cirrocumulus cloud cirrocumulus castellanus cloud The species-level term, 'castellanus', applies to Cirrus, Cirrocumulus, Altocumulus and Stratocumulus genera. The castellanus character is especially evident when the clouds are seen from the side. envoAtmo A cirrocumulus cloud which 1) has linearly arranged cumuliform protuberances which resemble crenellated turrets or towers, some of which are taller than they are wide in some portion of their upper parts, 2) possess a lower region or base which connects these protuberances.