Esponja arrecifal, con cangrejo hermitaño dentro.
AKA aggregated vase sponge or western nipple sponge...? ID as per Lamb & Hanby, p. 65.
Imperfect pic, sadly, but I suspec this might be a freshwater sponge in the family Spongillidae... or some kind of eggs case, though it really does look spongy. Of course, not too much info out there on freshwater sponges of the Sierras, at least after a cursory initial search. There's this record of Spongilla lacustris from Lake Tahoe, though I suspect that's not quite the right species. The white things we observed were around and under fist-sized rocks in a slow-moving part of a mountain creek that was draining a small lake, around 8000 ft.
in an overhang, intertidal
Sponges are animals of the phylum Porifera (/pɒˈrɪfərə/; meaning "pore bearer"). They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like mesohyl sandwiched between two thin layers of cells. Sponges have unspecialized cells that can transform into other types and which often migrate between the main cell layers and the mesohyl in the process. Sponges do not have nervous, digestive or circulatory systems. Instead, most...