Kribiodosis cantonensis Tang, 2021

Kribiodosis cantonensis Tang, 2021 View in CoL

( Figs. 1H–K View Fig , 3A, C, E–I View Fig )

Kribiodosis cantonensis Tang View in CoL in Han et al., 2021: 564 View Cited Treatment .

Larva. Body length 3.2–5.1 mm. Body colour unreported. Head capsule ( Fig. 1H View Fig ) length 340–350, ventral head length 195–245, pale yellow with golden teeth of mentum, apical mandible and premandible ( Fig. 1H View Fig ). Dorsal surface of head ( Figs. 1K View Fig , 3H View Fig ) with frontoclypeus lacking fenestra, flared distally; labral sclerites weakly demarcated. Antenna ( Figs. 1H View Fig , 3C View Fig ) 6-segmented, with short wedge-shaped segment 2, and longer segment 3 bearing large Lauterborn organs on apex and subapex of 3rd segment, lengths 140–145: 20–22: 29–35: 38–42: 18–20: 6–8; Antennal ratio 1.12–1.25. Basal segment with weak ring organ in proximal third, seta absent. Blade 90–100 long, extending beyond apex of 4th segment.

Labrum ( Figs. 3F View Fig ) with SI on conjoined bases, seemingly shaped as smooth-edged fan, with minor setal fringe, and SII placed on a distinct pedestal, blade-like, apical ¼ with inner fringe, 30–35 long; SIII simple, 30 long; SIVa, b weak. 6–7 plumose chaetae. Seta premandibularis simple. Labral lamellae lie largely beneath SI, fringed. Pecten eipharyngis comprising three separated plates, each with 5–8 teeth; 7–8 apically finely plumose chaetulae laterales, 2 apically branched chaetulae basales. Premandible ( Fig. 3G View Fig ) 70–80 long, with 4 sharply pointed teeth and modest brush. Mandible ( Figs. 1I, J View Fig , 3E View Fig ) 100–110, with dorsal tooth, pointed apical tooth and 3 pointed inner teeth. Pecten mandibularis comprising a 25–32 spine-like lamella, protruding to mandibular margin, other branches few, short, simple. Seta subdentalis ( Fig. 3E View Fig , inset) 30–35 long, arising from ventral surface, sickle-shaped, distally with comb, extending to notch delimiting apical mandibular tooth. Mola and inner margin smooth. Seta interna 4–5 branched, densely plumose, but short.

Mentum ( Figs.1H View Fig , 3A View Fig ) 60–75 wide, with 16 continuous pale gold teeth without a delimited ventromental component; central 2 teeth recessed, the 2nd and 3rd elevated thereafter evenly declining. Ventromental plate 80–85 wide, 40–45 deep, fan-shaped, with smoothly curved anterior margin, medially tapered to medially-directed (not upcurved) point, inter-plate distance subequal to two recessed median teeth; striae very fine, seemingly restricted to median, lateral / posterior plate, lappets/ hooklets indistinct. Setae submenti simple.

Abdomen ( Fig. 3I View Fig ) without lateral or ventral tubules nor dorsal hump. Anterior parapod claws pale, dense, fine, simple; posterior parapods claws golden, simple. Procercus pale yellow, 2× as high as wide (45–55 × 25–30), bearing 5 anal setae 400–750 long. Anal tubules elongate-ovoid (150–200 × 50–80), dorsal slightly shorter than ventral, subequal or slightly shorter than posterior parapods.

Comments. The larva of Kribiodosis does not key beyond the cluster with 6-segmented antenna and alternating distinctive Lauterborn organs on the apices of antennal segments 2 and 3 in Epler et al., 2013. The ‘wedge-shaped’ (triangular) ventromental plate directs to couplet Zavreliella Kieffer, 1920 vs Lauterborniella Thienemann & Bause, 1913 , both of which have case-bearing larvae and considered as sistertaxa on morphological grounds by Andersen et al. (2017). Of these, Kribiodosis resembles Zavreliella in having simple setae submenti (vs. plumose) and the dorsal head including a frontoclypeus (vs frons and isolated clypeus). A broad seta subdentalis with comb-like distal margin ( Fig. 1J View Fig ) occurs in Kribiodosis and Lauterborniella , and in a different form in the distant Goeldichironomus Fittkau, 1965 , Kiefferulus Goetghebuer, 1922 and Axarus Roback, 1980 . Kribiodosis will not key to any Holarctic taxon even if restricted to those in which a ventromentum is not delimited ( Apedilum ). Southern hemisphere genera belonging to a ‘ Microtendipes –group’ show permutations of larval features. Included are Oukuriella Epler, 1986 , Claudiotendipes Andersen, Mendes & Pinho, 2017 , Conochironomus Freeman, 1961 , Skusella Freeman, 1961 , Paraskusella Cranston, 2018 , Paraborniella Freeman, 1961 and Paucispinigera Freeman, 1959 ( Cranston, 2020). In the Neotropics, Kribiodosis keys unequivocally to Zavreliella / Lauterborniella based on the sub-triangular ventromental plates in near contact medially ( Silva et al., 2018). Claudiotendipes is excluded on these features. In the guide to Australian and New Zealand larvae (Cranston, 2019) despite the increased diversity, a similar conclusion is reached for identical reasons. Since the larva of Kribiodosis is unlikely to be case-bearing, judging by morphology, it can be excluded from Zavreliella or Lauterborniella . Larval keys indicate resemblance to several other taxa, amongst which is Beardius Reiss & Sublette, 1985 , a diverse New World genus that includes species with the diagnostic antenna of the ‘ Microtendipes –group’.

