weapon
2 large compound eyes and 2 simple eyes (used to see only light and dark)
Last pair of legs contains long claw-like appendages to clean gills
Gills are called book gills
Feeds on mollusks, worms, and detritus
Are the main diet of juvenile loggerhead turtles
Live to be about 20 years old
Don't mate until 9 years old
Male is smaller than female
Female digs a hole in the sand and deposits up to 88,000 pale green eggs. Male fertilizes them as they are deposited.
Uses:
Lobster bait
Lysate (an extract from their blood) used in cancer research and as an indicator of spinal meningitis
Illegal to fish these in SC unless for research or pharmaceutical purposes
Hermit Crabs
Outside of shell, they look like a lobster
Has a soft abdomen making it vulnerable to predators
Lives in vacant shells for protection
Shell is often 5x larger than body
1st pair of legs--> claws
2nd and 3rd pair-->walking
4th and 5th pair--> helps keep hermit in shell
In spring, larger male drags around female waiting for her to shed her shell, then he deposits sperm in her abdomen
Mantis Shrimp
Technically not a shrimp
Have eyes that have 16 different types of photoreceptors (we have 3)
Move like other shrimp/lobsters
Have distinct appendages used to smash or spear their prey
These appendages move FAST! about 23 meters per second (that's the speed of a bullet)
Fiddler Crab (Uca)
Burrows intertidally in sand and mud beaches from Cape Cod to Texas
Males have one greatly enlarged claw
Burrow holes very close together for mating purposes
Have a courtship ritual of claw-walking and rapping to attract females to burrows
Ghost Crab (Ocypoda)
At night (w/ flashlight), see crabs vanish right before your eyes (they are fast and camouflage well)--> "ghost"
360 vision but not up so they have to hide from birds
Have to go back to water to get O2 by water washing over gills
Also return to water to lay eggs
Spider Crabs
Not pretty!
Can't swim, stay on mud bottoms but will sometimes ride the backs of jellyfish (wooo!!!)
Can reach 12 feet (biggest crab species)
Sea Spiders (Class Pycnogonida)
Have 4+ pairs of jointed legs stretching from a small body
Very slow crawlers
Have camoflaging coloration
Feeds on hydroids, sponges, soft corals
Use their chelicera to tear off pieces of prey and suck up tissues with proboscis
Male fertilizes eggs as they are deposited from female
Male gathers them onto his legs until they hatch
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