Barnacles are exclusively marine crustaceans that live in shallow, tidal waters. They are sessile, filter-feeding encrusting organisms with shells composed of calcite. Most barnacles are hermaphroditic and have a life cycle that begins as a nauplius larva and progresses to a cyprid larva and then to an adult form. Some representative barnacle species include Balanus glandula, Balanus crenatus, Balanus nubilus, and Pollicipes polymerus, which vary in shell appearance and habitat.

1. Subphylum Crustacea, Class
Maxillopoda, Sublass Thecostraca

2. Balanus (Barnacles)
Balanus
Exclusively marine
Shallow and tidal
waters
Roughly circular

3. Balanus (Barnacles)
Sessile
Filter-feeders
Encrusters
Shells composed of calcite
Most are hermaphroditic

7. Balanus (Barnacles)
Life Cycle
Fertilized
egg
Nauplius Cyprid
Adult

8. Nauplius

9. Cyprid

10. Balanus (Barnacles)
Representative species:
1. Balanus glandula (Common
acorn barnacle)
-rugged white shell with a base
that is not much wider than the
top
-shallow rocky area

11. Balanus glandula

12. Balanus (Barnacles)
2. Balanus crenatus
(Crenate barnacle)
-flat & white
-attaches to discarded
bottles and other debris

13. Balanus crenatus

14. Balanus crenatus

15. Balanus (Barnacles)
3. Balanus nubilus (Giant
barnacle)
-Rugged white shell with two
inner plates that close
-Can grow individually, but often
seen in dense clusters growing on
top of one another.

16. Balanus nubilus

17. Balanus nubilus

18. Balanus (Barnacles)
4. Pollicipes polymerus
(Gooseneck barnacle)
-dense colonies on shallow,
current swept reefs and walls
-exterior shell covered with
distinctive white plates

19. Pollicipes polymerus

20. Pollicipes polymerus