Nematoda and Arthropoda in Depth Notes

Key Characteristics
- All bilaterally symmetrical
- All protostomes
- Have an outer covering called a cuticle
Nematode Cuticle
- Tough, leathery, flexible layer of tissue
- Allows for growth by molting
Arthropod Cuticle
- Rigid, jointed exoskeleton
- Must be shed periodically to allow for growth
Ecdysis
- Process of molting the cuticle
- Importance of molting:
- It limits growth and rapid growth follows molting

General Characteristics
- Non-segmented worms (roundworms)
- Shed cuticle for growth
- Contains chitin in cuticle and egg cases
- Most numerous multicellular organisms on Earth
- 20,000 identified species, estimated ~1 million species exist
- Separate sexes, many species microscopic and can be free-living or parasitic
Soil Nematodes
- Feed on soil microbes, some are plant parasites
- Each teaspoon of soil contains approximately 50 to 500 nematodes

Ascaris Overview
- Example of a human-infecting nematode
- Common in tropical regions, causes malnutrition, coughing, and poor health
- Females can produce up to 200,000 eggs daily
- Eggs remain viable in soil for months and infect humans via uncooked veggies, contaminated fingers, or fecal matter
Life Cycle of Ascaris
1. Eggs are ingested and hatch in the intestines.
2. Larvae travel via bloodstream to heart and lungs.
3. Mature larvae reach trachea, are swallowed, and reach intestines.
4. Larvae mature to adults and reproduce.
5. Eggs expelled in feces.

Trichinella spiralis
- Causes trichinosis, transmitted in undercooked pork
Filarial Worms
- Live in dog hearts (heartworms)
- Can reside in human lymphatic vessels, causing serious conditions like elephantiasis
Pinworms
- Most common parasitic roundworm in humans
- Affect significant numbers of children & adults across the globe

General Characteristics
- Large group of protostomes with exoskeletons and jointed appendages
- Most successful group among animals (includes insects, crustaceans, spiders, etc.)
Success Factors
- Exoskeleton
- Body segmentation and specialization
- Well-developed nervous system
- Variety of respiratory systems
- Life cycle includes metamorphosis

Rigid, jointed exoskeleton primarily made of chitin
Functions:
- Protection, muscle attachment, locomotion
- Prevents desiccation and microbial infection

Segments typically fused into a head, thorax, and abdomen
Each segment has a pair of jointed appendages adapted for various functions (locomotion, gathering food, defense, reproduction)

Comprises a brain and ventral nerve cord
Head has sensory organs; multiple types enhance interaction with the environment

Different systems for aquatic (gills) and terrestrial arthropods (book lungs, tracheae, and spiracles)

Significant changes occur between larval and adult forms
Reduces competition for resources
- Complete Metamorphosis: Distinct life stages
- Incomplete Metamorphosis: Gradual changes

Characteristics
- Hard exoskeleton with calcium carbonate
- Fused head and thorax (cephalothorax)
Types
- Decapods: lobsters, crabs, shrimp
- Copepods and krill: microscopic, herbivorous in oceans

Centipedes:
- Active predators with one pair of legs per body segment
- Possess venomous jaw-like appendages
Millipedes:
- Decomposers with two pairs of legs per body segment

Structure
- Divided into head, thorax, and abdomen
Functions
- Head: sensory organs and brain
- Thorax: legs and possibly wings
- Abdomen: reproductive structures and internal organs
Locomotion and Adaptations
- Wings improve survival through various functions (escaping, mating)

Extensive abilities (compound eyes, chemoreception) aid in environmental interaction

Includes spiders, ticks, and scorpions
Characterized by a fused head and thorax, with specific appendages for feeding/defense

Scorpions:
- Nocturnal, modified appendages for predation
- Potentially harmful venomous sting