اللافقاريات مقابل الفقاريات

Invertebrates vs. Vertebrates

• Vertebrates possess a backbone (vertebral column), while invertebrates do not.
• Circulatory systems can be open (invertebrates) or closed (vertebrates).
• Blood colors vary; invertebrates often have colorless or white blood, whereas vertebrates typically have red blood.
• Ventral nerve chords are characteristic of invertebrates.
• Digestion and reproduction methods differ significantly between the two groups.

Phylum Arthropoda

• The largest animal phylum, comprising approximately 78% of known animals.
• Inhabit diverse environments: soil, air, water, plants, and animals.
• The only invertebrate phylum with winged forms.

Importance of Arthropods

• Beneficial:*

• Food source (prawns, crabs, honeybees, silkworms).

• Natural compounds with therapeutic or cosmetic uses.

• Harmful:*

• Damage to wood, ships (barnacles).

• Crop, fruit tree, and stored grain pests.

• Disease vectors (insects).

• Stinging/poisonous arthropods (scorpions, spiders).

Characteristics of Phylum Arthropoda

• Body Symmetry: Bilateral symmetry.
• Tissue Layers: Triploblastic (three germ layers).
• Body Cavity: Coelomate (true body cavity).
• Body Segmentation: Metameric segmentation (head, thorax, abdomen).
• Appendages: Paired, jointed appendages (limbs).
• Exoskeleton: Chitinous exoskeleton for protection, rigidity, muscle attachment, and water retention.
  • Composed of three layers:
    • Epicuticle (thin, protein/lipid).
    • Exocuticle (narrow, chitin/pigments).
    • Endocuticle (thick, chitin/lime salts).
• Habitat: Diverse, including land, water, and soil.
• Muscular System: Well-developed, segmentally arranged muscles.
• Circulatory System: Open circulatory system with a dorsal heart, arteries, and blood sinuses (no veins). White blood.
• Digestive System: Complete digestive tract (mouth to anus) with distinct regions (foregut, midgut, hindgut).
• Respiration: Varies depending on environment (general body surface, gills, tracheae, book lungs).
• Excretion: Green glands, coxal glands, or Malpighian tubules.
• Nervous System: Well-developed central nervous system with sensory organs (compound eyes, antennae).
• Reproduction: Separate sexes, paired gonads and gonoducts, usually internal fertilization, larval stages often involved, often showing sexual dimorphism.

Subphylum Trilobita

• Flourished in the Cambrian period.
• Extinct for about 200 million years.
• Body divided into three longitudinal lobes.

Subphylum Crustacea

• Primarily aquatic.
• Some terrestrial forms (e.g., woodlice).
• Possess mandibles and antennae.
• Respiration via gills or integument.
• Body divided into two parts.

Subphylum Chelicerata

• Includes horseshoe crabs, scorpions, spiders.
• Aquatic and terrestrial forms.
• Predatory or parasitic.
• Body divided into:
  • Prosoma ("cephalothorax"): Simple eyes, chelicerae, pedipalps, walking legs (4 pairs).
  • Opisthosoma ("abdomen"): Limbless, sometimes with telson.
• Respiration: Book lungs (terrestrial) or gills (aquatic).
• Excretion: Malpighian tubules or coxal glands (or both).
• Horseshoe crabs are considered living fossils (unchanged for ~500 million years).
• Blood contains a copper-based compound (Limulus Amebocyte Lysate, LAL) used in medical equipment and drug sterility tests.

Subphylum Uniramia

• Includes insects, centipedes, and millipedes.
• Aquatic and terrestrial forms
• Insects: 3 pairs of legs.
• Centipedes and millipedes: Many legs.
• Respiration: Tracheae.

Penaeus japonicas (Example Species)

• Habitat: Marine, sandy/muddy bottoms.
• Nocturnal and omnivorous.
• Color change (reddish-gray to orange).
• Autotomy (self-amputation).