I'm from Arcata
Yes there are two to check out, but there is nothing that you couldn't find here.
Balanced Aquarium
5000 Valley West Blvd # 4
Arcata, CA 95521
(707) 826-0154
Fin-N-Feather
2931 F St, Eureka, CA 95501
(707) 443-4914
Just for the interesting, "Gee I wouldn't expect that here" comment, CPR, (CPR Bak Pak Skimmers) is right around the corner from Balanced Aquarium.
http://www.cprusa.com/
And last, right before you jab a stick in your eye because you are bored out of your skull, depressed because its probably foggy, and angered because nobody can seem to drive as if they wanted to get somewhere, the Humboldt State University Marine Labratory is in Trinidad and open to the public.
http://www.humboldt.edu/~marinelb/
And yes, it always feels like it is 1982 in Arcata and you feel like you are in a time warp. Go to the Arcata Plaza or Redwood Park and watch some Hippies in thier natural enviroment.
Ah home sweet home.