Zoological Studies

Vol. 63, 2024

Morphology and Phylogenetic Position of Sargassum Nudibranch Scyllaea fulva Quoy & Gaimard, 1824 (Nudibranchia: Scyllaediae): First Record in Hong Kong

Sam King Fung Yiu1,2,*, Thomas Ka Tung Leung2, Gabriel Yeung Lee2, and Meng Yan2,*

1School of Biological Science, The University of Hong Kong, Hong Kong, China. *Correspondence: E-mail: cyclesamyiu@hotmail.com (Yiu)
2State Key Laboratory of Marine Pollution, City University of Hong Kong, Hong Kong, China. *Correspondence: E-mail: mengyan@cityu.edu.hk (Yan)
    E-mail: thomas1126199716@gmail.com (Leung); auytfff1357924680@gmail.com (Lee)

(Received 13 July 2023 / Accepted 27 December 2023 / Published -- 2024)
Communicated by James D. Reimer

Scyllaeidae is a small group of nudibranchs comprising three genera (Scyllaea, Notobryon, and Crosslandia) with striking morphological similarities, making their identification challenging based on external features alone. Previous studies have highlighted the significance of central radular teeth in distinguishing Notobryon from Scyllaea and Crosslandia. The genus Scyllaea, commonly known as the sargassum nudibranch, currently consists of only two valid species, Scyllaea pelagica and Scyllaea fulva. These species inhabit seaweed Sargassum spp., feeding on hydroids. During a biodiversity survey conducted in April 2023, seven sargassum nudibranch individuals were collected from the seaweed Sargassum spp. at a depth of 2 meters in Tai She Wan through SCUBA diving. Initially, the specimens were misidentified based on their resemblance to Notobryon wardi and previous local records. However, thorough morphological and molecular examinations confirmed them to be Scyllaea fulva, representing the first record of this species in Hong Kong. Notably, our specimens lacked the blue spots observed in specimens from Thailand and the West Pacific Ocean, as reported in previous studies. Internally, a pineapple-like structure formed a honeycomb pattern on the surface of the masticatory edge of the jaw flap, with the presence of central radular teeth. A Maximum Likelihood tree analysis revealed Crosslandia to be the sister group of Scyllaea. Comparative analysis of intra-specific distances between individuals from the Philippines, French Polynesia, and Hong Kong indicated a close relationship between the Hong Kong specimens and those from the Philippines. Furthermore, we provide a detailed description of the external and internal morphology of Scyllaea fulva in this paper, integrating valuable morphological information for future species identification purposes.

Key words: Scyllaeidae, Sea slug, Mollusc, Subtropical reef, South China Sea

Citation: Yiu SKF, Leung TKT, Lee GY, Yan M. 2024. Morphology and phylogenetic position of sargassum Nudibranch Scyllaea fulva Quoy & Gaimard, 1824 (Nudibranchia: Scyllaediae): first record in Hong Kong. Zool Stud 63:04. doi:10.6620/ZS.2024.63-04.

Supplementary materials: Table S1Table S2Table S3Table S4