- paedophore
- pallial canal
- palp
- palpacle
- palpon
- papilla
- paragnaths
- parapodial lobe
- parapodium
- parasite
- pars incisiva
- parthenogenesis
- pectinate
- peduncle
- peduncle of first antenna
- pelagic
- pereion
- pereionite
- pereiopod
- pereiopods
- peripharyngeal bands
- peristomium
- peritrophic membrane
- perradius
- petasma
- pharynx
- phorozooid
- photophore
- phyllocyst
- phyllosoma
- phytophage
- phytoplankton
- pigment
- pinnules
- planktivore
- plankton
- planula
- pleon
- pleonite
- pleopod
- pleosome
- pleotelson
- pleura
- pleuston
- pleustonic
- pneumadenia
- pneumatophore
- polygastric stage
- polyhaline
- polyp
- post-antennal sinus
- post-ocular spine
- post-orbital groove
- postchaetal
- postlarva
- postlarval
- praniza
- prechaetal
- precoxa
- predator
- primary production
- proboscis
- processus mamillaris
- propodus
- propus
- prostomium
- protandrous
- protogynous
- protozoa
- protozoea
- proventriculus
- proximal
- pterygostomian spine
- puerulus
- pygidial cirri
- pygidium
- pylopods