A new species of Acanthodasys (Macrodasyida: Thaumastodermatidae) from the northern coast of São Paulo, Brazil

ABSTRACT

Thaumastodermatidae (Gastrotricha: Macrodasyida) is the most species-rich marine clade of the phylum, comprising vermiform animals characterized by a dorsal oral hood covering a large terminal mouth, multiple adhesive tubes distributed along the body (particularly on the caudal pedicles), and a richly ornamented cuticle. Acanthodasys currently includes 13 valid species, distributed predominantly across Europe and North America; only recently was the first species from the Southern Hemisphere described. Here, we describe a second species from Fome Beach, São Sebastião Island, Brazil, based on differential interference contrast (DIC) light microscopy and scanning electron microscopy (SEM). The new species is strap-shaped (409-606 μm in length) and differs from its congeners by a dorsal cuticle bearing exceptionally large, elongated, lanceolate uniancres that contrast with much smaller ventral uniancres, as well as simple, spineless scales with a central depression bearing one, two, or three small, oval, raised ornamentations per scale.

KEYWORDS:
Meiofauna; morphology; Neotropics; sandy beach; taxonomy

INTRODUCTION

The phylum Gastrotricha Metchnikoff, 1865 comprises microscopic acoelomate metazoans commonly found in all aquatic environments, from marine and brackish waters to freshwater or limno-terrestrial habitats (Kisielewski 1991, Balsamo et al. 2019, Garraffoni and Araújo 2020, Minowa et al. 2025). In marine ecosystems, gastrotrichs are a permanent and functionally important component of the meiofauna (Higgins and Thiel 1988, Garey 2002, Giere 2009, Schratzberger and Ingels 2018). They occur in high abundance among sediment grains from the intertidal and shallow sublittoral zones to the deep-sea floor (Kieneke and Zekely 2008, Sørensen et al. 2025), and from tropical to polar regions (Hochberg and Atherton 2010, Hochberg et al. 2014, Trokhymchuk and Kieneke 2024a, 2024b). However, research has historically favored temperate regions of the Global North since the early 20th-century studies in Europe; only recently has sampling expanded into the Southern Hemisphere. Consequently, estimates of gastrotrich (and more broadly, meiofaunal) diversity are likely skewed by uneven sampling efforts in the New World (Balsamo et al. 2008, Garraffoni and Balsamo 2017, Garraffoni et al. 2021, 2024, Araújo et al. 2024).

Along the 7,500-km heterogeneous coastline of Brazil, gastrotrich diversity correlates with tidal zones and sediment grain size (Garraffoni et al. 2016, 2024). Yet, most studies remain largely confined to the southeastern shores in São Paulo and Rio de Janeiro states (Todaro and Rocha 2004, 2005, Araújo et al. 2014, Hochberg 2014, Garraffoni et al. 2017, Campos and Garraffoni 2019, Bosco et al. 2020, Campos et al. 2025).

Thaumastodermatidae Remane, 1927 is the most species-rich clade within the order Macrodasyida Remane, 1925 (sensu Rao and Clausen 1970), comprising nearly 20% of known gastrotrichs (Remane 1925, 1927, Araújo et al. 2016). The family has a global distribution, with species inhabiting coarse shelly and medium- to fine-grained sands of intertidal and subtidal habitats (Hummon et al. 1998). The clade is supported by a large terminal mouth covered by an oral hood, considered to be an autapomorphy in the morphological phylogenies of Hochberg and Litvaitis (2000) and Kieneke et al. (2008), as well as by the presence of a pair of posterior adhesive pedicles and a richly ornamented cuticle bearing spines, sculpted plates, bowl-shaped scales, or single- to multi-spined scales (Garraffoni and Araújo 2017). Molecular data corroborate the monophyly of the family (Todaro et al. 2011).

Within the family, species of Diplodasyinae Ruppert, 1978 are characterized by a complex reproductive system that includes paired hermaphroditic gonads, a “rosette” organ, and anatomically disjointed frontal and caudal organs (Ruppert 1978, Guidi et al. 2020); i.e., the frontal organ is located mid-body, anterior to the developing eggs, whereas the caudal organ lies in the posterior trunk. This subfamily includes AcanthodasysRemane, 1927 and Diplodasys Remane, 1927-both possessing unique cuticular structures called uniancres, which are thorn-shaped, single-hooked spines with a cruciform cross-section formed by four longitudinal ridges arising from a quadrangular base. Species of Diplodasys display only lateral uniancres, whereas members of Acanthodasys bear uniancres on dorsal, lateral, and ventral surfaces (Todaro and Hummon 2008, Todaro et al. 2011, Bosco et al. 2020).

