Austroniscus indobathyasellus Kaiser, Kniesz & Kihara, 2024

(SOSA), Senckenberg Ocean Species Alliance, Brandt, Angelika, Chen, Chong, Engel, Laura, Esquete, Patricia, Horton, Tammy, Jażdżewska, Anna M., Johannsen, Nele, Kaiser, Stefanie, Kihara, Terue C., Knauber, Henry, Kniesz, Katharina, Landschoff, Jannes, Lörz, Anne-Nina, Machado, Fabrizio M., Martínez-Muñoz, Carlos A., Riehl, Torben, Serpell-Stevens, Amanda, Sigwart, Julia D., Tandberg, Anne Helene S., Tato, Ramiro, Tsuda, Miwako, Vončina, Katarzyna, Watanabe, Hiromi K., Wenz, Christian & Williams, Jason D., 2024, Ocean Species Discoveries 1 – 12 — A primer for accelerating marine invertebrate taxonomy, Biodiversity Data Journal 12, pp. e 128431-e 128431 : e128431-

Austroniscus indobathyasellus Kaiser, Kniesz & Kihara sp. nov.

Materials

Type status: Holotype. Occurrence: catalogNumber: SMF 61327 ; recordedBy: K. Kniesz & T. C. Kihara; individualCount: 1; sex: male; lifeStage: adult; preparations: 96 % EtOH; associatedSequences: http://www.ncbi.nlm.nih.gov/nuccore/OR825323; occurrenceID: 9C41CDEC-C376-5815-8ACD-49581FB40DDD; Taxon: scientificName: Austroniscus indobathyasellus Kaiser, Kniesz & Kihara ; kingdom: Animalia; phylum: Arthropoda; class: Malacostraca; order: Isopoda ; family: Nannoniscidae ; genus: Austroniscus ; specificEpithet: indobathyasellus ; taxonRank: species; scientificNameAuthorship: Kaiser, Kniesz & Kihara; nomenclaturalCode: ICZN; Location: higherGeography: Indian Ocean; waterBody: Central Indian Ocean Ridge; locality: Station No. I 19 _ 036 RO _ BB _ 01 ; verbatimDepth: 2628 m; locationRemarks: 150 m distance of a hydrothermal vent field; verbatimLatitude: 25 ° 28 ' S; verbatimLongitude: 69 ° 55 ' E; decimalLatitude: - 25.466675; decimalLongitude: 69.916682; Identification: identifiedBy: S. Kaiser, K. Kniesz, T. Kihara; dateIdentified: 05 / 2022; Event: samplingProtocol: Rock picking by Remotely Operated Vehicle, rock washing over sieves on deck; eventDate: 14 / 11 / 2019; Record Level: institutionCode: SMF; basisOfRecord: PreservedSpecimen

Description

Habitus (Fig. 40 A, E and Figs 41 , 42 , 43 ) body length 4.0 mm; body dorsoventrally flattened and broadened, body length 2.3 Prn 2 width and 1.9 maximum body width (pereonite 5); Prn 4–7 and Plt of similar width; Prn 1–3 with strongly frontally directed lateral margins, tipped with a small spine-like seta apically. Prn 1 narrowest, length 0.1 width; Prn 2 width 1.4 Prn 1 width, length 1.8 Prn 1 length; Prn 2 and 3 of similar length. Prn 4–6 similar length at mid-line, 2.5 Prn 1 length; Prn 7 longest, length 3.2 Prn 1 length; Prn 5 anterior margin straight; Prn 6–7 anterior margins strongly convex. Prn 2–7 coxa inserting ventrally and, hence, not visible in dorsal view; Prn 1 coxa inserting anteriorly, each with a spine-like frontally directed coxal extension, tipped with a small spine-like seta and clearly visible in dorsal view, almost reaching second art of A 1; length coxal extension 2.5 width, with width broadest in the middle and narrowing both proximally and distally. Plt length 0.3 body length, length 0.5 width; width 1.7 Prn 1 width, posterior margin semicircular and rounded, anterior margin slightly concave. Urp length 0.5 Plt length, slightly projecting beyond posterior margin.

Ceph (Figs 40 , 41 , 42 A) free, length 0.7 width. Rostrum well developed. Ceph anterior margin straight, posterior margin slightly rounded, A 1 and A 2 inserting anterolaterally in a deep fold between rostral crest and anterolateral, triangular projections; each fold with a single robust seta medially.

A 1 (Fig. 40 A – C and Fig. 42 A), broken off from third art onwards; first art ovoid and broad, length 1.2 width, distally with 1 long broom seta and 1 slender simple seta; second art length 1.3 art 1 length, 5.0 width, distally with 2 long broom setae and 2 simple setae.

A 2 (Fig. 40 C – D and Fig. 42 A); broken off, only peduncular art 1 – art 4 present; art 1 – art 4 short; art 2 with a small robust seta tipped with a small setula distally; art 3 with 1 large robust scale, tipped with a small seta distally.

