- balancer
- basal facet of mouthplate
- basal plate
- basis
- bathyal
- bathypelagic
- bayonet chaetae
- bell
- benthic
- benthopelagic
- bicuspate
- bidentate
- bifid
- bilateral
- bilaterally symmetrical
- bilobate
- biotope
- biramous
- bisubtropical
- blastostyle
- blastozooid
- boreal
- brackish
- bract
- branchial bars
- branchial basket
- branchial cavity
- branchial openings
- branchial plate
- branchial sac
- branchial seta
- branchial tube
- branchiostegal spine
- buccal cavity
- buccal cone
- buccal connectives
- buccal glands
- buccal mass
- buccal membrane
- buccal suckers
- buds