# Trepenoids in Marine Heterobranch Molluscs
## 3 Sesquiterpenoids
### Bicyclic Sesquiterpenoids
The genus _Hypselodoris_ (now _Felimida_ for Eastern Pacific, Atlantic, and Mediterranean species) [149] is a good example of sponge-derived furanosesquiterpenes, usually accumulated into particular structures, called Mantle Dermal Formations (MDFs) [3; 25]. _Hypselodoris peta webbi_ from the NW Atlantic presents the furanosesquiterpenes longifolia and tavacfuran, while _Hypselodoris peta azorica_ additionally presents microcionin-1 [150]. The South African _Hypselodoris capensis_ presents several known sesquiterpenes, the antifeedant nakafurans 8 (28) and 9 (Figure 4), and several sesquterepes (see below), from the sponges _Fasciospongia_ sp. and _Dysidea_ sp. on which it probably feeds [151]. Moreover, _H. infucata_ from Hawai'i presents nakafuran 8 and 9, probably from _Dysidea fragilis_[152]. _H. obscura_ from Australia presents dendrolasin, (-)-euryfuran, and (+)-pallescensin A, while _H. whitei_ possesses (-)-euryfuran (29) (Figure 4), (-)-furoydsin, (-)-furosydinin, and dendrolasin [90]. Some known sesquiterpenes, including dehydropolasescensin-2 are found in the Patagonian doridacean _Tyrinna nobilis_, together with an unusual diterpene (see below) [89]. In addition, several species of the genus _C. teratosoma_ from China contain bicyclic sesquiterpenoids. In particular, _C. teratosoma tribotatum_ and _C. gracillium_ contain the four furanosesquiterpenes, pallescensin B (30) (Figure 4), (-)-furodysinin, (-)-dehydrohebadysolidide, and (-)-herbadysolidide, previously found in _Dysidea_ spp. sponges, and suggested to be obtained from diet. These sea slug possess an interesting mechanism with dorsal horns containing MDFs fully loaded with furanosesquiterpenoids. Although a defensive role is highly probable, it remains to be further proved using sympatric predators [46; 153]. Recently, a study on 19 species of Chromodorididae nudibranch's from Australia reported 72 compounds, including many bicyclic fun'aosesquiterpenoids, among others, found in mantle and internal glands [154]. In particular, _Mexichromis festiva_ contains euryfuran and dendrolasin, while _M. mariei_ only possesses euryfuran. _Hynselodoris bennetti_ and _H. obscura_ both present euryfuran as major metabolite, but _H. bennetti_ contains also agassizin, dehydrohebady'solidide, and pallescensone. _H. obscura_ also presents furodysinin, furodysin, and dendrolasin, while _H. tryoni_ contains dehydrohebady'solidide, furodysinin, nakafuran-9, and dendrolasin. In the same study, _Ceratosoma tribotum_ was found to present furodysinin, furodysin, and dendrolasin in the viscera, while other compounds were found additionally in the mantle: agassizin and dehydrohebady'solidide, and _C. brevicaudatum_ possesses mixtures of the same metabolites and some unidentified compounds. In Dendronoids, the species _Tritonia hammerorum_ from Florida sequesters julieannafuran (31) (Figure 4), a furanogermacrane from its food, the sea fan _Gorognia ventulina_, which is deterrent against reef fish in field assays [155]. Furthermore, some byciclic sesquiterpenes are found in the mantle of _Tochuina tetraquetra_ and its food, the soft coral _Gersemia rubiformis_ from British Columbia [156]. These are totuinyl acetate and dihydrouchuinyl acetate, two cuparane sesquiterpenoids, found together with some dirpenes (see below). Their ecological activity has not been studied so far. Similarly, the Arminacean _Leminda millerca_ from South Africa presents several sesquiterpenes, probably from its octocoral prey (_Alcyonium foliatum_, _A. valdiviae_, _A. furi_, and _Capnella thyrsoidea_) [157; 158]. These are millecrones A (32) and B and millecrols A and B (Figure 4). Among them, millecrone A inhibited the growth of _Candida albicans_ at 50 ug/disk, while millecrone B was active against _Staphylococcus aureus_ and _Bacillus subtilis_ at 50 ug/disk; millecrol B was active only against _B. subtilis_ at 50 ug/disk [45]. In other sampling areas, _L. millercra_ presents some quinones, and some of its chemicals are described to be obtained from its diet, the gorognia _Leptogorgia palma_[158].