As this is being upvoted quite a bit, I'll post some information about the tank :)
This is a UK Native Marine tank. I live right by the beach in Dorset so the water is collected from the sea and the animals from rock pools. I only borrow creatures to observe for a while in the tank then they go back; I've never mixed with store-bought creatures, this makes it safe to release. I made this on a tiny budget. It's a 65 litre tank with a powerful undergravel filter and a pump to create some current that switches on and off. The only unnatural objects in the tank are the sassy duck (couldn't resist) and the gravel (seemed bad to take that from the beach, so I bought and washed some). There is a 1873 pottery manufacturer (Poole Pottery) nearby and in the past they would dump their broken creations into the sea. Over time these get taken by the tide out of Poole, around Brownsea Island and they wash up on a small beach down the coast a bit (Baiter). This has always fascinated me so I've decorated the tank with little bits of broken pottery and smoothed glassware I've found there.
Currently there is also a hermit crab, pagurus prideaux, he usually has a cloak anemone on his shell (together they form a symbiotic relationship), I collect shells from the seafront for him and another small hermit, a 'hairy hermit'. There is also a goby (fish), a common prawn (many more before but I put them back recently), several snails and a few types of anemone including this lovely snakelock.
My SO's father is a marine biologist and they've both given me a lot of help setting this up. I enjoy it as I get to have a little slice of nature in my flat, observe what they do and not experience any of the guilt I always feel when I keep regular pets. This is just a little crabby holiday. If you're tempted to do this, please read up lots first (although there's very limited information available; if it regards the UK, you can pm any me questions) and please never mix caught and store-bought animals - especially if you intend on releasing - you can spread diseases to ecosystem. This only works for me because I'm so close to the sea; I monitor salinity, temperature and how.. happy everyone looks and return animals if the conditions are not right. I love how fascinated visitors to my flat are about the tank!
For anyone concerned: He's a bit pale due to lack of sunlight for his algae, I guess as it is winter so there is even less getting in. Shall invest in daylight bulb or return to the sea :)
Other bits:
Silly little video I made the other night of my hermit crab and grumpy fish.
Hermit crab with cloak anemone on his shell.
Nice photo from a few months of a crab and some of the pottery.
Terrifying photo of the small hairy hermit eating a nasty worm thing out of a shell.
