Acricotopus, Kieffer, 1921

Laug, Andreas, Hamerlík, Ladislav, Anslan, Sten, Engels, Stefan, Turner, Falko, Wang, Junbo & Schwalb, Antje, 2019, Acricotopus indet. morphotype incurvatus: Description and genetics of a new Orthocladiinae (Diptera: Chironomidae) larval morphotype from the Tibetan Plateau, Zootaxa 4656 (3), pp. 535-544 : 536-539

Acricotopus indet. morphotype incurvatus

( Figure 1–3 )

Orthocladiinae type K3 ( Laug et al. 2018) Type Material. [all Beijing Museum of Natural History, P.R. CHINA: Tibet, Nakchu Province, 31.728468°N, 88.854926°E, 02.08.2018, A. Laug, slides mounted in Berlese medium]: Holotype Larva1, 4 th instar,, BMN- HC239441 , Holotype Larva 2, 3 rd instar, BMNHC239440 ; Holotype Larva 3, 3 rd instar, BMNHC239442 ; Holotype Larva 4, 2 nd instar, BMNHC239443 ; Holotype Larva 5, 4 th instar, anterior part of body missing, BMNHC239444 ; Holotype Larva 6, 3 rd instar, body missing, BMNHC239445 .

Diagnosis: Larva. Medium-sized larvae (5.7 mm body length), head capsule length 0.5 mm and about as long as wide, head coloration brown with occipital margin dark brown to black, wrinkles might be present, pale spot on the frons. This characteristic is not always visible in weakly sclerotized specimens.

Antenna. With 5 segments, about 1/6 to 1/7 as long as head capsule length, basal segment longer than flagellum, ring organ and basal setae close to the base, antennal segment 2 about as long as combined length of segments 3–5. Blade shorter than flagellum, reaching until the end of the 4 th segment, Lauterborn organs indistinct. Style as long as the 3 rd segment.

Labro-epipharyngeal region. S I palmate, with 4–5 lobes. S II and S III simple, pecten epipharyngis with 3 lobes, premandible with one apical and one basal tooth, brush absent.

Mandible. Apical tooth about as long as combined width of 4 inner teeth, one toothed lobe, subdivided into 2 parts, the length varying considerably between shorter than the margin of the mandible to overlying the inner teeth. Seta subdentalis notched with a hook, seta interna absent.

Mentum. With 3 median teeth, middle median tooth subequal to outer median teeth and can be notched. Up to 8 lateral teeth on a different focal plane than median teeth, first 2 lateral teeth reduced and on different focal plane than other teeth, partially behind of median and outer lateral teeth, 3 rd to 8 th lateral tooth in a distinct cluster and curved inwards. The 7 th and 8 th lateral tooth behind 3 rd to 6 th lateral tooth, because of the dark coloration of the mentum often not visible. Ventromental plate narrow anteriorly, extending into sclerotized, rounded plate beyond basal margin of mentum. Sparse beard with up to 10 is present even if reduced in comparison with the other Acricotopus described species, setae submenti positioned between ventromental plates. Large narrow plate, similar to the one of Tanytarsus gracilentus , with 4–6 teeth on each of two focal planes, positioned behind mentum.

Maxilla. Pecten galearis absent, setae maxillaris simple, maxillary palp slightly longer than wide.

Body. White, when stored in alcohol with blue coloration at the dorsal side between segments. Anterior parapods separate, each bearing apical crown of claws, sometimes claws with a distinct apical tooth. Posterior parapods separate, each with an apical group of simple claws, procercus about as high as wide, dark, strongly sclerotized, bearing 6 anal setae, anal tubules much shorter than posterior parapods.

Genetics. A total of five 28S, five COI high quality sequences and one 18S read were obtained for the studied specimens. Reads of 28S and COI did not exhibit any intraspecific sequence divergence. Lengths of the Acricotopus indet. morphotype incurvatus sequences used in the construction of maximum likelihood tree were 956 and 656 for 18S and 28S, respectively. In the phylogenetic tree, Acricotopus indet. morphotype incurvatus placed alongside other Orthocladiinae , with strong support values ( Fig. 4 ). However, as we used only 18S and 28S reads for the phylogenetic tree construction, the aim is not to resolve the phylogenetic replacement of the taxa, but to demonstrate the replacement to other Orthocladiinae . Adding COI alignments to the tree construction did not change the placement of Acricotopus indet. morphotype incurvatus, but induced a long branch to this group (data not shown). As the 28S reads were identical between Acricotopus indet. morphotype incurvatus specimens, in the tree we used only one specimen from which we were able to obtain also the 18S sequence ( Table S2 ).

In accordance, the closest blastn matches, against GenBank database, were against Orthocladiinae : 18S and 28S matched with 92.54 % and 97.29 % similarity to Acricotopus lucens ( AJ 586561 , AJ 586562 ), respectively; COI sequences exhibited 90.05 % to specimen assigned to Cricotopus sp. ( KM 571496 , Orthocladiinae ). Similarity of Acricotopus indet. morphotype incurvatus COI and 28S reads against A. longipalpus were 87.2 % and 88.1 % (Levenshtein distance), respectively, and against A. lucens , 86.0 % and 96.8 %, respectively. Similarity of Acricotopus indet. morphotype incurvatus 18S sequences against A. lucens was 92.0 % (no data for A. longipalpus 18S).

Etymology. The morphotype name “incurvatus” is inspired by the peculiar form of the larval mentum.

Remarks. Gut content: Detritus including inorganic particles like fine sand, and organic remains such as diatoms and other algae.

At the sample point SLChS 18-04 larvae have been found in sediment-, kicking- and floating-samples, but were absent from plant-samples.

Figures

FIGURE 1. Acricotopus indet. morphotype incurvatus 4th instar larva. a) Mentum. b) Mandible with seta subdentalis. c) Labrum with premandibles, S I and pecten epipharyngis. d) Sclerotized plate.

FIGURE 2. Acricotopus indet. morphotype incurvatus 4th instar larva, light microscopy pictures. a) Body without head capsule. b) Last abdominal segment with posterior parapods, anal tubules and anal setae. c) Head capsule. d) Mentum with sclerotized plate. e) Mandible. f) Labro-epipharyngeal region.

FIGURE 3. Acricotopus indet. morphotype incurvatus 4th instar larva, scanning electron microscope pictures. a) Head capsule. b) Antenna. c) Anterior parapods. d) Labro-epipharyngeal region with S I. e) Pecten epipharyngis with S I. f) Posterior parapods.

FIGURE 4. Maximum likelihood tree of 18S and 28S sequences, with the small subset chironomid taxa from different subfamilies. The numbers near nodes represent bootstrap supports (100 replications). The taxa in bold represent herein described species, Acricotopus indet. morphotype incurvatus. Forcipomyia brevipennis Macquart represents the outgroup.