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Learn about pseudocoelomates, including the phyla Gastrotricha, Rotifera, Kinorhyncha, Nematoda, Nematomorpha, Acanthocephala, Loricifera, Priapulida, and Entoprocta. Discover their unique characteristics, habitats, and reproductive strategies.
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Pseudocoelomates Aschelminths
Achelminth Phyla • Gastrotricha • Rotifera • Kinorhyncha • Nematoda • Nematomorpha • Acanthocephala • Loricifera • Priapulida • Entoprocta
Pseudocoelomates • Define pseudocoelomate. • formed directly from the cavity of the blastula • The cavity is small • Mostly filled with intestine and oviducts or testes.
Gastrotricha • Microscopic • Marine and freshwater species • Common in lakes, ponds and seashore sands
Rotifera • Ciliated crown or corona at the anterior end • Carnivorous or parasitic • Most common in freshwater environments • Body structure: • Head has corona • Trunk has ridged plates and spines • Foot has toes for attachment.
Kinorhyncha • About 150 species • Lives in marine sediment • Uses head as an anchor, pulls body after it. • Sexes are separate • Feed on algae and bacteria
Nematodes • bilaterally symmetrical • worm-like • surrounded by a cuticle secreted by epidermal cells • longitudinal muscles only
Nervous System - Nematodes • Simple ring of nervous tissue around pharynx • dorsal and ventral nerve cords running the length of the body
Nematode Movement • Contract longitudinal muscles • High internal pressure causes the body to flex • Moves by thrashing back and forth • No cilia or flagella
Excretory Systems • Some have specialized cells that excrete nitrogenous wastes • Others have canals • Others have canals plus specialized cells • Nematodes do not have flame cells
Nematode Reproduction • Most nematodes are dioecious • Males use special copulatory spines • The sperm move by pseudopodia, like amoebas
Nematode Diversity • Close to 500,000 species • Some species are generalists • Others are much more specialized - • one species of nematode is known only from felt coasters placed under beer mugs in a few towns in Germany.
Nematode Lifestyles • Many free living • Many also parasitic • Play critical ecological roles as decomposers and predators on microorganisms
Nematode-Caused Diseases • Roundworms - more than ½ the world's humans • Hookworms • Trichinosis • Pinworms infestations - extremely common parasite in the United States • can be transmitted from human to human by eggs floating in household dust • Filariasis (elephantiasis) • Onchocerciasis (river blindness).
Nematomorpha – Horsehair Worms or Gordian Worms • Up to 1m long, but very slender animals (1-3mm). • Free-living as adults • Often find adults in very clean streams
Acanthocephala - spiny headed worms • 2-host parasites • Must have invertebrate host • Spiny protrusible proboscis • About 1150 species • Dioecious • Both circular and longitudinal muscles
Acanthocephalans - Nutrition • Nutrition by diffusion • Proboscis attaches to host intestine • Cause extensive damage to the intestinal walls • Economic importance: Some forms cause serious discomfort and ill-health to domestic livestock
Excretion • Protonephridia lined with flame cells Reproduction • Reproductive structures are contained in strange ligament sacs. • In males two testes are contained within this sheath.
Loricifera • Discovered in 1974 • Dioecious • Have a large brain • Little else is known about them.
Priapulida – The Penis Worms • Only 9 species • All marine worms • Found in colder water • Predaceous • Fossils date back to Middle Cambrian.
Entoprocta (Bryozoa) • Ciliary feeding device - LOPHOPHORE • Were known as Bryozoa (moss animals) • 4000 species • Few > 0.5 mm long • All aquatic (marine and freshwater)
Entoprocta • Most are colonial • Lives in secreted exoskeleton (zoecium) that may be: • Gelatinous • Chitinous • Stiffened with calcium • Impregnated with sand. • Some ectoprocts could be mistaken for hydroids but their tentacles are ciliated.
