Yeah, that looks good.
I agree that we do indeed have the swarm version to attack larger creatures (and gives the swarm version a point to exist, so to speak, since they didn't really in 2e).
That's a good catch. I think it'd be appropriate, for sure.
I wouldn't give them a Hide bonus, other than whatever Spelljammer critters get because space is, you know, dark.
The centipede swarm is probably the closest comparison in the SRD. That's 9HD, so I guess anywhere in the 7-10HD range that we like is ok.
Also, looking at the SRD vermin makes me wonder if CR 1/4 is too high for the standard gossamer.
I'd prefer something close to the Stormwrack Jellyfish swarm and closer to 12 HD. 7 HD is... meh. There's enough of that. I'd like at least one set of 'space jellyfish' that's somewhat dangerous and comparable to what groundlings face. (If it were truly up to me, I'd have them have even more HD, because space is supposed to be dangerous.)
I think the standard gossamer might make more sense at CR 1/8.
Well, I'd choose 12HD over 7HD, I guess. We should just make them more dangerous somehow.![]()