Herein, we describe a second species of Acanthodasys from Fome Beach, São Sebastião Island, Brazil, occurring in sympatry with Acanthodasys australis Bosco et al., 2020 (see Bosco et al. 2020, Guidi et al. 2020). The new species is described based on observations under DIC light microscopy for internal anatomy and SEM for external morphology.

MATERIAL AND METHODS

Fieldwork was conducted at Fome Beach, São Sebastião Island (23°44’27.0”S; 45°16’01.0”W), São Paulo, Brazil, between 2014 and 2015. Sediment samples from the top 15 cm of the seabed were collected using plastic buckets via SCUBA diving at depths of 8-10 m. The sediment is characterized as well-sorted coarse sand, with a skewness of 1.25 and a kurtosis of 5.4. Further details on sampling procedures and granulometric measurements are provided by Garraffoni et al. (2017).

Gastrotrichs were extracted at the University of Campinas (UNICAMP) over a two-week period following the protocol described by Hochberg and Atherton (2010). Subsamples were immersed in a 7% MgCl₂ solution for approximately 10 minutes at room temperature and gently agitated. The supernatant was filtered through a 43-µm nylon sieve, and the filtrate was poured into Petri dishes containing seawater and examined under a Zeiss Stemi 2000 stereomicroscope to isolate the organisms. Each specimen was narcotized in 7% MgCl₂, mounted alive on a glass microscope slide, and digitally documented using a Zeiss Axio Imager M2 light microscope equipped with differential interference contrast (DIC) lenses and coupled with an AxioCam MRC5 digital video camera. Images were acquired using Zen Lite v.2.5 (2018), and morphometric measurements were obtained with ImageJ (https://imagej.net/ij/).

Two specimens were retrieved from the microscope slides by gently adding filtered ambient water to lift the coverslip, which was then removed using precision tweezers. Each individual was fixed in 2.5% glutaraldehyde in 0.2 M sodium cacodylate buffer (pH 7.4) for one hour at room temperature, thoroughly rinsed in the same buffer, and subjected to a graded ethanol dehydration series (20%, 30%, 40%, 50%, 60%, 70%, 95%, and two changes of 100% ethanol) using small custom plastic containers following Abolafia (2015). Specimens were subsequently critical-point dried using ethanol as a transitional medium in a BalTec CPD030 dryer. Each specimen was mounted on double-sided adhesive tape on an aluminum stub, sputter-coated with gold using an SCD050 Sputter Coater, and examined under a JSM 5800LV SEM at the Electron Microscopy Laboratory (Universidade Estadual de Campinas, São Paulo, Brazil) at an accelerating voltage of 10 kV. Images were digitally recorded using Semafore v.5.2.

Owing to the loss of taxonomic information that occurs in fixed animals (thoroughly discussed by Garraffoni and Freitas 2017 and Garraffoni et al. 2019), each animal was digitally documented in vivo to compose the schematic illustration of the holotype, in accordance with ICZN Article 73.1.4 (1999) in combination with ICZN Declaration 45. Morphological terminology follows the convention established by Hummon et al. (1992), in which the position of each character is expressed as percentage units along the longitudinal body axis from the anterior (U00) to the posterior (U100) apex. Species identification was based on a direct comparison with the original descriptions of all known species of the genus.

Abbreviations. co, caudal organ; du, dorsal uniancres; eg, epidermal gland; hd, oral hood; in, intestine; mo, mouth; ov, ovary; ph, pharynx; PhIJ, pharyngo-intestinal junction; sc, smooth scales; sci, sensory cilia; TbA, anterior adhesive tubes; TbL, lateral adhesive tubes; TbP, posterior adhesive tubes; TbVL, ventrolateral adhesive tubes; te, testes; vc, ventral ciliature; vd, vas deferens; vu, ventral uniancres.

TAXONOMY

Order Macrodasyida Remane, 1925 sensu Rao & Clausen, 1970

Thaumastodermatidae Remane, 1927

Diplodasyinae Ruppert, 1978

Acanthodasys Remane, 1927

Acanthodasys capricornicus sp. nov.

