SCUBA News 238
27 April 2020
SCUBA News (ISSN 1476-8011)
Issue 238 - April 2020
Hello. Thank you for continuing to subscribe in these difficult times. Diving is pretty much cancelled around the world but the dive operators and liveboards are rising to the challenge and changing their booking conditions to help their customers. For example, pay no deposit and cancel for free for 60 days on liveaboards booked via Divebooker. There are also many great deals around at the moment.
Be very careful though if you have had coronavirus. There may be lasting damage to your lungs so have a diving medical before going back in the water. The good news is, that according to John Hopkins University, your lungs can recover. However, it takes from three months to a year for lung function to return to pre-COVID-19 levels.
Keep safe and well.
Scuba diver's guide to the Greek Islands. Which one to choose?
The best diving in Antigua is in the south of the island, around English Harbour. The north is shallow and quite sandy, but calm and good for beginners.
Flatworms are very interesting animals. Looking very similar to nudibranchs: they are beautifully coloured, the same shape and may move similarly by muscular propulsion. However, they have thinner bodies than nudibranchs and also move by beating hair-like cilia on their undersides - rippling through the water. Some have short tentacles on their heads.
Flatworms are bilaterally symmetrical animals. The left and right sides of the animal are the same but the underneath and top are different. This is common in higher animals, but flatworms are one of the most simple creatures to exhibit this.
Their eyes are tiny, comprising just 2 to 3 cells. There are hundreds of eyes along the sides of the body, distinguishing between light and dark and determining the direction of light. They have two other types of sensors. One is sensitive to chemical stimuli, perceiving far-off substances and sensing them on contact (smell and taste). Another is stimulated by the passage of water over the flatworm's body and perceived by rheotactic sensors. The flatworm's simple brain can interpret information and even has the capacity to learn.
Like nudibranchs, some flatworms utilise nematocysts - the stinging cells they obtain when eating fire coral or other hydroids. These are not digested but passed to the body wall as a form of defense.
Mobile flatworms are carnivorous, and feed on slow-moving, sedentary or dead animals. Many capture living prey by wrapping themselves around it, entangling it in slime and pinning it to the ground. A few species may stab their prey with their penis!
Flatworms have amazing regenerative capabilities. When cut into a number of pieces, each will develop a head, tail and full complement of organs.
Although common, divers rarely see flatworms as they hide under rocks, dead coral or seaweed. When spotted they are often mistaken for nudibranchs. Look carefully at these amazing animals - the nudibranch you've seen may not be a nudibranch at all.
Coral Reef Guide Red Sea, by Robert Myers and Ewald Lieske, ISBN 0-0071-5986-2
Invertebrate Zoology, by Robert D Barnes, Harcourt Publishers Ltd, ISBN 0-0302-6668-8
Great British Marine Animals, by Paul Naylor, Deltor (2011), ISBN 0-9522831-3-1
Jacques Cousteau: The Ocean World, by Jacques Cousteau, Abradale Press, ISBN 0-8109-8068-1
The Red Sea in Egypt Part II, Invertebrates, by Farid S Atiya, Elias Modern Printing House, 1994, ISBN 977-00-6697-4
Read more Creatures of the Month.
RAID diving agency makes e-learning free to access
Underwater Photography Guide announces Safe Under the Sea Competition
Silence is golden for whales as lockdown reduces ocean noise
With Boats Stuck in Harbour Because of COVID-19, Will Fish Bounce Back?
How old are whale sharks? Nuclear bomb legacy reveals their age
For the Mediterranean, the Suez is a wormhole bringing in alien invaders
Warming climate undoes decades of knowledge of marine protected areas
Iceland won't be killing any whales this year
Enhanced underwater robots can boost ocean discoveries
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Photo credits: Tim Nicholson, Jill Studholme, Kristin Riser, Jianye Sui
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