Bryofaunal gastrotrichs from the Cerrado: First report of Dendroichthydium cf. ibyrapora from a Neotropical Savanna

Gastrótricos briofaunais do Cerrado: Primeiro registro de Dendroichthydium cf. ibyrapora de uma savana neotropical

Abstract

We present here a new record of Dendroichthydium cf. ibyrapora from epiphytic moss in Brazilian Cerrado within the Reserva do Roncador IBGE Ecological Reserve. This new finding provides further morphological data under light and electron scanning microscopy, and genetic data from 18S and 28S ribosomal DNA. The Cerrado animals fit neatly to the diagnostic morphological characteristics of the original description from Brazil’s Atlantic Rainforest, but they are smaller and feature genetic distance across both biomes.

Keywords
Meiofauna; Micrometazoan; limno-terrestrial; Chaetonotidae; Paucitubulatina

Resumo

Apresentamos aqui um novo registro de Dendroichthydium cf. ibyrapora de musgos epífitos no Cerrado brasileiro dentro da Reserva Ecológica do Roncador do IBGE. Essa nova descoberta fornece dados morfológicos adicionais sob microscopia de luz e eletrônica de varredura, além de dados genéticos do DNA ribossômico 18S e 28S. Os animais do Cerrado se encaixam perfeitamente nas características morfológicas diagnósticas da descrição original da Mata Atlântica do Brasil, mas são menores e apresentam distância genética entre registros de ambos biomas.

Palavras-chave
Meiofauna; micrometazoário; limnoterrestre; Chaetonotidae; Paucitubulatina

Introduction

Ground and epiphytic bryophytes are globally distributed and often serve as valuable “islands” of biodiversity in terrestrial environments, as they represent an important refugium for a range of microscopic lifeforms (Nelson & Marley 2000, Nelson 2002). The intricate three-dimensional spaces amidst the bryophytes stems and leaves create tree-related microhabitats (TreM) that moderate local environmental conditions (see Majdi et al. 2024). These spaces buffer temperature and moisture fluctuations for micro- and mesometazoans of the bryofauna, the community of hygrophilous/limno-terrestrial organisms, including protozoans, rotifers, nematodes and tardigrades (Božanić et al. 2013, Glime 2017). Many of these organisms are active only in presence of water, inhabiting the thin water film within moisturized leaf sheaths. Therefore, those found in the Cerrado savannas face particular challenges. The Cerrado is classified as Aw-type in Köppen’s system with marked and predictable seasonality featuring dry winters (Alvares et al. 2013), where water evaporates from the plants. This means the bryofauna has to adopt various drought-resistant strategies, such as entering dormancy (e.g. anhydrobiosis in tardigrades) or producing resistant eggs with cuticularized shelled eggs to endure desiccation until the rainy season (Hallas 1975, Guidetti et al. 2011, van Straalen 2021, 2023).

Gastrotricha is a phylum of free-living micrometazoans primarily associated with aquatic environments. It is found worldwide in freshwater psammon, periphyton, and micro-reservoirs of epiphytic plants, and in saline environments such as brackish and marine benthos (Higgins & Thiel 1988, Balsamo et al. 2014, Kieneke & Schmidt-Rhaesa 2015). However, there are also sporadic records of gastrotrichs of the suborder Paucitubulatina d’Hondt, 1971 found in limno-terrestrial habitats, such as highly moisturized forest leaf litter and soil samples (Franz 1950, Franz & Donner 1954, Varga 1954, 1959, 1963, Kisielewski 1981, Martin 1990, Strayer et al. 2010, Kolicka 2016, 2019, Bharti & Kumar 2019, Minowa et al. 2025). The most recent record of limno-terrestrial gastrotrich came from dried epiphytic mosses from fragments of Brazilian Atlantic Forest (Minowa et al. 2025), where fully mature adult specimens were found upon rehydration of epiphytic moss, rendering the description of the genus Dendroichthydium Minowa, Kieneke, Campos, Balsamo, Plewka, Guidi, Araújo et Garraffoni, 2025. The genus currently comprises two species: Dendroichthydium silvaticus (Varga, 1963), recorded in semiaquatic and limno-terrestrial environments in Europe (Varga 1963, Kisielewski 1981) and Dendroichthydium ibyrapora Minowa, Kieneke, Campos, Balsamo, Plewka, Guidi, Araújo et Garraffoni, 2025 in Brazilian Atlantic Forest.

Here, we report a new record of Dendroichthydium from the Brazilian Cerrado, discovered during a faunal inventory of tardigrades in this biome. In this study we offer morphological data from light microscopy and scanning electron microscopy, and molecular data, improving the taxonomic resolution of this peculiar group of epiphytic moss-dwelling gastrotricha.

