Strandesia buengkanensis, Savatenalinton, 2025

Strandesia Stuhlmann, 1888 View in CoL

At first glance, S. buengkanensis sp. nov. is very similar to S. kraepelini due to their Cp outlines and valve surface ornamentation (see Victor & Fernando 1981b; Savatenalinton & Martens 2010). However, the new Strandesia species has a larger anterior valve overlap, a less elongated Cp in lateral view, and a marginal anterior selvage in the LV (submarginal in S. kraepelini ). Additionally, differences can be seen in chaetotaxy of the limbs. For example, S. buengkanensis sp. nov. possesses a longer ya on the A1, a large A2 aesthetasc Y, a longer accompanying natatory seta on the A2, five spines and setae on the terminal segment of the Mx1-palp (six in S. kraepelini ), smooth large bristles on the third endite of the Mx1 (one smooth, one serrated in S. kraepelini ), a longer f seta on the T2, a shorter f seta on the T3, a long Sp seta and a longer Ga claw of the CR.

Apart from their similarity of Cp shape, S. buengkanensis sp. nov. also lacks a subapical dorsal seta on the A1 first segment, which makes it resemble S. kraepelini more. Thus far, the absence of this seta in Strandesia has been recognized only in three species, namely S. kraepelini (see Savatenalinton & Martens 2010), S. karanovicae ( Savatenalinton 2024a) and S. buengkanensis sp. nov. (present study). Strandesia kraepelini was described based on materials from Java ( Indonesia) (G.W. Müller 1906) and subsequently reported from other Southeast Asian countries ( Victor & Fernando 1981b, Savatenalinton & Suttajit 2016), while S. karanovicae was recently discovered from Thailand ( Savatenalinton 2024a). Hence, in the genus Strandesia , the absence of this seta is so far restricted to the Southeast Asian lineage. At present, the number of Strandesia species recorded in Southeast Asia is 20 ( Table 2). Most of them are endemic, which would suggest that these species originate from this area. In addition, three of them, including the new species, are sexual populations in which males and females are found.

Within the group in which the subapical dorsal seta on the A1 first segment is absent, sexually reproducing populations occur only in S. buengkanensis sp. nov. This allows the comparisons of the male reproductive organs between this group and other Cypricercinae members. The comparisons revealed that, in S. buengkanensis sp. nov., the number of ZO spiny whorls is close to that of Pseudostrandesia (see Savatenalinton 2021; Smith et al. 2021). Additionally, like in Pseudostrandesia , the Hp morphology of the new Strandesia species belongs to type C according to the Hp model proposed by Savatenalinton & Martens (2009 b) and additional data by Savatenalinton (2021) and Smith et al. (2021). This could suggest that Strandesia without the subapical dorsal seta on the A1 first segment form a group that is closer to Pseudostrandesia than other Strandesia , on the basis of the similarity of the male reproductive organs. This species group is also restricted to Southeast Asia, which is the proposed origin of Pseudostrandesia ( Savatenalinton 2021; Smith et al. 2021).