Let's go with a +2 racial bonus. I agree with all the rest.
Updated.
I think we'd better substitute "Chont" for most of the horseshoe crab(s) in the description. We should probably also rephrase the [The crushing noise the crab makes while eating has earned it the nickname "chont."] bit too.
The second paragraph could also do with some cleaning up, and I'd like to make some mention of a horseshoe crab's shell.
How about:
A chont is a magical giant horseshoe crab. These armored predators roam coastal waters and beaches, feeding on mollusks, worms, plants, carrion, and anything else they can catch.
Like a regular horseshoe crab, a chont's body and limbs are covered by a thick, dome-shaped shell and carapace, so from above it resembles a helmet with a tail trailing after it. Its tail is powerful and highly mobile, and is used as a prow when burrowing through sand and to right an overturned crab. Horseshoe crabs have three pairs of eyes: one set on the underside of its front rim, a large pair on the carapace, and a small hidden pair atop the abdomen.
On its underside a chont has a sucking mouth, flanked by two crablike claws. Behind this are bony, grinding ridges that crush food; everything a chont seizes is passed here by its claws, crushed and then transferred forward into the mouth, which will regurgitate undigestible material. (The name "chont" is due to the crushing noise the creature makes while eating.) Behind these mouthparts are five pairs of legs. The first four can be used as pincers and have spurlike spikes to grip and break up food; the last pair sport leaflike "wings" which aid in swimming and clear away mud when the crab is burrowing. Behind these legs, under the second segment of the carapace, are five pairs of gills with long flaps that keep water moving over the gill membranes and aid in swimming.
Chonts come ashore on certain beaches at certain times to mate, the eggs they lay then hatch into marine larvae that slowly grow to full size. Huge numbers of regular horseshoe crabs come ashore to breed at the same times and places. Chonts will always defend their smaller brethren if the latter are attacked.
Yes I guess so.
A chont is x feet long and weighs x pounds
I feel 25 feet is rather too big for them. However it's "up to 25 feet", suggesting that's the upper limit of their Large size, and presumably this includes their tail. So I'm thinking a Large Chont is 13-25 feet long, including a 5-10 foot tail, and weighs 500-4000 pounds.
So I'm thinking something like this:
A typical chont is 13 to 25 feet long, including a 5 to 10 foot long tail, and has a shell between 6 and 12 feet across. They weigh from 500 to 4000 pounds.