Your assignment is to prepare and submit a paper on commensal and parasitic barnacles. On the other hand, parasitic barnacles bore through the exoskeleton of the host and moves to the blood and the midgut of the animal until it branches into a mass of harmful tissue, thus killing the animal host (“Sacculina”). Overall, there are several types of barnacles but only four orders.
The first order of barnacles is the order Thoracica, or the “true barnacles” Newman & Abbott). The Thoracica are the most important because they are more abundant and more conspicuous than the species of the other orders. Although the Thoracica occurs most abundantly in the tropical Indo-Pacific region of the ocean, they are basically found in all types of marine environments, both in saltwater and freshwater. However, it remains a fact that “none completes its life cycle in freshwater” (Newman & Abbott).
The average size of a Thoracica barnacle is “generally moderate, a few centimeters in greatest dimension, but some…exceed 10 cm and others but a few millimeters” (Newman & Abbott). The adult Thoracica is basically “permanently attached” yet most do not shed off their calcareous shell all throughout their lives (Newman & Abbott).
It is actually the Thoracica barnacles that form symbiotic relationships with organisms that are much larger than the average size of the true barnacles: “whales, sea snakes, lobsters, medusa, corals and sponges” (Newman & Abbott). With the aforementioned animals, the true barnacles acted as commensals. However, a few true barnacles have actually become “nutritionally dependent” on larger animals like shark, corals or worms, especially during the earlier stages of barnacle evolution, and although their symbiosis was only for “support or protection,” these relationships were still considered parasitic (Newman & Abbott).
There are three suborders of Thoracica barnacles.