Figs 1-7, Table 1

https://zoobank.org/DF9DDBBC-09B0-4816-9917-780072CD2065

syn. Acanthodasys sp. 2 in Garraffoni et al. (2017)

Type material. Holotype. Adult specimen collected from sandy sediment in July 2015 at Fome Beach, São Sebastião Island, municipality of Ilhabela, São Paulo, Brazil (23°44’27.0”S, 45°16’01.0”W), at a depth of 8-10 m. Due to its fragile nature, the specimen was destroyed by coverslip pressure during DIC imaging and is no longer extant. In accordance with Articles 72.5.6 and 73.1.4, and Declaration 45 (Recommendations 73G-J) of the International Code of Zoological Nomenclature (ICZN), the holotype is illustrated in Fig. 1 and depicted in Figs 2 and 3. Following Recommendation 73J, all photomicrographs are available at the Museu de Diversidade Biológica under catalogue number ZUEC-PIC 0001246. Paratypes. Four adult specimens collected from the same locality as the holotype: two adults on 16 July 2015 and two adults on 13 August 2018. As with the holotype, the animals were lost during SEM preparation procedures and are no longer available. Photomicrographs and SEM images are deposited under catalogue numbers ZUEC-PIC 0001247-0001250. Due to an unfortunate accident, the SEM stub containing two of the paratypes was lost and they are no longer available.

Figure 1
Acanthodasys capricornicus sp. nov. schematic illustration. (A) Dorsal view. (B) Mid-plane optical section of internal organs. (C) Illustration of larger dorsal uniancres and transversal sections along its length, and smaller ventral uniancres. (D) Various lanceolate scales shapes and sizes, with different organization of oval bump ornamentation. Scale bars: A, B: 50 µm; C, D: 1 µm.

Diagnosis. Acanthodasys with body length 409-606 µm. Body strap-shaped, with maximum width at mid-body 70-98 µm; 61-86 µm at mouth and 32-51 µm at pharyngo-intestinal junction; 12-19 µm wide at caudal base. Pharynx 153-248 µm long, with pharyngeal pores near its base at U36. Dorsal and ventral cuticular armature composed of obliquely and transversely oriented uniancres and lanceolate spineless scales with a central depression with one, two, or three oval, central, raised ornamentations (bumps). Dorsal and lateral uniancres are long (10-18 µm), whereas ventral uniancres are much smaller (3.6-5.9 µm). At least 14-23 epidermal glands per side along the body. Two TbA per side in a single row along the ventral mouth margin; 10 TbL per side along the trunk; 7 TbVL per side from trunk midpoint to caudal base; 3 TbP per side (2 terminal, 1 medial) on caudal pedicles. Ventral locomotory cilia forming a complete field. Hermaphroditic, with paired testes and ovaries, followed by a mass of gland cells with unknown function, and a caudal organ. Frontal and rosette organs not observed.

Description. Description and measurements (unrounded values in Table 1) based on all live adult specimens digitally documented. Body strap-shaped, elongated, slightly tapered, 409-606 µm in total length (Figs 1, 2A). Body width 61-86 µm at oral hood (U02); narrowing slightly to 35-60 µm along pharynx (U04-U25) and 32-51 µm at pharyngo-intestinal junction (U26); expanding to 70-98 µm at trunk midpoint (U50); gradually tapering toward caudal base, 12-19 µm wide, leading to a pair of distinct caudal pedicles (Figs 2A, 3A-C). Entire body covered with spineless scales and spined scales (uniancres) (Figs 2B-D, 4, 6, 7B-D). Numerous epidermal glands of varying sizes (5-11 µm in diameter), arranged in several longitudinal columns, up to 14-23 per side; openings surrounded by a raised cuticular ridge. Ventral locomotory cilia forming complete field (Fig. 7A).

Table 1
Acanthodasys capricornicus sp. nov. taxonomic characters and measurements (in µm) of adult specimens.

