Granuloside, A Unique Linear Homosesterterpene from the Antarctic Nudibranch Charcotia granulosa

A new homosesterterpene with a unique linear skeleton, named granuloside (<b>1</b>), has been fully characterized from the Antarctic nudibranch Charcotia granulosa Vayssière, 1906 (Mollusca: Gastropoda). The planar structure of <b>1</b> was determined by extensive spectroscopic techniques on the methyl derivatives (<b>1a</b> and <b>1b</b>), and the <i>R</i> absolute configuration at C-4 is suggested by comparison of experimental and calculated ECD spectra of <b>1b</b>. Granuloside (<b>1</b>) is the first linear homosesterterpene skeleton ever reported and, despite the low molecular complexity, its chemical structure poses many questions about its biogenesis and origin in the nudibranch

Differential characters among <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. and <i>D</i>. <i>antarctica</i>.

Differential characters among D. carinova Moles, Avila & Wägele n. sp. and D. antarctica.</p

Phylogenetic tree of <i>Doto</i> species based on the combined COI, 16S, and H3 genes using Bayesian inference (BI) and maximum-likelihood (ML).

<p>Numbers on nodes indicate posterior probability values (BI) and bootstrap support values (ML). Specimens sequenced are in bold; <i>Doto antarctica</i> specimens are coloured in red. Schematic drawings of the reproductive system of <i>Doto</i> species are depicted (A–D), as well as the unsequenced <i>D</i>. <i>uva</i> Marcus, 1955 (E). <i>bc</i> bursa copulatrix; <i>gd</i> gonoduct; <i>nigl</i> nidamental glands; <i>pen</i> penis; <i>rs</i> receptaculum seminis; <i>vd</i> vas deferens.</p

Photographs of <i>D</i>. <i>antarctica</i> (left column: A,C,E,G) and <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. (right column: B,D,F,H); specimens subjected to micro-CT reconstruction.

<p><b>A</b> Live animal, where most of the cerata were lost; close up of the cerata. <b>B</b> Live picture right after collection, showing the <i>D</i>. <i>carinova</i> n. sp. spawning on top of the gorgonian <i>Primnoisis antarctica</i> (Isididae). <b>C</b>–<b>D</b> Lateral and dorsal view of the preserved animals. <b>E</b>–<b>F</b> Ventral view of the preserved animals. <b>G</b>–<b>H</b> Lateral view of the preserved egg masses.</p

Histological slide of outer surface of the egg mass in <i>Doto carinova</i> Moles, Avila & Wägele n. sp.

<p>Histological slide of outer surface of the egg mass in <i>Doto carinova</i> Moles, Avila & Wägele n. sp.</p

Scanning electron micrographs (SEM) of the radular teeth of <i>D</i>. <i>antarctica</i>.

<p>Scanning electron micrographs (SEM) of the radular teeth of <i>D</i>. <i>antarctica</i>.</p

The End of the Cold Loneliness: 3D Comparison between <i>Doto antarctica</i> and a New Sympatric Species of <i>Doto</i> (Heterobranchia: Nudibranchia)

<div><p>Although several studies are devoted to determining the diversity of Antarctic heterobranch sea slugs, new species are still being discovered. Among nudibranchs, <i>Doto antarctica</i> Eliot, 1907 is the single species of this genus described from Antarctica hitherto, the type locality being the Ross Sea. <i>Doto antarctica</i> was described mainly using external features. During our Antarctic research on marine benthic invertebrates, we found <i>D</i>. <i>antarctica</i> in the Weddell Sea and Bouvet Island, suggesting a circumpolar distribution. Species affiliation is herein supported by molecular analyses using cytochrome <i>c</i> oxidase subunit I, 16S rRNA, and histone H3 markers. We redescribe <i>D</i>. <i>antarctica</i> using histology, micro-computed tomography (micro-CT), and 3D-reconstruction of the internal organs. Moreover, we describe a new, sympatric species, namely <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp., and provide an anatomical comparison between the two Antarctic <i>Doto</i> species. Egg masses in both species are also described here for the first time. We demonstrate that micro-CT is a useful tool for non-destructive anatomical description of valuable specimens. Furthermore, our high resolution micro-CT data reveal that the central nervous system of both <i>Doto</i> species possesses numerous accessory giant cells, suggested to be neurons herein. In addition, the phylogenetic tree of all <i>Doto</i> species sequenced to date suggests a scenario for the evolution of the reproductive system in this genus: bursa copulatrix seems to have been reduced and the acquisition of a distal connection of the oviduct to the nidamental glands is a synapomorphy of the Antarctic <i>Doto</i> species. Overall, the combination of thorough morphological and anatomical description and molecular analyses provides a comprehensive means to characterize and delineate species, thus suggesting evolutionary scenarios.</p></div

Micro-CT reconstructions of the internal organs of <i>D</i>. <i>antarctica</i> (left column) and <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. (right column).

<p><b>A</b>–<b>B</b> Right antero-lateral view of all reconstructed organs. <b>C</b>–<b>D</b> Left antero-lateral view of the circulatory, digestive, excretory, and nervous systems. <b>E</b>–<b>F</b> Right lateral view of the male reproductive system. <b>G</b>–<b>H</b> Left lateral view of the reproductive system (mucus gland is not depicted here since it covers the whole view). <i>am</i> ampulla; <i>adiv</i> ampulla diverticulum; <i>au</i> auricle; <i>bc</i> bursa copulatrix; <i>cis</i> circulatory sinuses; <i>cgl</i> capsule gland; <i>cpg</i> cerebropleural ganglion; <i>dg</i> distal gonoduct; <i>dgdiv</i> digestive gland diverticula; <i>dgl</i> digestive gland (only depicted in <i>D</i>. <i>carinova</i> n. sp.); <i>gc</i> giant cells; <i>gon</i> gonad; <i>ht</i> heart; <i>int</i> intestine; <i>kid</i> kidney; <i>megl</i> membrane gland; <i>mugl</i> mucus gland; <i>oes</i> oesophagus; <i>od</i> odontophore; <i>ot</i> oral tube; <i>ov</i> oviduct; <i>peg</i> pedal ganglion; <i>pen</i> penis; <i>per</i> pericardium; <i>pg</i> proximal gonoduct; <i>pha</i> pharynx; <i>pro</i> prostate; <i>rad</i> radula; <i>rhg</i> rhinophoral ganglion; <i>rhi</i> rhinophore; <i>rhs</i> rhinophoral sheath; <i>sgl</i> salivary gland; <i>sin</i> sinus; <i>sp</i> sphincter; <i>sto</i> stomach; <i>vag</i> vagina; <i>vd</i> vas deferens; <i>ven</i> ventricle.</p

Sampling stations where <i>D</i>. <i>antarctica</i> and <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. were collected.

<p>Kapp Norvegia is situated in the eastern Weddell Sea.</p

Left antero-lateral view of the micro-CT reconstruction of the nervous system of <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. <i>cpg</i> cerebropleural ganglion; <i>gc</i> giant cells; <i>peg</i> pedal ganglion; <i>rhg</i> rhinophoral ganglion; <i>sin</i> sinus.

<p>Left antero-lateral view of the micro-CT reconstruction of the nervous system of <i>D</i>. <i>carinova</i> Moles, Avila & Wägele n. sp. <i>cpg</i> cerebropleural ganglion; <i>gc</i> giant cells; <i>peg</i> pedal ganglion; <i>rhg</i> rhinophoral ganglion; <i>sin</i> sinus.</p