Arthropods Continued

Question 1

Common features of Arthropods

Answer 1

• Bilaterally symmetrical body
• segments that have become fused into function groups (tagma)
• One of these tagma always includes a head

Question 2

Cephalothorax

Answer 2

A fused head and thorax (found in arachnids)

Question 3

Exoskeleton

Answer 3

Body covered by a cuticle - a tough, lightweight exoskeleton made of protein and chitin - which is secreted by the epidermal cells.

To permit movement, the exoskeleton has joints and hinges where the cuticle is soft and flexible.

In marine species the exoskeleton is strengthened by calcium carbonate, while in terrestrial species it is topped by a thin layer of waterproof wax to prevent them from drying out.

Question 4

Class: Pycnogonida (Sea Spiders)

Answer 4

Maine arthropods with a small segmented body and long, slender legs that give them superficial resemblance to terrestrial spiders.

All species have a small head and 3 trunk segments.

Question 5

Class: Merostomata (Horseshoe Crabs)

Answer 5

Large marine arthropods that are survivors of a diverse group that flourished in the seas 300 million years ago.

They have a fused head and thorax and 6 pairs of limbs, which are covered by a tough carapace.

Question 6

Class: Arachnida

Answer 6

• Largely terrestrial arthropods

• Have a cephalothorax, which is joined to the abdomen, in some species by a narrow stalk

• In Scorpions, the abdomen has a tail-like extension bearing a sting

• The cephalothorax carries a pair of pincer like chelicerae used for consuming prey, a pair of limb like pedipalps, and 4 pairs of normal walking legs

• Mostly predatory, although a few are scavengers and some mites are parasitic.

• They have narrow mouths and cannot eat large pieces of food, so they rely on enzymes to pre digest their prey outside the body or in a preoral cavity.

Includes Spiders, scorpions, harvestmen, ticks, mites, pseudo scorpions, whip-scorpions, and whip-spiders.

Question 7

Class: Crustacea

Answer 7

•They have 2 pairs of antennae, compound eye stalks, and a cuticle that is often strengthen with calcium carbonate.

• The head and thorax are often covered by a shield like shell or carapace, which extends forward to firm a projection called a rostrum

•The thoracic limbs are 2-branched and specialized to carry out a range of functions, such as feeding, locomotion, sensing the environment, and respirations by means of basal gills

•The 1st pair of legs may be enlarged to form chelipeds with strong claws for food handling, defense, and signaling

•The vast majority of species live in freshwater or the sea

Range from tiny copepods - barely visible to the naked eye- to heavy-bodied crabs and lobsters

Question 8

Superclass: Myriapoda (Centipedes and Millipedes)

Answer 8

• Terrestrial arthropods with biting mandibles and a single pair of antennae.

• They are confined to moist habitats because they do not have a waterproof cuticle.

• Centipedes are fast moving and carnivorous with elongated, slightly flattened bodies. The trunk segments each bear a single pair of legs, the 1st pair modified as poison claws used to subdue prey.

• Millipedes are mostly herbivorous or scavenging species with elongated, cylindrical or flattened bodies. The 1st 3 segments of the trunk have no legs, but the remaining segments are fused in pairs known as diplosegments, each bearing 2 pairs of legs.

Question 9

Internal Systems of Arthropods Include?

Answer 9

• Open Circulatory System - Internal organs are bathed in a fluid known as hemolymph, which is moved to the front of the animal by a dorsal, tubelike heart.

• Gaseous exchange is carried out by means of gills, leaflike book lungs, or a branching system of minute, air-filled tubes called tracheae.

• The Central Nervous System consists of a brain situated in the head, connected to paired nerve cords running along the underside of the body.

Question 10

Class: Insecta

Answer 10

• Mainly terrestrial, there are a significant number of aquatic species

• The body of an insect is divided into 3 main sections - the head, thorax, and abdomen

• The head bears the external mouthparts, 1 pair of antennae, and a pair of compound eyes

• The thorax bears 3 pairs of legs and, typically, 2 pairs of wings

• The abdomen contains the major organ systems for digestion and reproduction.

• The immature stages of some aquatic species have gills, but all adult insects breathe air and have a well-developed tracheae system joined to the outside through a number of small holes called spiracles

• They are the only invertebrates capable of powered flight and this, together with their small size and waterproof cuticle, has allowed them to colonize a vast range of habitats

• The most abundant animals on Earth