Known from tropical western Pacific (Papua New Guinea, Okinawa, Japan).
Hachijo Island, Japan, 7m, 8-10mm long. 1 July, 2001. Photos: Nishina Masayoshi.
Gosliner describes the colour as:
"The general body colour is pale yellowish white to lemon yellow. Scattered orange mottlings may be present on the head shield and visceral hump.... An area of opaque white is generally present at the base of the head shield just anterior to the beginning of the visceral hump. Black pigment adorns the apex of the siphon, the tip of the siphonal crest, the parapodial margin, and the flagellum and its base."
Similar in colour to Siphopteron brunneomarginatum (Carlson & Hoff) but that species is a uniform yellow with a dark brown parapodial border, dark brown tip to the siphon, dark brown flagellum and a dark brown line across the visceral hump. In his message below Terry Gosliner also notes that S. nigromarginatum is a far more delicate species than S. brunneomarginatum and has a thinner marginal line. Also the parapodia usually overlap in S. brunneomarginatum, but do not in S. nigromarginatum.
• Gosliner,T.M. (1989): Revision of the Gastropteridae (Opisthobranchia: Cephalaspidea) with descriptions of a new genus and six new species. The Veliger, 32(4): 333-381.
Rudman, W.B., 2001 (July 30) Siphopteron nigromarginatum Gosliner, 1989. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/siphnigr
A juvenile Siphopteron nigromarginatum
From: Takao Urasawa, February 11, 2006
Siphopteron nigromarginatum from Hachijo
From: Nishina Masayoshi, August 12, 2002
Siphopteron nigromarginatum? from Kii Peninsula
From: Yasuhiro Shirai, August 23, 2001
Re: Siphopteron cf. brunneomarginatum
From: Nishina M. & J. Imamoto, August 4, 2001
Re: Siphopteron from Japan
From: Terry Gosliner, August 2, 2001
Siphopteron cf. nigromarginatum from Japan
From: Nishina Masayoshi, August 1, 2001