Exocelina sugayai, Balke & Ribera, 2020
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publication ID |
https://dx.doi.org/10.3897/subtbiol.34.50148 |
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publication LSID |
lsid:zoobank.org:pub:E82D45EF-B6AF-4A17-831D-ED8D4DBD5A4E |
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persistent identifier |
https://treatment.plazi.org/id/D7A59208-6691-4E3E-8899-9942AC745D4A |
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taxon LSID |
lsid:zoobank.org:act:D7A59208-6691-4E3E-8899-9942AC745D4A |
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treatment provided by |
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scientific name |
Exocelina sugayai |
| status |
sp. nov. |
Exocelina sugayai sp. nov.
Type locality.
Malaysia, Pahang, Cameron Highlands, Tanah Rata, 4.474705, 101.384043.
Material examined.
Holotype male (ZSM): Malaysia, Pahang, Cameron Highlands, Tanah Rata, Mount Berembun, 4.474705, 101.384043, 1,500m, 27.-29.ii.2012, K. Sugaya leg.
Paratypes: 4 males (1 used for DNA extraction and sequencing, voucher No. IBE-AN1160) and 2 females, same label data as holotype (IBE, KSc, NMW, ZSM).
Description of holotype.
Size and shape: Smallest Exocelina known (length of holotype including head 2.7 mm, length without head 2.4 mm, greatest width 1.0 mm). Abdomen comparably parallel sided; pronotum also comparably parallel sided, slightly constricted before base, hind angles produced backwards (Fig. 1A View Figure 1 ).
Coloration.
Testaceous and slightly translucent (Figs 1A, B View Figure 1 , 2A-F View Figure 2 ).
Surface sculpture.
Head and pronotum with distinct microreticulation formed by small regular cells and fine moderately dense punctation. Elytra with distinct microreticulation formed by small regular cells and dense, coarse, setiferous punctation (Fig. 1A, D View Figure 1 ). Ventral side with distinct microreticulation formed by small regular cells, including distinct microreticulation on metacoxal processes (Figs 3A View Figure 3 , 4A-C View Figure 4 ).
Structures.
Eyes fully reduced, with only small black scars remaining on surface of head (Figs 1A, B View Figure 1 , 2A, B View Figure 2 ). Male antennomeres strongly modified: 2 and 3 moniliform, 4 slightly broadened in dorsal view, 5-11 strongly expanded, 11 flat and blade like (Fig. 1A View Figure 1 ). Fore tarsus dilated, fore angle of tarsomere 4 ventrally produced (Fig. 1C View Figure 1 ) and with two thicker setae (but no hook as in other Exocelina ), on tarsomere 5 ventrally without obvious setation; pro and mesotarsomeres 1-3 with 4 rows of stalked suction discs (2 per row). Pronotum with faint lateral bead not reaching an terior nor posterior corners (Fig. 2B, D, F View Figure 2 ). Prosternal process short, lanceolate, deflexed, gently rounded ventrally (Figs 3A View Figure 3 , 4A View Figure 4 ); metaventrite broadly triangular, its lateral “wings” very narrow (Fig. 4B, C View Figure 4 ). Membranous wings strongly reduced, with only very short stubs visible at the wing base. Metacoxal “lines” broadly diverging, fainting well before hind margin of metaventrite (Figs 3A View Figure 3 , 4B View Figure 4 ). Metacoxal processes small, more elongate oval, with wide gap in middle (to possibly enable higher mobility of hindlegs) (Figs 3A View Figure 3 , 4B View Figure 4 ). Last ventrite apically rounded. Median lobe of aedeagus simply curved in lateral view, parameres of simple, Copelatinae -type triangular shape (Fig. 5A, B View Figure 5 ).
Female.
Antennomeres filiform to slightly moniliform (Fig. 1B View Figure 1 ). Pro and mesotarsomeres 1-3 not bearing stalked suction discs and protarsomere 4 not modified.
Variation. Length of beetle including head 2.4-2.8 mm. Two paratypes are darker orange (see Fig. 1B View Figure 1 ). According to the collector, this is due to subsequent darkening in alcohol storage.
Etymology.
Named after Kazuki Sugaya, the discoverer of this species.
Differential diagnosis.
This species differs from all other Dytiscidae by: Copelatinae with reduced eyes; beetle length < 3 mm; body with well visible microreticulation; prosternal process short and deflexed; metacoxal processes small, more elongate oval (in other Copelatinae , including the groundwater species Exocelina abdita Balke et al. 2004, this structure is more rounded, and the metacoxal “lines” can be more parallel sided, Figs 3B View Figure 3 , 4D View Figure 4 ); male with strongly modified antennomeres.
Habitat.
Collected from two helocrenes on a slope in forested area. The beetles were observed creeping around and were not swimming when observed (K. Sugaya personal communication 2019) (Fig. 6A, B View Figure 6 ).
Phylogenetic affinities.
The best evolutionary model fitting the data according to Modelfinder was a GTR+F for all partitions. Exocelina sugayai sp. nov. was recovered deeply subordinated within Exocelina , as the sister of the Chinese E. shizong Balke & Bergsten, 2003 and the New Caledonian E. nehoue Balke et al., 2014. These three species are part of a clade ( “C4” in Toussaint et al. 2015) otherwise containing E. parvula (Boisduval, 1835) from Hawaii as well as a clade of New Caledonian and one Vanuatu species (Fig. 7 View Figure 7 ). The other two subterranean species of Exocelina are E. abdita Balke et al., 2004 and E. rasjadi Watts & Humphreys, 2009 from Australia. The former was included in our phylogenetic analysis and placed in a different clade than Exocelina sugayai sp. nov. (Fig. 7 View Figure 7 , included subterranean species in red). Data for E. rasjadi were not available.
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