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Turbellaria (within lobster mouth parts)                              

Brandon Meteyard (2012)



Fact Sheet



Physical Description


Life History & Behaviour

Anatomy & Physiology

Evolution & Systematics

Biogeographic Distribution

Conservation & Threats

References & Links

Anatomy & Physiology


Nervous System
The nervous system varies greatly among turbellaria. The general layout consist of a ringlike brain, nerve cords and a nerve net located throughout the body wall (Halton & Gustafsson, 1996). Many turbellarian have developed two distinct nerve cords making a clear distinction between peripheral and central nervous systems (Riser & Morse, 1974). Similarly, developing a concentrated bilateral brain has centralised the nervous system to the anterior end of the animal making it a highly efficient and organised system (Ruppert et al., 2004). The turbellarian found in my study has a ladder like nervous system where the longitudinal cords are joined at regular intervals by transverse commissures, giving a segmented type pattern (figure 1) (Riser & Morse, 1974).
Figure 1: Ladder-like nervous system (Ruppert et al., 2004)

Ocelli (Eyes)

The eyes seen in figure 2 are not used in the same function as we use our eyes. Turbellarians eyes are referred to as "simple eyes" only able to detect the presence of light (Riser & Morse, 1974). The detection of light can rapidly change the behaviour of turbellarians as a sudden detection can arrest locomotion causing it to seek darkness where it cannot be detected (Ruppert et al., 2004). 

Figure 2: Presence of Ocelli 

Digestive System and Nutrition 

The digestive system of turbellaria is relatively simple with little variation among different taxa. The shape of the gut is related to the size of the worm where microturbellaria gut is simple (blind-gut) (Riser & Morse, 1974). However, the pharynx shows the most specialisation among taxa as its structure depends on the feeding mechanism of the turbellarian (fig 3) (Riser & Morse, 1974). The pharynx enables it to swallow its prey intact or pierce and suck the body contents out, which is then ingested where the pharyngeal glands excrete proteolytic enzymes enabling digestion (Ruppert et al., 2004). The gastrodermis cells are differentiated both morphologically and physiologically in most turbellarians (Riser & Morse, 1974). The first are excretory cells loaded with proteinaceous spheres, whereas the second is phagocytic.(Riser & Morse, 1974). The excretory cells are responsible for extracellular digestion whilst phagocytic cells are the site of intracellular digestion (Riser & Morse, 1974). In small turbellarians diffusion from the central gut is the primary means nutrient transportation to nearby tissues (Ruppert et al., 2004). 


Figure 3: Left hand-side; Birds-eye view of the pharynx structure. Right hand-side; lateral view of the protruding pharynx during feeding (Ruppert et al., 2004) 



Because turbellarians are so small and lack a coelom structure, means of excretion are complex. Nitrogen is converted to ammonia via protein metabolism, diffusing the waste across the epidermis (Ruppert et al., 2004). Cells are generally scattered throughout the body within diffusion distance to easily attain nutrients. Protonephridia (ciliated excretory tubule opening to the external environment) are present in animals lacking blood vessels or a coelom (Ruppert et al., 2004). Their function is to excrete waste by rapidly beating cilia propelling waste products into excretory tubules, which is utilised by turbellarians (Ruppet et al., 2004). 







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