Phyllidia fontjei, Wägele & Raubold & Papu & Undap & Yonow, 2025

Wägele, Heike, Raubold, Lina Marie, Papu, Adelfia, Undap, Nani & Yonow, Nathalie, 2025, On two new Phyllidia species (Gastropoda, Nudibranchia, Doridina) and some histology from the Coral Triangle, ZooKeys 1245, pp. 1-18 : 1-18

Phyllidia fontjei sp. nov.

Fig. 1 A – C

Phyllidia sp. : Eisenbarth et al. 2018: fig. 20 a, b; same specimen (holotype) depicted and described as Phyllidia sp. a in Papu et al. 2022: fig. 6 a (Bunaken Is., Indonesia).

Phyllidiopsis monacha Yonow: Gosliner et al. 2008: 300, photograph top right (Kepulauan Seribu, Indonesia).

non Phyllidiopsis monacha Yonow : Gosliner et al. 2008: 300, photograph top left (Eilat, Israel).

Type material.

Holotype (serially sectioned): • Phsp 17 - Bu 1 [ LIBHIS 00004 ], Panorama , Bunaken Island, North Sulawesi, Indonesia [1°36'50"N, 124°46'3.4"E], collected in September 2017 on a sponge at 25.3 m depth, 16 mm in length alive . The only available CO 1 sequence ( MZ 964307 ) is published in Papu et al. (2022 as Phyllidia sp. a).

Diagnosis.

The single specimen is white with a narrow, granulated, orange mantle margin followed by a wide white band, a narrower black line, and then a white ring that also forms an elevated ridge on its inner margin. The central part is orange and shows a prominent and elevated white central ridge (Fig. 1 A ). The holotype also has a black elongate mark in this central white ridge, which is missing in other individuals that were identified from images (see Distribution below). The species is not tuberculate but bears three ridges. Minute granules are present all over the white part of the dorsum. The yellow / orange rhinophores emerge from the inner white ring and bear 12 lamellae on each rhinophoral clavus. Rhinotubercles are absent. The dorsal anus lies near the posterior margin of the central orange part. Ventrally, the foot of Phyllidia fontjei sp. nov. has a white appearance and the oral tentacles are yellow-tipped. The hyponotum is rather transparent, and the dorsal orange and black lines show through (Fig. 1 B ), as does a reddish gut content that perhaps comes from the dark orange sponge on which the animal was probably feeding (Fig. 1 C in situ).

Distribution.

Western Pacific Ocean: Indonesia: Bunaken Is., North Sulawesi ( Eisenbarth et al. 2018; provided georeference: 1.61389, 124.76761); Timor Leste (https://nudipixel.net/photo/00032422); Lembeh (https://nudipixel.net/photo/00009806); Pulau Seribu (https://nudipixel.net/photo/00005577); Kepulauan Seribu ( Gosliner et al. 2008: 300, photograph top right as P. monacha ). Malaysia: (https://www.inaturalist.org/observations/177306163; provided georeference: 4.24570, 118.63158).

Indian Ocean: Andaman Sea: Similan Islands, Thailand (https://nudipixel.net/photo/00011938, https://www.facebook.com/photo/?fbid=657059971085019&set=a.219891531468534 [with tubercles]), Surin Islands (https://www.facebook.com/photo/?fbid=591593289670092&set=a.219891531468534 [tiny individual], https://www.facebook.com/photo/?fbid=539864628176292&set=a.219891531468534, https://www.facebook.com/photo/?fbid=539804631515625&set=a.219891531468534), Krabi (https://www.facebook.com/photo/?fbid=3501673139957007&set=a.219891531468534); Andaman and Nicobar (https://nudipixel.net/photo/00039161).

Remarks.

Phyllidia fontjei is most similar to Phyllidia monacha Yonow, 1986 and Phyllidia koehleri Perrone, 2000 . Phyllidia monacha is also a small yellow, black, and white species with ridges formed by minute tubercles on the dorsum. Phyllidia fontjei sp. nov. is illustrated by Gosliner et al. (2008: 300, top right) as Phyllidiopsis monacha . We assume that this individual was erroneously assigned to the genus Phyllidiopsis due to previous (also erroneous) synonymisation with Phyllidiopsis dautzenbergi (Vayssière, 1912) by Brunckhorst (1993); both species are discussed and illustrated by Yonow (2021). Phyllidia monacha has distinct tubercles, which seem to be present (but less pronounced) in images of larger individuals of P. fontjei . Phyllidia monacha has a central black irregular ring, similar to P. fontjei sp. nov.; however, in P. monacha there are black radiating lines extending from this black area towards the mantle margin and separately enclosing the rhinophores, which are each located on an individual white or yellowish patch. In P. fontjei sp. nov. there is only one simple black ring and the rhinophores lie in the yellow band within this black band.

Phyllidia fontjei sp. nov. is also similar to Phyllidia koehleri , a completely yellow species with a bold black ring encircling the central dorsum that can break up into rays extending to the margin (e. g., Yonow 2012: 61, pl. 65), a median black line dorsally, and minute tubercles forming ridges centrally on the dorsum; however, P. koehleri lacks the white pigmentation present in both P. fontjei sp. nov. and P. monacha . Including a recently published CO 1 sequence of this species ( Cunha et al. 2023) in our Phyllidia dataset from Papu et al. (2022) renders this species a sister group to P. fontjei , with both being sister group to P. ocellata .

These three species are all small compared to many other species that may reach 60 mm and more ( Gosliner et al. 2018), and all have restricted distributions: the maximum preserved lengths of P. koehleri and P. monacha are 17 mm and 14 mm, respectively; P. fontjei measured 16 mm alive. The first two species are endemic to the Maldives and the Red Sea, respectively, while P. fontjei is restricted to Indonesia, Malaysia, and the Andaman Sea (see Distribution records listed above). Phyllidia fontjei is distinctive and can be accurately identified from photographs.

Etymology.

We name this species after our dear colleague Prof. Dr. Fontje Kaligis from Sam Ratulangi University, Manado, who initiated our Indonesian co-operation on describing marine Heterobranchia diversity around North Sulawesi. He passed away in September 2017, too early to see all the publications resulting from the joint collecting efforts. He enabled the extensive biodiversity studies in North Sulawesi and thus greatly extended our understanding of sea slugs in this area.

Figures

Figure 1. A – C. Phyllidia fontjei sp. nov. holotype (Phsp 17 - Bu 1, Panorama, Bunaken Island), living specimen 16 mm. A. Dorsal view; B. Ventrolateral view; C. In situ on a dark-orange sponge on the roof in a small cave at 25 m depth. Note that the colour of the sponge is similar to the coloration of the digestive tract showing through the ventral body in Fig. 1 B; D. Phyllidia ocellata (Phoc 16 Sa- 4, Sangihe Island), living specimen 16 mm.