Sunday, August 28, 2005

Basic Facts

Basic Facts

Two pill bugs next to each other--one extended and the other half way into a ball.

The pill bug is a small, segmented land creature that can roll into a tiny ball for protection. The pill bug is NOT an insect, but is an isopod or another type of arthropod.

Arthropods are the most numerous animals on Earth. They are a phylum of invertebrate animals that have an exoskeleton, a segmented body, and jointed legs; they do not have a backbone. Arthropods are cold-blooded. In other words, their body temperature depends on the temperature of their environment.

Pill bugs are also crustaceans which are a group of animals that have a hard exoskeleton, jointed legs, and a segmented body that is bilaterally symmetrical. Crustaceans include crabs, lobsters, crayfish, and shrimp. They have two pairs of sensory antennae, one pair of mandibles or lower jaw bones for chewing food, and two pairs of maxillae or upper jaw bones which help the mandibles in positioning the food.



Diagram of pill bug anatomy.
Pill bugs are usually a quarter to a half inch long (0.7 to 1.5 cm) and are covered with a hard exoskeleton or cuticle made of chitin.

Identifying Features--Appearance or Morphology

  • Three body parts: head, thorax, abdomen
  • One prominent pair of antennae and one inconspicuous--hidden or not readily noticeable--pair
  • Simple eyes
  • Seven pairs of legs
  • Seven separate segments on thorax
  • Paired appendages at end of abdomen called uropods
  • Color varies from dark gray to white with or without pattern

Some Characteristics of Crustaceans

  • A hard exoskeleton made of calcium--no internal skeleton.
  • The head has two compound eyes, two pairs of antennae, and three pairs of mouthparts.
  • It has a pair of green glands excrete wastes near the base of antennae.
  • The abdominal segments have swimmerets--swimming legs
  • The sexes are separate. Eggs are attached to the swimmerets (swimming legs) of the female. The first pair is enlarged in the male--it is used to pass sperm to the female.
  • The tail is fan-shaped, and ends in uropods and a telson.
  • The circulatory system is open; there is no heart and the "blood" is pumped by vessels into sinuses, and does not flow in a closed loop.
  • The nervous system consists of a primitive ventral nerve cord and ganglia system--similar to those of an earthworm.