Altainella mongoliensis Ji, Camacho, Lee and Min, 2024

Ji, Su-Jung, Camacho, Ana Isabel, Lee, Chi-Woo & Min, Gi-Sik, 2024, The first report of Bathynellacea in the subterranean water of Mongolia: A new species of Altainella Camacho, 2020 (Crustacea, Bathynellidae), Biodiversity Data Journal 12, pp. e 130024-e 130024 : e130024-

Altainella mongoliensis Ji, Camacho, Lee and Min sp. nov.

Materials

Type status: Holotype. Occurrence: catalogNumber: Not yet ; recordedBy: Ji, Camacho, Lee and Min; individualCount: 1; sex: male; lifeStage: adult; occurrenceID: 9FEAE306-3418-59AD-8419-CBB7CD56BF83; Taxon: scientificName: Altainella mongoliensis ; phylum: Arthropoda; class: Malacostraca; order: Bathynellacea ; family: Bathynellidae ; genus: Altainella ; specificEpithet: mongoliensis ; Location: country: Mongolia; stateProvince: Khentii; verbatimLatitude: 48.290972; verbatimLongitude: 110.210286; Identification: identifiedBy: Su-Jung Ji; Event: eventDate: 22-07 - 2022; Record Level: language: en; institutionCode: MNCN 20.04 / 21011; basisOfRecord: PreservedSpecimen

Type status: Holotype. Occurrence: catalogNumber: Not yet ; recordedBy: Ji, Camacho, Lee and Min; individualCount: 1; sex: female; lifeStage: adult; occurrenceID: 09A234BD-A807-5637-8F13-8FE354D29F9C; Taxon: scientificName: Altainella mongoliensis ; phylum: Arthropoda; class: Malacostraca; order: Bathynellacea ; family: Bathynellidae ; genus: Altainella ; specificEpithet: mongoliensis ; Location: country: Mongolia; stateProvince: Khentii; verbatimLatitude: 48.290972; verbatimLongitude: 110.210286; Identification: identifiedBy: Su-Jung Ji; Event: eventDate: 22-07 - 2022; Record Level: type: Paratype; language: en; institutionCode: NNIBRIV 118588; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: Not yet ; recordedBy: Ji, Camacho, Lee and Min; individualCount: 1; sex: male; lifeStage: adult; occurrenceID: 3742219F-4318-5F5E-B2B0-AA1AA218F6DB; Taxon: scientificName: Altainella mongoliensis ; phylum: Arthropoda; class: Malacostraca; order: Bathynellacea ; family: Bathynellidae ; genus: Altainella ; specificEpithet: mongoliensis ; Location: country: Mongolia; stateProvince: Khentii; verbatimLatitude: 48.290972; verbatimLongitude: 110.210286; Identification: identifiedBy: Su-Jung Ji; Event: eventDate: 22-07 - 2022; Record Level: language: en; institutionCode: MNCN 20.04 / 21012; basisOfRecord: PreservedSpecimen

Type status: Paratype. Occurrence: catalogNumber: Not yet ; recordedBy: Ji, Camacho, Lee and Min; individualCount: 1; sex: female; lifeStage: adult; occurrenceID: 34CF4994-0EA5-5D6A-8A7E-F2C450F4EB5C; Taxon: scientificName: Altainella mongoliensis ; phylum: Arthropoda; class: Malacostraca; order: Bathynellacea ; family: Bathynellidae ; genus: Altainella ; specificEpithet: mongoliensis ; Location: country: Mongolia; stateProvince: Khentii; verbatimLatitude: 48.290972; verbatimLongitude: 110.210286; Identification: identifiedBy: Su-Jung Ji; Event: eventDate: 22-07 - 2022; Record Level: language: en; institutionCode: NNIBRIV 118589; basisOfRecord: PreservedSpecimen

Description

Description of adult male

Total body length 1.6 mm (Fig. 2 ). Body elongated, segments widening slightly towards the posterior end. Head longer than wide. Pleotelson with one small barbed dorsal seta on each side.