P 5 (Fig. 40 H) basis length 3.9 width, with 2 long broom setae and 1 simple seta dorsally, with 3 simple setae ventrally and 1 somewhat longer simple seta distoventrally; ischium length 0.7 basis length, length 2.9 width, with 3 simple setae (2 small, 1 somewhat more robust) dorsally, with 2 simple setae ventrally; merus length 0.4 ischium length, length 1.2 width, with 2 robust simple setae distodorsally, with 1 slender simple seta distoventrally; carpus length 3.8 merus length, length 4.1 width, with a row of 17 long natatory setae each bearing 1 row of setulae and 3 robust unequally bifid setae dorsally, with 1 long broom seta and 1 small simple seta distodorsally, with 8 setae (4 simple and 4 robust unequally bifid) ventrally; propodus as long as carpus, length 6.6 width, with a row of 17 long natatory setae each bearing 1 row of setulae and 1 unequally bifid seta dorsally, with 8 unequally bifid setae ventrally; dactylus length 0.3 propodus length, length 5.0 width, with 3 simple setae medially; unguis length 0.3 dactylus length, with 2 slender setae between unguis and ventral claw.

Plp 1 (Fig. 40 F and Fig. 43 A); length 3.0 proximal width; distal projection width 0.7 proximal width, lateral margins straight; lateral lobes tapering sharply; distal margins almost straight, with 10–11 simple setae of varying length each.

Urp (Fig. 40 E, G and Fig. 43 A); biramous; sympod triangular, length 2.9 distal width, with 2 simple setae of varying size laterally, with 3 setae distally (2 long simple, 1 broken off); exopod length 0.6 sympod length, length 5.1 width, with 2 setae laterally (1 simple, 1 broken off), with 7 setae terminally (4 broken off, 3 long slender); endopod length 1.2 exopod length, length 5.4 width, with 4 simple setae of varying size laterally, with 9 (3 broom, 6 broken off) setae terminally.

Diagnosis

Pereonite 1 lateral margins frontally directed; coxae of pereonite 1 inserting anteriorly, each with a spine-like frontally directed appendix, tipped with a small spine-like seta and clearly visible in dorsal view, almost reaching second article of the antenna I; length-width ratio of the coxal extension <3; pereonites 1–3 anterolateral margins each with a spine-like seta. Pleopod 1 distal margins almost straight, lateral lobes tapering sharply.

Molecular diagnosis: The new species is differing in the COI-gene from other species within Austroniscus in the nucleotides G (position 47 of the alignment), T (48), G (62), C (69), C (80), C (95), C (111), C (145), T (173), T (175), C (206), T (208), A (232), A (278), G (298), A (391), G (430), C (438), T (449), A (514), C (518), T (520), C (595) and C (601).

Etymology

The specific epithet indobathyasellus is a compound noun in apposition, crafted from Greek and Latin elements representing origin, habitat and morphological resemblance of the new species. It is to be treated as a Latin noun in nominative singular. The element indo refers to the ocean where the species dwells, honouring the first report of the genus and family in this region. The element bathy refers to the bathyal hydrothermal vents near which the holotype was found, implying potential adaptations to this habitat. The element asellus, along with the element oniscus in Austroniscus , refers to the terrestrial isopod Oniscus asellus Linnaeus, 1758, highlighting the new species’ form similarity with its terrestrial counterpart.

Taxon discussion

Creating a taxonomic description based on a single individual, especially when lacking many appendages, is not considered optimal. However, the new species has distinctive features, notably the anteriorly inserting coxae of pereonite 1, that help distinguish it from all other known species of the genus. Furthermore, since the specimen is a male, there may be gender-dependent differences that are not accounted for. Nonetheless, species in the genus typically display minimal or only slightly expressed sexual dimorphism (e. g., Kaiser et al. 2023), allowing us to make reasonable inferences about the female characteristics.

This new species marks the first formal description of a species within the genus Austroniscus from the Indian Ocean. Even more remarkably, this constitutes also the first described species within the family Nannoniscidae originating from this vast geographical region. This highlights how little is known about the deep-sea areas of this region. Moreover, it stresses the potential of new species discoveries through enhanced exploration and taxonomic analysis to bridge existing biogeographic gaps.

The new species exhibits similarities with a cluster of species distinguished by a wide body width (where body length is less than 2.1 times the maximum body width) from all other species in the genus, specifically A. chelus , A. brandtae , A. obscurus and A. ovalis . Additionally, the new species displays a distinctive elongation of the coxae of pereopod 1, extending notably beyond the anterolateral margins of pereonite 1 (in dorsal view), a feature shared with A. chelus , A. brandtae and A. obscurus . The comparison of the new species is limited to this specific group.

