Arthropod Anatomy and Physiology

Body Segmentation and Exoskeleton

Arthropods possess a segmented body covered by a hard exoskeleton made of chitin, which provides protection and structural support. The exoskeleton is divided into regions with specialized functions.

• Tergum: The dorsal (upper) part of a segment.

• Sternum: The ventral (lower) part of a segment.

• Pleuron: The lateral (side) part of a segment.

• Articulating membrane: Flexible regions that allow movement between segments.

Open Circulatory System

Arthropods, such as grasshoppers, have an open circulatory system in which blood (hemolymph) is not confined entirely to vessels.

• Tubular heart: Pumps hemolymph through the body cavity (hemocoel).

• Ostia: Openings in the heart that allow hemolymph to enter.

• Distribution vessels: Carry hemolymph to tissues.

• Collecting vessels: Return hemolymph to the heart.

Respiratory System: Tracheal Tubes

Insects breathe through a network of tracheal tubes that deliver oxygen directly to tissues.

• Spiracles: Openings on the body surface for air intake.

• Tracheae: Tubes that branch throughout the body.

• Tracheoles: Fine branches that reach individual cells.

Digestive and Excretory Systems

Insects have specialized organs for digestion and excretion.

• Crop: Storage organ for food.

• Malpighian tubules: Excretory organs that remove wastes from hemolymph and help conserve water.

• Midgut: Site of digestion and absorption.

• Hindgut: Reabsorbs water and forms feces.

Head and Mouthparts

Arthropod head structures are adapted for feeding and sensory functions.

• Compound eye: Provides a wide field of vision.

• Antennae: Sensory organs for touch and smell.

• Mandible, maxilla, labrum, labium, hypopharynx: Mouthparts specialized for biting, chewing, or sucking.

Other Arthropod Groups

• Chelicerates: Includes spiders and scorpions, characterized by chelicerae (mouthparts) and pedipalps.

• Crustaceans: Includes lobsters, with specialized appendages for feeding and movement.

Mollusk Anatomy and Physiology

General Body Plan

Mollusks are soft-bodied animals, often protected by a hard shell. Their body plan includes a mantle, foot, and visceral mass.

• Mantle: Secretes the shell and forms a cavity for respiration and excretion.

• Foot: Muscular structure for movement.

• Visceral mass: Contains internal organs.

• Shell: Provides protection.

Digestive System

Mollusks have a complete digestive tract with specialized organs.

• Mouth: Entry point for food.

• Digestive gland: Secretes enzymes for digestion.

• Gut: Absorbs nutrients.

• Anus: Expels waste.

Respiratory System

Mollusks use gills for gas exchange, located in the mantle cavity.

• Gill: Extracts oxygen from water.

• Mantle cavity: Houses the gills.

• Incurrent and excurrent siphons: Direct water flow through the mantle cavity.

Reproductive System

Mollusks have gonads for producing gametes.

• Gonad: Organ that produces eggs or sperm.

Comparative Anatomy of Mollusk Groups

Mollusks are classified into several groups based on their anatomy.

• Bivalves: Have two shells and filter-feed using gills.

• Gastropods: Have a single shell and a distinct head.

• Cephalopods: Have a reduced or absent shell and highly developed nervous system.

• Chitons: Have multiple shell plates and a broad foot.

Radula: Feeding Structure

The radula is a toothed, chitinous ribbon used by mollusks to scrape or cut food.

• Odontophore: Supporting structure for the radula.

Summary Table: Comparison of Arthropod and Mollusk Organ Systems

Example: Grasshoppers use tracheal tubes for respiration and Malpighian tubules for excretion, while bivalve mollusks use gills for respiration and nephridia for excretion. Additional info: These notes cover the structure and function of major organ systems in arthropods and mollusks, relevant to introductory biology topics such as animal diversity, organ systems, and comparative anatomy.