Monday, April 2, 2007


Arthropods respire in many different ways, utilizing everything from the unique tracheal system of some terrestrial arthropods, to gills of aquatic arthropods. The tracheal system is unique to some terrestrial arthropods, and involves air entering the system through a small opening called spiracles. These lead to a system of tubes, called tracheae. These branch out further to become tracheoles, through which the air passes, then gets to individual or small groups of cells inside the body. There is a wide area provided by these cells for respiratory exchange.


Since there are so many different ways of feeding in the phylum Arthropoda, there are also many various digestive systems. Therefore, we will look at only one, the digestive tract of the grasshopper. The order that food passes through the grasshopper includes: the mouth, the esophagus, which conveys food from the pharynx to the crop, a stomach of sorts. Next to the true stomach, then the intestine, which leads to the rectum, then to the anus. Other arthropods have different digestive systems, according to their method of feeding, and body structure.


The phylum Arthropoda makes up 80% of Kingdom Anamalia, and is very diverse. This corresponds to their rather varied feeding habits. There are some Arthropods who feed in every way. Ways in which they feed include scavenging, filter feeding, deposit feeding, suspension feeding, hunting prey, eating some varieties of plants, and some arthropods are even parasitic. Arthropods have several different mouth structures as well, including the grasshopper’s mouth, which is better adapted for cutting and chewing then the mosquito’s, which is better adapted for piercing skin and sucking blood (in the case of the female). A butterfly’s mouthparts are useful for sucking nectar through a long tube, and a bee has mouthparts used for chewing and gathering nectar. Honeybees also use their legs to store pollen while out gathering.

Grasshopper Dissection

The internal view of a grasshopper.

A grasshopper's jumping leg.

External view of a grasshopper.

Sunday, April 1, 2007

Comparisons To Other Phyla

There are many distinguishing features that separate the arthropods from any other phylum. The word “arthropod” comes from two Greek words, arthros, meaning jointed, and pods, meaning feet. The members of this phylum are easily recognizable because of their jointed appendages.

All arthropods have a distinct head, which is sometimes merged with the thorax to form a large structure called the cephalothorax. The cephalothorax contains all mouthparts, including the antennae and the thoracic appendages, and is covered by a protective exoskeleton called a carapace. The cephalothorax is easily the most distinguishing feature of the arthropod phylum.


Most arthropods have a well-developed nervous system, containing a pair of ganglia and two long nerves down the esophagus, connecting the brain to a nerve cord that runs along the ventral part of the body. The ganglia serve as the main communication centers which coordinate the movement of the legs and the wings. There are several ganglia for each major body part.

Arthropods also contain simple sense organs such as statocysts and chemical receptors. Compound eyes are one of their main sensory organs, holding a myriad of separate lenses which can detect colour and movement extremely well, as well as ultraviolet light, which is invisible to humans.

Both crustaceans and insects have a well-developed sense of taste, smell, movement, and hearing. Taste receptors are located on their mouthparts, antennae and legs, while sensory hairs are situated all across the body. Insect ears are often found in unusual places, such as the eardrums of a grasshopper, which are located behind the legs.


An ant queen
  • males produce sperm
  • females produce eggs
  • fertilization occurs in the female body
  • In spiders and some crustaceans...
    --->male deposits a packet of sperm and the female picks it up
  • Most insects and crustaceans...
    --->male uses a special reproductive organ to deposit sperm inside female
  • Some insects form colonies
    --->they have reproductive females called queens
    --->they lay eggs
    --->usually only have 1 queen (which is usually the largest compared to the rest)


  • undigested food becomes solid waste
  • it leaves the anus of the animal
  • Terrestrial arthropods remove nitrogen-containing wastes by...
    --->using a set of Malpighian tubules
    --->found in the body sinuses
    --->remove waste from blood, concentrate them, and then add undigested food allowing it to leave through anus
    --->may have small excretory glands at bases of legs
  • Aquatic arthropods remove nitrogen-containing wastes by...
    --->through a pair of green glands found by base of antennae
    --->eliminated through a pair of opening on the head