Characters	Holotype	Paratypes				Range
		1	2	3	4
Body total length	526.00	533.30	409.30		606.3	409.30-606.30
Body width at mouth (U03)	60.75	85.80	72.15	80.25		60.75-85.80
Body width at PhIJ (U26)	44.24	44.86	32.00		51.0	32.00-51.00
Body width at midpoint (U50)	75.20	98.00	72.70		70.5	70.50-98.00
Mouth width	40.50	66.00	48.10	53.50		40.50-66.00
Pharynx length	153.20	247.70	177.40	227.00		153.20-247.70
Pharynx width	40.00	35.00	44.60	59.50		35.00-59.50
Pharyngo-intestinal junction width	35.70	32.40	51.50		51.4	32.40-51.50
TbA length		7.50-9.00		7.60-90		7.50-9.00
TbL length			10.50-14.50			10.50-14.50
TbP length	7.30-12.00	8.00-13.00	6.10-13.50			6.10-13.50
Number of epidermal glands per side	20.00-23.00	14.00-15.00	14.00-15.00			14.00-23.00
Mouth cilia length		9.00-13.50		10.50-13.80		9.00-13.80
Dorsal uniancre length		10.00-18.50		11.80-14.50		10.00-18.50
Ventral uniancre length		3.60-4.80		4.10-5.90		3.60-5.90
Dorsal smooth scale width		3.50-8.60			3.1-6.2	3.10-8.60
Ventral smooth scale width		4.40-6.10		2.10-5.90		2.10-6.10

Figure 2
Acanthodasys capricornicus sp. nov., DIC photomicrographs. (A) Whole-body mid-plane section showing pharynx and internal organs. (B-C) Dorsal cephalic and neck cuticular ornamentation. (D) Ventral cephalic ornamentation with dorsal uniancres, lanceolate scales, and adhesive tubes. (E) Anterior ventral close-up with adhesive tubes and sensory cilia. Scale bar: 50 µm.

Figure 3
Acanthodasys capricornicus sp. nov., DIC photomicrographs. (A-C) Posterior mid-plane sections showing adhesive tubes, vas deferens and caudal organ, and caudal pedicles. Scale bar: 50 µm.

Figure 4
Acanthodasys capricornicus sp. nov., DIC photomicrographs of cuticular ornamentation. (A) Lateral view, with dorsal cuticle to the upper left and ventral to the bottom right side. (B) Ventral and ventrolateral view with sensory cilia. (C) Dorsal view showing uniancres and lanceolate scales. (D) Ventral view with smaller uniancres and lanceolate scales. (E) Lateral view with adhesive tubes and uniancres. (F) Ventral uniancres and smooth scales. Scale bar: 50 µm.

Figure 5
Acanthodasys capricornicus sp. nov., DIC photomicrograph. Mid-plane section showing portions of the male reproductive system, including vas deferens and caudal organs.

Figure 6
Acanthodasys capricornicus sp. nov., SEM images. (A) Whole-body view. (B-E) Details of cuticular ornamentation. Scale bars: A: 50 µm; B-E: 10 µm.

Figure 7
Acanthodasys capricornicus sp. nov., SEM images. (A) Frontal view of the anteriormost head region, showing mouth opening, lateral and ventral cuticular ornamentation, and ventral ciliature. (B-D) Details of ventral and dorsal cuticular ornamentation. (E) Lateral view of four ventral uniancres torn away from cuticle, showing the basal scale from where four lateral ridges emerge. Scale bar: 10 µm.

Cuticular armature. Spined scales (uniancres) and spineless scales covering the entire body surface except oral hood, interspersed and oriented obliquely and transversely (Figs 2B-D, 4A-F, 6B-E, 7B-D). Large uniancres (10-18 μm long) arranged dorsally and dorsolaterally on trunk and caudal pedicles; ventral surface covered with smaller uniancres (4-6 μm) (Figs 2B-D, 4, 6B-E, 7B-D). Uniancres emerging from a quadrangular base, featuring sharp apex with a cruciform transverse section and a longitudinal ridge on each of four columns (Figs 6B-E, 7D-E). Spineless scales arranged in various orientations (longitudinal, transversal, and oblique) along the entire body surface (Figs 2D, 4, 6B-E). Simple scales elongate lanceolate (3-9 µm long, 1-3 µm wide), with a central depression (3-9 µm long, 2-6 µm wide) including one, two, or three small, oval, raised bumps (Figs 4A-F, 6C-E, 7B-D).

Adhesive tubes. TbA: two pairs (7-9 µm long), arranged along the ventral margin of mouth (U03) (Fig. 2D-E). TbL: 10 per side (10-14 µm long), restricted to trunk region (U33-U70) (Figs 2A, 3, 4E). TbVL: 7 per side (14-17 µm long), arranged from a medial column on the trunk toward the lateral edge of the caudal peduncle (U73-U90) (Figs 3, 4E). TbP: 3 per side, grouped on each caudal pedicle as 2 terminal tubes (6-13 µm long) and 1 medial tube (6-8 µm long) at base of each caudal pedicle (U95-U99) (Figs 3A-C, 6D).