Antennule (Fig. 3 A). Seven-segmented; first three articles longer than the last four combined; first article longer than the last, which is more slender than the rest of the articles; fourth and fifth articles shortest and equal in length; small trapezoidal inner flagellum; setation as in Fig. 3 A; segment three with four smooth setae; segment six with three aesthetascs, similar in size; seventh segment with three aesthetascs, similar in size. Antennule as the antenna in length.

Antenna (Fig. 3 B). Seven-segmented; with medial seta on exopod; first article long; second and third shortest; fourth and sixth similar in length to the first; fifth small, measuring just over half the length of the distal article, which is the longest; setal formula: 0 + 0 / 2 + 0 / 2 + 0 / 2 + 0 / 0 + 0 / 2 + 2 / 5.

Labrum (Fig. 3 C). Distal smooth free edge with irregular central protuberances.

Paragnath (Fig. 3 D). Almost rectangular, globose, with a distal claw; setulation on the distal half.

Mandible (Fig. 4 A). Palp with three articles, third article with two claws of different lengths, one strong and barbed, one small and smooth first and second articles rectangular and robust and third article small and almost square. Masticatory part: incisor process (pars incisiva) with two teeth, processus incisivus accessorius with two teeth, pars molaris with two teeth and a lobe with small denticles on the distal part.

Maxillule (Fig. 4 B). Proximal endite with four setae, all setulose; distal endite with six teeth, four denticles; three plumose setae of similar length on the outer margin.

Maxilla (Fig. 4 C). Four-segmented; setal formula 7, 4, 7 and 5.

Thoracopods I to VII (Fig. 4 D – F and Fig. 5 A – D). Well-developed; thoracopod I – III (Fig. 4 D – F) progressively longer; thoracopod IV – VI (Fig. 5 A – C) of similar length; thoracopod VII (Fig. 5 D) slightly longer than rest and dimorphic; thoracopod I without epipod; coxa with long strong plumose seta; rectangular basipod with three smooth setae on thoracopod I, with two setae on thoracopods II and III, only one seta on thoracopods IV to VI and without seta on thoracopod VII; thoracopods II to VII with epipod, a little longer than half the basipod. Exopod of thoracopods I to VII one segmented and shorter than endopod, reaching the middle of the third endopodal article in thoracopods I to VI and as long as the first two segments combined in thoracopod VII, with five barbed setae (two terminal, one dorsal and two ventral); endopod four segmented in all thoracopods, with first three articles similar in length in thoracopod I (Fig. 4 D) and second article longer than the first one in thoracopods II to V (Fig. 4 E, F and Fig. 5 A and B) and of equal length to the third article in thoracopods VI and VII, which is longer than the second article in thoracopods I to V; four articles very small in all thoracopods; thoracopod VII with a coxal structure like a very pointed ‘ spur’ (Fig. 5 D), with distal internal edge serrated, extending beyond the distal end of the basipod; first article of the endopod modified with a basal dilatation, with a seta and an external row of spines that extends to the distal end of the article. Setal formula for endopods:

Thoracopod I: (3) 3 + 0 / 2 + 1 / 2 + 0 / 3

Thoracopod II – III: (2) 2 + 0 / 2 + 1 / 2 + 0 / 3

Thoracopod IV – V: (1) 1 + 0 / 1 + 1 / 1 + 0 / 3

Thoracopod VI: (1) 1 + 0 / 0 + 1 / 0 + 0 / 2 (1)

Thoracopod VII: (1) 1 + 0 / 0 + 1 / 0 + 0 / 2 (1)

Male thoracopod VIII (Fig. 6 A). Large and long; basal region of the penial complex well-developed; a penial region with two lobes of similar length, outer and inner lobes, with the distal end of frontal projection rounded and vertical large basipod, with very small frontal crest, one distal seta at the base of the exopod and a row of small spines on inner surface from the middle of the basipod to almost the distal end; exopod very elongated, three times longer than the endopod, with five setae, two distal, two subdistal and one on a dorsal protrusion on the proximal half; endopod small, rectangular, bearing two setae.