Internal Transport

  • have well-developed heart
  • open circulatory system: blood not always within vessels
  • In spiders and some insects...
    --->heart is long and narrow which stretches along abdomen
  • In lobsters and crayfish...
    --->blood pumps through arteries and go into smaller vessels
    --->enters tissues and then leaves vessels into sinuses (spaces in tissue)
    --->the blood is found in a cavity around heart where it re-enters heart through openings


Movement in arthropods is achieved by muscles attached inside the skeleton, which coordinates with their nervous system. The muscles work by generating force through contradicting, then transferring that force to their exoskeleton. At each body joint, muscles are either positioned to flex the joint or extend it. The pull of muscles against the exoskeleton allows the arthropod to function accordingly, whether it is by beating their wings, flexing their legs, or thumping their flippers.

Monday, February 5, 2007

General Info

Arthropods can be considered as the most successful phylum of Kingdom Animalia. They have been on the Earth since 600 million years ago. They are found on the terrestrial land, underwater, and even in the air. Arthropods are also known as animals with jointed appendages. Arthro- means joint; -pod means foot. They very diverse and abundant because vary in size, shape,and habits.

They have three important features:

1. A tough exoskeleton:
  • made of chitin
  • can be leathery and flexible (ie:insects) or hard (ie:crabs)
  • provides protection, structure and prevents desecation
  • many are waterproof
  • cannot grow as the animal grows
  • allows movement only at joints

2. A series of jointed appendages:

  • primitive arthropods (ie:trilobites)= each segment has 1 pair
  • as body segments are lost, so are appendages
  • modify into antennae, claws, wing, flippers, etc.

3. A segmented body:

  • some have many (ie: millipede)
  • due to evolution, some have little (ie:crabs)

Arthropods are divided into 4 subphylums:


  • the oldest of arthropods
  • lived in the sea
  • extinct =(


3 scorpions

  • lack sensory "feelers"
  • body divided into:
    1. cephalothroax (anterior end)
    --------->contains brain, eyes, mouth, mouthparts, and esophagus
    2. abdomen (posterior end)
    --------->contains most internal organs
  • has 2 pairs of appendages by mouth as mouthparts:
    --->1st pair called chelicerae
    --->2nd pair called pedipalps
  • ie: spiders, ticks, scorpions


A shrimp
  • have stony exoskeleton usually made of calcium carbonate (limestone)
  • 1st two pairs of appendages = antennae ("feelers")
    --->contains sensory hairs
    --->used as sense organs or filter feeding
    --->water fleas use them for movement (to push through water)
  • 3rd pair of appendages = mandibles (mouthparts)
    --->many are short and heavy: used for biting and grinding food
    --->some are bristly: used for filter feeding, finding food, picking up ditrius
    --->some are needle-like: suck blood from host
  • body parts are:
    --->head, thorax, and abdomen
    --->cephalothorax (fusion of head and thorax); covered by tough shell called carapace
  • ie: Crabs, shrimp, barnacles


A grasshopper

  • largest subpylum of arthropods
  • have 1 pair of antennae and appendages
  • ie: centipedes, millipedes, and insects
  • Centipedes
    --->carnivores (eat earthworms, toads, mice, etc.)
    --->have a pair of poison claws on head
    --->North American can be 3-6 cm long; Tropical can be up to 26 cm long
    --->have 15-170 pairs of legs
    --->1 pair of leg per segment except last 3 segments (which has no legs)
  • Millipedes
    --->2 pairs of legs per segment
    --->live in damp places such as decaying logs
    --->eat dead/decaying plant material
    --->for protection, they roll into a ball
    --->some can give off a disgusting odour
  • Insects
    --->have 3 body parts: head, thorax, and abdomen
    --->3 pairs of legs attached to thorax
    --->has 1 pair of antennae
    --->has 1 pair of compound eyes
    --->2 pairs of wings found on thorax
    --->uses tracheal tubes for respiration