Phyllidiella nigra ( van Hasselt, 1824 )

Papu, Adelfia, Bogdanov, AleXander, Bara, Robert, Kehraus, Stefan, König, Gabriele M., YonoW, Nathalie & Wägele, Heike, 2022, Phyllidiidae (Nudibranchia, Heterobranchia, Gastropoda): an integrative taxonomic approach including chemical analyses, Organisms Diversity & Evolution (New York, N. Y.) 22 (3), pp. 585-629 : 609

Phyllidiella nigra ( van Hasselt, 1824)

All 25 collected specimens of Phyllidiella nigra (Fig. 9.3a–f) exhibit a greater extent of black background compared to P. pustulosa and most clades. Additionally, the mantle margin is black in contrast to the white rim in all subclades of P. pustulosa and P. cf. pustulosa . The specimens have irregular single or coalesced tubercles distributed all over the mantle. The coalesced tubercles are smaller and usually conical, whereas the single tubercles are relatively larger and rounded. Their colour can vary between white to pink and green. The rhinophores are black, and the black anal opening exits from the black notum, sometimes in-between two small tubercles. The foot sole is grey to black. The oral tentacles are black; however, they can also be pale pink with dark grey-black tips or with dark lateral grooves. Originally, P. nigra (type locality Tahiti) was described as having tall pink-red rounded tubercles irregularly dispersed on the dorsal notum; the living specimen is illustrated in Bergh (1887: pl. 6, fig. 6). The oral tentacles were black and the foot sole was grey. We also collected animals that have the rather reticulate black pattern typical for P. pustulosa (e.g., Phpu15Bu7, Fig. 9.3a), but these specimens group together with the eight P. nigra sequences of Stoffels et al. (2016) (see Table S3) with highest bootstrap values (100) in the concatenated and CO1 data set.

LC-HRMS analysis of Phyllidiella nigra (Phpu15Bu7, Fig. 9.3a; Phu15Bu10, Phpu15Bu18, Phpu15Bu19) shows that all four specimens share the same major metabolites present as sesquiterpenoids (Fig. S9e). Relatively large extract amounts allowed fractionation and subsequent isolation and structure elucidation of five known sesquiterpenes (Fig. S4a), i.e., two bisabolene-type isonitriles ( Iwashima et al., 2002; Manzo et al., 2004), 10-isocyano-5-cadinen-4-ol ( Hirota et al., 1998), and an epimeric mixture of 9-thiocyanatopupukeananes ( Yasman et al. 2003). However, the major metabolites were highly volatile or unstable and repeated isolation attempts failed (extraction of chemically identical large P. nigra specimens Phpu15Bu6 and Phpu15Bu43).