Mad as a Marine Biologist

astronomy-to-zoology:

How do certain invertebrates know if they are rightside up?

the science of statocysts 

certain types of invertebrates like bivalves,echinoderms and cnidarians lack sensory receptors, buy yet they know if they are upside down or not and can right themselves up if knocked over. This is due to a special balance sensory receptor called a statocyst, a statocyst can be easily described as a marble inside a basketball, as the statocyst consists of a sac-like structure with a small ball-like mass inside of it called a statolith. The walls of this fluid filled sac are lined with small setae (hairlike structures). Which when the animal moves or is overturned the statolith inside the sac will respond to gravity and fall into the hairs which in turn will activate neurons that tell the animal what orientation it is in so it can adjust accordingly.

Further reading

Image sources: 1,2

High-res alchymista: Polychaete Worms Polychaetes, or bristle worms, are a very common and diverse class of worms with over 10,000 species described so far. Commonly overlooked, these mostly marine worms can be brightly coloured and are to be found in tubes and burrows in the sand and mud of the beach to the depths of the ocean or even just free-living in the water. They all have bristles on their segmented bodies - in fact ‘polychaeta’ means ‘many bristles’. They come in an impressive range of sizes from just 1mm to 3m long.

alchymista:

Polychaete Worms

Polychaetes, or bristle worms, are a very common and diverse class of worms with over 10,000 species described so far. Commonly overlooked, these mostly marine worms can be brightly coloured and are to be found in tubes and burrows in the sand and mud of the beach to the depths of the ocean or even just free-living in the water. They all have bristles on their segmented bodies - in fact ‘polychaeta’ means ‘many bristles’. They come in an impressive range of sizes from just 1mm to 3m long.

High-res Wentletrap Snail [family Epitoniidae] by Karen Chen The word Wentletrap is from the Dutch ‘Wenteltrap’ meaning spiral staircase, referring to the high spired shells of these snails. They are predatory or ectoparasitic [live on the surface]. Not a whole lot is known about them, but they do know that this snail can exude through its salivary gland a pink or purplish dye that may have an anaesthetic effect on its prey!

Wentletrap Snail [family Epitoniidae] by Karen Chen

The word Wentletrap is from the Dutch ‘Wenteltrap’ meaning spiral staircase, referring to the high spired shells of these snails. They are predatory or ectoparasitic [live on the surface]. Not a whole lot is known about them, but they do know that this snail can exude through its salivary gland a pink or purplish dye that may have an anaesthetic effect on its prey!