Overview of Lophotrochozoans and Their Characteristics (lab 9)

Lophotrochozoans

One of two groups of protostomes (the other is ecdysozoan) characterized by bilateral symmetry and classified by the presence of a trocophore larval stage or lophophore.

Acoelomate

Animals that have no enclosed body cavities, such as Platyhelminthes (flatworms) and Nemertea.

Pseudocoelomate

Animals that have body cavities but no mesoderm lining, such as Nematoda and Rotifera.

Coelomate

Animals that have body cavities lined by mesoderm-derived tissues, including Molluska and Annelida.

Coelom formation

Begins in the gastrula stage, where the developing digestive tube of the embryo forms a pouch called the archenteron.

Schizocoely

In protostomes, coelom forms by the splitting of the mesoderm into two layers, creating a coelom.

Enterocoely

In deuterostomes, coelom forms by mesoderm budding from the walls of the archenteron and hollowing to become coelomic cavities.

Open circulatory system

A system where hemolymph is pumped into hemocoels and bathes organs, returning to the heart through ostia, found in arthropods and most mollusks.

Closed circulatory system

A system where blood circulates unidirectionally from the heart around the body and back, with distinct separation of blood and tissue fluid, found in all vertebrates and some invertebrates.

Phylum Rotifera

Triploblastic pseudocoelomates known for their crown of cilia (corona) that beat in synchrony to draw in prey.

Mastax

A jaw-like structure found in rotifers.

Phylum Platyhelminthes

The flatworms, which are triploblastic acoelomates with a two-way digestive tract and no circulatory system.

Class Turbellaria

A class within Phylum Platyhelminthes that includes Planaria, which are mostly free-living and marine.

Class Trematoda

A class within Phylum Platyhelminthes that includes flukes, which are obligate parasites that attach to hosts with suckers.

Class Cestoidea

A class within Phylum Platyhelminthes that includes tapeworms, which are internal parasites with a scolex and body segments called proglottids.

Phylum Annelida

Coelomates characterized by metamerism (segmentation) and a fluid-filled coelom that allows for hydrostatic movement.

Class Oligochaeta

A class within Phylum Annelida that includes earthworms, which are hermaphroditic and move through alternating muscle contractions.

Clitellum

A structure in earthworms that excretes a chitinous band to collect sperm and eggs for external fertilization.

Phylum Mollusca

A diverse group of soft-bodied coelomates that lack segmentation and often have a calcium carbonate shell.

Class Cephalopoda

A class within Phylum Mollusca that includes octopuses and squid, known for their high speed and developed nervous systems.

Dual pumping mechanism

In cephalopods, a system where two branchial hearts send blood to gills for gas exchange, returning to a single systemic heart.