Arthropoda
 

General

  • Etymology - from the greek name from its distinctive jointed appendages, Arthron "joint" and Pous "Foot" or "Leg"
  • Over 1,000,000,134,000 species identified, found world-wide
  • Aquatic species includes Lobsters, Crabs, Hermit Crabs, Crayfish, Shrimps and Barnacles
  • Non aquatic species include Insects, Spiders, Scorpions 
  • Thought to have originated from Annelids

Defining Characteristics

  • Protostomes, develops mouth before anus
  • Most possess a straight gut with an anus, body cavity has a true coelom
  • Bilaterally symmetry (mostly)
  • Two main body types in the aquatic realm: shrimp like and crab like
  • Body is divided into 2 or 3 sections
  • Has distinctive jointed appendages, may be modified in a number of ways to form antennae, mouthparts and reproductive organ
  • Do have a nervous system including a brain and ganglia
  • Do possess a respiratory system in the form of trachea and spiracles (mostly)
  • Do possess a open or lacunar circulatory system with a simple heart, on or more arteries, and no veins (mostly) 

Body    

  • Body possess an external skeleton (mostly), Stiff cuticle, usually a hard outer. Body covering made of chitin and proteins, form an exoskeleton which may or may not be stiffened further with calcium carbonate, like jointed armour.
  • Segmented bodies with various patterns of segmented fusion (tagmosis) to form integrated units (heads and abdomen)
  • Body possesses 3 – 400+ pairs of jointed legs 

Reproduction / Life Cycle

  • Sexual Reproduction: Most common, with separate sexes and internal fertilization, although aquatic species can use external fertilization.
  • Asexual Reproduction: Some can reproduce via parthenogenesis, where unfertilized eggs develop (e.g., honey bee drones).
  • Sperm Transfer: Can involve direct transfer or indirect methods like spermatophores (sperm packets).

Life Cycles & Development Types

Complete Metamorphosis (Holometaboly): Four distinct stages with radical changes. Stages: Egg → Larva (e.g., caterpillar, maggot) → Pupa (inactive transformation stage) → Adult.

Examples: Butterflies, beetles, flies.

Incomplete Metamorphosis (Hemimetaboly): Three stages with gradual changes. Stages: Egg → Nymph (looks like small adult, lacks wings/sex organs) → Adult.

Examples: Grasshoppers, true bugs, cockroaches.

Direct Development: No larval stage; young resemble miniature adults.

Examples: Spiders, some crustaceans.

Key Processes

  • Molting: Shedding the exoskeleton to grow, a crucial part of development.
  • Metamorphosis: The transformation from larva to adult, allowing different stages to exploit different resources.
  • Can take up to 12 stages to metamorphose into adult
  • Normally sexual, involving capulation and gonochoristic


Feeding

Feed on everything

 

Victorian Species

Scientific Name:         Pallenella ambigua   

Common Name:         Sea Spider

 

Scientific Name:         Nymphon sp. 

Common Name:         Sea Spider

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