I'd  like to add a few spp to Mr. Mr. Froelich's short list of Maine
tidal-pool findings.  These are ones he should be able to dig up from
these great little remnants of the ocean-bottome left behind at low
tide, based upon what i find in New Scotland, just next door:
 
Ischnochiton albus (L)
Tonicella ruber (L)
T. marmoreus (Fabricius)
(The above three in deeper pools, on under-side of rocks)
 Puncturella noachina (rare, but i have seen them)
Margarites helicinus (Phipps)
M. striatus (Leach) (perhaps not in Maine- certainly in Newfoundland,
and i found one in N. S.)
Lacuna vincta (Mont.)
L. pallidula (da Costa) (in southern Maine, perhaps not northern)
All three Littorina (saxatilus incl.) are oftern found in the same small
pool.
Hydrobia truncata Vanatta (in Salt Marsh areas)
Bittiolum alternatum Say (" " ")
Crep. fornicata (L)
Polinices triseriata (Say)
Buccinum undatum (L)
Astyris lunata (Say)
Illynassa obsoleta (Say)
no Turridae, for some strange reason (any ideas why not???)
Odostomia bisuturalis (Say)
O.seminuda (C.B. Adams)
Turbonilla sp.
Acteocina canaliculata (Say)
The Pulmonates (Melampus, Ovatella) will not normally be found in tidal
pools, but may be found aroun the edges of them, in Salt Marsh areas
Mytilus trossulus A.A. Gould ( I think this species makes it to Maine)
Crassostrea virginica (Gmelin) (Salt Marsh areas)
Anomia is a possibility for the area, but i can's specifically recall
finding one
Mysella planulata (Stimpspson)
Macoma balthica (L)
Ensis directus Conrad is easier to find intertidally, but probably
occurs in tidal pools also
Gemma gemma (Totten)
(Mya Arenaria (L)???) As with Ensis, i see no reason why this should be
excluded from tidal pools, but would be hard to find.
Barnea truncata (Say)
Zirfaea crispata (L)
(Above 2 spp are rock borers- uncertain if found in Maine- they occur in
the warmer waters of the inner Bay of Fundy)
Hiatella arctica (L)
Petricola pholadiformis (Lam.)  (Sorry - out of order!)
Pandora gouldiana (Dall)
Lyonsia hyalina Conrad (Salt Marsh)
 
I probably missed a few, but with a little searching, a LOT of
interesting things (molluscan or otherwise) can be found in tidal pools,
even up here in Labrador Current (the reason why we get the deep-freeze
effect in marine watters here, even in August) territory!!
 
                                                                                                                        -ross M.