Intestinal tract. Terminal mouth 40-66 µm in diameter, surrounded by numerous sensory cilia (9-14 µm long each) (Fig. 2D-E). Pharynx wide and long (153-248 µm long, 35-60 µm wide), with pharyngeal pores near its base (U36), not observable in all specimens (Fig. 2A). Pharynx connecting to intestine via a narrow pharyngo-intestinal junction at U37 (Fig. 2A). Intestine narrow, tapering toward rear body (32 µm wide at U50, 12 µm at U95); anus not observed (Figs 2A, 3A).

Reproductive system. Hermaphroditic. Genital system comprising paired testes lateral to PhIJ (U37), extending posteriorly as two sperm ducts joining large caudal organ (U91) (Figs 3A, 5). Paired ovaries occurring at U85, followed by mass of gland cells with unknown function (Figs 3A, 5). Frontal and rosette organs not observed.

Etymology. The specific epithet is named after the Tropic of Capricorn, which lies near the type locality. Under the International Code of Zoological Nomenclature, the name falls under species-group names that are adjectives and must agree in gender with the generic name (ICZN Article 31.2).

Remarks. Currently, 13 valid species of Acanthodasys are recognized (Bosco et al. 2020). Among them, the new species is morphologically similar to 10 congeners-A. aculeatus Remane, 1927, A. algarvense Hummon, 2008, A. arcassonensis Kisielewski, 1987, A. australis Bosco et al., 2020, A. carolinensis Hummon, 2008, A. comtus Lee, 2012, A. ericinus Lee, 2012, A. fibrosus Clausen, 2004, A. lineatus Clausen, 2000, and A. paurocactus Atherton & Hochberg, 2012-by the presence of uniancres on both the dorsal and ventral sides of the body, with dorsal uniancres being larger than the ventral ones.

Within this group, only A. arcassonensis, A. australis, A. comtus, and A. paurocactus, along with the new species, exhibit two morphologically distinct scale types. However, only A. australis, A. comtus, A. paurocactus, and the new species possess scales with a central depression. Among these latter species, only A. australis, A. paurocactus, and the new species share elongated, lanceolate (eye-shaped) scales.

The most distinctive feature of the new species lies in the raised ornamentation of all elongated lanceolate scales, which consistently exhibit one, two, or three oval central bumps. Although both A. paurocactus and the new species possess centralized bumps, the scales of A. paurocactus bear only two bumps or a single median bar/ridge.

DISCUSSION

Species of Gastrotricha are found in almost every ocean and continent. However, due to historical biases, the majority of described species are from Europe and North America, where most taxonomic expertise is concentrated (Garraffoni and Balsamo 2017, Araújo et al. 2024). Consequently, most species currently appear to have limited or very localized geographic distributions (Garraffoni and Balsamo 2017). This same pattern is also evident in Acanthodasys, for which all species, except A. australis, have been described from the Northern Hemisphere.

A second pattern observed in Acanthodasys, and more broadly in Gastrotricha, is that few species have vastly broad distributions-such as Acanthodasys aculeatus, ranging from the Mediterranean and Black Sea, to India, the Maldives, and even the USA (Gerlach 1961, Evans 1992, Todaro et al. 2003, Naidu and Rao 2004, Hochberg and Atherton 2010, Atherton and Hochberg 2012, Souid et al. 2025)-while many exhibit localized distributions restricted to their terra typica (Clausen and Båmstedt 2000, Clausen 2004, Hummon 2008, Lee 2012, Garraffoni and Balsamo 2017).

Sympatric species of Acanthodasys, therefore, are rarely documented (Ruppert 1977), and this is the first case of sympatry in Acanthodasys from Brazil, characterized by the coexistence of two closely related species at the same site. Sympatric species are frequently morphologically divergent, a pattern often interpreted as resulting from evolutionary mechanisms of competition avoidance through ecological differentiation (Futuyma 1992). Although our sampling methods do not allow us to determine the precise lifestyle of the organisms-due to sediment disturbance during collection that may have mixed their original spatial distribution-certain morphological traits offer clues about their ecological habits.

