lecture 5 10/27 (NEMATODA AND ANTHROPODA)

What are the two major and incredibly diverse animal groups explored in the lecture?

Nematodes (roundworms) and Arthropods (insects, crustaceans, spiders, etc.).

What were Trilobites, and when did they go extinct?

Trilobites were fascinating extinct marine arthropods, with approximately 20,000 described species. They went extinct around 250 million years ago during the Permian-Triassic extinction event.

What is the approximate age of the specific trilobite fossils found near I-35 and Keystone Lake, Oklahoma?

Approximately 300 million years, placing them in the Carboniferous period.

What is the common characteristic of Nematodes and Arthropods that provides protection and structural support?

A tough, flexible, yet rigid outer layer called a cuticle, which is non-cellular and secreted by the epidermis.

Explain the process of 'Ecdysis'.

Ecdysis, or molting, is the process of shedding the old, rigid cuticle to allow for an increase in body size, as the cuticle does not grow with the animal. This is a metabolically demanding and vulnerable stage.

What is the primary polysaccharide that forms the structural component of the cuticle layer in both nematodes and arthropods?

Chitin, which is highly resistant to degradation and contributes to the strength and durability of the exoskeleton.

What is the common name for Nematodes, and what is their estimated diversity?

Nematodes are commonly known as Roundworms. Approximately 30,000 recognized species have been described, but this is considered a small fraction of their actual diversity, with estimates ranging into the millions of undescribed species.

Describe the general lifestyle of Nematodes.

Nematodes exhibit both parasitic (obligate parasites extracting nutrients from hosts like plants, insects, vertebrates, and invertebrates) and free-living lifestyles (thriving independently in soil, sediments, and aquatic habitats, playing crucial roles in decomposition and nutrient cycling).

Why is *C. elegans* a significant model organism in research?

*C. elegans* is a widely studied free-living nematode used in developmental biology, genetics, and neuroscience due to its simplicity, rapid life cycle, transparent body, and invariant cell lineage (approximately 1000 somatic cells), which makes its development precisely traceable.

Describe the life cycle and transmission of *Trichinella* (causing Trichinosis).

Adult *Trichinella* worms reside in the mucosal lining of the small intestine of carnivorous mammals. Females produce live larvae that migrate through the bloodstream and lymphatic system into muscle tissues, where they encyst. Humans contract trichinosis by consuming undercooked or raw flesh (commonly pork, bear, rat, or other game meats) containing these infective cysts.

Explain the life cycle and transmission of *Dirofilaria immitis* (Heartworm).

Heartworm primarily affects canids, with adult worms residing in the pulmonary arteries and right ventricle of the heart. Microscopic larval stages (microfilariae) circulate in the bloodstream of infected hosts. A mosquito ingests these microfilariae during a blood meal, where they develop into an infective stage within the mosquito. The mosquito then transmits these infective larvae to a new host during another blood meal.

List the four main characteristics of Arthropods.

1. Jointed appendages,

2. Segmented bodies (often grouped into tagmata like head, thorax, abdomen),

3. A rigid chitinous exoskeleton, and

4. They are coelomate animals.

What percentage of all described animal species are Arthropods?

Arthropods comprise an astonishing 80 ext{%} of all described animal species.

Name the five major subdivisions of Arthropods.

Trilobites (extinct),

Cheliceriforms (spiders, scorpions),

Myriapods (centipedes, millipedes),

Crustaceans (crabs, lobsters), and

Hexapods (insects).

What distinct feature do Cheliceriformes possess, and what is their typical body structure?

Cheliceriformes possess chelicerae, specialized fang-like or pincer-like mouthparts. Their body is typically divided into two main tagmata: the cephalothorax (prosoma, a fused head and thorax region) and the abdomen (opisthosoma).

How do millipedes and centipedes differ in terms of leg count per segment and diet?

Millipedes (Class Diplopoda) have two pairs of legs per body segment and are detritivores (feeding on decaying plant matter). Centipedes (Class Chilopoda) have one pair of legs per body segment and are predatory carnivores, possessing venomous fangs (forcipules).

What is the characteristic body plan of Hexapods (Insects)?

A distinct body plan characterized by a clear head, thorax (bearing three pairs of legs and typically one or two pairs of wings in adults), and abdomen.

What are 'Instars' in insect development?

Instars are the developmental stages between each molt (ecdysis). Insects undergo a series of instars, growing larger with each shedding of the cuticle as they progress towards maturity.

Define 'Holometabolous Development' (complete metamorphosis) in insects.

Holometabolous development is a developmental pathway that includes distinct larval stages that are morphologically and ecologically very different from the adult (e.g., egg { o} larva (caterpillar) { o} pupa (chrysalis) { o} adult). This allows larvae and adults to exploit different resources and avoid competition.

List a few vital ecosystem services provided by arthropods.

Arthropods are vital for food webs (as primary consumers, decomposers, and food sources), provide crucial pollination services for over 80 ext{%} of flowering plants, contribute to soil aeration, and engage in pest control.

What is the estimated global economic value of pollination services provided by insects annually?

Up to 300 billion dollars annually.

Name an arthropod that serves as a foundational scientific model and its research applications.

*Drosophila melanogaster* (the common fruit fly) serves as a foundational model in genetic research, developmental biology, neuroscience, and toxicology due to its rapid life cycle, ease of breeding, and well-understood genome.

How is 'Forensic Entomology' utilized?

Forensic entomology is the study of insect colonization of remains, used in criminal investigations to provide crucial information, particularly in estimating the Post Mortem Interval (PMI) or time of death, based on insect species composition, developmental stages, and ecological succession patterns.

Provide two examples of invasive arthropod species and their negative impacts.

Examples include the Japanese beetle (*Popillia japonica*), which causes extensive damage to lawns, gardens, and agricultural crops, and the Argentine fire ant (*Linepithema humile*), which displaces native species, disrupts ecosystems, and inflicts painful stings.

In the context of diseases, what is a 'vector,' and give examples of diseases transmitted by arthropod vectors.

Arthropods act as vectors by transmitting a wide array of pathogens. Examples include nematode diseases (e.g., filariasis transmitted by mosquitoes), viruses (e.g., West Nile virus, dengue, Zika transmitted by mosquitoes), bacteria (e.g., Lyme disease by ticks, plague by fleas), and protozoa (e.g., malaria by mosquitoes, Chagas disease by kissing bugs).

Explain the difference between 'Head and Thorax' and 'Cephalothorax' in arthropod anatomy.

In Hexapods (insects), the body is clearly segmented into three distinct regions: the head and the thorax. The 'Cephalothorax' is a fused head and thorax region (prosoma) found in Cheliceriformes (e.g., spiders, scorpions) and Crustaceans (e.g., crabs, lobsters), combining sensory, feeding, and locomotory functions.

What is the role of the 'Abdomen' in arthropod anatomy?

The Abdomen is the posterior body region (opisthosoma) in insects and other arthropod groups (like Cheliceriformes and Crustaceans), housing organs for digestion and reproduction.