ASCHELMINTHES

Question 1

What is aschelminthes?

Answer 1

A grouping of convenience of 8 phyla whose origins and membership remain controversial.

Question 2

What are the features shared among aschelminthes?

Answer 2

Triploblastic organization (extensive mesoderm)
Small size (eutely: fixed cell no.)
Pseudocoelom or no fluid-filled body cavity
Lack a blood vascular system
Protonephridia excretory system
Odd determinate cleavage with mesoderm from blastopore lip
Retractile or eversible spiny head end
Cuticle: Extracellular outer-body covering

Question 3

Describe a pseudocoelom.

Answer 3

Partial or no epithelium separating fluid from tissues
Develops like a hemocoel in other protostomes except the gut is often free of mesodermal tissue
Not associated with a pumping heart (fxn mainly as hydrostatic skeleton)

Question 4

What are the functions of collagen or chitin cuticle in Aschelminthes?

Answer 4

• Thin and flexible (rotifers): assoc with circular and longitudinal muscles
• Tough and must be molten (nematodes etc): antagoniza longitudinal muscles
• Lines the pharynx in many forms & may give rise to teeth around the mouth/body spines important in locomotion/feeding

Question 5

What are the shared characteristics of the Phylum Nematoda?

Answer 5

Most are free living, many are also parasitic
Little morphological diversity
Large forms have extensive pseudocoelom
Seperate sexes or hermaphroditic

Question 6

Describe the morphology of the Phylum Nematoda.

Answer 6

Cylindrical/spindle-shaped bodies surrounded by a thick cuticle
Have a mouth, straight gut, terminal anus
Typically fluid feeders
Longitudinal body wall muscles
4 nerve cords: dorsal, ventral (locomotory), 2 lateral (sensory)

Question 7

Describe the phylum Rotifera.

Answer 7

Among the smallest metazoans
Exhibit eutely
Syncytial tissues
Exhibit a huge variety of body forms and life cycles
Most are suspension feeders through their corona (ciliated crown)
Phenotypic plasticity

Question 8

What is phenotypic plasticity exhibited by the Phylum Rotifera?

Answer 8

Dramatic change in body form in response to scent of predators. Some can switch b/w sexual (separate sexes) and asexual reproduction

Question 9

Describe the Phylum Nematomorpha.

Answer 9

Terrestrial, fresh water, semi parasitic
Extremely long, slender worms resembling nematodes
Single large pseudocoelom, sometimes filled with mesenchyme
Like nematodes, lack circular muscles

Question 10

What is the difference between the larval and adult stage of the Phylum Nematomorpha?

Answer 10

Larvae: parasitic in terrestrial insects, induce host to fresh water
- have a spiny, eversible head end (introvert)
Adult: nonfeeding, reproduce

Question 11

Describe the phylum Priapulida.

Answer 11

Marine, bottom dwelling, free living
Thick bodied, can be large
Typically predatory worms with large, spiny, eversible head end
Distinctive, plumose caudal appenge
Single large pseudocoelom, separate sexes
Common invertebrate of Cambrian seas

Question 12

Describe the phylum Acanthocephela.

Answer 12

Spiny-headed worms. Fresh water parasites
Small-bodied, exclusively endoparasitic (guts of vertebrates)
Require 2 hosts (arthropod: intermediate, vertibrate: final)
No mouth or gut
Single large pseudocoelom, separate sexes (must copulate)
Spiny, eversible head end (introvert) to anchor on the gut lining
Syncytial epidermis, anterior flagella or sperm, similar 18S rRNA sequence

Question 13

Describe the phylum Cycliophora.

Answer 13

Newest animal phylum

Very weird life cycle (parasitic male, female larva carries eggs)