Sea-hare

In Mollusca, bioluminescence occurs in a great variety of organisms having distinctly different appearances, such as the classes Gastropoda (limpets, snails and sea hares), Bivalvia (clams), and Cephalopoda (squids and octopuses). All luminous molluscs currently known are marine organisms, except the New Zealand fresh water limpet Latia neritoides and the Malaysian land snail Quantula (Dyakia) striata. No information is yet available on the biochemical aspects of the Quantula luminescence. 

It is most probable that sleep and waking stem from an inherent cycle of neuronal activity that can be influenced dramatically by changes in sensory stimulation. This is demonstrable not only in humans and laboratory animals, but also in invertebrates. Thus, while we cannot be sure that other animals sleep in the same way that we do, they do show a circadian cycle of motor activity. In some (nocturnal) species, such as the rat, this activity is actually highest during darkness. Even aplysia, the sea hare, has such a rhythm but this is more like that of humans in being maximally active during daylight (diurnal). 

It is generally accepted [47] that sea hares, opisthobranch molluscs belonging to the order Anaspidea, are protected by dietary metabolites obtained by... 

More recently [135], 72 and 73 were also found in the sea hare Stylocheilus longicauda but, surprisingly, only dehalogenated 73 was present in the algal food source, Lyngbya majuscula. This metabolic comparison suggested an uncommon in vivo bromination of 73, but further experiments need to ascertain whether L. majuscula is the unique food source of S. longicauda. 

Structural similarities between the monomeric units of aplydilactone (144) and the red algal metabolites constanolactone A (145) and B (146), suggest an analogous biosynthetic origin. Dehydration of two m3 unsaturated eonstanolac-tone-type units could result in the formation of the unsymmetrical dimer (Scheme 11). Since sea hares are known to feed extensively on red algae and sequester natural products from this source, it remains possible that aplydilactone (144) derives, at least in part, from a dietary source. 

Watson M, Rayner MD (1973) Midgut gland toxins of Hawaiian sea hares. II. Preliminary pharmacological study. Toxicon 11 269-276... 

An illuminating example of a community consequence of plant defensive metabolites, and of a grazer s adaptation to exploit its host plant, is the ability of some herbivores to sequester plant-derived secondary metabolites for their own defenses (e.g., Avila 1995 Marin and Ros 2004). In terrestrial systems, several specialist insects can sequester defensive chemicals from their host plants (e.g., Nishida 2002), but in aquatic plant-herbivore systems with a prevalence of generalist herbivores this is less common. However, sea hares (Anaspidea) and some other herbivorous opisthobranch molluscs are known to be able to sequester defenses from their algal foods (Avila 1995 Marin and Ros 2004). For the opisthobranch species that are known to obtain metabolites from their food, algae were the... 

Johnson PM, Kicklighter CE, Schmidt M, Kamio M, Yang HC, Elkin D, Michel WC, Tai PC, Derby CD (2006) Packaging of chemicals in the defensive secretory glands of the sea hare Aplysia califomica. J Exp Biol 209 78-88... 

Panacene (61) is a metabolite of the sea hare Aplysia brasiliana and acts as a fish antifeedent [61]. The synthesis of the racemic natural product, published by Feldman et al. [77] in 1982, takes advantage of the anti-selective SN2 -substitution of the propargylic mesylate 67 with LiCuBr2 (Scheme 18.21). In contrast, the later attempted biomimetic synthesis by treatment of the enyne 68 with NBS or 2,4,4,6-tetrabromocyclohexadienone did not proceed stereoselectively and led to a 1 1 mixture of the target molecule 61 together with its allenic epimer [78]. 

Predators ignore sea hares because, like other mollusks without shells, they have chemicals that afford them the protection once given by a shell. (We saw earlier that a compound from a tropical sea hare is now a promising anticancer drug.) Many sea hares have an acrid or fetid odor that is distinctly unpleasant to humans. Their egg masses and their skin must be distasteful, because one exploratory bite is enough to convince a would-be assailant to look elsewhere for food. For some species, the deterrents responsible for these properties may come directly from their seaweed diet, but other species seem to synthesize these defenses for themselves. The evidence is mixed and confusing. 

There is also another defensive secretion that sea hares release less readily than ink. This is a milky white liquid called opaline, so viscous that it can be stretched out through the air into a long string. For sea hares, opaline is what is known as a defining characteristic, because all sea hares emit opaline whereas no other species are known to do so. In spite of its defining role, opaline remains poorly understood. It contains proteins and perhaps components derived from the animals diet the evidence here is in dispute. A sea hare releases opaline less readily than ink but seems to do so as a second response to serious predatory assaults. When touched by a sea anemone s tentacles, a sea hare discharges a shot of opaline, which causes the anemone s tentacles to contract. No one yet understands how opaline deters predators or what chemicals are responsible for its activity. 

Reef fishes Sea hares Stylocheirus Alkaloids malyngamide A and B, Paul and... 

Paul, V. J. and Pennings, S. C. (1991). Diet-derived chemical defenses in the sea hare Stylocheirus longicauda (Quoy et Gaimard 1824). Journal of Experimental Marine Biology and Ecology 151,227-243. 

Debromoaplysiatoxin and aplysiatoxin were first isolated from the midgut gland of the sea hare Stylocheilus longicauda by Kato and Scheuer in 1974 (4). The two toxins were accompanied by the... 

It is interesting that the digestive tracts of sea hares and fish that feed upon L. ma.iuscula are not affected by the aplysia-toxins and lyngbyatoxin A. Preliminary studies by Fujiki suggest that the cells of sea hares may lack the tumor promoter-binding receptors that are so common in mammalian cells (34). 

Fedorov, S.N. Shubina, L.K. Kalinovsky, A.I. Lyakhova, E.G. Stonik, V.A. (2000) Structure and absolute configuration of a new rearranged chamigrane-type sesquiterpenoid from the sea hare Aplysia sp. Tetrahedron Lett., 41,1979-82. 

FIGURE 5.1 Structure of dolastatin 10 derived from the sea hare (mollusk) Dolabella auricularia. 

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