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205. Grey Bonnet (Phalium glaucum)



Subject:

A Grey Bonnet (Phalium glaucum) is exploring a shallow sandy area on Bali's northern shore.


Grey Bonnets are large seashells that prefer shallow sandy substrates and seagrass beds. They are a widespread tropical Indo-Pacific species, found from the eastern coast of the African continent to Melanesia in the southwestern Pacific Ocean and Japan in the northwestern Pacific Ocean.


These large gastropods can reach a total length of 15cm/6inch or so and employ their strong, muscled foot to bury themselves in the substrate, revealing only their siphon, a trumpet-like fleshy organ that the snail uses to taste and smell in its quest for food. Only gastropod mollusks that are scavengers or predators possess a such a siphon.


These gastropods are active hunters of Heart and Biscuit Urchins. To locate their prey, they roam sandy areas primarily at night. When the snail identifies its ideal victim, it elevates its large shell quite high and drops it suddenly on the urchin, clamping the urchin between the sea snail and the substrate, ensuring the urchin is completely immobilised and unable to escape. At this stage the snail squirts its neurotoxic saliva over the urchin to neutralise its venomous spines, then uses its radula (a tongue-like organ) to make a small hole in the trapped urchin's exoskeleton, injecting a sufficiently potent acidic secretion to dissolve the sea urchin's internal body parts and organs. Finally, the Grey Bonnet consumes the dissolved tissues of the urchin, leaving behind only a lifeless exoskeleton. It is believed that these sea snails can detect a buried urchin from more than 30cm/1 foot away. In addition to these urchins, their preferred food, it is believed that the Grey Bonnet occasionally also preys on other echinoderms such as sea cucumbers and sea stars (starfish).


Technique:

This older footage was captured more than 10 years ago in 1080i resolution. The "1080" represents the number of vertical pixels in the image, and the "i" signifies the interlaced scan method, which is no longer commonly used. Nowadays, 4K resolution, once considered very high-tech in the early 2000s, has become the standard, and most cameras today record in 4K using a progressive scan method. This means that these cameras capture all the lines in a single frame simultaneously, without interlacing horizontal lines. Interlaced footage can sometimes be identified by a number of noisy horizontal lines in the video. Progressive scan provides significantly better video quality and eliminates the need to deinterlace the footage during post-production.


In this short underwater videoclip, you can observe a tiny reddish coloured shrimp making a frantic loop next to the shell's spire, ultimately ending up in the sand-filled outer lip of the Grey Bonnet's shell. To accentuate this short scene, a few typical cartoon sounds were added because this event is so brief that, without sound emphasis, it would likely go unnoticed by most viewers. The sluggish crawling sounds were also included in this underwater video shot to make the movements of the Grey Bonnet in this scene appear more realistic.


Filming location:

This short underwater videoclip has been filmed in Bali, Indonesia 🇮🇩


More about this subject:

To learn more about Heart Urchins, the Grey Bonnet’s preferred prey please go to our vlog post 98 or click this link: https://www.beyondscuba.com/post/a-burrowing-heart-urchin


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