Siphopteron makisig Ong & Gosliner, 2017

Description

A small siphopteran 4 mm in length. Parapodia, head shield and foot translucent white to faint vermillion red. Head shield roughly triangular, tapering posteriorly to siphon. Medial yellow line present on the anterior part of head shield. Additional red orange line found along lateral margins of head shield and extending to tip of siphon with medial white ridge along its posterior edge, extending to red orange apex. Apex higher than lateral margins.
Parapodia lined with yellow and orange marginal accents. Visceral hump more opaque white than head shield or parapodia with bright red orange ring around posterior end of visceral hump. Flagellum translucent white with bright orange-red tip. Foot translucent white with central yellow stripe down in the middle. Flagellum found on the right side of visceral hump. Gill with four simple folds.
Shell: No trace of shell found in dissected specimen. Radular formula 18 × (4·1·0·1·4) in one specimen (NMP 041186). Inner lateral teeth broad with single primary cusp. Masticatory margin of inner laterals broad with two large, triangular, well-separated denticles. The penis is complex with elongate, highly convoluted prostate. Penial sac straight, containing five spines that gradually diminish in size. From basal spines, conical penial papilla extending anteriorly. Papilla bearing a few minute tubercles or spines. Secondary papilla found at anterior end of penial sac, terminating in large, acutely pointed cuticular spine.

Distribution

Type locality: Bilbago Reef South, Calatagan, Batangas, Luzon, Philippines. Thus far, known from the Philippines, Indonesia and Australia.

Etymology

Verbatim from the original description (Ong et al., 2017, p.778):

The species epithet, makisig, is a Tagalog word meaning

elegant or refined"."

Remarks

Originally described as Siphopteron makisig Ong & Gosliner, 2017. This species corresponds to specimens previously studied or figured as Siphopteron sp. 1 (Lange et al., 2013) and Siphopteron sp. 5 (Gosliner, Valdés & Behrens, 2015). Lange et al. 2013 used this species to describe the details of hypodermic mating interactions.
The colour pattern of S. makisig, with a white body colour with prominent red-orange pigment on the siphon, flagellum and visceral hump spots, is unique to this species. Morphologically, this species is similar to Siphopteron quadrispinosum Gosliner, 1989, where both species have an inner radular tooth with two large quadrangular cusps. S. quadrispinosum differs in its colour pattern with a yellow body with red pigment on the apex of the siphon and on the flagellum. This species also has a white margin along the edge of the parapodia.
In S. quadrispinosum, the base of the penis has four large spines surrounding the base of the penial papilla, while in S. makisig there is a row of five penial spines that are graduated in size. Siphopteron flavolineatum and S. nakakatuwa also have inner radular teeth with similar features but differ in their colour pattern and in the morphology of the penis. Phylogenetically, S. makisig is sister to a clade containing four individuals of S. quadrispinosum. For the COI gene, the uncorrected p-distance ranges between 9.0 and 9.9 %, and the ABGD analysis clearly recognizes S. makisig and S. quadrispinosum as distinct species.

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References

• シフォプテロン・クアドリスピノーサム, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.
• シフォプテロン・クアドリスピノーサム, 中野理枝. (2004). 本州のウミウシ. ラトルズ.
• シラタマウミコチョウ（新称）, 中野理枝, 今川郁 & 今本淳. (2013). 南西諸島の後鰓類1. 頭楯亜目. ちりぼたん. 43(1-4): 1-22.
• Siphopteron sp. 5, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• Siphopteron makisig sp. nov., Ong E., Hallas J.M. & Gosliner T.M. (2017). Like a bat out of heaven: the phylogeny and diversity of the bat-winged slugs (Heterobranchia: Gastropteridae). Zoological Journal of the Linnean Society. 180(4): 755-789. https://doi.org/10.1093/zoolinnean/zlw018