Flat Worms Flashcards
What are the general characteristics of a Platyhelminthes (flat worm)?
Exhibit bilateral symmetry( 2 equal half’s) and have an anterior and posterior ends; dorsal (top) and ventral (bottom). They also exhibit cephalization (concentration of nervous tissue at the anterior end)
What forms during gastrulation
The endoderm and ectoderm interact to form a third layer called the mesoderm
What are the three layers for a flatworm?
Ectoderm (outside layer). Forms the epidermis and associated structures.
Mesoderm (middle layer), the organs develop out of this tissue.
Endoderm (inside layer) forms the digestive tract and associated structures
What type of level of organization do flatworms have?
They have an organ, level of organization, (reproductive, muscular, and excretory organs)
Flatworms lack a coelom or body cavity, this makes them what?
This makes them acoelomates, meaning they do not have a fluid filled Coleen or body cavity
What are the three classes of platyhelminthes?
Class Turbellaria- planaria
Class Trematoda- parasitic flukes
Class Cestoda- parasitic tapeworms
Characteristics of class Turbellaria?
This group contains the “free living”flatworms. Meaning they are not parasitic. Most members are marine. Some are found in freshwater and a few are terrestrial
What occurs during ingestion?
In the ventral surface, the muscular pharynx extends out of the mouth. The phonics is inserted into the prey (small invertebrates) or dead, decaying materials(detritus)
What occurs during digestion?
Inserted pharynx secretes enzymes to partially digest the food externally(external digestion). Pieces of food, are than sucked up through the pharynx and into the gastrovascular cavity
What occurs during elimination?
Undigested food is expelled out the mouth, via the pharynx
What occurs during circulation?
The gastrovascular cavity circulates nutrients to the tissues. The GVC is so extensively branched so that all the tissues are close to branch. Extensive branching also provides more surface area for a more efficient absorption of nutrients from GVC into the body cells.
What occurs during the first part of excretion?
The cilia of flame cells beat, drawing fluids from surrounding tissues into the flame cells (via the current).
What occurs during the second part of excretion?
This fluid contains excess water and nitrogenous waste. N waste and excess water is drawn into excretory tubules and exits, the body, by the way of excretory pores.
What occurs during respiration?
No respiratory organs, O2 and CO2. Enter and exit the body surface (skin) by diffusion. The extensive circulatory system is directly under the skin to pick up the gases into facilitate the exchange across the skin.
What is in Platyhelminthes nervous system and how does it work?
The nervous system of planarians resembles a ladder. It has two ventral nerve cords with a ganglia at the interior end. Transverse nerves that connect the two ventral cords keep movements of the two sides coordinated.