Material and Methods

A 3 × 3 cm sample of an epiphytic bryophyte mat (Sematophyllum (Hedw.) Mitt., 1864) growing at the base of a buriti palm (Mauritia flexuosa L.f., 1782) was collected on May 17, 2024 from the palm swamps (veredas) at Stream Escondido’s source (15°55’34.6”S, 47°53’07.3”W), within the Reserva do Roncador (RECOR) IBGE Ecological Reserve, Brasília, Federal District. This is a core area of the Cerrado Biosphere Reserve created by UNESCO in 1993. The sampling site is characterized by the ground being covered by club moss (Lycopodium L., 1753), growing prostrate along the wetland surrounding the stream’s source. The area had recently been affected by wildfire, leaving mosses only in areas close to the ground, while many trees bore charred bark.

The sample was transported in paper bags, stored under ambient conditions, and processed at the Universidade de Brasília (UnB/DF). Subsamples were immersed in distilled water for 10 minutes, agitated, and the supernatant was filtered through a 40-µm plankton sieve. The filtrate was transferred into Petri dishes, and sorted under a Leica S8AP0 stereomicroscope, and organisms were isolated and narcotized in 2% MgCl₂. Five adult specimens were mounted onto microscope slides for further identification under phase-contrast Leica DM2000 light microscope, equipped with a Leica DFC295 digital camera. Specimens were fixed in 100% ethanol for DNA extraction, and 70% ethanol for scanning electron microscopy (SEM) processing, before being stored in 1.5 ml Eppendorf tubes. At the University of Campinas (UNICAMP/SP), specimens were recovered from the tubes and mounted on glass slides with a wet-mount solution for digital imaging using a Zeiss Axio Imager M2 light microscope with differential interference contrast (DIC) lenses and an AxioCam MRC5 camera. After imaging, each specimen was retrieved from the slide for further morphological and molecular processes. Photomicrographs and video records from four adults specimens are available in the Museu de Diversidade Biológica at the University of Campinas (MDBio) under ZUEC-PIC 0001194–0001198 accession numbers at https://www.ib.unicamp.br/museu_zoologia/ and in the authors’ collection.

For SEM, a single individual was placed in a small tube-shaped metal container with both ends sealed with 1500-mesh grids for transmission electron microscopy purposes, according to Trokhymchuk & Kieneke (2024). The animal underwent dehydration in a graded ethanol series (70% to 100%, in 10% increments, 10 minutes each), desiccated in a Baltec CPD030 critical point dryer before being sputter-coated with gold in a Leica EM SCD050 sputter coater. Finally, it was documented under a JEOL JSM 5800LV SEM at an acceleration tension of 5kV with a secondary electron detector (SE).

Genomic DNA was extracted from four whole specimens using a QIAamp DNA Kit (Qiagen). Nuclear 18S and 28S rDNA were amplified using GoTaq® DNA polymerase protocol (Promega) in ٢٠ µL PCR reactions, following Minowa et al. (2025). The PCR products were checked on 1% agarose gels, purified with ExoSAP-IT™ PCR Product Clean-up Reagent (Thermo Fisher Scientific/Life Technologies®). Sequencing was done using BigDye Terminator reactions in a 3500xL Genetic Analyzer (Life Technologies®) at the Centro de Biologia Molecular e Engenharia Genética (CBMEG), Campinas, São Paulo, Brazil. Our sequences were assembled and edited using Geneious Prime version 2023.2.1 (Biomatters Inc., Auckland, New Zealand) and deposited in GenBank NCBI (accession number PQ857176–PQ857178 for 18S, PQ857173–PQ857175 for 28S). Genetic distances were obtained in MEGAX (Kumar et al. 2018) inferred from 1,000 replicates, and computed using the Kimura two-parameter methods with gaps/missing data treatment adjusted using pairwise deletion (Table S1).

