1. Schedule of activities
quiz
dissections!

3. ANIMAL PHYLOGENY PROTOSTOMIA BILATRERIA ANIMALIA
CHORDATA
HEMICHORDATA
DEUTEROSTOMIA
ECHINODERMATA
ARTHROPODA
TARDIGRADA
ONYCHOPHORA
NEMATODA
ECDYSOZOA
NEMATOMORPHA
PRIAPULIDA
KINORHYNCHA
PROTOSTOMIA
BILATRERIA
ANIMALIA
BRYOZOA
BRACHIOPODA
PHORONIDA
ANNELIDA
LOPHOTROCHOZOA
MOLLUSCA
SIPUNCULIDA
PLATYHELMINTHES
PLACOZOA
CNIDARIA
PRE-BILATERIANS
PORIFERA
PROTISTA
MODIFIED FROM Valentine et al., 1999

4. nematodes among protostomes that molt a cuticle (undergo ecdysis):
the Ecdysozoa

5. NEMATODES

6. Caenorhabditis elegans
PHYLUM NEMATODA
The roundworms:
elongate worms, tapered at either end,
round in cross-section
highly abundant in numbers and species
about 10,000 described
>1,000,000 species estimated,
3-9 billion nematodes per acre of soil
90,000 per rotting apple
many are free-living
many are parasitic on plants or animals
-nematodes destroy 15% of agricultural production annually, $80B/yr.
- Recent estimates suggest that intestinal nematodes continue to infect more than one billion people (de Silva et al., 2003; Bethony et al., 2006).
Caenorhabditis elegans
“the worm”
is a nematode!

7. PHYLUM NEMATODA Homogeneous general body plan, Enormous size variation
most species are a few millimeters in length
Placentonema gigantissimum – a nematode parasite in placenta of sperm whale; probably the longest nematode reaching 8.5 m in length with a diameter of 8-9 mm
Dioctophyme renale – female worm is over 100cm long
They also vary in shape
Dioctophyme renale
in kidney of a ferret
Citrus nematode

8. PHYLUM NEMATODA Pseudocoelomates
have body cavity: pseudocoelom NOT a true coelom, it is not completely bound by tissue of mesoderm origin such as muscle
pseudocoelom contains fluid under pressure which helps nematode to maintain shape, it serves as “hydrostatic skeleton”
Body is covered by a resistant cuticle (multilayered, flexible) prevents digestion by host, is typically molted four times during life cycle.
Cuticle is secreted by a hypodermis which is metabolically active, possesses four structures called cords which protrude into the pseudocoelom

9. PHYLUM NEMATODA
nervous system consists of two nerve rings (one around esophagus, one around rectum) which are joined by longitudinal nerves in the dorsal and ventral cords
specialized sensory structures may be present, these are of taxonomic significance
- amphids are located on the head end of the body and are chemoreceptors or secretory structures
- phasmids are located at posterior end of body and are probably chemoreceptors

10. PHYLUM NEMATODA
have a complete digestive system with mouth, harynx,intestine,rectum and anus (nematodes are a "tube within a tube")
cilia and flagella are absent, even on sperm cells which in nematodes move by ameboid movement
(some sensory structures may have modified cilia)
they lack a circulatory system
the osmoregulatory system is glandular or tubular, gut probably functions in excretion also, excretory system can be seen in cross-section in the lateral cords
Ameboid sperm of
nematode

11. PHYLUM NEMATODA most species are dioecious Female:
usually larger than male
genital pore opens separately from anus
Male:
often coiled posterior end, both genital pore and digestive system open into a cloaca at posterior end of body
often possesses spicules which are used to hold the female genital pore open during copulation

12. PHYLUM NEMATODA
the cuticle is often ornamented

13. PHYLUM NEMATODA
Generalized nematode life cycle: four larval stages and four molts
L1 larva emerges from egg, grows, then molts, becomes L2 which grows, molts, becomes L3 which grows, molts, becomes L4 which grows, molts, becomes adult, (no more molts, growth occurs between molts)
Prior to each molt a new cuticle is formed under the old one, then old cuticle is shed
Remember L3

15. PHYLUM NEMATODA
Caenorrhabditis elegans was the first multicellular organism to have its genome completely sequenced
The finished genome sequence was published in 1998, although a number of small gaps were present (the last gap was finished by October 2002).
The C. elegans genome sequence is approximately 100 million base pairs long and contains approximately 20,000 genes.
- In 2003, the genome sequence of the related nematode C. briggsae was also determined, allowing researchers to study the comparative genomics of these two organisms.

16. PHYLUM NEMATODA
It is relatively easy to study the development of C. elegans and a map is available stating what each cell becomes during its development
the adult hermaphrodite has 959 cells in its body, 302 of these constitute the nervous system which possesses 118 different cell types and forms 8000 synapses (the nervous system has been described in a 500 page document)
the adult male has 1031 cells
The patterns of cell lineage are largely invariant between individuals

17. PHYLUM NEMATODA
A useful feature of C. elegans is that it is relatively straightforward to disrupt the function of specific genes by RNA interference (RNAi).
Silencing the function a gene in this way can sometimes allow a researcher to infer what the function of that gene may be.
The nematode can either be soaked in (or injected with) a solution of double stranded RNA, the sequence of which is complementary to the sequence of the gene that the researcher wishes to disable.
Alternatively, worms can be fed on genetically transformed bacteria which express the double stranded RNA of interest.

19. Strongylodiasis
Angiostrongyliasis
Ascariasis
Enterobiasis
Trichinellosis
Trichuriasis

20. Anisakiasis
Dracunculosis
Filariasis