Unit 3 - Worms Flashcards

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Questions and Answers

What are the general characteristics of phylum Platyhelminthes?

Bilateral symmetry, triploblastic, protostome, lophotrocozoan, acoelomate, monoecious, dorsoventrally flattened, incomplete or absent gut, moderate cephalization, cerebral ganglia, protonephridia.

What are the classes under Platyhelminthes?

Turbellaria, Trematoda, Monogenea, Cestoidea.

What are the characteristics of class Turbellaria?

Free-living, crawling scavengers or predators that are triploblastic, acoelomate, monoecious, bilaterally symmetric, and move using cilia.

What are the three tissue layers of Turbellarians?

Epidermis, parenchyma, gastrodermis. Signup and view all the answers

What is parenchyma?

Loosely packed tissue that fills the space between the organs, tissues, and body walls in Turbellaria. Signup and view all the answers

What are the three glandular epidermal cells in Turbellaria?

Rhabdites, adhesive glands, releaser glands. Signup and view all the answers

What are Rhabdites?

Glandular cells in Turbellaria that secrete a protective mucous sheath in response to threats. Signup and view all the answers

Describe Turbellarian locomotion.

Smaller Turbellarians use cilia to move, while larger ones use muscular contractions, gliding over a mucous layer. Signup and view all the answers

Describe the digestive system of Turbellarians.

Turbellarians ingest food via the eversible pharynx, with an incomplete digestive system that may be branched. Signup and view all the answers

How do Turbellarians exchange gases?

By simple diffusion across the body wall. Signup and view all the answers

Describe Turbellarian osmoregulation.

Freshwater Turbellarians are hypertonic and prevent excessive water influx through protonephridia and flame cells. Signup and view all the answers

What are flame cells?

Structures that arise from parenchyma and cover protonephridia tubule networks, drawing water in and pushing it out. Signup and view all the answers

Describe the Turbellarian nervous system.

Turbellarians have a primitive brain with two anterior ganglia and a double longitudinal nerve cord. Signup and view all the answers

What are the main Turbellarian sensory structures?

Ocelli (photoreceptors) and auricles (chemoreceptors). Signup and view all the answers

What is the most common method of reproduction among Turbellarians?

Transverse fission. Signup and view all the answers

Describe the Turbellarian reproductive system and sexual reproduction.

Turbellarians are monoecious with many paired testicles and ovaries; eggs can be fertilized and laid in cocoons. Signup and view all the answers

What are the characteristics of class Trematoda?

Flattish worms that are almost entirely parasitic on vertebrates as adults, with some stages using invertebrates or plants. Signup and view all the answers

Study Notes

General Characteristics of Phylum Platyhelminthes

Bilateral symmetry and triploblastic structure
Develop as protostomes and belong to the lophotrocozoan group
Acoelomate body plan
Monoecious reproductive strategy
Dorsoventrally flattened shape
Incomplete or absent digestive system
Moderate level of cephalization
Possess cerebral ganglia for nervous coordination
Waste excretion handled by protonephridia

Classes Under Platyhelminthes

Four recognized classes: Tubellaria, Trematoda, Monogenea, Cestoidea

Characteristics of Class Turbellaria

Free-living organisms; scavengers or predators
Size ranges from less than 1 cm to 60 cm
Habitat includes freshwater, marine, and moist terrestrial environments
Triploblastic, acoelomate, and bilaterally symmetric
Locomotion through cilia on their body surface

Tissue Layers of Turbellarians

Composed of three distinct tissue layers:
- Epidermis
- Parenchyma
- Gastrodermis

Parenchyma

Loosely packed tissue found between organs, tissues, and body walls in Turbellaria

Glandular Epidermal Cells in Turbellaria

Three types of glandular cells:
- Rhabdites: secrete protective mucus
- Adhesive glands: assist in attachment
- Releaser glands: facilitate detachment

Turbellarian Locomotion

Smaller species move primarily via cilia
Larger species rely on muscular contractions, utilizing longitudinal and circular muscles
Glide over a mucous layer to enhance adhesion and traction

Digestive System of Turbellarians

Ingestion occurs through an eversible pharynx leading to the mouth
Features an incomplete digestive system, known as a blind cavity
May have either branched or unbranched structures to maximize surface area
Digestion occurs both extracellularly and intracellularly

Gas Exchange in Turbellarians

Gases exchanged via simple diffusion through the body wall, necessitating a flat body shape

Osmoregulation in Turbellarians

Marine species are isotonic to their environment, while freshwater species are hypertonic
Freshwater turbellarians use protonephridia and flame cells to regulate water intake
Protonephridia consist of tubule networks covered by flame cells to pump excess water out

Flame Cells

Structures formed from parenchyma; cover protonephridia
Consist of fenestrated bulbs that use cilia to regulate water movement

Nervous System of Turbellarians

Contains a primitive brain with two anterior ganglia
Composed of sensory, motor, and associative neurons
Features a double longitudinal nerve cord linked by lateral commissures

Main Sensory Structures in Turbellarians

Ocelli act as light-sensitive photoreceptors
Auricles serve as chemoreceptors
Additional sensory structures are dispersed throughout the body

Reproduction in Turbellarians

Main method of asexual reproduction is transverse fission
Monoecious with paired testes and ovaries
Penises may facilitate sperm exchange during mating
Eggs develop directly; may be laid singly or in masses, encased in protective cocoons

Characteristics of Class Trematoda

Flattish, primarily parasitic on vertebrates
Immature stages can exploit invertebrate hosts or plants

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Description

Test your knowledge on the characteristics and classifications of phylum Platyhelminthes with these flashcards. This quiz covers general traits, as well as specific classes such as Tubellaria and Trematoda. Perfect for students studying zoology or biology.