Pleopod (Fig. 6 B). Two segmented; the first segment with very long smooth seta; the second segment with six setae — three smooth and three barbed of different length.

Uropod (Fig. 6 C). Sympod 60 % longer than wide and 40 % longer than endopod, with six equal distal spines; the endopod is almost 1.5 times longer than the exopod, with three strong spines, the distal one longer than second which is longer than the first, two distal barbed setae, the internal more than twice as long as the external one and one plumose seta located dorso-laterally; exopod with four setae, two terminals, one of them very long and two medial setae.

Pleotelson (Fig. 6 D). One barbed dorsal seta on each side near the base of the furca, slightly longer than that of the furca.

Furcal rami (Fig. 6 D). Almost square, bearing five spines, the first slightly longer than the second and third, which are similar in length and almost twice as long as the fourth, similar in length to the dorsal spine.

Description of adult female

Females have the same morphological characteristics as males, excluding the parts of the body where sexual dimorphism is manifested — the mandible and thoracopods VII and VIII.

Mandible (Fig. 7 A) is similar to that of males, except for the second article of the mandibular palp, which is longer than that of males and bears two distal barbed claws of similar sizes.

Thoracopod VII (Fig. 7 B) without coxal structure like ‘ spur’ and with the first article of endopod unmodified.

Thoracopod VIII (Fig. 7 C). Coxa with small tooth; very large epipod, exceeding the length of basipod; small trapezoidal endopod one-segmented with two unequal barbed apical setae; exopod 2.5 times as long as endopod and third of the length of the basipod, with three smooth apical setae similar in length and slightly shorter medial setae.

Diagnosis

Antennule and antenna seven segmented. Antenna exopod with median seta. Mandible: mandibular palp sexually dimorphic; pars molaris formed by two small teeth near the processus incisivus accessorius and a lobe with a distal region covered by denticles. Endopod of thoracopods I – VII four-segmented; coxapod of thoracopod VII sexually dimorphic, with a spur-shaped structure in males. Male thoracopod VIII: a penial region with two lobes of similar length, outer and inner lobes and frontal projection; basipod large, vertical, with frontal crest and one distal seta; exopod very elongated, with dorsal protrusion and setae; endopod with two setae. Female thoracopod VIII: a very large epipod, as long as an exopod, much longer than an endopod. Uropod: sympod with six spines; endopod with three spines. Furcal rami with the first spine longer than the other four.

Etymology

The species name " mongoliensis " is a combination of " Mongolia ", the country from where the new species was collected and the suffix " - ensis. "

Taxon discussion

The differences and similarities between the new species and Altainella calcarata Camacho, 2020 are summarised in Table 1 . Here, we review the morphological characteristics of the two species of the genus Altainella .

Size and mouthparts: Both species were similar in size and large for the average species of the family Bathynellidae . In the antennule, the first article of the new species is rectangular, whereas A. calcarata is small and almost square. Comparing the lengths of the antennule and antenna, A. calcarata had a slightly longer antenna than the antennule, whereas, they were almost similar in length in the new species. In the new species, the exopod of the antenna did not reach the third segment of the antenna; however, in A. calcarata , it extended well beyond the third segment. The paragnaths were thicker in the new species than in A. calcarata . In the new species, the male mandibular palp had a longer first article and shorter external setae in the third article compared to A. calcarata . The maxillule of the two Altainella species had four setae in the proximal segment. However, unlike A. calcarata , the new species has setae in the rows on the outer edge of the distal segment. The maxillae were similar in articles and setation for both species.

