branch England english February Great Britain heathland nature Quercus petraea sessile oak Surrey tree trunk winter clouds emarginate green leaf leaves natural oak sessile sky summer Sussex wavy animal Balanus barnacle boulder cluster crowd crustacea Gower group invertebrate marine pool rock sea wales alone bracken heath isolated landscape lone meadow one single barnacles Cirripedia coast Cornish cornwall low tide Mollusca mussels Mytilus rocks seashells shellfish rockpool