Sternodea arcana Leschen and Gimmel, 2023

Leschen, Richard A. B. & Gimmel, Matthew L., 2023, Sternodea arcana, new species (Coleoptera: Cryptophagidae: Caenoscelini): part of the Nearctic fauna?, Zootaxa 5278 (2), pp. 396-400 : 397-398

Sternodea arcana Leschen and Gimmel , new species

( Figs. 1–5 )

Type specimen. HOLOTYPE, male ( CNCI), labeled: “FLA. Monroe Co. Upper Matacumba Key , Isla Moranda, Ber. 225, 8.VIII.74, S. Peck // Sternodea floridensis sp. n. det. C. Johnson 1992 [partly handwritten, unpublished name] // HOLOTYPE Sternodea arcana , new species, desig. by Leschen & Gimmel 2023 [red label]”.

Diagnosis. Sternodea arcana is the sole member of the genus in the United States (assuming the label data to be correct) and can be distinguished from members of the widespread Caenoscelis by having a short, rounded body and antennal club with two antennomeres ( Fig. 1 ) (body elongate, parallel-sided, and antennal club with three antennomeres in Caenoscelis ) and the more similar Renodesta , known from California, by the antenna with 11 antennomeres and antennal club with two antennomeres ( Fig. 1 ) (antenna with 10 antennomeres and antennal club with one antennomere in Renodesta ).

With respect to the described species from the Palearctic ( Reitter 1888; Lyubarsky 1987; Johnson et al. 2007; Johnson 2012; Sasaji 1984), S. arcana can be distinguished from S. grilati Reitter and S. raddei Reitter by having dense and coarse punctation on the pronotum ( Fig. 2 ) and sparse and fine punctation on the elytra (both surfaces coarsely [ S. grilati ] or finely [ S. raddei ] punctate in the other species), and from S. baudii Reitter and S. japonica Sasaji by the presence of a transverse punctate-crenulate line on the pronotum ( Fig. 2 ) (transverse crenulate line absent in those two species). In S. arcana , the prosternal process is distinctly dilated posteriorly ( Fig. 3 ), while S. franzi Johnson has the prosternal process slightly dilated posteriorly and the process is parallel-sided in S. lederi and S. miki .

Description. Length 1.29 mm, breadth 0.82 mm. Body short-oval. Color of body dark reddish-brown, antennae and legs lighter. Dorsal setae uniformly golden, pronotum and elytra with long, decumbent, suberect, curved setae; microsculpture absent. Ventral surfaces with recumbent setae, about the same length compared with those on dorsum; prosternal process with sparse, short, curved setae along margins; punctation dense on most surfaces, less impressed and sparser on elytra and abdominal ventrites 2–5; abdominal ventrite 1 with punctures about as dense as on metaventrite, ventrite 5 bearing a patch of posteriorly-directed setae and sensory pegs.

Antenna ( Fig. 1 ) with 11 antennomeres; antennomere 3 shorter than 4 and 5 combined, lengths of antennomeres 4 and 5 equal and slightly longer than antennomeres 6 and 8, antennomere 9 slightly wider than antennomere 8, antennomere 11 asymmetrical and twice the length of antennomere 10. Eye with 10 ommatidia. Pronotum ( Fig. 2 ) with length/width ratio ~0.61; front margin weakly procurved and anterior angles projecting; lateral carina lacking a distinct bead (absent at base), margin irregularly and weakly crenulate; posterior margin sinuate, with a weak scutellar lobe; setae long, regular and curved; with slightly procurved transverse punctate-crenulate line present at middle third, loosely extended by a row of larger punctures that end near the posterior margin; punctation relatively uniform over most of disc, punctures separated by about 1.3 diameters, with smooth and shiny interspaces, separated by about 2–4 diameters and finer behind transverse line. Hypomeron densely punctate, punctures separated by about 1.3 diameters. Prosternal process ( Fig. 3 ) elevated, 0.24 mm, anteriorly acute with a short longitudinal carina, strongly dilated posteriorly, about 2.0× longer than width at posterior margin, posterior margin evenly arcuate, marginal bead present. Elytra with sides rounded near base, about 1.05× longer than combined width, about 1.15× wider than pronotum at greatest width (at basal one-fourth), about 2.22× longer than pronotum at greatest length; setae dual, rows of suberect curved setae (approximately 0.08 mm) alternating with rows of more adpressed setae of about similar lengths; punctation less dense and less impressed than on pronotum, punctures one-fourth to one-half the diameter of those on pronotum, denser near basal margin and separated by 1–2 puncture diameters, sparser on disc. Abdominal ventrite 1 with moderately broad intercoxal process, femoral lines and median carina absent, bead broadened near base of intercoxal process.

Aedeagus ( Figs. 4, 5 ) with tegminal strut absent, tegminal arms broad and fused at middle without a suture; parameres separate and partially fused to phallobase, thick and orbiculate, each with an inner dorsal cavity, apically truncate, length about 1.2× longer than width, apices unisetose; basipenis 3.3× longer than distipenis, with a welldeveloped median keel on ventral surface about half the length distipenis; distipenis relatively short (about 1.2× longer than wide), internal sclerites symmetrical; internal sac (broken) lacking sclerites; straight, not kinked.

Remarks. This species is known only from the male holotype. The abdomen (mounted dorsally), the terminalia and the aedeagus were mounted separately from the remaining body on the card with a male symbol. It is missing much of the protarsomeres (the right one absent and tarsomeres 4 and 5 are missing from the left), the left hind leg, and the anterior portion of the internal sac was also broken.

Etymology. The specific epithet is from the Latin adjective arcana , meaning “mysterious”, alluding to the mysterious geographic origin of the holotype.

Figures

FIGURES 1–5. Sternodea arcana, new species, holotype. 1) Antenna; 2) Pronotum, dorsal view showing punctation in anterior portion and transverse punctate-crenulate line; 3) Prosternal process, ventral view (not to scale); 4) Aedeagus, dorsal view; 5) Aedeagus, lateral view. Scale bars = 0.1 mm.