Cyerce nigricans ( Pease, 1866 )

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 nigricans ( Pease, 1866)

( Figs 2A, B, 3, 4A)

Lobifera nigricans Pease 1866: 206–207 . Type locality: Pacific Islands.

Cyerce nigra Bergh 1871: 113–118 [in part], pl. 16, figs 23, 26–28 [non C. nigra Bergh 1870 : pl. 1, fig. 10].

Cyerce nigra var. ocellata Bergh 1873: 155–158 [83–86], pl. 9, figs 8, 9, pl. 11, figs 13–26, pl. 12, figs 2, 3. Type locality: Samoa.

Type material Lobifera nigricans Pease, 1866 —no type material known to exist, not found at MCZ. Cyerce nigra var. ocellata Bergh, 1873 —no type material known to exist, it was originally deposited at the Museum Godeffroy.

Material examined

Heron Island , Queensland, Australia, 13 Dec 1984, 17 m depth, leg. T. Gosliner, 1 specimen 20 mm preserved length ( CASIZ 071449 ) . Pandane Beach , Jangamo, Inhambane Province, Mozambique, 6 Feb 2008, 0–1.5 m depth, leg. M. Pola and J. Reis, 1 specimen 12 mm preserved length, dissected (isolate MM72 , CASIZ 176993 ); 1 specimen 14 mm preserved length, dissected (isolate MM73 , CASIZ 176994 ); 1 specimen 7 mm preserved length (isolate MM74 , CASIZ 176995 ) . Pointe Evatra , Toliara, Madagascar, 30 Apr–6 May 2010, 38 m depth, leg. Atimo Vatae, South Madagascar Expedition, 1 specimen (isolate MM93 , CASIZ 194048 ); 1 specimen 15 mm preserved length, dissected (isolate MM94 , CASIZ 194049 ); 1 specimen ( CASIZ 194083 ) .

Range

Widespread in the Indian and Western Pacific oceans (Rudman 1999c, Nimbs and Smith 2017, Nakano 2018, Gosliner et al. 2018; present study).

Description

External morphology: Body colour black, with light banding running along both sides; black line down the middle of the body ( Fig. 2A, B). Pericardium oval, elevated, black spotted in orange. Head black with orange band running down medially between eyes. Rhinophores black, outlined with two orange striations. Tentacles black with similar pattern to rhinophores. Cerata inflated, fan-shaped, black, covered with elevated orange-yellow dots on both sides. Cerata margin outlined by white band. Orange band situated infra-marginally of cerata.

Internal morphology: Pharynx about 5 mm in length, buccal bulb and pharyngeal pouch similar in size. Radula with 24 teeth in a 12-mm preserved length specimen ( CASIZ 176993). Radular teeth moderately narrow, with wide bases, and sharp tips ( Fig. 3A). Tips with small, sharp projections, located medially between first pair of denticles. Leading tooth about 250 µm in length, with two rows of ~20 denticles along either side of tooth, followed by ~15 smaller lateral notches ( Fig. 3B). Denticles recurved, triangle shaped. Denticle size varies along tooth, smaller near base, larger towards middle of tooth, smaller at tip. Ascus with about 25 used teeth ( Fig. 3C). Penis surrounded by thick dark tissue. Penial stylet at opening of penis, about 200 µm ( Fig. 4A). Penial stylet cylindrical, straight, hollow with oval opening, pointed triangular tip; wide base.

Ecology

Feeds on the green algae Chlorodesmis spp. ( Gosliner et al. 2018), typically diurnal.

Remarks

Pease (1866) originally described Lobifera nigricans Pease, 1866 based on an undetermined number of specimens collected from the ‘Pacific Islands’ (no specific locality was provided). Pease (1866) did not include details of the internal morphology; thus, it is not possible to compare the anatomy of the original specimen/s to that of similar specimens subsequently described by Bergh (1871, 1873), or the specimens examined herein and assigned to this species. Pease (1866) described L. nigricans as being deep velvet black in colour, having cerata with a yellow infra-marginal band and covered with yellow dots, which is consistent with the modern usage of the name (Rudman 1999c, Gosliner et al. 2018). Bergh (1877) regarded the genus Lobifera as ‘partially identical’ to Cyerce and for the first time treated L. nigricans as a member of Cyerce .

