A crocheted jellyfish is nice and funny to play with.
I enjoyed myself very much while working in this pattern. I hope you like it too!

IMPORTANT: a lovely raveler found some inconsistencies in the way the tentacles and arms were placed in the pattern.
This is the revised body:

the instructions were a bit messy (at the least!)
changes:
round 4: 3 arms in pink
round 6: 3 tentacles in pink
round 8: 6 tentacles in fuchsia
round 10: 6 short tentacles in pink

(if you prefer, tentacles can be crocheted at round 4 and arms in round 6)

the body and arms/tentacles part should be:

Tentacle: ch 50, sl st in 2nd ch from hook and all the way back, sl st at the base.
Short tentacle: ch 30, sl st in 2nd ch from hook and all the way back, sl st at the base.
Arm: ch 30, 3dc in 2nd ch from hook and in each st across. Sl st at the base.

Using pink:
Round 1: magic ring, 6 sc (alternatively, 2 ch and 6 sc in 2nd ch from hook).
Round 2: 2sc in next 6 st, (12 sts)
Round 3: 2sc in next stitch, 1sc in next st. repeat 6 times (18 sts)
Round 4: 2sc in next stitch, sc in next st and tentacle, sc in next st, 2sc in next stitch, sc in next 2st.] repeat 3 times (24 sts and three tentacle )
Round 5: 2sc in next stitch, sc in next 3st. repeat 6 times (30 sts)
Round 6: 2sc in next stitch, sc and arm in pink, sc in next 9st. repeat 3 times (36 sts)
Round 7: 2sc in next stitch, sc in next 5st. repeat 6 times (42 sts)
Round 8: 2sc in next stitch, sc and tentacle in fuchsia, sc in next 5st. repeat 6 times (48 sts)
Round 9: 2sc in next stitch, sc in next 7st. repeat 6 times (54 sts)
Round 10: working in BLO, short tentacle in pink, sc in next 8st repeat 6 times (54 sts)
Round 11-16: sc in each st across (54 sts)