Nematoda vs annelida

Nematoda vs Annelida

Core concept (Nematoda)

• Roundworms, phylum Nematoda, are characterized by elongated cylindrical bodies that are tapered at both ends and covered by a tough cuticle.

• Nematodes are bilaterally symmetrical and are the simplest animals with a complete digestive tract with two openings: a mouth and an anus, thus they have a tube-within-a-tube body plan.

• These animals are pseudocoelomate, possessing a pseudocoel located between the endoderm and mesoderm, enabling them to move freely than more primitive forms and it provides more space for organs.

Core Concept (Annelida)

• The segmented worms, phylum Annelida, are distinguished by bodies that are divided into segments.

• Annelids have a tube-within-a-tube body plan. The body wall, which is covered with ectoderm, is the outer tube, while the digestive tract, which is lined with endoderm, makes up the inner tube.

• A fluid-filled cavity, the coelom, is found between the inner and outer tubes. The coelom is lined with mesoderm and outgrowths from this hold the body organs in place, allowing the development of a more complex organization.

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• The phylum contains three classes: Polychaeta(marine sandworm), Oligochaeta (earthworm) and Hirudinea (leech).

Keywords (Nematoda)

• Nematoda• roundworms• complete gut• cuticle• ganglion• pseudocoel• pseudocoelomate• tube-within-a-tube body plan

Keywords (Annelida)• Annelida• Oligochaeta• Polychaeta• Hirudinea• closed circulatory system• coelom/coelomate• ganglion/ganglia• nephridia• parapodia• segmentation• septum• setae• trochophore larva

Characteristics (Nematoda)

• the name: NEMA (thread) + ODA (like)• smooth narrow cylindrical body tapered at

both ends and covered by a protective layer called a cuticle

• bilaterally symmetrical, triploblastic, pseudocoelomate

• pseudocoelom containins fluid that acts as a blood vascular system that transport nutrients throughout the body

• tube-within-a-tube body plan with the development of a complete digestive tract, i.e., the gut is the inner tube which t is open at both ends – mouth and anus, while the body wall is the outer tube

• are among the most numerous animals ranging from microscopic free-living forms to the larger parasitic nematods

Structure and function• Feeding – complete gut with two openings

(mouth and anus)• Respiration and excretion of metabolic wastes –

through the body wall• No internal transport – through diffusion• Nervous system – several ganglia in the head

region, but no brain; simple sense organs present, nerves extend from ganglia

• Movement – longitudinal muscles in strips down the length of the body wall thrashing movement

Reproduction

• most are dioecious; females generally larger than males

• internal fertilization• zygote is resistant (capable of surviving harsh

conditions)• development is direct in free-living forms;

parasitic forms have a complex life cycle with two or three hosts

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Examples • Free-living nematodes• Turbatrix aceti – vinegar eel• C. elegans – soil nematode; used in research• • Parasitic nematodes• Ascaris – infects intestines of pig, horse & man• Filaria worm (Wuchereria bancrofti) – causes elephantiasis• Trichina worm (Trichinella spiralis) – causes trichinosis; larvae encyst in

muscles• Eyeworm (Loa loa) – infects tissues just below the skin• Pinworm (Enterobius) – deposits eggs in anal region• Hookworm (Ancylostoma and Necator) – infect people walking barefoot

on contaminated soil• •

Characteristics (annelid)

• The name: ANNELLUS (ring) ringed/segmented worms• The body is divided externally and internally into

segments separated internally by a membrane (septum), wherein most segments are identical except for some that are modified to perform specific functions; while segmentation is obvious externally as a series of rings separating the segments.

• Annelids have elongated bodies that are bilaterally symmetrical with a tube-within-a-tube body plan, possessing a complete digestive tract/gut.• Between the gut and other body organs there is a fluid-

filled cavity called the coelom which acts as a hydrostatic skeleton, while the lining of the coelom holds the organs in place.• Annelids thrive in marine, freshwater & terrestrial

habitats; most are free-living, while a few species are parasitic.

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Structure and Function

• digestive system – complete gut; may be carnivorous, herbivorous or detritus feeders• respiratory system – through the skin or gills• circulatory system – closed type (blood travels through

vessels)

• excretory system – metabolic waste via nephridia; solid wastes through anus• nervous system – ganglionic w/ dorsal brain & ventral

nerve cord• muscular system – body wall contains muscles

(longitudinal and circular) for burrowing & swimming

Reproduction

• asexual by budding (rare)• most reproduce sexually – dioecious - through external fertilization (spawning)– monoecious/hermaphroditic - through internal

fertilization

• CLITELLUM specialized segment that secretes mucus ring into w/c sperm & eggs are released

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Taxonomy

• Class Polychaeta– POLY (many) + CHAETA (bristles)– paired paddle-like appendages (parapodia) that

are tipped w/ bristles– w/ well-defined head (has eyes & antennae)– e.g. marine annelids sea mouse– bloodworms– marine sandworm (Nereis)

• Class Oligochaeta– OLIGO (few) + CHAETA (bristles)– bristles help in anchoring or burrowing– most live in soil or fresh water, some marine– e.g. earthworms (Lumbricus terrestris)– tubifex worms

• Class Hirudinea– includes leeches– body flattened & tapered at both ends; w/o

bristles– suckers for attaching to host (anterior & posterior)– PROBOSCIS to penetrate the skin of the host– fresh water, marine or terrestrial– e.g. medicinal leech (Hirudo medicinalis)

secretes HIRUDIN w/c prevents blood from clotting (used to treat hematoma)