Bergh (1870; 1871) described the new species Cyerce nigra Bergh, 1870 based on a single specimen collected from Palau. Bergh (1871) indicated that the specimen, which was illustrated alive by (Carl Gottfried) Semper [colour drawing reproduced by Bergh 1870: pl. 1, fig. 10 and herein ( Fig. 5C)] was hardened due to preservation, and the internal organs were accidentally lost while ‘being softened in aqueous fluid’. Bergh (1871) also indicated there was a second specimen belonging to a different ‘form’ also from Palau, which was examined in the field by Semper. Semper made drawings of the radula and the penis of this second specimen (also reproduced by: Bergh 1871: pl. 16, fig. 23, and Bergh 1871: pl. 16, figs 26–28, respectively). Bergh (1871) provided a comprehensive description of the external morphology of the first specimen (holotype), which is currently deposited at the NHMD (GAS-002150) and it is consistent with the current usage of the name C. nigra (Rudman 1999b, Gosliner et al. 2018, Nakano 2018). For example, Bergh (1871) mentioned that the dorsum of the specimen was black and the cerata were also black above, with a yellow border, yellow spots, and numerous black transverse stripes. Two years later Bergh (1873) re-emphasized the fact that the two specimens collected by Semper in Palau belong to different species, and that the animal that was examined more closely by Semper deviated from the typical C. nigra by showing only a few yellow spots on the black cerata, instead of the yellow stripes typical of C. nigra . Bergh (1873) examined a third specimen collected from Samoa that according to him was consistent morphologically with the animal examined by Semper in the field. Bergh (1873) described this latter specimen under the new name Cyerce nigra var. ocellata Bergh, 1873 and reproduced the original drawing of the live animal collected by Graeffe ( Bergh 1873: pl. 9, figs 8, 9) also reproduced herein ( Fig. 5A, B), which is consistent with the modern usage of the name C. nigricans (see: Rudman 1999c, Gosliner et al. 2018). Moreover, the illustrations of the male reproductive system made by Semper, reproduced by Bergh (1871: pl. 16, figs 26–28), show a short penial stylet with an oval opening and pointed tip; the penial stylet of this specimen closely resembles the specimens of C. nigricans here examined. On the contrary, the penial stylet of the specimens of Cyerce nigra studied herein is long and curved with a pointed tip (see: description of C. nigra below). Thus, the specimen examined by Semper in the field clearly belongs to C. nigricans , as well as the animal from the Museum Godeffroy (Hamburg) that Bergh (1873) described as Cyerce nigra var. ocellata . This was later confirmed by Bergh (1877), who mentioned that he received one of Pease’s specimens of C. nigricans (collected by Garrett) for examination and verified that it was the same species as Cyerce nigra var. ocellata . Bergh (1877: pl. 10, figs 10, 11) also illustrated the penis of the specimen of Cyerce nigra var. ocellata , which is also short and straight, consistent with the drawings by Semper and different from the true C. nigra .

A specimen from Lizard and Eagle islands ( Australia) identified as Cyerce nigricans by Klussman and Dinapoli (2006) and Händeler and Wägele (2007) was recovered as a member of this species ( Fig. 1). Moreover, images of live specimens identified as C. nigricans obtained from the Lizard Island research station of Australia closely resemble our specimens of Cyerce nigricans from the Indian Ocean (see: Australian Museum Lizard Island Research Station 2022) confirming they are conspecific. However, phylogenetic analyses recovered two specimens from New Caledonia originally identified as C. nigricans in a distinct clade, named Cyerce takanoi sp. nov. herein ( Fig. 1A). The species delimitation analyses further supported this clade as a distinct candidate species ( Table 3). Morphological examination of specimens of C. takanoi sp. nov. and C. nigricans reveal these species share several external morphological traits such as the black cerata with orange spots and yellow-orange band along the margin. However, the colour pattern of the head of C. takanoi sp. nov. differs from the pattern observed in C. nigricans , which has a medial orange line along the head of the animal (consistent with the original description), whereas C. takanoi sp. nov. has two orange transverse patches on the head. Also, the presence of scattered orange spots along the margin of the rhinophores of C. takanoi sp. nov. rather than a solid orange line in C. nigricans seems like a distinction. Moreover, Bergh (1873) mentioned and illustrated yellow longitudinal striations along the body of Cyerce nigra var. ocellata (= C. nigricans ) ( Fig. 5A,B), which are present in the specimens here examined but are absent in C. takanoi sp. nov.

Phylogenetic analyses recovered all specimens of C. nigricans in an unsupported clade. This could be due to the inclusion in the analyses of short sequences from GenBank. But all species delimitation analyses confirmed C. nigricans is a distinct species as mentioned above.