Nematodes Overview and Classifications

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Questions and Answers

What is Phylum Nematoda commonly known as?

Segmented worms

Annelids

Roundworms (correct)

Flatworms

Which class is found in Phylum Nematoda and contains paired glandular structures called phasmids?

Class Annelida

Class Polychaeta

Class Adenophorea

Class Secernentea (correct)

What key feature distinguishes Class Adenophorea?

Segmented body

Free living and parasitic species

Presence of phasmids

No phasmids (correct)

What are the characteristics of the phylum Nematoda?

Triploblastic, bilateral, vermiform, unsegmented, pseudocoelomate, complete digestive tract. Signup and view all the answers

What does the term aschelminth refer to?

A group of phyla including those that do not molt and those that do molt. Signup and view all the answers

What is a pseudocoelomate?

Animals having a pseudocoelom. Signup and view all the answers

What is the function of the cuticle in nematodes?

It serves as a protective layer. Signup and view all the answers

What is molting?

The periodic renewal of feathers or the shedding of the exoskeleton. Signup and view all the answers

Define ecdysis.

The shedding of the arthropod exoskeleton or cuticle. Signup and view all the answers

What is an amphid?

A pair of chemosensory organs on the anterior end of nematodes. Signup and view all the answers

What is a phasmid?

A sensory pit near the tail of certain nematodes. Signup and view all the answers

What is trichinosis?

A disease caused by Trichinella spiralis larvae. Signup and view all the answers

What is elephantiasis?

A chronic filarial disease due to infection of lymphatic vessels. Signup and view all the answers

What causes heartworm disease in dogs?

The nematode Dirofilaria immitis. Signup and view all the answers

What are horsehair worms also known as?

Gordian worms or hairworms. Signup and view all the answers

What is a zonite?

The individual body unit of a member of the phylum Kinorhyncha. Signup and view all the answers

What are scalids?

Complex spines found on kinorhynchs and other related animals. Signup and view all the answers

What are placids?

Plates on the Kinorhyncha. Signup and view all the answers

What is an introvert in the context of certain worms?

The anterior narrow portion that can be withdrawn into the trunk. Signup and view all the answers

Study Notes

Phylum Nematoda Overview

Nematodes, commonly known as roundworms, comprise about 16,000 described species.
They play various roles in ecosystems, including free-living and parasitic forms.

Class Secernentea (Phasmidea)

Characterized by paired sensory structures known as phasmids located in the tail region.
Amphids, similar but less developed structures, are found in the anterior end.
Notable species include Ascaris, Enterobius, Rhabditis, Tubatrix, Necator, and Wuchereria.
Approximately 5,000 species categorized under this class.

Class Adenophorea (Aphasmidia)

Phasmids are absent in this class.
Most species are free-living; however, some are parasitic.
Key genera include Dioctophyme, Trichinella, and Trichuris, with around 3,000 species described.

Key Characteristics of Nematodes

Triploblastic, bilateral symmetry, and vermiform in shape; unsegmented and pseudocoelomate.
Body structure: round cross-section and covered by a layered elastic cuticle, with molting typical during juvenile growth.
Features a complete digestive system with a mouth often surrounded by sensory-laden lips.
Unique excretory systems typically involve one or two renette cells or collecting tubules.
Body wall contains only longitudinal muscles, enabling specific locomotion.

Terminology and Concepts

Aschelminth: Refers to phyla divided into those that do not molt (Lophotrochozoa) and those that do molt (Ecdysozoa), including Nematoda.
Pseudocoelomate: Animals with a pseudocoelom, exemplified by aschelminths.
Cuticle: A protective organic layer secreted by the hypodermis of many invertebrates.
Molting: The shedding of exoskeleton or body covering, also known as ecdysis.
Ecdysis: The process of shedding the exoskeleton in arthropods or the cuticle in aschelminths for growth.

Sensory Structures

Amphid: Chemosensory organs located at the anterior end of certain nematodes.
Phasmid: Sensory pits near the tail end of nematodes in the Secernentea class.

Disease Associations

Trichinosis: An infection from Trichinella spiralis larvae, often from undercooked meat, leading to symptoms like muscular pain and fever.
Elephantiasis: A chronic filarial disease caused by Wuchereria spp., affecting lymphatic vessels, mainly in tropical locations.
Heartworm Disease: Parasitic infection in dogs due to Dirofilaria immitis nematode.

Horsehair Worms: Pseudocoelomate animals from the phylum Nematomorpha, also known as Gordian worms.
Zonite: The individual body unit of Kinorhyncha members.
Scalid: Complex spines found on certain marine worms, serving various functions.
Placid: Plates present on Kinorhyncha.
Introvert: The retractable anterior section of certain worm types, capable of being introverted into the trunk.

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Description

Explore the fascinating world of phylum Nematoda, including the subclasses Secernentea and Adenophorea. Learn about their unique characteristics, ecological roles, and the notable species that define them. This quiz will test your knowledge on these essential organisms in the ecosystem.