Locomotion

Turbo undulatus, as with many gastropods, balance the shell on the cephalopedal mass and crawl (Beesley, 1998). 
Turbo undulatus have a large fleshy muscular foot which is used for locomotion over a variety of substrates, propelled by either cilia or waves of small muscular contractions along the foot surface. Gliding is made possible by mucus secretions at the foot (Colin and Arneson, 1995). The foot is in the form of a muscular creeping sole separated from the head and visceral mass and is retractable into the shell (Stachowitsch, 1992). 


   Picture of the muscular foot of a Turbo undulatus

Muscles are an important part of locomotion. It causes the soft bodied animal to erect its shell which (contains the viscera) over the head-foot when crawling over a horizontal surface. During locomotion, its tentacles are also extended and waves of muscular contraction passes along the foot. Its has a hydrostatic skeleton (the blood which is contained in the haemal spaces) which provides effective skeletal support against which the muscles can operate (Beesley, 1998). 

The movement speed of Turbo undulatus is a function of the rate of muscle contraction and amplitude of the ripples along the foot (Miller, 1974).

Experiment: Movement behaviour
Turbo undulatus are often found in clumps on the same coral boulder on the reef crest.

Question1: Do they colonise to better defend against predators and have better mating opportunities? If yes, it means they have to compete for space, mates and food.

Question2: Do they exhibit directional movement, indicative of chemoreception (using their tentacles) and photoreception (using their eyes)? Or is their movement non-directional, indicative that they do not use chemoreception and/or photoreception when moving. Note: it is noticed that all Turbo undulatus use mechanoreceptors (on their tentacles) to feel their surrounding during movement.

Hypothesis1: Because they are often found in clumps together on the same coral boulder on the reef crest, they do colonise to better defend against predators and have increase mating opportunities.

Hypothesis2: They will exhibit directional movement because they have pallial tentacles that contain chemoreceptors and mechanoreceptors. They also have eyes that are able to detect changes in light (photoreception). 

To test if they move to colonise, find cover, find a suitable habitat, 4 Turbo undulatus were placed equally apart from each other in a round glass petri dish full of filtered seawater to observe where they would move to.  

Methods

Treatment1: 4 specimens of Turbo undulatus were placed equally apart from each other in a round glass petri dish full of filtered seawater. Their movements were recorded with a video camera. Each experiment ended when all animals stopped moving.
Movement experiment1: 4 Turbo undulatus in empty glass petri dish
For easy reference, the 4 turbo specimens will be referred to in numbers:
 

Result: Turbo number 4 used its tentacles to sense around and seemed to move directionally towards Turbo number 2 initially. Turbo number 3 moved directionally towards turbo number 4. Turbo number 4 then turned around and moved directly to turbo number 3. Then, it used its tentacles to feel the shell of number 3 and stayed beside it. Replicate experiments were carried out and the same behaviour was observed where individual Turbo undulatus specimens would go towards each other and stay beside each other.

Discussion: Turbo number 4 exhibited directional movement towards Turbo number 2 initially.The constant sweeping of its tentacles throughout the water indicated that it was using its tentacles as a mechanoreceptor to feel around. Its' sudden turn around after turbo number 3 was following in closely behind strongly indicates the presence of chemoreception as turbo number 4 was able to sense Turbo number 3 from behind it. This could not have been possible with photoreception as its eyes are at its anterior end. Mechanoreception is also not a viable explanation as it was not in contact with Turbo number 3. The choice of Turbo number 4 to stay besides Turbo number 3 shows that they are colonial. Replicate experiments carried out yielded similar results further supporting the hypothesis that they move to colonise. During the experiment, there people were walking pass the experimental tank. This created transient shadows over the petri dish. This change in light was sensed by the Turbo and caused them to retract, delaying their emergence to continue moving. This clearly shows that their eyes have a role in photoreception.

 To test if they moved to each other to colonise or just to seek a hard substrate for habitat or cover, treatment 2 was set up.

Treatment2: 4 specimens of Turbo undulatus were placed equally apart from each other in a round glass petri dish full of filtered seawater and with a piece of coral rubble in the middle of the round glass petri dish. 

Result: Turbo number 2 moved directionally to the coral rubble and Turbo number 4 moved directionally to Turbo number 3.

Discussion: This shows that they move not only to colonise but also to seek cover or look for a hard substrate for habitat. They move directionally, indicating that they use chemoreception and photoreception to decide their direction of movement. This is followed by mechanoreception using their tentacles to confirm the presence of the substrate.

To test if they move to look for a hard substrate because of habitat preference or just to seek cover, treatment 3 is set up.

Treatment3: 4 specimens of Turbo undulatus were placed equally apart from each other in a round glass petri dish full of filtered seawater with a sea cucumber, Holothuria leucopsilota, in the middle of the round glass petri dish. 

Result: Turbo 1 moved directly to the sea cucumber, used its tentacles to feel the sea cucumber and moved along it, eventually staying stationary beside it. Turbo number 4 moved directionally towards Turbo number 3.

Discusion: Directional movement indicates chemoreception and photoreception. Use of tentacles to feel sea cucumber indicates mechanoreception. Movement of turbo to the cucumber indicates that they do not move to find a habitat but to seek cover from either a hard substrate (coral rubble) or other species. This is supported by the observation that they are usually found in holes in coral rubble.

To confirm if they exhibit directional movement by either chemoreception or photoreception, treatment 4 was set up.

Treatment4: 4 specimens of Turbo undulatus were placed equally apart from each other in a round glass petri dish full of filtered seawater with a transparent small round glass petri dish in the middle of the round glass petri dish. If the snails go to the plastic, it shows that they do not use chemosensory (petri dish is clean and glass which does not give off chemicals) or photoreception (as the petridish is transparent) to find cover but have found cover by chance. How ever if they ignore the small glass petri dish and moves to each other, this shows the use of chemoreception and photoreception. 

Movement experiment4: 4 Turbo undulatus in empty glass petri dish with a clear small glass petri dish

Results: All 4 specimens of Turbo undulatus ignore the small glass petri dish and end up in a clump.

This supports the hypothesis that they colonise and seek cover, use their eyes for photoreception and use their tentacles for chemoreception and mechanoreception.

To confirm if they use photoreception in their eyes to move directionally to find cover even without the use of chemoreception, treatment 5 is set up.

Treatment5: 4 specimens of Turbo undulatus were placed equally apart from each other in a round glass petri dish full of filtered seawater with a clean round black bottle cap in the middle of the round glass petri dish. If the turbo moves directionally towards the colored plastic, it uses changes in light or the shadow of the plastic to orientate and move.

Movement experiment5: 4 Turbo undulatus in empty glass petri dish with a black bottle cap 

Picture showing the 4 Turbo undulatus, after 1 hour, which did not move from their position 

Results: All 4 specimens of Turbo udulatus exhibit directional movement to the black plastic cap and to each other. They end up in a clump beside the black substrate.

Discussion: This indicates that photoreception plays a large role in their movement.

In summary, Turbo undulatus move to seek cover and protection from each other or other hard substrata. They also use mechanoreceptors, chemoreceptors and photoreceptors in directional movements. However, more replicates have to be used to achieve a stronger data set and unbiased results.