Phylum Arthropods Overview

Phylum Arthropods

• Arthropods are a diverse group of animals characterized by a segmented body, jointed appendages, and a hard exoskeleton.
• The images illustrate various arthropod types, showcasing their diverse forms and structures.
• Arthropods are classified into various subphyla, including Trilobitomorpha (extinct), Chelicerata, Myriapoda, Crustacea, and Hexapoda.

Classification of Phylum Arthropoda

• Subphylum Chelicerata:
  • Body divided into two regions: prosoma (cephalothorax) and opisthosoma (abdomen).
  • Lack jaws
  • Have six appendages
  • Four pairs of walking legs
  • Includes Arachnida (spiders, ticks, scorpions)
• Subphylum Crustacea:
  • Includes various crustaceans like crabs, shrimps, lobsters.
• Subphylum Hexapoda:
  • Includes insects.
• Subphylum Myriapoda
  • Includes centipedes and millipedes.

Subphylum Chelicerata Details

• Cephalothorax(prosoma): fused head and thorax
• Opisthosoma(abdomen): contains essential organs like digestive, excretory and respiratory
• Sensory, feeding, and locomotion
• Have six appendages
• Lack antennae
• Usually have eyes.
• Most suck liquid food from prey
• Appendages attached to cephalothorax:
  • Pair of chelicerae (pincer-like feeding appendages)
  • Pair of pedipalps (usually sensory or feeding)
  • Four pairs of legs

Class Arachnida

• All arachnids are carnivores, primarily feeding on insects.
• Lack antennae
• Usually have eight simple eyes.
• Use coxal glands and/or Malpighian tubules for excretory functions.
• Possess book lungs for respiration
• Have air intake tubes called trachea, opening through spiracles.
• Dioecious (separate sexes)

Spider Body Parts

• Unlike insects, spiders have two body sections: cephalothorax and abdomen.
• Cephalothorax: fused head and thorax, covered by a hard carapace.
• Simple eyes (usually eight), mouthparts (chelicerae, pedipalps), four pairs of segmented legs.
• Abdomen: contains internal organs like the digestive system, reproductive organs, and respiratory structures(book lungs).
• Spinnerets (silk spinning organs): located on the abdomen, used to produce silk for webs and cocoons.

The Abdomen

• Organ protection:Book lungs, delicate internal organs are protected by covers on the outside of the abdomen.
• Genital opening and sperm or egg release.
• Silk glands: produce fluid protein for silk production.
• Reproductive organs (ovary or testes).

Spinnerets

• Spinnerets are tubular or conical structures.
• Silk is produced in liquid form, and turns to filament when exposed to air.
• Silk is drawn into threads, used for webs and cocoons.

Scorpion Anatomy and Characteristics

• The scorpion body has three sections: prosoma, mesosoma, and metasoma.
• The prosoma has a shell.
• The mesosoma has six segments. The second segment has pectines and the first segment has the genital operculum. The third segment onwards have the stigmata, leading to the book lungs.
• The metasoma has six segments with an anus. The last segment bears the stinging apparatus (telson)
• Scorpions are venomous arthropods.
• They have a segmented body and predaceous carnivores.
• They often hide during the day.
• They feed primarily on insects, spiders, etc.

Scorpion Protection and Feeding

• Scorpions have a venomous sting in their telson(tail).

• Their pincers are used to grasp prey and paralyze them with venom.

• Scorpions are aggressive, and their venom can be lethal to humans.

• Scorpions can camouflage themselves in their habitat.

• They feed mainly on crickets, bugs, and small rodents/lizards.

• Insect vs Spider:

  • Insects have three body sections (head, thorax, abdomen) and six legs.
  • Spiders have two body sections (cephalothorax, abdomen) and eight legs.
  • Spiders do not have wings as Insects do.