Acanthodasys capricornicus sp. nov. exhibits larger dorsal uniancres compared to its ventral ones, suggesting a role in protection against threats from above on a two-dimensional epibenthic plane. In contrast, Acanthodasys australis bears relatively uniform uniancres across the dorsal, lateral, and ventral surfaces of the body, a cuticular armature configuration likely advantageous for organisms navigating the complex three-dimensional environment of interstitial spaces by deflecting abrasion from sediment grains. Within a sympatric context, it is plausible that, although both species co-occur at the same site, they exploit distinct niches within different microhabitats (i.e., ecological niche partitioning) as a competition avoidance mechanism. To our knowledge, this is the first instance of such a phenomenon reported within Acanthodasys, as congeners have been previously reported from the same continent, or occasionally the same region, but not from the same sampling site, let alone from the same sample.

Fome Beach, on São Sebastião Island, has often been regarded as an exceptional hotspot for meiofaunal assemblages. It features clear waters with minimal suspended organic matter and medium-grained sediments, supporting abundant Acoelomorpha, Cephalochordata, Cnidaria, Kinorhyncha, Nematoda, Nemertea, Platyhelminthes, Polychaeta, and Rotifera, along with Gastrotricha (Garraffoni et al. 2016, 2017). However, this beach has recently become a heavily visited tourist destination and appears to have suffered a decline in the diversity and abundance of marine micrometazoans. Subsequent samplings conducted after 2022 to obtain additional specimens of Acanthodasys capricornicus sp. nov. have consistently returned empty-handed, making it impossible to achieve the same level of integrative description as was possible for its sympatric congener, A. australis (see Bosco et al. 2020, Guidi et al. 2020).

ACKNOWLEDGEMENTS

We are grateful to Maikon di Domenico for his assistance with SCUBA diving, and we thank the Electron Microscopy Laboratory (LME/UNICAMP) for providing access to equipment and technical assistance. We also extend our gratitude to Rick Hochberg and the anonymous reviewers for their valuable comments, which greatly improved the quality of this manuscript.

