Phylum Platyhelminthes Flashcards

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Questions and Answers

What does the name 'Platyhelminthes' mean in Latin?

platy = flat, helminth = worm

What is the phylogenetic diagnosis of Phylum Platyhelminthes?

First organisms to evolve bilateral symmetry, 2. Most are dorsoventrally flattened, 3. Acoelomate with packed parenchymal cells, 4. Small degree of cephalization, 5. Three germ cell layers, 6. Undergo determinate spiral cleavage, 7. Parenchymal cells make up the mesoglea.

Describe the evolutionary advances 'pioneered' by phylum Platyhelminthes.

Cephalization, 2. Bilateral symmetry, 3. Tripoblasty

What is primary bilateral symmetry?

Body can be divided along only one plane to yield two mirror images. Signup and view all the answers

What are the characteristics of Phylum Acoelomorpha?

Small flat worms less than 5mm, live in marine sediments, cellular and ciliated epidermis, parenchyma with muscles. Signup and view all the answers

Describe the general features of phylum Platyhelminthes.

Commonly called flatworms; range from a few mm to many meters; some are free-living, others are parasitic. Signup and view all the answers

List some representatives of each class in phylum Platyhelminthes.

Trematoda: Sheep-liver fluke, Schistosoma spp.; Cestoda: Taenia saginata; Monogenea: Polystoma integerrimum; Tubellaria: Planaria spp. Signup and view all the answers

Which three classes of Platyhelminthes are parasitic? Which class is non-parasitic?

Parasitic: Trematoda, Cestoda, Monogenea; Non-parasitic: Tubellaria. Signup and view all the answers

How do the body forms of parasitic and non-parasitic flatworms differ?

Tubellarians have cilia and a dual-gland adhesive system; parasitic classes lack cilia as adults and have a neodermis. Signup and view all the answers

What are rhabdites?

Rodlike cells of the turbellarian epidermis that secrete mucus. Signup and view all the answers

What are the two glands of the dual-gland adhesive organ of Tubellarians?

Viscid gland cells and releasing gland cells. Signup and view all the answers

Which class in phylum Platyhelminthes lacks a digestive system?

Class Cestoda. Signup and view all the answers

Describe the sensory capabilities of Platyhelminthes.

Tubellarians and others possess ocelli, tactile and chemoreceptive cells, and can electrically sense prey. Signup and view all the answers

How do Tubellarians reproduce?

Asexually by transverse fission and sexually by ectolecithal development. Signup and view all the answers

What is the difference between ectolecithal and endolecithal development?

Ectolecithal involves yolk outside of the embryo, while endolecithal has yolk within the embryo. Signup and view all the answers

Study Notes

Phylum Platyhelminthes Overview

"Platyhelminthes" translates to "flat worms" with "platy" meaning flat and "helminth" meaning worm.
Characterized by bilateral symmetry, acoelomate structure, and a flattened body shape.
Possess a region filled with parenchymal cells between the gut and epidermis, providing structural support.

Evolutionary Advances

Cephalization allows for enhanced sensory capabilities concentrated in the head region.
Exhibits primary bilateral symmetry, facilitating directed movement and body organization.
Triploblastic construction, possessing three germ layers: ectoderm, endoderm, and mesoderm.
Undergo determinate spiral cleavage during embryonic development.

General Features

Size ranges from a few millimeters to several meters, with both free-living and parasitic species.
Parasitic species possess a protective layer called the neodermis to guard against host digestive enzymes.
Gas and ion exchange occur through the body surface.

Class Representatives

Class Trematoda: Includes sheep-liver fluke, Schistoma spp., Clonorchis sinensis.
Class Cestoda: Notable for Taenia saginata (beef tapeworm).
Class Monogenea: Includes Polystoma integerrimum, which parasitizes amphibians.
Class Turbellaria: Encompasses Planaria spp., recognized as free-living flatworms.

Parasitic vs Non-Parasitic Differences

Parasitic classes (Trematoda, Cestoda, Monogenea) generally lack cilia in adulthood and possess a neodermis.
Non-parasitic Tubellarians feature a dual-gland adhesive system, cilia throughout life, and specialized features for osmoregulation in freshwater species.
Parasitic flatworms have higher reproductive output due to reduced energy requirements for obtaining nutrients.

Rhabdites

Rhabdites are rod-shaped cells found in the epidermis of Turbellarians, producing mucus that enhances locomotion and prevents desiccation.

Dual-gland Adhesive Organ

Tubellarians have two types of glands: viscid glands for attachment to substrates and releasing glands for quick detachment.

Digestive System

Class Cestoda is unique in lacking a digestive system, whereas other classes maintain a mouth, pharynx, and intestine.

Sensory Capabilities

Tubellarians and Monogeneans have ocelli for light detection and tactile/chemoreceptive cells for sensory perception.
Parasitic species detect prey via nerve endings on oral suckers and genital pores, enhancing electrical sensing.

Reproduction in Tubellarians

Tubellarians reproduce asexually through transverse fission and sexually via ectolecithal development, involving yolk provision outside the embryo.

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Description

This quiz features flashcards about Phylum Platyhelminthes, focusing on key terms and concepts related to flatworms. Learn the meaning of 'Platyhelminthes' and explore their phylogenetic significance and anatomical features. Ideal for biology students studying invertebrates.