Cincticostella sp. A

Martynov, Alexander V., Selvakumar, C., Palatov, Dmitry M., Subramanian, K. A., Sivaramakrishnan, K. G., Vasanth, M. & Jacobus, Luke M., 2021, Overview of Indian and Nepali representatives of the Cincticostella nigra (Ueno, 1928) complex (Ephemeroptera, Ephemerellidae), with discussion about Cincticostella Allen, 1971 species complexes, ZooKeys 1040, pp. 123-166 : 123

Cincticostella sp. A

Diagnosis.

Immature larva: (i) genae moderately developed, rounded; (ii) anteromedian emargination of labrum shallow (labrum height in emargination/maximum labrum height ratio - 0.85); (iii) maxillary palp well-developed; (iv) segment III of maxillary palp, thin, elongated, rounded apically; (v) group of 13-16 setae different-sized, stout, hair-like situated on surface of galea-lacinia near base; (vi) prothoracic anterolateral projections small; (vii) mesothoracic anterolateral projections well-developed, subparallel to lateral aspect of body, not notched; (viii) surface of thorax covered with scattered short, thin, hair-like setae and few scale sockets and very short rounded scales with feathered margins in some of them; few waved and hooked setae cover mainly wing pads; (ix) dorsal surface of fore femur with sparse, transverse row of mainly long, stout setae with slightly convergent margins and bifurcated apices; (x) tarsal claw with one large denticle and several subapical setae; (xi) pairs of pointed projections present on abdominal terga II-IX; those on terga V-VIII strongest; those on tergum IX moderately developed, rounded apically.

Distribution.

Nepal.

Remarks.

Two middle larval instars (body length 5.5-6.5 mm; caudal filaments length 5.2-5.3 mm) of this operational taxonomic unit (OTU) were collected in Nepal in 2014. However, the poor material and absence of late larval instars do not allow us to describe a new species adequately. We hope that this account will facilitate discovery of additional material of this OTU.

Habitat.

Larvae of Cincticostella sp. A inhabit cold, moderate flowing springs with stones, gravel and clumps of moss. Larvae were collected from such a spring (up 1.3 m wide) in medium high mountains, on the southern slope of the Great Himalayan Range. This was a small, lotic waterbody with relatively low water temperature (10 °C in sampling period), average current velocity (0.2-0.6 m/s), mosaic bottom and a low degree of anthropogenic pressure.

Material examined.

Nepal: 2 larvae (one on slide 634), Gandaki Zone, Kaski District, stream at the Tolka-Lambruk Road , 28.365000°N, 83.831667°E, h ~ 2000 m a.s.l., 27.i.2014, Chertoprud M.V., Marinskiy V.V. leg. - IN Nepa 1 Cinsp [NMNH NASU] .

Cincticostella of India and southern limit of the genus distribution

To date, nine species of the genus Cincticostella are known from India: C. bifurcata Xie, Jia, Chen, Jacobus & Zhou, 2009; C. braaschi Jacobus & McCafferty, 2008; C. changfai Martynov & Palatov, sp. nov.; C. funki Martynov, Selvakumar, Palatov & Vasanth sp. nov.; C. gosei (Allen, 1975); C. insolta (Allen, 1971); C. ranga Selvakumar & Subramanian, 2019; C. richardi Martynov & Palatov, 2019 and C. wangi Selvakumar, Martynov & Subramanian, sp. nov. ( Martynov et al. 2019, new data). Distribution of the species within India falls within the Himalayan Region. In all known cases, the species inhabit coldwater streams and rivers with significant current velocity and coarse substrate.

Overall, only three of all known species of Cincticostella occur at latitudes that are more southern than the Himalayan Region, namely C. gosei , C. insolta and C. femorata . The southernmost records of C. insolta are from Thailand, where the species inhabits coldwater flows in northern upland region of the country ( Martynov et al. 2019). Cincticostella femorata inhabits similar waterbodies in the Region ( Martynov et al. 2019; Zheng and Zhou 2021). However, this species and C. gosei penetrate southwards in Thailand, where they would seem to prefer warmer biotopes (e.g. Gose 1969). These records form the southern border of the genus distribution at about 12.6°N latitude.

Species complexes in Cincticostella

Cincticostella comprises at least 21 valid species (Table 2 ) ( Jacobus and McCafferty 2008; Xie et al. 2009; Martynov et al. 2019; Auychinda et al. 2020; new data), but it remains poorly investigated. For the vast majority of species, only the larval stage is known - as is the case for all representatives of the C. insolta complex, except for C. femorata ( Zhang et al. 2020; Zheng and Zhou 2021).

Allen (1975) divided all representatives of the genus into two species groups, based on larval characters: the Cincticostella nigra -group and the Cincticostella insolta -group. According to Allen (1975), representatives of the Cincticostella nigra -group lack head tubercles and their middle and hind pairs of femora are narrow, not enlarged and the margins are without serration; the Cincticostella insolta -group was characterised by possessing suboccipital head tubercles and the middle and hind pairs of femora being enlarged with serrated margins and/or protuberances. Later, the Cincticostella insolta -group was designated as the separate subgenus Cincticostella Rhionella Allen, 1980; all other species, including C. gosei , were placed in Cincticostella s.str. ( Allen 1980). In the revision of Ephemerellidae genera, Rhionella was strictly synonymised with Cincticostella ( Jacobus and McCafferty 2008), based on the position of its type species within the tree of other Cincticostella species (fig. 94 in Jacobus and McCafferty 2008).

In light of the several new species described since Jacobus and McCafferty (2008) revised the generic classification of the group and considering possible polyphyly, we re-evaluated the larval morphology of Cincticostella species for understanding the difference of complexes and expediency of their designation; available material and literature data were used for this analysis ( Tshernova 1952; Allen 1975; Braasch 1981; Kang and Yang 1995; Ishiwata 2003; Jacobus and McCafferty 2008; Xie et al. 2009; Martynov et al. 2019; Auychinda et al. 2020; Zhang et al. 2020; Zheng and Zhou 2021).

Based on our research, we conclude that the establishment of the discussed complexes was for expediency. In fact, the C. insolta and C. nigra complexes are more distanced morphologically from each other than previously thought (see Allen 1975), based on our new distinguishing characters (see characters 3-10 in Table 1 , below). All but one species of Cincticostella clearly fit into the C. insolta or C. nigra complexes as here defined; only C. gosei has a combination of characters that does not completely fit into any of these two complexes. Therefore, the monotypic C. gosei complex is proposed herein (Tables 1 and 2 ). We acknowledge possible paraphyly of the other complexes.

The following morphological features place C. gosei closer to the C. insolta complex than to the C. nigra complex: presence of numerous large, rounded, scale sockets on body surface, absence of maxillary palp (this character state may prove to be related to significant reduction of the maxillary palp, including reduction of segments’ articulations), number of stout setae on the outer margin of the fore femur and absence of numerous stout setae on dorsal surfaces of the middle and hind femora, complete absence of stout setae on dorsal surfaces of abdominal terga and paired projections.

Ogden et al. (2009) included only two species from this genus in their combined evidence for phylogenetic analyses of Ephemerellidae . Further investigation of imaginal characters after new stage associations (e.g. Zhang et al. 2020; Zheng and Zhou 2021) and molecular investigation (Martynov, in progress) will help to better understand the structure and relationships of species in the genus Cincticostella .

Figures

Figure 15. Larva of Cincticostella gosei (Allen, 1975) A fore femur B middle femur C hind femur D tarsal claw E-H gills III-VI.