Thoracopods I to VII: Thoracopods are similar in both species, but unlike A. calcarata , the new species lacks an epipod on thoracopod I. The new species has reduced seta formation on the thoracopods compared to A. calcarata . The spur-like protrusion of the male thoracopod VII is longer and more pointed in the new species than in A. calcarata . The first segment of the endopod of the male thoracopod VII was highly enlarged in the new species compared to A. calcarata .

Thoracopod VIII: The exopod of female thoracopod VIII in the new species is much shorter and stubbier and the exopod is longer than that of other species. The male thoracopod VIII differs in both species, especially in the penial region, where the frontal projection of the new species is larger than that of A. calcarata , which has a smaller outer lobe and larger basipod crest.

Pleopod: The new species bears six setae on the second segment in pleopod, while A. calcarata had 12 setae.

Furcal rami and uropod: In the new species, the four spines on the furcal rami, excluding the dorsal spine, gradually increase in length towards the outer edge. However, in A. calcarata , the second and third spines are almost equal in size, whereas the first spine is nearly twice as long. In the uropod of the new species, there was only one median seta on the outer edge of both the endopod and the exopod. However, in A. calcarata , there were two setae each — one at the one-third and two-thirds points. This is consistent with the reduced thoracopod seta formula in the new species compared with that in the existing species.

Molecular data

In this study, a single 486 bp of CO 1 and two 1,701 bp of 18 S gene sequences were obtained. The interspecific genetic distances between the new species and the Russian Altainella species were 15.0 % for CO 1 and 1.4 % for 18 S gene sequences. The two obtained 18 S rRNA gene sequences were included in the Maximum Likelihood ( ML) phylogenetic analysis depicted in Fig. 8 . We submitted three sequences to the NCBI (National Center for Biotechnology Information) database: PQ 032499 for CO 1; PQ 037633 and PQ 037634 for 18 S rDNA sequences.

18 S-based Maximum Likelihood ( ML) analysis

The 18 S rDNA alignment dataset comprised 1,433 bp derived from 21 sequences (Fig. 8 , Table 2 ). The analysis revealed that the new species, Altainella mongoliensis sp. nov., formed a well-supported clade with A. calcarata from Russia, which was the only other known species within the genus ( PP = 90). This close phylogenetic relationship between the two species suggests a strong evolutionary affinity and supports the placement of the new species. Additionally, the results of the ML analysis supported three distinct clades representing three subfamilies — Bathynellinae, Gallobathynellinae and Austrobathynellinae — within the family Bathynellidae ( PP = 74, 100 and 100, respectively), which supports their morphological classification and previous molecular phylogenetic studies ( Camacho et al. 2013, Camacho et al. 2020).

Figures

Figure 2. Habitus of Altainella mongoliensis sp. nov. (holotype).

Figure 3. Altainella mongoliensis sp. nov., holotype male. A Antennule; B Antenna; C Labrum; D Paragnath. Scale bars: 0.05 mm.

Figure 4. Altainella mongoliensis sp. nov., holotype male. A Mandible; B Maxillule; C Maxilla; D Thoracopod I; E Thoracopod II; F Thoracopod III. Scale bars: 0.05 mm.

Figure 5. Altainella mongoliensis sp. nov., holotype male. A Thoracopod IV; B Thoracopod V; C Thoracopod VI; D Thoracopod VII. Scale bars: 0.05 mm.

Figure 6. Altainella mongoliensis sp. nov., (A) Paratype male, (B – D) Holotype male. A Thoracopod VIII; B Pleopod; C Uropod; D Pleotelson and furcal rami. Scale bars: 0.05 mm.

Figure 7. Altainella mongoliensis sp. nov., paratype female (NNIBRIV 118589). A Mandible; B Thoracopod VII; C Thoracopod VIII. Scale bars: 0.05 mm.

Figure 8. Maximum Likelihood and Bayesian Inference analyses, based on nuclear 18 S gene sequences (majority consensus tree of ML). Numbers on nodes represent ultrafast bootstrap values from 1,000 replications for Maximum Likelihood and Bayesian posterior probabilities.