TWO EXAMPLES OF SEA SLUGS (NUDIBRANCHS = “SEA HARES”)

Phylum Mollusca

Class Gastropoda

Order Nudibranchia

Family Tethydidae

Genus Tethys Linnaeus, 1767

Species fimbria

This group of gastropods is also called nudibranchs because they lack a hard shell. They are among the most unusual looking marine gastropods in the world! Their head is covered by a hood, and the upper part of their body has projecting external gills that can be brightly colored.

Tethys, which is one of the two living genera of this family, consists of three living species. One unforgettable example is Tethys fimbria, which lives today in the temperate waters of the Mediterranean Sea, as well as along the east coast of the Atlantic Ocean; from Portugal to the Gulf of Guinea (in western Africa). This animal crawls around on sandy and muddy bottoms, in relatively deep waters (i.e., below maximum diving depth for collectors using compressed air). But this gastropod migrates to shallower waters to spawn. It prefers to crawls around on the ocean bottom, but, if disturbed, it can swim. Tethys fimbria can grow up to 30 cm (12 in.) in length.

Figure 1. Sketch of an adult specimen of T. fimbria. Image is derived and modified from a Wikipedia image. I highly recommend that you go to Wikipedia to see amazingly beautiful images of this animal!

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Family Aplysiidae

Genus Aplysia

Species californica (Cooper, 1863)

This species of nudibranch is referred to as the “California Brown Sea Hare.” Adult specimens can be up to 40 cm long (16 inches) (Morris et al., 1980, p. 313) and weighing several kilograms; making it the largest known gastropod in the world. Juvenile specimens have no spots. This species is found all along the California coast, as well as that of Baja California and western Mexico (Wikipedia, 2024).

Figure 2. Sketch of an adult specimen of A. californica. Image is derived and modified from Morris et al. (1980, “page” P97 pertaining to the illustrations but not to the main text of their work, fig. 14.8a).     

Figures 3 and 4. An adult specimen, estimated 15 cm long (6 inches) of Aplysia californica in a southern California tide pool at Abalone Cove, Palos Verdes Peninsula, Los Angeles County. Images taken by Cathy Groves (affiliated with the Natural History Museum of Los Angeles County) and kindly provided by Lindsey T. Groves, Collection Manager of Mollusks, Natural History Museum of Los Angeles County, California. 

References Consulted

Linnaus, C. 1767. Systema Naturae, v. 1, 10^th edition. British Museum of Natural History, Regnum Animalae.

Morris, R.H., D.P. Abbott, and E.C. Haderlie. 1980. Stanford University Press, Stanford, California, total 690 pp., including a separate section of only photographs, numbered P1-P200.

Wikipedia, 2004