PHYLUM NEMATODA

Presented By:Faderog, Mary Grace Soriano, Hannah ShaneAng, Mary Grace Joy

Sample Animals

Free-living species Caenorhabditis elegans▪ Excellent model organism to study biological phenomena Parasitic speciesAscaris lumbricoides ▪ Responsible for the most common intestinal worm infection ascariasis

Body Cavity

Pseudocoelomate

(pseudo=false),because they do not have a true coelom. This means that they do have the peritoneal cavity ( or gut), but it is not lined with mesoderm.

Body Symmetry

• Head – Radially symmetrical • Many planes divide organism into two mirror image • Body – Bilaterally symmetrical • Single plane divides organism into two mirror images

Nervous System

Ganglial• Cerebral ganglion (“brain”) – Anterior neural ring with most of the sensory nerve bodies• Two main longitudinal ganglial chords – Dorsal – Ventral

Digestive System

• Complete digestive tract with specialized regions – Anterior mouth – Muscular and glandular pharynx (esophagus) – Long, straight midgut (intestine) – Rectum – Ventral anus• Secretion of digestive enzymes by phanyngeal glands• Absorption of nutrients through microvilli of midgut cells Excretory System

Excretory System

• canal along each side of body regulates nutrients and waste content

• excretes nitrogenous waste in the form of ammonia through body Wall

Locomotion/Musculature

• long muscles under the cuticle, aligned longitudinally under the epidermis, side to-side movement

only (no crawling or lifting itself); free swimming looks like it

is thrashing about aimlessly• muscles activated by two nerves, one along ventral (belly) and one along dorsal (back)

Skeletal Type

• the cuticle is the closest thing Nematodes have to a skeleton• functions as support and a leverage point for movement• fluid in pseudocoelom serves as hydrostatic skeleton

Sensory Structures/Features

• the epidermis consists of a mass of cellular material and nuclei without separate membranes; secretes thick cuticle that is tough, yet flexible• the cuticle is periodically shed; up to times before adult stage

Reproduction

• Nematodes are sexual animals• the male is generally slightly smaller than the female, which usually displays a bent tail• Nematode reproduction in free-living specimens is a very interesting process involving six stages including an egg stage, four larval stages (L1, L2, L3, L4), and an adult stage.

More Reproduction…

• Males are dioecious in that they can have one or two testes and can have a variety of accessory sex organs depending on the species• Females give rise to eggs that are then fertilized and laid• Once embryos, these eggs are mature and hatch. After four molts, they becomes adults capable of reproduction• During molting, a nematode will shed its skin in order to facilitate growth. The third L3 larval stage is normally the infectious stage for parasitic nematodes

Other Features…

• many nematodes are able to suspend their life processes completely when conditions become unfavorable• resistant states in which they can survive extreme drying, heat, or cold, and then return to life when favorable conditions return• this is known as cryptobiosis• this feature is shared between nematodes and rotifers

Oh Gosh, There’s MORE!

• They live not only in almost every geographic location on Earth, but in such extreme habitats as ice and hot springs, as well as living on or in almost every kind of animal and plant alive today. • Free-living nematodes – soils– sediments, where they feed on bacteria and detritus.

• plant parasites and may cause disease in

GRRRR!!!!!economically important crops.• animal parasites (including humans); well-known parasitic

nematodes include hookworms, pinworms, Guinea worm (genus Dracunculus), and intestinal roundworms (genus Ascaris)

Parasitic forms of Nematodes Ectoparasite of plants - lives outside the plant

Endoparasite of plants - lives and breeds inside the plant having entered as a juvenile

Saprophagous - juveniles and adults are free living, juveniles enter invertebrate animal host and cause no harm, but feed on dead tissues when the host dies.

Zooparasitic juvenile stages only - juveniles parasitize a host organism and then leave when it becomes adult, the adult does not feed and may not have a functioning gut.

Phytoparasitic juvenile, Zooparasitic adult - juvenile lives in a plant which is taken in by the animal host when it feeds. The adult then parasitizes the adult and infects the larvae of the host with juvenile worms which are then ready to enter and parasitize the plant host again.

Zooparasitic adult females only - young live in the soil, males die after fertilizing females in the soil, pregnant females then enter the host

Roundworms

Common name of phylum nematoda. They are among the most numerous of all animals.

Round worms were given the name of nematodes because they resemble a thread.

In Greek, “nematos” actually means thread hence why they are called nematodes.

Roundworms are slender, unsegmented worms, with tapering end. They can be microscopic or up to a meter length.

Most roundworms are free living, inhabiting soil, soil flats, aquatic sediments from polar to tropical regions.

Still others are parasitic and live in host that include almost every kind of animal and plant.

Unlike platyhelminthes , nematodes have a digestive tract with 2 openings the body wall and the digestive tract, the body plan called “a tube within a tube”

Characteristics of Roundworms

Cylindrical shaped Flexible non living cuticle Lack of motile cilia or flagella Lack of photonephridia Muscle of body wall run only

longitudinally

Feeding Carnivorous Other free living nematodes feed on

phytoplankton such as diatoms, algae and fungi. Many terrestrial species feed on plant roots, penetrating the cells and sucking out the contents. 

Species that live in sediments and other aquatic environments ingesting particles of the substrate when they digest associated bacteria and / or organic material.

Others feed more directly on dead organic material such as decomposing plants and animals or dung. Some in these environments feed on the bacteria or fungi that are feeding on the decomposing material.

Class CLASS ADENOPHOREA (APHASMIDA; 12 ORDERS) Mainly free-living; without phasmids; amphids located

posteriorly in the head region; sensory bristles and papillae on the head and body; excretory organ, when present, single-celled and without collecting tubules; males without lateral extensions of the tail region.

Desmodora, Dioctophyme, Monhystera, Enoplus, Strongyloides, Trichinella, Trichuris.

CLASS SECERNENTEA (PHASMIDA; 8 ORDERS) Mostly terrestrial or parasitic; with phasmids; with amphids

 located anteriorly in the head region and opening and opening on lateral lips; excretory system includes collecting tubules; without somatic setae or papillae, except sometimes on the tail of males; Males often with lateral extensions of the tail region.

Ancylostoma, Necator, Ascaris, Gnathostoma, Dracunculus, Filaria, Camallanus, Wuchereria.