In both Zavreliella and Lauterborniella the basal antennal segment has a distinct ‘antennal’ seta located subapically but this seta is lacking in Kribiodosis . In the plate of line drawings of Australian larval ‘ Zavreliella ’ ( Cranston, 1996), the mentum and antenna of taxon ‘K1’ ( K = Kakadu , northern Australia) and S1 (S=Sydney) ( Fig. 3B, D View Fig ), closely resemble those of Kribiodosis described here, in contrast to Australian Zavreliella marmorata ( Wulp, 1859) on the previous page that conforms to the (‘true’) Zavreliella larva (and pupa). Access to these specimens is currently unavailable due to databasing, reorganisation and relocation of slide collections at ANIC. These could confirm differences between genera as reported above. It is likely that Kribiodosis is to be found in tropical Australian waters. Unfortunately, as the associated pupae of both Kribiodosis species are unavailable to us, the presumed pupal type described in Cao & Tang (2017) is an unreliable individual association.

Molecular results and discussion. Our molecular multi-gene analysis uses a set derived from exemplars of the ‘ Microtendipes –group’ of genera for which DNA data are available, including Conochironomus and Skusella , presumed relatives of Paraskusella . This is anchored with Riethia and Tanytarsus as outgroups which consistently have formed the sister group to tribe Chironomini (e.g., Cranston et al., 2011; Han et al., 2021). New sequences for Paraskusella and a second species of Kribiodosis from this report have been incorporated into an ongoing expanded study. Most genera represented by multiple species have been pruned to a single terminal, recognisable in Fig. 4 View Fig by the published codes that follow the genus name (e.g., Microtendipes TH 02, HW013). Bayesian inference analysis revealed several strongly supported nodes identified by PP (posterior probability) = 0.99–1, indicated on Fig. 4 View Fig by ***, fewer weaker supported nodes (** PP= 0.95–0.98, * PP = 0.90-0.95) and with critical nodes lacking Bayesian support (PP <0.90 (unlabelled). Bootstrap values (72–100) are indicated only for nodes with Bayesian support> 0.90.

Kribiodosis mulu , new species, is sister to K. cantonensis Tang, 2021 View in CoL from oriental China with maximal Bayesian support, confirming their morphological assignment as congeners. The species are well separated on long branches usually associated with substantial difference. The Kribiodosis species pair are sister to a core ‘ Microtendipes View in CoL –group’, with maximal support (Bayes 1, BS 87), in keeping with Han et al. (2021). The internal structure within the ‘ Microtendipes View in CoL – group’ finds variable support at many nodes in both analyses, but resembles relationships from previous analyses lacking Kribiodosis View in CoL . Ongoing study incorporating more species and genera in this important and diverse clade should produce resolution with enhanced support. The relationships proposed here from molecular data are compatible with the discussion above on larval morphology, as previously on the male ( Han et al., 2021). Our molecular results support Freeman’s hypothesis that (African) Kribiodosis View in CoL is very close to Lauterborniella View in CoL and also supports his argument for considering these as two independent genera ( Freeman, 1958). Minimally, we provide a hypothesis testable by expanded sampling.

The relationships of Paraskusella View in CoL are clarified by our molecular analysis. As argued based on morphology of combined life stages, the genus is placed in a clade with Conochironomus View in CoL and Skusella View in CoL with high Bayesian support. This clade forms the sister group to all included ‘ Microtendipes View in CoL –group’ taxa. Morphological evidence suggested Paraskusella View in CoL was allied with Skusella View in CoL (as the ‘para’ indicates) but with features in each semaphoront precluding consideration as congeners ( Cranston, 2018). Previous molecular analyses including Conochironomus View in CoL and Skusella View in CoL showed these to be sister taxa (e.g., Cranston et al., 2011, Han et al., 2021) so it is unsurprising that Paraskusella View in CoL belongs in a clade with Skusella View in CoL and Conochironomus View in CoL , although internal relationships are weakly supported. Morphological features including the pupal abdominal lateral setal fringe, comb teeth on T VIII, and the larval antenna structure needs to be reconciled with this conditional molecular result.

Biogeography. The revelation of ever-increasing taxa in the subfamily Chironominae , notably in the tribe Chironomini , showing African – (Australian) – Oriental distributions has been reported in Han et al. (2021) with regard to Kribiodosis . To the examples discussed there, we add Paraskusella , previously known from Africa and Australia, now reported from Borneo in the Oriental region. The closest relatives Conochironomus and Skusella each show the same distribution pattern, referred to as the tropical Gondwana track by Matile (1990) and discussed by Cranston (2005). Whether this remains a valid descriptor given recent discoveries of these taxa in (non-Gondwanan) oriental China is unclear at present. A robust and dated phylogeny that includes these taxa at species-level will be necessary to further explore this pattern.