Siphopteron vermiculum Ong & Gosliner, 2017

Location: Batu Niti, Tulamben, Pulau Bali, Indonesia
Date: 2018/04/22
Length: 5mm
Depth: 20.0m
Water temperature: 30.0℃

Description

A small siphopteran 4–5 mm in length. Living animals have a bright vermillion red ground colour. Parapodia and foot ground colour clear to translucent white to vermillion red. Parapodia lined with yellow and orange accents. White and orange spots dotting parapodia and head shield.
Visceral hump more opaque than appendages, vermillion with white spots. Parapodial margin lined by translucent outer margin, followed by vermillion submarginal band and orange inner submarginal band. Elongate flagellum opaque white with opaque white band, located centrally on visceral hump. White pigment transitioning into yellow band, followed by orange or brownish dot tip.
Foot of animal translucent white, lined with vermillion lateral edges and central opaque white medial stripe, becoming interrupted and orange posteriorly. Flagellum centred on midline of visceral hump. Head shield quadrangular anteriorly with orange transverse band. Two symmetrical orange dots present on either side of head shield, vermillion ground colour converging on siphon. Central white stripe present on the anterior side of siphon. Siphon lined with orange dots on either side. Posterior side of siphon with vermillion ridge, extending on to appendage extending slightly above lateral margins siphon. Gill small with only three small filaments.
Shell: No trace found in single specimen dissected. Radular formula 18 × (2–3·1·0·1·2–3) in one specimen (NMP 041183). Inner lateral teeth broad with single primary cusp. Masticatory margin of inner laterals broad with irregular series of 2–3 wide areas. Under higher magnification, these areas bear numerous striations, suggesting they may represent fusion of denticles. The penis is complex with elongate, sharply curved prostate. Penial sac straight, containing arch of c. 23 interiorly directed, acutely pointed cuticular spines. Second row of 20 much smaller spines found inside arch of the larger spines. Secondary papilla found at anterior end of penial sac, lacking any armature.

Distribution

Type locality: Cemetery Beach, Tingloy, Batangas, Luzon, Philippines. Thus far, known only from the Philippines.

Etymology

Verbatim from the original description (Ong et al., 2017, p.769):

The species epithet, vermiculum, refers to the vermillion colour ornamenting the body of this species.

Remarks

Originally described as Siphopteron vermiculum Ong & Gosliner, 2017. This species corresponds to specimens previously figured as Siphopteron sp. 4 (Gosliner, Valdés & Behrens, 2015).
Based on its coloration, S. vermiculum is distinct from other members of the genus, being the only species with a bright vermillion red ground colour. Based on internal morphological characters, S. vermiculum appears to be most similar to Siphopteron nigromarginatum Gosliner, 1989 and Siphopteron flavum (Tokioka & Baba, 1964). All three are the only members of the family known to have a complex penis with two papillae where the primary papilla has a series of cuticular spines and where the secondary papilla lacks armature. All three species have an irregularly shaped masticatory margin of the inner lateral tooth, but the denticles are reduced to striations in S. vermiculum, whereas they are more prominent in S. nigromarginatum and S. flavum. S. vermiculum has two rows of penial spines, whereas S. flavum possesses only a single band of penial spines, and S. nigromarginatum has four distinct bands of spines. In the molecular analysis, S. vermiculum is sister to Siphopteron sp. 2 (AM421863), with a COI p-distance of only 4.4 %, suggesting that they may be the same species.