Acutogordius koljai Schmidt-Rhaesa & Karraker, 2017, n. sp.

Acutogordius koljai n. sp.

(Figure 5)

Holotype. One male from type locality, deposited in the Zoological Museum Hamburg, accession number V13404. Etymology. The species name “ koljai ” is chosen after the youngest son of the senior author, Kolja Tore.

Type locality. Malaysia, Sabah, Mt. Kinabalu, Liwagu stream (UTM Zone 50Q, 664160N/44913E), elevation 1515 m; collected by N.E. Karraker on June 20, 2010 (paratype) and July 13, 2010 (holotype).

Paratype. One male from type locality, deposited in the Zoological Museum Hamburg, accession number V13405.

Description. The holotype is 170 mm long and measures 1.0 mm in width. The paratype is 150 mm long and 0.9 mm in width. Both specimens are light brown, with a dark collar present.

The body cuticle is smooth. At the posterior end, the tail lobes strongly taper (Fig. 5 A–C). The postcloacal crescent is semicircular (holotype, Fig. 5 D) to slightly parabolic (paratype, Fig. 5 E). The measurements differ in both specimens. The holotype has a thicker (60 µm posterior of the cloacal opening) and narrower (200 µm distance between both tips) crescent than the paratype (40 µm thick and 240 µm broad). The postcloacal crescent is almost immediately posterior of the cloacal opening (Fig. 5 D, E). Characteristic for the species is a curved line that extends from the posterior tips of the crescent in posterior direction and towards the inner face of the tail lobes (Fig. 5 D, E). It borders a clearly separated region posterior of the postcloacal crescent. The cuticle is structured in this region into roundish to polygonal areas resembling areoles (Fig. 5 D, E). Scattered spines are found on the lateral sides of the tail lobes.

Remarks: The genus Acutogordius includes so far 10 described species, all from southern, Gondwana continents (Schmidt-Rhaesa & Geraci 2006, Schmidt-Rhaesa & Schwarz 2016). Characteristic for the genus is that the tail lobes taper distinctly towards a more or less pointed posterior tip. Recent SEM investigations (Schmidt- Rhaesa & Geraci 2006, Schmidt-Rhaesa & Schwarz 2016, Schmidt-Rhaesa & Lalramliana 2016) have discovered fine cuticular characters such as bristles and spines on the body cuticle and in the posterior end, which were probably overlooked in earlier descriptions. A region as described as above from posterior of the postcloacal crescent has been described from no species before and is, given its occurrence in two specimens, assumed to be a characteristic feature of this new species. Additionally, the cloacal opening appears to be in none of the previously described species so close to the postcloacal crescent as in the new species.

The species Acutogordius doriae (Camerano, 1890) Heinze, 1952 is the only species reported from Malaysia (Camerano 1899) and therefore from the same region as A. koljai. Both species correspond in having a narrow postcloacal crescent, but differ in several other characters. Acutogordius doriae does not have the curved line and the spines present in the posterior end of A. koljai. Additionally, the tail lobes appear to be stronger pointed in A. doriae as compared to A. koljai (see Camerano 1890, Schmidt-Rhaesa & Geraci 2006).