Defenses
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  Acid secretions
 

Defenses of nudibranchs and relatives include acid secretions, considered in this section, and
CAMOUFLAGE (CRYPSIS),
FAST CRAWLING & SWIMMING,
MUCOUS COATINGS,
CERATAL AUTOTOMY,
NUTRITIONAL CONTENT
,
SPICULES
,
NEMATOCYSTS
,
VACUOLATED SKIN WITH PROTECTIVE SPINDLES,
INK & OPALINE SECRETIONS,
SECONDARY METABOLITES
,
ALARM PHEROMONES,
APOSEMATIC (WARNING) COLORATION & BATESIAN MIMICRY, and
NAVANAX: A SPECIAL CASE STUDY, considered in other sections. 

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Research study 1
 

drawing of epidermis of Berthella californica showing distribution of pigment granules an acid-secreting cellsphotograph of notoaspidean Berthella caifornica courtesy Dong Bum Ko, KoreaAt least one west-coast species of opisthobranch, the notaspidean Berthella californica, secretes acid onto its skin for defense, but there are many more species worldwide that employ this strategy. The acid, a mixture of sulphuric and hydrochloric with a pH of 1-2, is contained within vesicles in acid-secreting cells in the skin.  When the nudibranch is irritated, special muscles around the vesicles contract and force the acid onto the skin surface.  Preliminary laboratory experiments on the defensive role of the secretions in related species in Port Erin, England show that the flesh of the nudibranchs is rejected as food by several fishes, including blennies, flatfishes, and pollack.  As for Berthella, pufferfishes in the Gulf of California will bite at them but then spit them out.  Thompson 1960 J Mar Biol Ass UK 39: 115; Gillette et al. 1991 J Exp Biol 156: 335. Photograph courtesy Dong Bum Ko, Korea and seaslugforum.

Berthella californica 1X

 
Research study 2
 

Another acid-secreting west-coast notaspidean is Pleurobranchaea californica, which releases its acid in response to skin abrasion or compression. Interestingly, exposure of this or other acid-secreting species to small aliquots of acidified seawater (HCl) elicits aversive behaviour, including withdrawal of affected parts, retraction of oral veil and head, turning, and rapid locomotion.  The responses, shown in the photo series below for an individual P. californica attached to the side of an aquarium, last for several minutes.  Additionally, in the case of P. californica, a treated individual may commence swimming using dorsal-ventral flexions to lift itself off the substratum.  Application of dilute solutions of the amino-acid taurine, a feeding stimulant in many marine invertebrates, also induces acid secretion in PleurobranchaeaGillette et al. 1991 J Exp Biol 156: 335.

NOTE of pH 2-3; thus, less acidic than their own secretions: applied in 1ml aliquot to head region

 
photograph 1 in a series showing aversive response of notaspidean Pleurobranchaea californica to application of acidified seawater photograph 2 in a series showing aversive response of notaspidean Pleurobranchaea californica to application of acidified seawater photograph 3 in a series showing aversive response of notaspidean Pleurobranchaea californica to application of acidified seawater photograph 4 in a series showing aversive response of notaspidean Pleurobranchaea californica to application of acidified seawater
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