Siphopteron citrinum (Carlson & Hoff, 1974)

Description

A small gastropterid headshield slug, reaching about 4 mm in body length. The body is translucent and varies from a uniform bright lemon-yellow to entirely pink, with many individuals showing a mixture of yellow and pink. Unlike the closely related Siphopteron brunneomarginatum and Siphopteron nigromarginatum, the parapodial margins are not bordered with dark pigment; only a small amount of black pigment is present near the apex of the siphonal crest. A slender, elongate flagellum is present on the right side of the body, and the parapodia are well separated rather than overlapping. The radular formula is 21 × 3-1-0-1-3, and the inner lateral teeth bear a broad, curved primary cusp with a single small triangular denticle near the outer margin. The penial bulb lacks rows of chitinous spines, a condition shared within the genus only with Siphopteron brunneomarginatum and Siphopteron pohnpei.

Distribution

Guam, Mariana Islands. Type locality is Guam.

Etymology

The specific epithet citrinum is derived from the Latin citrinus (lemon-coloured), in reference to the vivid yellow body colour of the species.

Remarks

Originally described in the genus Gastropteron, the species was transferred to Siphopteron in a 1989 revision of the Gastropteridae. Although superficially reminiscent of Siphopteron tigrinum, that species is readily separated by its orange ground colour with bright blue and purple lines and by the well-developed rows of chitinous hooks in the penial bulb, both of which are absent in S. citrinum.

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References

• Gastropteron citrinum n.sp., Carlson C.H. & Hoff P.J. (1974). The Gastropteridae of Guam, with descriptions of four new species (Opisthobranchia: Cephalaspidea). Publications of the Seto Marine Biological Laboratory. 21(5/6): 345-363.
• Siphopteron citrinum (Carlson & Hoff, 1974) comb. nov., 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.