Results

1. Taxonomic account

Order Chaetonotida Remane, 1925 [Rao & Clausen, 1970]

Suborder Paucitubulatina d’Hondt, 1971

Family Chaetonotidae Gosse, 1864 [sensuGarraffoni, Araújo, Lourenço, Guidi & Balsamo, 2017]

Subfamily Chaetonotinae Kisielewski, 1991

Genus Dendroichthydium Minowa, Kieneke, Campos, Balsamo, Plewka, Guidi, Araújo et Garraffoni, 2025

Dendroichthydium cf. ibyrapora

Measurements based on five adult specimens, given in rounded values (exact values in Table 1). Small species with slender, fusiform body, 73–103 μm in length (Figures 1–3). The head is 16–18 μm wide, and neck constriction is 10–14 μm wide, noticeable at the level of the pharyngeal-intestinal junction at U28 (Figures 1–2). The trunk is elongated and elliptical, wider than the head (25–27 μm, at U51), and gradually tapers toward a sharply separated, narrow cylindrical furcal base (Figures 1–2). The adhesive tubes are long (12–19 μm) and curved with a proximal swelling and gradually tapers distally (Figure 1). The head is oval, round without visible lobes (Figure 1D). The cephalion is small, visible as a thin crescent (8 μm wide and 5 μm long) (Figure 1D). Small elliptical hypopleurae are located laterally to the sub-terminal mouth ring (4–8 μm in diameter) (Figure 3). The hypostomion is reniform (Figure 3). The pharynx is 17–26 µm long, and cylindrical, without evident swelling in both ends (Figure 1D). The pharyngeal-intestinal junction is at U28. The intestine is straight and with constant width (5–8 µm wide) (Figure 1E). Three pairs of cephalic ciliary tufts emerge from between the cephalic plates (Figures 1A–B). The cilia of the posteriormost tuft are longer than anterior ones (Figure 1A). Ventral locomotory cilia arranged in two segmented ventral longitudinal bands, the cilia are densely arranged in tufts from posterior to the hypopleurae to the neck base (U31), followed posteriorly by a pair of single cilia rows (U71) (Figure 3). A pair of conspicuous dorsal posteriormost sensory bristles at the base of the cylindrical furcal base (U90) (Figure 1C).

Table 1
Comparative morphometric table.The measurements of the four specimens sampled in present study compared to morphometric values of original description of Dendroichthydium ibyrapora. Measurements in µm.

	Specimens considered in the present study						Minowa et al. (2025)
Features measurement	Ind01	Ind02	Ind03	Ind04	Range	Average	Range	Average
Total body length	81.70	72.60	102.90	82.30	72.60–102.90	84.88	130.00–160.00	148.00
Maximum head width	17.97	16.54	16.76	15.75	15.75–17.97	16.75	29.00–30.60	29.70
Maximum neck width	13.70	10.89	12.20	9.69	9.69–13.70	11.62	20.00–23.30	21.40
Maximum trunk width	27.25	27.26	25.80	25.15	25.15–27.26	26.37	36.00–50.10	45.20
Hypostomium width	–	6.67	–	–	6.67	6.67	6.00–9.80	8.00
Hypostomium length	–	2.63	–	–	2.63	2.63	3.00–4.90	3.60
Cephalion width	7.88	8.45	–	–	7.88–8.45	8.16	14.00–15.10	14.30
Cephalion length	04.01	5.13	–	–	4.01–5.13	4.57	6.5	6.50
Diameter of mouth ring	5.98	7.59	5.74	4.36	4.36–7.59	5.92	8.00–9.80	9.20
Pharynx length	24.85	17.14	26.36	23.96	17.14–26.36	23.08	34.00–40.50	37.30
Pharynx width	7.80	4.90	6.70	6.17	4.90–7.80	6.39	7.00–11.90	9.50
Width of intestine junction	5.16	-	-	-	5.16	5.16	9.00–11.70	10.40
Intestine length	38.00	31.00	42.90	36.00	31.00–42.90	36.98	55.00–89.60	70.90
Pharynx-intestine ratio I	0.65	0.55	0.61	0.67	0.55–0.67	0.62	0.50–0.60
Furca length	25.90	25.90	30.02	25.05	25.05–30.02	26.72	28.00–37.60	32.10
Length of adhesive tube	19.07	12.36	19.03	15.25	12.36–19.07	16.43	16.00–20.10	17.70
Width of adhesive tube	1.38	0.71	1.57	1.50	0.71–1.57	1.29	2.00–3.60	2.30
Number of scales in single dorsal longitudinal column	–	–	–	40	40.00	40.00	57.00–90.00	70.00
Total number of longitudinal alternating rows of scales	–	–	–	67	67.00	67.00	50.00–80.00	65.00
Total number of interciliary plates	–	–	–	41	41.00	41.00	30.0	30.0
Interciliary plates width	–	–	–	8.3	8.3	8.3

Figure 1
Dendroichthydium cf. ibyrapora photomicrographs of fresh animals in differential interference contrast (A) and phase contrast (B–E). A. Ventral view, with lateral slight squeezing in the mid-trunk by the semicircular muscles, adhesive tubes bent outward from the furcal base. B. Mid-plane optical section view, with large eggs filling the entire trunk, furcal base with short spined furcal scales. C. Composition image of mid-plane optical section. D. Mid-plane of the head. E. Dorsal view of posterior trunk with straight intestine in between the large eggs, furcal base covered laterally by keeled scales. Abbreviations: at, anterior ciliary tuft; ce, cephalion; eg, egg; fks, furcal keeled scales; fs, furcal base short-spined scales; mo, mouth; pb, posterior sensory bristle; ps, pedunculated scales; scm, semicircular muscle insertion. Scales: A–E. 10 µm.

