Pehaps a stickleback...?
Saw three on lupines .
Found in gap among coastal shrubland .
This was at a marsh edge in full sun .
Could be Castilleja affinis ssp. Neglecta
These guys live among the rocks along brackish estuary. Largest have about 4 inch wide carapace.
Seen along gray trail on cattle ranch land in Point Reyes.
Seen at dusk in brackish water. S/he caught a fish and took it over to the bank to eat.
Many shells in muddy banks of brackish estuary at low tide.
Fleshy red stem. Roots in fresh water seep.