No males have been described for A. obscurus and A. chelus . Therefore, comparisons with the new species are based on differing genders for these species. Only in the case of A. brandtae , the comparison with the new species is focused on male features. A. indobathyasellus sp. nov. differs from these species by the following characters: 1) coxa of pereonite 1 inserting anteriorly (vs. centrally in the other species); 2) length-width ratio of the coxal extension <3 (vs.> 4); 3) width of the coxal extension broadest in the middle and narrowing both distally and proximally (vs. width progressively tapering towards the distal end); and 4) pereonite 1 width ≤ 0.7 pereonite 2 width (vs. pereonite 1 width> 0.8 pereonite 2 width). A. indobathyasellus sp. nov. can be further distinguished from A. brandtae as follows: Pleopod 1 distal margins almost straight, lateral lobes tapering sharply (vs. distal margins semicircular, lateral lobes rounded).

Notes

Methods

The holotype was collected from hard substrates with maximum distance of 500 m to hydrothermal vents, but at least 20 m apart from active venting of a newly-discovered hydrothermal vent field on the Central Indian Ridge. Samples were obtained during the INDEX 2019 expedition onboard RV Sonne (SO 271-1) (Station No. I 19 _ 036 RO _ BB _ 01; latitude - 25.466675, longitude 69.916682, 2628 m depth) through rock picking using a remotely operated vehicle ( ROV). Upon retrieval on deck, the rocks were washed over sieves and the samples promptly fixed in 96 % ethanol. For DNA analyses of the mitochondrial cytochrome c oxidase subunit 1 ( COI) gene, extraction, amplification and sequencing were carried out following protocols provided by Kniesz et al. (2022) and the resulting sequences are accessible via GenBank (accession no. OR 825323).

Morphological examination was conducted using a Leica MZ 8 stereomicroscope, pencil drawings being created using a Leica DM 750 microscope with a camera lucida and subsequently inked. Confocal laser scanning microscopy ( CLSM) was performed following the methods described in Kaiser et al. (2023). Morphological terminology follows Hessler (1970) and Riehl and Brandt (2010), whilst morphological measurements follow methods proposed by Hessler (1970). In addition, body length to maximum body width was measured, where body length is defined as the mid-sagittal distance from the anterior edge of the cephalothorax to the posterior tip of the pleotelson and maximum width is determined at the specimen's broadest extent observed from the ventral view. Finally, the length of the coxal extension was measured ventrally from the distal end to the proximal mid-point where it meets the coxa and width determined at its broadest point from the ventral view. The specimen is stored in the Crustacean collection of the Senckenberg Research Institute and Natural History Museum in Frankfurt am Main ( SMF) under catalogue number SMF 61327.

The species was compared with relevant primary literature to assess its similarities with other species in the genus ( Kaiser and Brandt 2007; Kaiser et al. 2023), as well as with the type material of the following species: Austroniscus brandtae, Senckenberg Research Institute and Natural History Museum, holotype male ( SMF 57927) and paratype female ( SMF 57930) and Austroniscus rotundatus , holotype male, Museum für Naturkunde Berlin (No. 17685).

For molecular diagnosis, we employed the open-access tool DeSignate ( Hütter et al. 2020) to discern pairwise diagnostic disparities (i. e. nucleotide variations) amongst species using the COI marker. A reference alignment was generated using the MAFFT plugin with default settings in Geneious v. 2023.2. 1, encompassing the new species and four congenerics, where data were available in GenBank: Austroniscus cf. groenlandicus (GenBank accession No. MZ 151074.1); Austroniscus sp. voucher D 3 D 51 ( MZ 151108.1); Austroniscus sp. Voucher D 3 D 30 ( MZ 151128.1); Austroniscus brandtae ( OM 892250.1).

Figures

Figure 40. Austroniscus indobathyasellus Kaiser, Kniesz & Kihara, sp. nov., holotype male (SMF 61327). A. Habitus, dorsal view; B. Pereonite 1 coxal extension, ventral view; C. Antenna 1 articles 1–2 and antenna 2 articles 1–4, drawn in situ; D. Right antenna 1, articles 1–4, ventral view, drawn in situ; E. Pleotelson, ventral view; F. Pleopod 1, detail: distal margin, drawn in situ; G. Uropod, drawn in situ; H. Pereopod 5, details: i) carpus distal margin, ii) setulae on natatory seta, iii) dactylus and unguis. Scale bars: 500 µm (A, E), 100 µm (B – D, F – H).

Figure 41. Austroniscus indobathyasellus Kaiser, Kniesz & Kihara, sp. nov., holotype male (SMF 61327), confocal laser scanning microscopy images. A. Habitus, dorsal view; B. Habitus, ventral view. Scale bar: 500 µm.

Figure 42. Austroniscus indobathyasellus Kaiser, Kniesz & Kihara, sp. nov., holotype male (SMF 61327), confocal laser scanning microscopy images. A. Cephalothorax and pereonite 1 and 2, dorsal view; B. Cephalothorax and pereonite 1 and 2, ventral view. Scale bar: 400 µm.

Figure 43. Austroniscus indobathyasellus Kaiser, Kniesz & Kihara, sp. nov., holotype male (SMF 61327), confocal laser scanning microscopy images. A. Pleotelson, ventral view; B. Pleotelson posterior margin and uropods, dorsal view. Scale bar: 400 µm.