Pseudocoelomates:
Gnathifera
= more vermiform animals,
but with a pseudocoelom this time…..
Advantages of a Body Cavity
A body cavity, pseudocoel or coelom,
has several advantages. It provides:
– Greater freedom of movement.
– Space for development of organ
systems.
– A simple means for circulation of
materials around the body.
– Storage place for waste products.
– A hydrostatic skeleton
Common Features of all
Pseudocoelomates
1. All have a body wall of epidermis, a dermis, and muscles
surrounding the pseudocoel.
2. Almost all have a complete digestive tract.
3. The epidermis of many secretes a nonliving cuticle with
bristles & spines.
Pseudocoelomates do not form a clade.
Some are part of superphylum
Lophotrochozoa, others are in superphylum
Ecdysozoa.
All share the pseudocoelomate body plan.
Clade Gnathifera
Possess small cuticular jaws with a homologous
microstructure.
Numbers of pairs of jaws vary.
Gnathostomulida, Micrognathozoa, and Rotifera are tiny,
free-living, aquatic animals.
Acanthocephalans are worm-like endoparasites living as
adults in fish or other vertebrates.
Phylum Gnathostomulida
= includes the jaw worms.
!Very small - <2mm.
!Live in interstitial spaces of
fine coastal sediments.
!Can endure low O2.
Phylum Gnathostomulida
Feed by scraping bacteria and fungi from the substratum
with a pair of jaws on the pharynx.
Poorly developed parenchyma layer.
Sexual stages include males, females, and hermaphrodites.
= Fertilization is internal.
Phylum Micrognathozoa
Micrognathozoans are tiny animals that live interstitially
(between sand grains).
Body consists of a two-part head, a thorax, and abdomen
with short tail.
Move using cilia and have a unique ventral ciliary adhesive
pad that produces glue.
Three pairs of complex jaws.
Phylum Micrognathozoa:
Lifestyle
Simple gut
Anus opens to outside only periodically.
Reproductive system is not well
understood:
– Only female reproductive organs
have been identified.
– May reproduce
parthenogenetically.
– Cleavage and subsequent
development have not been
studied.