Sequestration and Cyanobacterial Diet Preferences in the Opisthobranch Molluscs Dolabrifera nicaraguana and Stylocheilus rickettsi

A multidisciplinary approach was used to assess chemical ecological dietary interactions between marine organisms as a tool to isolate novel ecologically relevant compounds with biotechnological potential. First, laboratory-based feeding preference assays of the sea hare Dolabrifera nicaraguana (previously known as D. dolabrifera), an anaspidean mollusc, were conducted by simultaneously offering six food options collected from nearby tidal pools in the Coiba National Park in the Tropical Eastern Pacific of Panama. An evaluation of preferred dietary repertoire revealed D. nicaraguana significantly preferred cf. Lyngbya sp. over the cyanobacterium Symploca sp., green alga Chaetomorpha sp., and red alga Spyridia sp. A no-choice feeding assay using cf. Lyngbya sp. or green alga Cladophora sp. supported this finding. Secondly, we conducted bioactivity-guided fractionation using the preferred food source of D. nicaraguana, the ‘hair-like” cf. Lyngbya sp. from which we also isolated and elucidated two new depsipeptide compounds, veraguamide M (1) and veraguamide N (2). Veraguamides M (1) and N (2) showed in vitro activity toward the malaria-causing parasite Plasmodium falciparum with GI50 values of 4.2 and 4.3 μM, respectively, and therapeutic windows of 7.0–8.0 (based on moderate cytotoxicities to mammalian Vero cells with GI50 values of 29.3 and 34.1 μM, respectively). Veraguamide N (2) was also active against Leishmania donovani, the causative agent of visceral leishmaniasis, with a GI50 value of 6.9 μM. We then evaluated sequestration of these new compounds by D. nicaraguana used in the feeding assays and found trace amounts of the dietary sequestered compounds. Finally, we evaluated sequestration of these new compounds by the sea hare Stylocheilus rickettsi (previously known as S. striatus) that were grazing on the cf. Lyngbya sp. used in the feeding assays and found both to be sequestered. This study is the first example whereby compounds with significant activity against tropical parasites have been found in both the sea hare S. rickettsi and its cyanobacterial food source. These results suggest that chemical ecological studies involving sea hares and cyanobacteria continue to provide a diverse source of bioactive compounds with biotechnological potential.

Antiproliferative and Antimicrobial Potentials of a Lectin from Aplysia kurodai (Sea Hare) Eggs

In recent years, there has been considerable interest in lectins from marine invertebrates. In this study, the biological activities of a lectin protein isolated from the eggs of Sea hare (Aplysia kurodai) were evaluated. The 40 kDa Aplysia kurodai egg lectin (or AKL-40) binds to D-galacturonic acid and D-galactose sugars similar to previously purified isotypes with various molecular weights (32/30 and 16 kDa). The N-terminal sequence of AKL-40 was similar to other sea hare egg lectins. The lectin was shown to be moderately toxic to brine shrimp nauplii, with an LC50 value of 63.63 µg/mL. It agglutinated Ehrlich ascites carcinoma cells and reduced their growth, up to 58.3% in vivo when injected into Swiss albino mice at a rate of 2 mg/kg/day. The morphology of these cells apparently changed due to AKL-40, while the expression of apoptosis-related genes (p53, Bax, and Bcl-XL) suggested a possible apoptotic pathway of cell death. AKL-40 also inhibited the growth of human erythroleukemia cells, probably via activating the MAPK/ERK pathway, but did not affect human B-lymphoma cells (Raji) or rat basophilic leukemia cells (RBL-1). In vitro, lectin suppressed the growth of Ehrlich ascites carcinoma and U937 cells by 37.9% and 31.8%, respectively. Along with strong antifungal activity against Talaromyces verruculosus, AKL showed antibacterial activity against Staphylococcus aureus, Shigella sonnei, and Bacillus cereus whereas the growth of Escherichia coli was not affected by the lectin. This study explores the antiproliferative and antimicrobial potentials of AKL as well as its involvement in embryo defense of sea hare.

Saved by the Shell: Molecular Analysis Detects the Cryptic Sea Hare, Aplysia concava G. B. Sowerby I, 1833 (Mollusca: Heterobranchia: Aplysiidae), from Oceania, with a Redescription

A recent taxonomic revision split the circumglobal sea hare Aplysia parvula into 10 constituent taxa, of which only three are likely to be found in the Southern Pacific. This prompted an investigation of animals previously identified as A. parvula from Australia. Specimens collected from Eastern Australia and Hunter Island, east of New Caledonia, could not be satisfactorily identified with any of the currently accepted taxa based on morphological diagnostic features listed in the revision; however, the presence of a highly concave shell is diagnostic. Quantification of genetic divergence using Cytochrome Oxidase I (COI) supports the delineation of this species as a distinct taxon, and a phylogenetic reconstruction based on concatenated COI, 16S and H3 markers reveals a sister relationship with the newly described Aplysia ghanimii from the Atlantic and Western Indian Oceans and an undescribed species from Japan. As a result, the name Aplysia concava G. B. Sowerby, I, 1833 is resurrected for this species. As the original description was based solely on a shell, a redescription is provided here with photographs of living animals and microscope images of internal anatomical structures.

Short communication: Environment and morphometric of sea hare Dolabella auricularia from shrimp pond, Sorong, West Papua, Indonesia

Sofian A, Suhermanto A, Saidin, Sayuti M, Novianto D, Widyasari F. 2021. Short communication: Environment and morphometric of sea hare Dolabella auricularia from shrimp pond, Sorong West Papua, Indonesia. Biodiversitas 22: xxxx. Dolabella auricularia is a herbivorous marine biota living on the shallow seabed, which is found mostly in Indo-Pacific waters. The purpose of this study was to analyze the environmental and morphometric characteristics of Dolabella auricularia which live in vaname shrimp pond, Sorong, West Papua, Indonesia. Samples were collected from April to June 2020. From the measurement of pond waters environmental conditions, the following data were obtained: temperatures ranging from 31.47 ± 1.08oC, salinity ranging from 31.91 ± 2.29 ppt, pH ranging from 8.02 ± 0.20, brightness 108.00 ± 45.63 cm, and Dissolved Oxygen (DO) ranging from 4.10 ± 0.22 mg/L. The morphometrics of D. auricularia consisted of R-Anterior resp distances with sizes ranging from 38.9 ± 17 mm, wet weight ranging from 170 ± 34 g total lengths ranging from 112 ± 57.83 mm, posterior diameters ranging from 71 ± 41 mm. D. auricularia was found in pond waters as a pest for shrimp culture. However, D. auricularia also has biomedical and economic potentials as raw materials for the pharmaceutical industry. So, further studies are needed for their development.

NICANDER'S JAUNDICE

At Alexipharmaca 472–5, Nicander compares the sea hare to the cuttlefish and describes the latter's defensive mechanism of ink emission before turning to a symptom of sea hare poisoning, a change of skin colour: οἷά τε σηπιάδος φυξήλιδος ἥ τε μελαίνει οἶδμα χολῇ δολόεντα μαθοῦσ’ ἀγρώστορος ὁρμήν. τῶν ἤτοι ζοφόεις μὲν ἐπὶ χλόος ἔδραμε γυίοις ἰκτερόεις […] [the sea hare also resembles] the cowardly cuttlefish, which blackens the swell with its bile upon learning of the fisherman's crafty attack. A dark green, indeed, runs over the limbs of [those who ingest sea hare], similar to that of jaundice.