Coronula diadema Linnaeus, 1767

Common name(s): Whale barnacle

Synonyms: Single barnacle
Phylum Arthropoda 
Subphylum Crustacea 
Class Maxillopoda 
Order Sessilia 
Superfamily Coronuloidea 
Family Coronulidae 
Subfamily Coronulinae 
Coronula diadema on the lower side of the throat of a humpback whale on a Washington coast beach. Both the whale and the barnacle are thoroughly dead. The barnacle's rostrum and the front of the whale are to the left. The diameter of this barnacle is about 3 to 3.5 cm.
(Photo by:  Dave Cowles, July 2021)

Description:Coronula diadema is one of only six living species of barnacles that have been found on whales. This species is distinct from other whale barnacles because it stands tall and upright on the whale skin without being deeply embedded, but does not grow a fleshy stalk. It has six fixed plates which stand largely upright and have strong vertical ridges and which also have horizontal undulations near their basal ends. This plate configuration gives it the diadema (crown) designation and is sometimes referred to as "barrel-shaped" in the literature. Its movable plates (terga and scuta) are not as well developed as they are in barnacles from Family Balanidae but they do have an opercular membrane which is yellowish and contains one pair of valves which can close the opening (see photo above). The barnacle can grow to 30-59 mm tall, projecting from the whale's skin, and to 8.5 cm diameter. 

How to Distinguish from Similar Species:Coronula reginae, the most similar species, also is common on humpback whales. It also has six plates but does embed somewhat in the skin. It only grows to about 13-19 mm tall and in larger individuals the wall plates become flattened rather than standing tall as they do in C. diadema.

Geographical Range:  Worldwide, northern and southern hemisphere

Depth Range:  Epipelagic (on whales)

Habitat:  Mainly on humpback whales, especially around the head, fins, and throat. Occasionally on other whale species such as blue, right, fin, sei, and sperm whales. 

Biology/Natural History:  The rostrum of this species faces the anterior end of the whale, so that the cirri (feet), when extended, face the oncoming current as the whale swims. The cirri do not project far out of the aperture, however, probably due to the high current speeds the barnacle would encounter due to the whale's swimming speed. The species is thought to be a commensal symbiont, living on the whale while doing it no harm or benefit. Some humpback whales may use rough parts of their skin, covered with barnacles, to fend off orca whales however, in which case the barnacles would be mutualist symbionts. Another barnacle, the smaller stalked Conchoderma auritum and less often Conchoderma virgatum, often attach to the downstream fixed plates (carina) of this species. C. diadema is thought to have a lifespan of one year or less. Observers have reported that the species has mostly small individuals in early summer, with larger individuals in late summer and in winter, but these may disappear in late winter, replaced by settling larvae.  The larvae hatch as nauplii then transition to a nonfeeding cypris larva which settle when exposed to a piece of the whale's skin.



Dichotomous Keys:
  Kozloff, 1987, 1996 (mentioned but not keyed)

General References:
  Morris et al., 1980

Scientific Articles:

Cornwall, I.E., 1924. Notes on West American whale barnacles. Proceedings of the California Academy of Sciences Series 4, 13 (26): pp. 421-431

Cornwall, I. E., 1927. Some North Pacific whale barnacles. Contributions to Canadian Biology and Fisheries 3: pp. 503-517

Crisp, D.J., and H. G. Stubbings, 1957. The orientation of barnacles to water currents. Journal of Animal Ecology 26: pp. 179-196

Darwin, Charles, 1854. A monograph on the sub-class Cirripedia, vol. 2. Royal Society of London. 684 pp., 30 plates

Newman, W.A., and A. Ross, 1976. Revision of the balanomorph barnacles; including a catalog of the species. San Diego Natural History Museum Memoir 9: pp. 1-108

Nogata, Yasuyuki and Klyotaka Matsumura, 2005. Larval development and settlement of a whale barnacle. Biological Letters 2: pp. 92-93.

Scarff, James E., 1982. Occurrence of the barnacles Coronula diademaC. reginae and Cetopirus complanatus (Cirripedia) on Right Whales. Scientific Report Whales Research Institute No. 37 pp. 129-153

Web sites:

General Notes and Observations: Locations, abundances, unusual behaviors:

More Coronula diadema barnacles on the same whale. Notice how a slight flap of skin covers the very base of the barnacles but they are not sunken into the skin.More barnacles

The whole barnacleed whale, lying belly-up (supine) on the beach. This individual appears to be a juvenile. Whole whale

Authors and Editors of Page:
Dave Cowles (2021):  Created original page
CSS coding for page developed by Jonathan Cowles

Salish Sea Invertebrates web site provided courtesy of Walla Walla University