Amphipods most commonly seen intertidally grazing on algae are mostly gammarids, while those most noticeable subtidally are caprellids. There are about 35 families of west-coast gammarid amphipods, comprising several hundred species. 

NOTE  common names for intertidal amphipods are “beachhoppers" or "beach fleas”; for supratidal/semiterrestrial species, “sandhoppers or sand fleas”; and for terrestrial species, “landhoppers”.  Most or all species inhabiting the high intertidal and supratidal shore regions are talitrids, as are all terrestrial forms.  The terms “supratidal” and “semiterrestrial” are used synonymously in the ODYSSEY to refer to the zone above the reach of the highest tides, but still influenced by them, such as by spray, and gradients of moisture and salt.  “Terrestrial” refers to habitats independent of the sea  

Phylum Arthropoda (lit. “jointed legs” G.)

Subphylum Crustacea (lit. “crust or rind, characterised by” L.), referring to the hard calcified exoskeleton

Class Malacostraca includes all the “advanced” crustaceans

Order Amphipoda (lit. “on both sides”  “feet” G.)

      SubOrder Gammaridea (lit. “a kind of lobster” L.)

Family Talitridae (lit, "to strike with the finger"), including semiterrestrial species such as Traskorchestia spp. and Megalorchestia spp.

Family Corophiidae, including about 2 dozen species of burrow-inhabiting, deposit-feeding species

Family Oedicerotidae, including small (3-6mm) burrow-inhabiting forms, favouring wave-surge areas, such as Americehelidium spp.

SubOrder Caprellidea (lit. "goat" G.)

Family Caprellidae is a large group that includes about 30 species (in California, and many more in other west-coast areas) with unusual morphology, behaviour, and feeding habits; found subtidally among hydroids and other bottom growth