Emerald Sea Slugs (Elysia chlorotica) and Chloroplasts From Yellow Green Algae (Vaucheria litorea)

The above-mentioned yellow green algae carry the scientific name Vaucheria litorea. The formal description of the genus dates to 1801. It expresses the expertise of Geneva-born Swiss botanist and phytogeographer Augustin Pyramus de Candolle (February 4, 1778 – September 9, 1841), whose love for plants was sufficiently compelling to inspire three generations of direct descendants to emulate him:

• Alphonse Louis Pierre Pyrame de Candolle (October 28, 1806 – April 4, 1893);

• Anne Casimir Pyrame de Candolle (February 20, 1836 – October 3, 1918);

• Richard Émile Augustin de Candolle (December 8, 1873 – May 9, 1920).

The genus honors Geneva-born Swiss botanist and pastor Jean Pierre Étienne Vaucher (April 17, 1763 – January 6, 1841).

The official presentation of the particular algal species goes back to 1823. It has as its taxonomist Båstad-born Swedish botanist, phycologist (algae specialist), representative, and theologian Carl Adolph Agardh (January 13, 1785 – January 28, 1859), whose scientific diligence was so inspiring as to compel his son, Lund-born Swedish botanist, phycologist, and taxonomist Jacob Georg Agardh (December 8, 1813 – January 7, 1901), to equal him. The species name has as etymological origins the Latin feminine singular adjective litorea (“of or relating to the seashore”). It honors its coastal presence since the Vaucherian genus includes estuarine, freshwater, marine, and terrestrial species. Intertidal, littoral yellow green algae specifically inhabit coastal brackish and salt-marsh waters along:

• Europe;

• North America.

Intertidal, littoral yellow green algae appear filamentous, stringy, and tubular. They attach to the ground through anti-drifting, rhizoid “hold-fasts.” They branch into hollow tubes. They do not subdivide into cross-walls except after injury or around reproductive organs. Chloroplasts, cytoplasm, nuclei, and nutrients flow smoothly through the Vaucherian algae's central, cytoplasm-filled, hollowed-out compartments known as vacuoles. Vaucherian yellow green algae have:

• Beta-carotene;

• Carotenoid diadinoxanthin;

• Chlorophyll a and c.

They lack chlorophyll b and fucoxanthin. Reproduction may be carried out:

• Asexually by fragmenting into floating small sections;

• Sexually by the hook-shaped, slender male reproductive organ (antheridia) fertilizing the single egg cells of the spherical female reproductive organs (öogonia).

They serve as the preferred food sources of emerald sea slugs.  

The formal identification of emerald sea slugs dates to 1818. It draws upon the expertise of the Nice-born botanist and naturalist (April 8, 1777 – August 25, 1845) who is claimed by:

• France as Antoine Joseph Risso for being bilingual in French and Niçard (Ligurian/Occitan language dialect) before French annexation of the subsequent Alpes Maritime’s departmental capital through the Treaty of Turin on March 24, 1860;
• Italy as Antonio Giuseppe Risso for being the member of an ancient, Italian-speaking, noble family of the northwestern peninsula and Sardinia.

The genus name Elysia generally evokes the Elysian Fields, the resting place of ancient Greece’s benevolent and brave, even though here it specifies the slug’s leaf-like shape from fleshy lateral protrusions.

Beneficent and bold are adjectives which may or may not characterize Elysian sea slugs. The official taxonomy of the species goes back to 1870. It honors New Ipswich-born United Statesian physician Augustus Addison Gould (April 23, 1805 – September 15, 1866), as:

• Conchologist (specialist through investigation of mollusc shells);
• Malacologist (specialist through study of mollusc organisms).

The taxonomic date is posthumous to specify the information contained in the second edition -- released in 1870 -- of the above-mentioned scientist’s Report on the Invertebrata (from the United States Exploring Expedition, 1838 – 1842 under Lieutenant Charles Wilkes [April 3, 1798 – February 8, 1877]) -- originally published in 1841. The species name chlorotica recognizes the sacoglossan’s (sap-sucker) color (χλωρός [khlōrós, “green-yellow”]).

Emerald sea slugs frequent depths of 1.64 feet (0.5 meters) within coastal eastern North America’s:

• Freshwater creeks and pools;
• Tidal marshes 3 – 32% saline.

They experience life cycles and natural histories as:

• Eggs hatching within 7 – 8 days;
• Larval feeders on phytoplankton;
• Red-spotted, brown-bodied juvenile feeders on algae 16 days.

Cross-copulating, self-fertilizing hermaphroditic adults have:

• Paired eyes, parapodia (wings), and tentacles;
• Radula (piercing tooth) to ingest algal cytoplasm and nuclei;
• Red-spotted, white-veined bodies measuring 0.28 - 1.77 inches (7 – 45 millimeters);
• Snail-like head and neck;
• 10 – 12-month lifespans.

Until next spring’s egg-laying, they make chlorophyll by:

• The kleptochemistry of “stolen” algal camouflage-friendly pigments and predator-toxic metabolites;
• The kleptoplasty of “stolen” algal chloroplasts, anti-herbivory compounds, and photosynthesizing proteins.

Like people and pets, emerald sea slugs end up resembling yellow green algae. As coastal plant-eaters, they give innovative twists to digesting favorite intertidal, littoral prey. They have coral-like, live-in food sources. But un-coral-like, they invade algal cells to extract chloroplasts. They keep kleptoplasts (abducted disks) in cells throughout their super-branched guts. These plant-like animals know how to:

• Effectuate horizontal gene transfer since their DNA includes algal psbO genes for making photosynthesis-friendly proteins;
• Manufacture chlorophyll;
• Pass chlorophyll-making powers from parent to progeny since slug circulatory systems flow algal nuclear DNA directly into the slug’s hermaphroditic reproductive organs.

The implications of the above-mentioned skill set make emerald sea slugs animals of interest to wildlife-loving amateurs and professionals worldwide.

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Eysia chlorotica consumes Vaucheria litorea, its obligate algal food; K. Pelletreau et al., Lipid Accumulation, PLOS ONE, vol. 9, issue 5 (May 2014), Figure 1A, page 2: CC BY 4.0, via PLOS ONE @ https://journals.plos.org/plosone/article/figures?id=10.1371/journal.pone.0097477

University of Geneva campus: Orangery in background was replaced by Wall of the Reformation in 1909; Collection de la Société d'Arts, Palais de l'Athénée, Genève

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Chemical image created with Discovery Studio Visualizer: Jynto, Public Domain (CC0 1.0), via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Chlorophyll-a-3D-spacefill.png

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