LITERATURE CITED

• Abolafia J (2015) A low-cost technique to manufacture a container to process meiofauna for scanning electron microscopy. Microscopy Research and Technique 78: 771-776. https://doi.org/10.1002/jemt.22538
  » https://doi.org/10.1002/jemt.22538
• Araújo TQ, Balsamo M, Garraffoni ARS (2014) A new species of Pseudostomodella (Gastrotricha, Thaumastodermatidae) from Brazil. Marine Biodiversity 44: 243-248. https://doi.org/10.1007/s12526-013-0196-x
  » https://doi.org/10.1007/s12526-013-0196-x
• Araújo TQ, Minowa AK, Garraffoni ARS (2024) Trends on Gastrotricha research: a bibliometric analysis. Biologia 79: 2095-2107. https://doi.org/10.1007/s11756-024-01686-6
  » https://doi.org/10.1007/s11756-024-01686-6
• Araújo TQ, Wieloch AH, Vidigal THD, Hochberg R, Garraffoni ARS (2016) Pseudostomella dolichopoda Todaro, 2012 and P. cataphracta Ruppert, 1970 (Gastrotricha: Thaumastodermatidae): new records from Brazil and USA and an updated key to the genus. Check List 12: 1986-1986. https://doi.org/10.15560/12.6.1986
  » https://doi.org/10.15560/12.6.1986
• Atherton S, Hochberg R (2012) Acanthodasys paurocactus sp. n., a new species of Thaumastodermatidae (Gastrotricha, Macrodasyida) with multiple scale types from Capron Shoal, Florida. ZooKeys 4: 81-94. https://doi.org/10.3897/zookeys.190.2975
  » https://doi.org/10.3897/zookeys.190.2975
• Balsamo M, d’Hondt J-L, Grilli P (2019) Phylum Gastrotricha. In: Rogers DC, Thorp J (Eds) Thorp and Covich’s Freshwater Invertebrates. Elsevier, Amsterdam, 149-218. https://doi.org/10.1016/B978-0-12-804225-0.00007-1
  » https://doi.org/10.1016/B978-0-12-804225-0.00007-1
• Balsamo M, d’Hondt J-L, Kisielewski J, Pierboni L (2008) Global diversity of gastrotrichs (Gastrotricha) in fresh waters. Hydrobiologia 595: 85-91. https://doi.org/10.1007/s10750-007-9006-4
  » https://doi.org/10.1007/s10750-007-9006-4
• Bosco I, Lourenco AP, Guidi L, Balsamo M, Hochberg R, Garraffoni ARS (2020) Integrative description of a new species of Acanthodasys Remane, 1927 (Gastrotricha, Macrodasyida, Thaumastodermatidae) based on four distinct morphological techniques and molecular data. Zoologischer Anzeiger 286: 31-42. https://doi.org/10.1016/j.jcz.2020.03.003
  » https://doi.org/10.1016/j.jcz.2020.03.003
• Campos A, Garraffoni ARS (2019) A synopsis of knowledge, zoogeography and an online interactive map of Brazilian marine gastrotrichs. PeerJ 7: e7898. https://doi.org/10.7717/peerj.7898
  » https://doi.org/10.7717/peerj.7898
• Campos A, Araújo TQ, Todaro MA, Senna Garraffoni AR (2025) Description of a new species of Paraturbanella, new record of Paraturbanella tricaudata and new insights on reproductive traits in Turbanellidae (Gastrotricha:Macrodasyida). Zoologischer Anzeiger 317: 46-59. https://doi.org/10.1016/j.jcz.2025.05.010
  » https://doi.org/10.1016/j.jcz.2025.05.010
• Clausen C (2004) A new species of Acanthodasys (Gastrotricha: Thaumastodermatidae) from the west coast of Norway. Sarsia 89: 137-141. https://doi.org/10.1080/00364820410004972
  » https://doi.org/10.1080/00364820410004972
• Clausen C, Båmstedt U (2000) Gastrotricha Macrodasyida from the Tromsø region, northern Norway. Sarsia 85: 357-384. https://doi.org/10.1080/00364827.2000.10414588
  » https://doi.org/10.1080/00364827.2000.10414588
• Evans WA (1992) Five New Species of Marine Gastrotricha from the Atlantic Coast of Florida. Bulletin of Marine Science 51: 315-328.
• Futuyma DJ (1992) Biologia evolutiva. SBG, CNPq. https://books.google.com.br/books?id=vGBMygAACAAJ
  » https://books.google.com.br/books?id=vGBMygAACAAJ
• Garey JR (2002) The Lesser-Known Protostome Taxa: An Introduction and a Tribute to Robert P. Higgins. Integrative and Comparative Biology 42: 611-618. https://doi.org/10.1093/icb/42.3.611
  » https://doi.org/10.1093/icb/42.3.611
• Garraffoni ARS, Balsamo M (2017) Is the ubiquitous distribution real for marine gastrotrichs? Detection of areas of endemism using Parsimony Analysis of Endemicity (PAE). Proceedings of the Biological Society of Washington 130: 198-211. https://doi.org/10.2988/17-00011
  » https://doi.org/10.2988/17-00011
• Garraffoni ARS, Araújo TQ (2017) Phylogeny of Pseudostomella Swedmark, 1956 (Gastrotricha: Macrodasyida) base on morphological data and first insights on the historical biogeography of Thaumastodermatidae. Proceedings of the Biological Society of Washington 130: 223-239. https://doi.org/10.2988/17-00014
  » https://doi.org/10.2988/17-00014
• Garraffoni ARS, Freitas AVL (2017) Photos belong in the taxonomic Code. Science 355: 805. https://doi.org/10.1126/science.aam7686
