Hi, it's my first post, so go easy on me!
I've adapted the knitty nautie pattern which has been on the web for a while so that it can be crocheted. The owner has given her permission for me to post the pattern and seemed very pleased that it can now be crocheted as well as knitted.
As I haven't posted 10 times yet, I've had to link to the pictures. Sorry about that!
Here we go...

SHELL
Magic ring 3 sts, (or ch 2 and work 3 sc into the second chain).
Row 1 - SC around
Row 2: sc-inc, sc to end - 4 sts.
Row 3: sc around
Row 4: sc around
These four rows are tough on the fingers, but it will get easier.
Rows 5-8: Work as for Rows 1-4 - 5sts.
COILING THE SHELL
Add a little stuffing at this point and roll the shell towards the hook. Once you get the shape you like, you basically need to SC into one of the shell stitches to keep the coil in place. It really is up to you where you choose to pick up the stitch, but try to keep to the centre of the shell as far as you can, and don't pick up too low down or you don't get much of a coil.

Now, you started this process with 5 sts in your round. Now you have 6. What you should do is SC the coil stitch with the stitch on your hook (sc-dec) to return to 5 sts again, but if you forget and end up with 6 sts, it's not the end of the world. The nautiloid is very forgiving and so long as you keep more or less to the number of stitches, it will look ok.
So, that was row 9.
Round 10: sc around
Round 11: sc around
Round 12: sc inc - sc around. 6 sts.
Round 13: coil shell, sc around.
And again;
Round 14: sc around
Round 15: sc around
Round 16: sc inc, sc around. 7 sts
Round 17: coil shell, sc around.
Just continue working in these blocks of 4 rows until you get the shell size you want. I went to about 28 sts, but you could make a mini nautiloid or a monster nautiloid if you felt like it.
HEAD
I kept increasing by 6 sts each row until I had a half ball shape which more or less fitted into the neck of the shell. So,
Magic ring 6 sts
Row 1 - 1 sc inc into each stitch - 12 sts
Row 2 - 1 sc inc, sc - repeat to end of row - 18 sts
Row 3 - 1 sc inc, 2 sc - repeat to end of row - 24 sts
And so on until the circumference is about right. Then sc around for as many rows as it takes to get the head the right length. I think I did about 2/3 extra sc rows, but it's up to you. Don't close the head, just leave the end open and once you start to attach it to the shell, get the stuffing in.
A word of warning - if you make the head too big, it will look ever so slightly phallic when you sew it on!
To attach the head to the shell, make sure the head fits inside the shell so that the shell gives a sort of collar effect. Either add safety eyes before attaching and stuffing, or sew the eyes on afterwards as in my example.
The tentacles are dead easy - just make a set of chains as long as you like. I made 8 chains of about 19 sts each and sewed them on.
And voila!
As I was taking the photographs, I stepped backwards and stood on a snail, coiled shell an' all. I didn't feel too bad about this as he had just been chomping through my campanula.
http://horseofhistory.blogspot.com/2008/07/its-prawn.html