- palisade
- palmate
- palmate chela
- papilla
- paratangential
- parenchymella larva
- paucispicular tracts or fibres
- pedunculate
- phyllotriaene
- pinacocyte
- pinnate
- pithed
- placochela
- plagiotriaene
- plate
- plesiaster
- plumoreticulate skeleton
- plumose skeleton
- polytylote
- pore grooves
- pore sieve
- porocalyx
- primary fibre
- primary spicules
- prosodus
- prosopyle
- protoclad
- protriaene
- punctate surface
- pycnaster