Figure 2
Dendroichthydium cf. ibyrapora photomicrographs (differential interference contrast) of fixed animals. A. Lateral view of contracted specimen, with adhesive tubes bent ventrally from the furcal base. Dorsally positioned egg lightly squeezed at the middle by semicircular muscle. B. Mid-plane optical section with internal organs. C-D. Dorsal view. Abbreviations: ce, cephalion; eg, egg; mo, mouth; ps, pedunculated scales; scm, semicircular muscle insertion. Scales: A. 20 µm, B–D 10 µm.

Figure 3
Dendroichthydium cf. ibyrapora composition from scanning electron microscope micrographs. Ventral view showing ventral plates from base of hypostomium to terminal plates in posteriormost furcal base. Abbreviations: ad, adhesive tubes; ci, ventral locomotory row’s cilia insertion; ct, cephalic ventral cilia tuft; hy, hypostomium; pl, hypopleurae; ps, pedunculated scales; tp, terminal plates; vp, ventral plates. Scale: 5 µm.

The dorsal, dorsolateral, lateral and ventrolateral body surfaces are evenly covered with small pedunculated scales (Figures 1B, 2A), these scales are distributed in 67 alternating columns of scales, with 40 scales in the central column, without gaps or overlapping each other (Figure 1E, 2D). The dorsal cylindrical furcal base is armored with four longitudinal alternating columns of 4–5 elongated spined scales (Figure 1A, E). The cylindrical furcal base is laterally covered by keeled scales (Figure 1E). The ventral interciliary area is covered with 41 rectangular plates (8.3 μm wide) from the hypostomion (U05) to the cylindrical furcal base (U70) (Figure 3). All specimens were bearing one or more large rounded eggs filling the whole dorsal trunk (Figures 1–2). A set of muscles at the mid-trunk constrict the middle of the body transversally, squeezing the egg in half (Figures 1A, 2B), giving the slight impression of hour-glass shape. Neither X-organ nor packets of sperms were observed.

2. Taxonomic remarks

The specimens found in RECOR neatly fit all the diagnostic features of the genus Dendroichthydium. They feature the same peculiar habitus, exhibiting a slim body with a narrow furcal base, forming a distinct cylindrical furcal segment, with externally bent adhesive tubes. They possess a dorsal cuticle with a dense and well-organized arrangement of pedunculated scales, except for short spined scales on furcal base as dorsal cuticular ornamentation, and a single column of rectangular ventral plates. However, they were smaller (73–103 μm long) than Dendroichthydium ibyrapora described in fragments of Atlantic Forest (130–186 μm long) in São Paulo among epiphytic Hyophila-moss (Minowa et al. 2025). For that, a definite species identification has to be done with caution, so we kept the cf. between genus name and species name (Bengtson 1988), indicating that the determination is provisional, due to not optimally preserved specimens for the light microscopy.

3. Molecular remark

The Basic Local Alignment Search Tool for nucleotide (BLASTn) method (Altschul et al., 1990) implemented by GenBank NCBI hit best identity for the 18S gene on NCBI on December 20, 2024, was with Dendroichthydium ibyrapora PP694049 for voucher DF3 to DF5 (96% identity and 15 gaps, 92% identity and 25 gaps; and 97% identity and 7 gaps respectively), and for 28S gene was with Dendroichthydium ibyrapora PP694053 (91%, 41 gaps) for DF3, Dendroichthydium ibyrapora PP694054 (99%, 11 gaps) for DF4, Dendroichthydium ibyrapora PP694054 (99%, 11 gaps) for DF5. Genetic divergence analysis shows that divergence among Dendroichthydium ibyrapora from Atlantic Forest (AF) specimens are genetically identical or extremely similar, while Cerrado specimens (CE) show some variation among themselves, suggesting they are genetically more diverse than the AF group. Furthermore, the lowest distance among the CE group suggests that at least one of them was closer to the AF group than to other CE specimens, and it may imply some level of gene flow or recent divergence.

