|Hi Anna Lu!
ad 1) Branchias are kind of 'underwater lungs'. Almost all underwater creatures use them to breath [by taking dissolved oxygen from water]. Many underwater larvae have got external branchias - i.e. larvae of Ephemeroptera or damselflies. Surprisingly most underwater insects breath with atmospheric oxygen - i.e. true bugs and beetles, also one and only Polish underwater spider breath this way. This is very interesting problem and if you wish I could write more about it.
ad 2) This is creature, not plant, but very simply in structure. Hydras are one of most simplified creatures. They're something similiar to i.e. corals. They can reproduce sexually, but most often they reproduce by gemmiparity [and now I understand my mistake ;-) In Polish word 'paczkowanie' comes from word 'paczek' - 'bud' - and means gemmiparity]. Bigger part is old one and smaller - new, young one. After few days young creature will separate from old one.
ad 3) Yes, that's right. Dotted substance which grows around 'twigs'. In fact this is colony of hundreds creatures which looks like small and very thin sea anemones.
ad 4) This is larva of phantom midget ;-) It will stay transparent and after first transformation it will change its shape. I'll try to send some pictures of it next time. It is about 1cm long max. It is dangerous predator for many smaller plankton creatures.
Thanks for your question, it is pleasure to answer Anna Lu!
Ready For Winter (I) (34)