Protostomes Lecture Review

Classification of Protostomes
- Divided into two major groups:
- Ecdysozoa: those that molt
- Lophotrochozoa: those that have lophophore or trochophore larvae
Major phyla under each classification:
- Ecdysozoa includes:
- Nematoda
- Arthropoda
- Lophotrochozoa includes:
- Platyhelminthes
- Rotifera
- Mollusca
- Annelida
- Nemertea
- Bryozoa
- Brachiopoda

Ecdysis is the process of molting in certain protostomes.
Hormonal Control:
- Ecdysone: hormone responsible for initiating molting.
- Molt inhibiting hormone: prevents the molting process.
Example:
- Video of a molting cicada (Image by U.S. Forest Service, Bob Rabaglia & Adhi Prayoga/Solent News).

General Characteristics:
- They belong to the Lophotrochozoa and are classified as protostomes and ecdysozoans.
- Related phyla include:
- Micrognathozoa
- Rotifera
- Chaetognatha
- Platyhelminthes
- Cycliophora
- Mollusca
- Annelida
- Bryozoa
- Brachiopoda
- Loricifera
- Nematoda
- Kinorhyncha
- Arthropoda
- Onychophora
- Tardigrada
- Echinodermata
- Chordata
Habitat:
- Most nemerteans are marine; some live in freshwater and humid terrestrial environments.
Anatomy:
- Possess a complete digestive system.
- Have a closed circulatory system.
- Notable feeding structures include:
- Proboscis with a stylet.
- Rhynchocoel: a fluid-filled coelomic cavity important for feeding.

Reproductive Strategies:
- Sexual reproduction: dioecious organisms (separate female and male individuals).
- Asexual reproduction: occurs via fragmentation.
Notable Example:
- Lineus longissimus is reported to be the longest animal known, measuring up to 60 meters in length.

General Information:
- Also known as water bears and found in diverse environments: marine, freshwater, and terrestrial.
- Some species are extremophiles, surviving extreme conditions.
Significant Research:
- Research by Jonsson et al. in 2018 indicates tardigrades can survive and recover from the vacuum of space.
- They serve as model organisms in studies of ecology and genetics.

Characteristics:
- Exhibit bilateral symmetry.
- Body structure is unsegmented and cylindrical.
- Covered by a thick cuticle that is molted.
- Habitat diversity includes marine, freshwater, parasitic, and free-living lifestyles.
Cellular Composition:
- Adults have a fixed number of cells; for example, Caenorhabditis elegans has exactly 959 cells, making it significant in genetic and developmental research.
- Notably, C. elegans with green fluorescent protein (gfp) expressions in their neurons provides insights into neural studies.
Digestive System:
- Consists of a complete digestive tract.
- Stylets: piercing organs located near the mouth utilized for feeding.
- Pharynx: functions to create a sucking action for ingestion.
- Anus: serves as the exit for waste.
Reproduction:
- Dioecious, with distinct male and female individuals.
- Sexual dimorphism: males are generally smaller, equipped with a hooked end for mating.
- Internal fertilization occurs within the species.

Approximately 50 nematode species are known to cause human diseases.
Notable Examples of Parasitic Nematodes:
- Hookworms:
- Commonly found in southern U.S., causing anemia.
- Trichinella:
- Causes trichinosis, forming cysts in muscle tissue, transmitted via consumption of undercooked meat.
Example Illustration:
- Different views of Ascaris (parasitic roundworm).

General Characteristics:
- Arthropoda is the most successful animal phylum, showcasing numerous adaptations:
1. Body segmentation enhances mobility and specialization.
2. A rigid exoskeleton composed of chitin provides protection and structure.
3. Jointed appendages facilitate a wide range of movements and functions.
Examples:
- Scorpion fly and Golden tortoise beetle.

The body may be specialized into tagmata:
- Head, thorax, and abdomen.
- The head and thorax may fuse into a cephalothorax or prosoma.

Coelom: described as degenerate, leading to an open circulatory system.
- Hemocoel: the main body cavity filled with hemolymph (equivalent to blood).
Nervous System:
- Comprises a double chain of segmented ganglia. Most activities are controlled by ventral ganglia.
- Even with the brain removed, arthropods can continue basic functions such as eating, moving, or copulating.
Digestive System:
- Foregut: consists of the pharynx, esophagus, and crop.
- Midgut: includes the stomach, gastric caeca, and Malpighian tubules (for waste excretion and osmoregulation).
- Hindgut: comprises the intestines and rectum.

Aquatic Arthropods: primarily diffuse waste through gills.
Terrestrial Insects and Some Others: employ Malpighian tubules for excretion.
- The process involves:
1. Active transport of salts and uric acid into the tubule lumen from hemolymph.
2. Osmosis brings water into the lumen.
3. Fluid moves to the hindgut where reabsorption occurs before excretion.

Aquatic Species:
- Utilize gills and book gills featuring branched and folded tissues to increase surface area for gas exchange.
Terrestrial Species:
- Rely on book lungs and tracheal systems with spiracles which branch into tracheoles, connecting directly to body cells to allow efficient gas exchange.
- Spiracles are the openings to the exterior that regulate air intake.

Compound Eyes:
- Found in many arthropods, composed of multiple independent visual units called ommatidia.
Simple Eyes (Ocelli):
- May occur in addition to compound eyes, providing the ability to detect light and darkness with single lenses.