Me and my flatmate got into a bit of a barney yesterday, over whether horses and sea horses are related or not. Does anyone have the answer???

hm i guess it depends what you mean by related. categorizations of life forms are human constructs... they are certainly related in that they share, in some languages, a name. they are also certainly related in that they share quite some genetic code. but then, humans and cabbages share about 50% of genes. does that make us related?

Mmmm - ok, I'm not a science person so some of this stuff is going to go above me (although I get what you are saying). Does it make it any clearer if I say ... did horses derive from sea horses?

No. They are separated at the class level. Seahorses are "fish" and horses are mammals.

Seahorses are so cool to watch swim about, really relaxing. Kinda weird that the male in the species is the one that gets pregnant though.

Hmmm. Ok, well both horses and seahorses are vertebrates (have a backbone), but that's the closest they're related... so we're about as related to a seahorse as a horse is.
Horse: A vertebrate - mammal (i.e. have hair and produce milk, there are some egg-laying mammals!) - Eutheria (placental mammal i.e. give birth to live young) - Perissodactyla (odd-toed ungulate like the rhino & tapir... hooved!) - Equus (includes horses, asses, donkeys & zebra)
Seahorse: A vertebrate - Actinopterygii (in the same class as all ray-finned fishes i.e. not sharks but including your Nemo clownfish, herring, sea bass... all those yummy fish we eat!) - Synganthidae - the family which includes all seahorses and pipefish - Hippocampus = seahorse.

I love this thread.

Maybe we could start up a list of other burning questions we've been dying to know?