Discussion

Specimens of Dendroichthydium ibyrapora were discovered almost by accident in limno-terrestrial environments during an expedition conducted by undergraduate and graduate students as part of a university course on meiofaunal organisms (Guidetti et al. 2021). The expedition aimed to investigate the diversity of limno-terrestrial tardigrades and freshwater gastrotrichs in fragments of Atlantic Forest within the Serra do Japi Ecological Reserve. However, active gastrotrichs were found under stereomicroscope amidst the mosses, among other bryofaunal organisms (ARS Garraffoni, personal communication). The formal description of these limno-terrestrial gastrotrichs was provided after further incursions to gather sufficient specimens for several morphological and molecular processes (Minowa et al. 2025). The serendipity of finding additional members of the genus in the Cerrado has helped further uncover the diversity and distribution of these supposedly rare taxa. The ecological preference of gastrotrichs for fully aquatic environment may have influenced research priorities; gastrotrichologists have traditionally focused on aquatic systems, while limno-terrestrial habitats have been primarily investigated by researchers focused on terrestrial to limno-terrestrial microinvertebrates, such as the tardigradologists. This division of focus likely contributes to the perceived rarity of limno-terrestrial gastrotrich records.

Similarly to nematodes and rotifers, gastrotrichs of the Paucitubulatina suborder reproduce through parthenogenesis, producing viable unfertilized eggs. However, unlike many other bryofaunal taxa, gastrotrich adults lack dormancy capabilities (Balsamo et al. 2014, Araújo et al. 2024). Their presence among bryophyte-associated fauna has been attributed to their ability to produce larger, heavily shelled eggs that withstand desiccation, effectively creating an environmental “egg bank” awaiting favorable conditions (Araújo et al. 2024, Minowa et al. 2025). However, in the Cerrado—a savanna environment shaped by seasonal droughts and frequent fire (Costa et al. 2013, Júnior et al. 2014, Colli et al. 2020, da Silva Arruda et al. 2024)—the egg bank hypothesis alone is insufficient to explain persistence of epiphytic gastrotrichs, as recurrent fires would likely eliminate these resistant eggs. Instead, dispersal capacity of micrometazoans must be considered a mechanism facilitating the rapid recolonization of burned areas, allowing populations to reestablish shortly after fire events.

Several members of bryofauna are reportedly capable of dispersing through various means, such as wind currents, surface run-off, macrofauna movement (phoresis) or human activity, and can quickly recolonize affected habitats (Vicente et al. 2013, Kolicka et al. 2015, Kolicka 2016, 2019, Mogle et al. 2018, Ptatscheck et al. 2018a, b, Araújo et al. 2024). This was confirmed by the presence of Dendroichthydium in freshly regenerating epiphytic mosses soon after a wildfire at RECOR.

Nonetheless, fires have also an indirect impact on moss-inhabiting micrometazoan by destroying the soil, altering flora composition, affecting the substrate availability, and altering larger vertebrate behaviors, or promoting fragmentation of ecosystems (Vicente et al. 2013). Consequently, the wildfire affected all means of bryofauna to reach and establish in these affected areas. This results in losses of biodiversity due to the higher magnitude and frequency of wildfires and is further exacerbated by an unprecedented increase in human-driven ignitions (York 1999, Vicente et al. 2013). Ultimately, while moss-dwelling gastrotrichs and other micrometazoans may be capable of rapidly recolonizing newly available habitats, this adaptability does not offset the broader biodiversity losses triggered by wildfires (da Silva Arruda et al. 2024).

Supplementary Material

The following online material is available for this article:

Table S1 - Estimates of Evolutionary Divergence between Sequences.

Acknowledgments

This work wouldn’t be possible without the financial support from Brazilian research agencies Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brazil (CAPES) by the Programa de Internacionalização (PrInt) (process n. 88887.716041/2022-00) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (Process number 141482/2021-4), Fundação de Amparo à Pesquisa do Estado de São Paulo (Fapesp Process number 2023/05724-9). This study was partially supported by the Brazilian fostering agency ‘Conselho Nacional de Desenvolvimento Científico e Tecnológico’ through a productivity grant to ARSG (CNPq proc. 04/2021). We thank the IBGE Ecological Reserve for access to sampling site. The authors thank Roman Trokhymchuk and the anonymous referee for their precise and constructive comments, which significantly improved the quality of the manuscript.

Data Availability

The sequences generated in this study are deposited in the GenBank repository with the accession number PQ857176–PQ857178 for 18S, PQ857173–PQ857175 for 28S.

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Edited by

• Associate Editor
  Mercedes Marchese

Publication Dates

• Publication in this collection
  07 Apr 2025
• Date of issue
  2025

History

• Received
  30 Jan 2025
• Accepted
  06 Mar 2025