Cyerce nigra Bergh, 1870

Moreno, Karina, Medrano, Sabrina, Gosliner, Terrence M., Wilson, Nerida G., Krug, Patrick J. & Valdés, Ángel, 2025, Phylogenetic systematics of the genus Cyerce Bergh, 1870 (Mollusca: Heterobranchia: Sacoglossa: Caliphyllidae) from the Pacific and Indian oceans with descriptions of nine new species, Zoological Journal of the Linnean Society 204 (1) : -

Cyerce nigra Bergh, 1870

( Figs 2C, D, 4B, 6)

Cyerce nigra Bergh 1870 : pl. 1, fig. 10; Bergh 1871: 113–118 [in part], pl. 16, figs 1–22, 24–25. Type locality: Palau.

Type material

Cyerce nigra — holotype at NHMD (GAS-002150), Palau, Jun 1862, not examined .

Material examined

Inner side of Tabat Island, North of Nagada Harbor, near Madang, 11 Aug 1990, leg. T. Gosliner and D. Mack, 1 specimen, ( CASIZ 75866 ) . Kanaman , Madang Province, Papua New Guinea, 13 Nov 2012, leg. H.H. Tan, 5 specimens 11 mm preserved length (isolates MM84 A–E, CASIZ 191170 ). Madang Province, Papua New Guinea, 3 Dec 2012, leg. C.-W. Lin, 1 specimen 2 mm preserved length, dissected (isolate MM91 , CASIZ 191510 ). Guam, Sep 2009, leg. P. Krug, 1 specimen 10 mm preserved length, dissected (isolate 09Gua07, LACM 187260 ) ; 20 Jun 2009, leg. A. Valdés and E. Ornelas, 1 specimen 2 mm preserved length (isolate MM110 , CPIC 00624 ) .

Range

Western Pacific Ocean ( Wells and Bryce 1993, Rudman 1999b, Nakano 2018, Gosliner et al. 2018; present study).

Description

External morphology: Body colour black, with scattered orange spots, outlinedwithorange-yellowbandalongmargin ( Fig.2C,D). Pericardium oval, black, slightly elevated. Head orange with black line running medially between eyes. Eyes covered by thick dermal tissue.Two or three black lines from eyes extending to rhinophores. Rhinophores long, pointed; colour semi-translucent with orange patching, speckled with minute white dots; longitudinal black line running length of rhinophores.Forehead outlined with alternating orange and black transverse striations. Tentacles with similar pattern as rhinophores. Cerata inflated, fan-shaped, semi-translucent black; one side of each ceras with scattered elevated orange-yellow spots; opposite side with horizontal black striations and minute white to fluorescent green specks forming striations. Both sides of cerata with infra-marginal light orange band, covering several scattered white specks. Ceratal margin outlined by black band. Foot dorsally outlined with orange-yellow band.

Internal morphology: Pharynx about 2 mm in length, buccal bulb and pharyngeal pouch similar in size. Radula with 17 teeth in a 2-mm preserved length specimen ( CASIZ 191510); 9 teeth on descending limb, 8 teeth on ascending limb ( Fig. 6A). Radular teeth moderately narrow, with wide bases, sharp tips. Leading tooth about 65 µm in length, with two rows of ~9 denticles along either side of tooth ( Fig. 6B). Denticles rhomboidal, some blunt; varying in size along tooth, becoming larger towards tip. Ascus with about 11 used teeth ( Fig. 6C). Penis covered with tissue, with penial stylet at opening, about 200 µm in length ( Fig. 4B). Penial stylet cylindrical, thin, curved, hollow with oval opening; pointed triangular tip ( Fig. 4B).

Ecology

Feeds on the green algae Udotea geppiorum Yamada, 1930 and potentially other Udotea spp. ( Gosliner et al. 2018; present study).

Reproduction

Development of specimens in Guam was planktotrophic. Egg masses lacked extra-capsular yolk. One clutch had a mean egg diameter of 57.2 µm ± 1.6 SE (N = 18). Larval shell size was measured across the aperture to estimate mean size for two clutches at hatching; mean larval shell width was 126.2 µm ± 5.7 SE (N = 25) for one egg mass, and 132.5 µm ± 3.6 SE (N = 25) for a second egg mass.

Remarks

Phylogenetic analyses recovered Cyerce nigra as a monophyletic group represented in the Western Pacific ( Fig. 1), also supported by all methods of species delimitation analysis ( Table 3). Cyerce nigra was recovered within a clade containing C. nigricans and other black and yellow species, but anatomically C. nigra shares a long, curved penial stylet with several species from clade 2 such as Cyerce blackburnae sp. nov., Cyerce tutela sp. nov., and Cyerce trowbridgeae sp. nov.

Bergh’s (1870; 1871) original description of Cyerce nigra was based on a single specimen collected in Palau and illustrated alive by Semper; the colour drawing was later reproduced by Bergh (1870: pl. 1, fig. 10) and herein ( Fig. 5C). Bergh (1871) also illustrated some anatomical traits of a second specimen examined by Semper, which most likely belongs to C. nigricans (see: above). The current usage of the name C. nigra in the literature (Rudman 1999b, Gosliner et al. 2018, Nakano 2018) is consistent with the original description and the specimens examined herein. For example, Bergh (1871) mentioned the presence of an infra-marginal yellow band, orange yellow spots on one side and black horizontal stripes on the opposite side of the cerata, both present in the specimens here examined. Bergh (1871) also mentioned the presence of several yellow transverse bands on the forehead of C. nigra similarly seen in our specimens. All evidence supports the material studied herein as C. nigra .

Specimens of C. nigra have been collected from, and observed to feed on, Udotea spp. However, DNA barcoding identified several green algal plastids excluding Udotea within C.nigra ( Christa et al. 2014b) , including specimens we recovered within C. nigra in our analyses ( Fig. 1A). This raises the possibility that C. nigra has a broader host range but all of our collections and other reports to date confirm an association with Udotea ( Gosliner et al. 2018) . Methodological concerns over how accurately the barcoding approach used by Christa et al. (2014b) can identify ecologically relevant host algae for sacoglossans have been previously noted ( Krug et al. 2016, Moreno et al. 2023).