Navanax inermis

Navanax inermis, common name the California aglaja, is a large species of predatory sea slug, a marine opisthobranch gastropod mollusk in the family Aglajidae. Navanax is not a nudibranch, even though it somewhat resembles one; it belongs to a more ancient lineage of opisthobranchs called the cephalaspideans or head shield slugs and snails.

California aglaja
From Santa Barbara, California
Scientific classification
Kingdom:
Animalia
Phylum:
Mollusca
Class:
Gastropoda
(unranked):
clade Heterobranchia
clade Euthyneura
clade Euopisthobranchia
clade Cephalaspidea
Superfamily:
Philinoidea
Family:
Aglajidae
Genus:
Navanax
Species:
N. inermis
Binomial name
Navanax inermis
(Cooper, 1863)
Synonyms
  • Doridium purpureum (Bergh, 1894)
  • Posterobranchaea maculata d'Orbigny, 1835 (nomen oblitum)
  • Strategus inermis J.G. Cooper, 1863 (basionym)

Description

The body of N. inermis can be tan, black, or purple, with yellowish streaks.[1] Yellow or orange streaks and blue dots are visible on the margins.[1] It has two large parapodial folds that run the length of either side of the body, and almost touch at the midsection.[1] This species possesses a small internal shell.[1][2] Individuals are typically between 2.5 and 10 inches in length.[1]

N. inermis does not possess a radula or organs associated with vision.[1][3]

Distribution and habitat

This species occurs in the eastern Pacific Ocean and Gulf of California. Its range is from Monterey, California to Baja California.[4]

N. inermis can commonly be found on rocky intertidal regions and subtidal mudflats.[1][2][3]

Ecology

Diet

Navanax inermis is a voracious carnivorous predator.[2] Common prey items include other sea slugs, like bubble snails and nudibranchs, and small fish.[4][5] As N. inermis lacks visual perception, it finds prey by using its chemoreceptors to follow the slime trails of other organisms.[1][3][4]

Reproduction

N. inermis is a simultaneous hermaphrodite.[6] Copulation can occur in groups, commonly referred to as chains, of up to four individuals.[6] In the southern portion of its range, N. inermis spawns year round, producing upwards of 800,000 eggs at a time.[4] After 7 to 19 days of development, embryos are released and live as plankton.[4]

N. inermis with a yellow base color

Locomotion

N. inermis slides over surfaces with the help of a mucopolysaccharide slime trail.[3]

Defense

When disturbed, N. inermis secretes a bright yellow substance into its slime trail, which can persist for several hours. This secretion causes some other organisms to break pursuit of the slug.[3]

References
  1. N., Kerstitch, Alex (1989). Sea of Cortez marine invertebrates : a guide for the Pacific Coast, Mexico to Ecuador (1st ed.). Monterey, Calif.: Sea Challengers. ISBN 978-0930118143. OCLC 18520858.
  2. C., Brusca, Richard (1980). Common intertidal invertebrates of the Gulf of California (Rev. and expanded, 2nd ed.). Tucson: University of Arizona Press. ISBN 978-0816506828. OCLC 5310036.
  3. Sleeper, Howard L.; Paul, Valerie J.; Fenical, William (January 1980). "Alarm pheromones from the marine opisthobranch Navanax inermis". Journal of Chemical Ecology. 6 (1): 57–70. doi:10.1007/bf00987527. ISSN 0098-0331.
  4. Paine, Robert T. (1965). "Natural History, Limiting Factors and Energetics of the Opisthobranch Navanax Inermis". Ecology. 46 (5): 603–619. doi:10.2307/1935000. JSTOR 1935000.
  5. "The Sea Slug Forum - Navanax inermis". www.seaslugforum.net. 2010-07-15. Retrieved 2018-08-12.
  6. Leonard, Janet L.; Lukowiak, Ken (1985). "Courtship, copulation, and sperm trading in the sea slug, Navanax inermis (Opisthobranchia: Cephalaspidea)". Canadian Journal of Zoology. 63 (12): 2719–2729. doi:10.1139/z85-406. ISSN 0008-4301.
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