Phylum Acanthocephala

• Spiny-headed worms
• Endoparasites in the intestinal tracts of vertebrates (especially fishes)
• Pseudocoelomates, that lack a digestive tract, an adaptation to a parasitic lifestyle, as these worms absorb nutrients that were digested by the host
• Eversible (capable of being turned inside out) proboscis covered with recurved spines that provides a means of attachment in the host’s intestine
• Considered part of Rotifera by some taxonomists

Phylum Annelida

• Ringed or segmented worms
• Various ecologies, marine, freshwater, terrestrial, some parasites
• Basic annelid form consists of multiple segments with the same sets of organs and, in most polychaetes, has a pair of parapodia that many species use for locomotion
• Generally have well-­developed coelom that acts as a hydrostatic skeleton; aids in locomotion via peristalsis (“ripples” that pass along the body) or by undulations that improve the effectiveness of the parapodia

Phylum Mollusca

• Snails, slugs, clams, and cephalopods
• Generalized mollusk has a single “limpet-like” shell on top, secreted by a mantle covering the upper surface
• Underside consists of a single muscular “foot” for locomotion; some groups (squid and octopus) use the mantle for jet propulsion
• Coelom is relatively reduced, surrounding only the area around the heart
• Many have a specialized, rasping feeding structure called a radula

Phylum Platyhelminthes

• Flatworms
• Acoelomate, with a body flattened dorsoventrally. The space between the gut and outside is filled with mesodermal muscle fibers and undifferentiated parenchyma. Fluid-filled spaces in the parenchyma serve as a hydrostatic skeleton.
• Most free-living flatworms have a gastrovascular-type digestive system (a mouth is present but no anus), while parasitic forms generally have no digestive system.
• Endolecithal eggs ( yolk for developing embryo is within the egg cell itself)

Phylum Rotifera

• Microscopic pseudocoelmates
• Ciliated organ called a corona (wheel organ) on the head creates currents that draw small plankton into the mouth, which opens into a muscular pharynx called a mastax
• Pedal glands on the foot (when present) secrete a sticky substance that anchors the animal to the substrate or allows it to creep through the environment

Phylum Ectoprocta (aka Bryozoa)

• Marine moss animals that exploit many firm substrates, including shells, rocks, marine timbers, and ship bottom
• Coelom, and lophophore for feeding and gas exhange
• Colonial, with each member of a colony living in a tiny chamber called a zoecium (“animal house”), secreted by the epidermis

Phylum Brachiopoda

• Lampshells
• Coelomates that resemble bivalve mollusks, but with shells located on the ventral and dorsal side rather than left and right
• Attach themselves to substrate by a pedicel on the ventral valve, by cementing the ventral valve to the substrate, or burrowing into sediment
• Lophophore surrounding the mouth used for feeding and gas exchange.