Bio Lab: Chap 30 Review

Ecdysozoans

Overview of Ecdysozoans

Ecdysozoans are a major group within the animal kingdom characterized by their ability to molt their exoskeleton through a process called ecdysis. This group includes several phyla, but two of the most studied are Phylum Nematoda (roundworms) and Phylum Arthropoda (arthropods).

• Ecdysozoa: A superphylum of protostome animals, including those that molt their cuticle.

• Ecdysis: The process of shedding or molting the outer cuticle or exoskeleton to allow for growth.

Phylum Nematoda (Roundworms)

External Anatomy and Sexual Dimorphism

Roundworms are unsegmented, cylindrical worms with a tough outer cuticle. They are found in diverse habitats and can be free-living or parasitic.

• External Structures: Includes the cuticle, mouth, and anus. The cuticle provides protection and must be shed during growth (ecdysis).

• Sexual Dimorphism: Males are typically smaller and have a curved posterior end, while females are larger and have a straight posterior end.

Example: Ascaris lumbricoides is a common parasitic roundworm in humans.

Phylum Arthropoda

General Features

Arthropods are the largest animal phylum, characterized by segmented bodies, jointed appendages, and a chitinous exoskeleton. They undergo ecdysis to grow.

• Subphyla Studied: Myriapoda (centipedes and millipedes), Crustacea (crabs, crayfish, etc.), Hexapoda (insects).

Animal Comparison Chart

The comparison chart for major animal groups typically includes features such as body symmetry, segmentation, presence of a coelom, and type of development. (Additional info: Table not provided; see below for inferred summary.)

Phylum	Body Plan	Segmentation	Exoskeleton	Molting
Nematoda	Unsegmented, cylindrical	No	Cuticle	Yes
Arthropoda	Segmented	Yes	Chitinous exoskeleton	Yes

Additional info: Table inferred from standard biology texts.

Subphylum Myriapoda (Centipedes and Millipedes)

Comparison of Centipedes and Millipedes

• Centipedes: One pair of legs per body segment; carnivorous; flattened bodies.

• Millipedes: Two pairs of legs per body segment; detritivorous; cylindrical bodies.

Example: Scolopendra (centipede), Diplopoda (millipede).

Subphylum Crustacea (Crabs, Shrimp, Lobster, Crayfish, etc.)

External Anatomy of Crayfish

• Cephalothorax: Fused head and thorax region.

• Abdomen: Posterior body region, segmented.

• Antenna and Antennule: Sensory appendages.

• Rostrum: Forward extension of the carapace between the eyes.

• Compound Eye and Eyestalk: Visual organs.

• Maxillipeds: Appendages for manipulating food.

• Cheliped: Large claw-bearing leg for defense and feeding.

• Carapace: Hard protective covering over the cephalothorax.

• Tergum: Dorsal segment of the exoskeleton.

• Telson and Uropod: Tail structures used for swimming.

• Anus: Terminal opening of the digestive tract.

• Swimmerets: Appendages on the abdomen for swimming and, in females, carrying eggs.

• Walking Legs: Used for locomotion.

• Sexual Dimorphism: Males and females can be distinguished by the shape and size of swimmerets and the presence of gonopores.

Internal Anatomy of Crayfish

• Green Gland: Excretory organ, removes waste from the blood.

• Gills: Respiratory organs for gas exchange.

• Stomach: Digestive organ, often divided into cardiac and pyloric regions.

• Digestive Gland: Secretes digestive enzymes and absorbs nutrients.

• Heart: Pumps hemolymph through the open circulatory system.

• Ostium: Openings in the heart for hemolymph to enter.

Subphylum Hexapoda (Insects)

Grasshopper Metamorphosis

• Grasshoppers undergo incomplete metamorphosis (hemimetabolous development), where juveniles (nymphs) resemble adults but lack fully developed wings and reproductive organs.

External Anatomy of Grasshopper

• Head: Contains sensory organs and mouthparts.

• Thorax: Bears legs and wings.

• Abdomen: Contains digestive and reproductive organs.

• Compound Eye: For vision.

• Antenna: Sensory structure for touch and smell.

• Fore Wing and Hind Wing: Used for flight; forewings are leathery, hindwings are membranous.

• Tympanic Membrane (Tympanum): Hearing organ located on the abdomen.

• Spiracles: Openings for gas exchange along the sides of the abdomen.

• Sexual Dimorphism: Females have an ovipositor for laying eggs; males lack this structure.

Internal Anatomy of Grasshopper

• Crop: Stores food before digestion.

• Gastric Ceca: Secrete digestive enzymes and increase surface area for absorption.

• Stomach: Main site of digestion.

• Malpighian Tubules: Excretory organs that remove waste from the hemolymph.

• Intestine: Absorbs nutrients.

• Rectum: Reabsorbs water and forms feces.

• Hearts: Multiple chambers pump hemolymph.

• Trachea: Network of tubes for gas exchange.

Summary Table: Key Features of Ecdysozoan Groups

Group	Body Segmentation	Legs per Segment	Respiratory System	Excretory System
Nematoda	No	None	Diffusion	Renette cells
Centipedes (Myriapoda)	Yes	1 pair	Tracheae	Malpighian tubules
Millipedes (Myriapoda)	Yes	2 pairs	Tracheae	Malpighian tubules
Crustacea	Yes	Varies	Gills	Green glands
Hexapoda (Insects)	Yes	3 pairs (thorax)	Tracheae	Malpighian tubules

Additional info: Table inferred from standard biology references for clarity and completeness.