  » https://doi.org/10.1126/science.aam7686
• Garraffoni ARS, Araújo TQ (2020) Phylum Gastrotricha. In: Rogers DC, Damborenea C, Thorp J (Eds) Thorp and Covich’s Freshwater Invertebrates . Academic Press, 4^th ed., 125-144. https://doi.org/10.1016/B978-0-12-804225-0.00007-1
  » https://doi.org/10.1016/B978-0-12-804225-0.00007-1
• Garraffoni ARS, Di Domenico M, Amaral ACZ (2016) Patterns of diversity in marine Gastrotricha from Southeastern Brazilian Coast is predicted by sediment textures. Hydrobiologia 773: 105-116. https://doi.org/10.1007/s10750-016-2682-1
  » https://doi.org/10.1007/s10750-016-2682-1
• Garraffoni ARS, Di Domenico M, Hochberg R (2017) New records of marine Gastrotricha from São Sebastião Island (Brazil) and the description of a new species. Marine Biodiversity 47: 451-459. https://doi.org/10.1007/s12526-016-0486-1
  » https://doi.org/10.1007/s12526-016-0486-1
• Garraffoni ARS, Kieneke A, Kolicka M, Corgosinho PHC, Prado J, et al. (2019) ICZN Declaration 45: a remedy for the nomenclatural and typification dilemma regarding soft-bodied meiofaunal organisms? Marine Biodiversity 49: 2199-2207. https://doi.org/10.1007/s12526-019-00983-7
  » https://doi.org/10.1007/s12526-019-00983-7
• Garraffoni ARS, Sørensen MV, Worsaae K, Di Domenico M, Sales LP, et al. (2021) Geographical sampling bias on the assessment of endemism areas for marine meiobenthic fauna. Cladistics 37: 571-585. https://doi.org/10.1111/cla.12453
  » https://doi.org/10.1111/cla.12453
• Garraffoni ARS, Campos A, Minowa AK, Santos É, Moura M, et al. (2024) Expanding the taxonomic catalog of Brazilian meiofauna: diversity and distribution of the neglected phyla Tardigrada, Gastrotricha, and Kinorhyncha. Zoologia 41: e23060. https://doi.org/10.1590/S1984-4689.v41.e23060
  » https://doi.org/10.1590/S1984-4689.v41.e23060
• Gerlach SA (1961) Über Gastrotrichen aus dem Meeressand der Malediven (Indischer Ozean). Zoologischer Anzeiger 167: 471-475.
• Giere O (2009) Meiobenthology: the microscopic motile fauna of aquatic sediments. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-68661-3
  » https://doi.org/10.1007/978-3-540-68661-3
• Guidi L, Garraffoni ARS, Semprucci F, Balsamo M (2020) Spermatozoa ultrastructure, spermatogenesis and reproductive system of Acanthodasys australis (Gastrotricha, Macrodasyida). Zoologischer Anzeiger 286: 108-116. https://doi.org/10.1016/j.jcz.2020.04.006
  » https://doi.org/10.1016/j.jcz.2020.04.006
• Higgins RP, Thiel H (1988) Introduction to the study of meiofauna. Smithsonian Institution Press, Washington, D.C.
• Hochberg R (2014) Crasiella fonseci, a new species of Gastrotricha (Macrodasyida, Planodasyidae) from São Paulo, Brazil. Marine Biodiversity 44: 237-242. https://doi.org/10.1007/s12526-013-0165-4
  » https://doi.org/10.1007/s12526-013-0165-4
• Hochberg R, Litvaitis M (2000) Phylogeny of Gastrotricha: a morphology-based framework of gastrotrich relationships. The Biological Bulletin 198: 299-305. https://doi.org/10.2307/1542532
  » https://doi.org/10.2307/1542532
• Hochberg R, Atherton S (2010) Acanthodasys caribbeanensis sp. n., a new species of Thaumastodermatidae (Gastrotricha, Macrodasyida) from Belize and Panama. ZooKeys 61: 1-10. https://doi.org/10.3897/zookeys.61.552
  » https://doi.org/10.3897/zookeys.61.552
• Hochberg R, Atherton S, Kieneke A (2014) Marine Gastrotricha of Little Cayman Island with the description of one new species and an initial assessment of meiofaunal diversity. Marine Biodiversity 44: 89-113. https://doi.org/10.1007/s12526-013-0186-z
  » https://doi.org/10.1007/s12526-013-0186-z
• Hummon WD (2008) Gastrotricha of the North Atlantic Ocean: 1 Twenty four new and two redescribed species of Macrodasyida. Meiofauna Marina 16: 117-174.
• Hummon WD, Balsamo M, Todaro MA (1992) Italian marine Gastrotricha: I. Six new and one redescribed species of Chaetonotida. Italian Journal of Zoology 59: 499-516.
• Hummon WD, Tongiorgi P, Todaro MA, Balsamo M (1998) Italian marine Gastrotricha: V. Four new and one redescribed species of Macrodasyida in the Dactylopodolidae and Thaumastodermatidae. Italian Journal of Zoology 65: 109-119. https://doi.org/10.1080/11250009809386731
  » https://doi.org/10.1080/11250009809386731
• Kieneke A, Zekely J (2008) Desmodasys abyssalis sp. nov. - first record of a deep-sea gastrotrich from hydrothermal vents. Marine Biodiversity Records 1: e88. https://doi.org/10.1017/S1755267207008950
  » https://doi.org/10.1017/S1755267207008950
• Kieneke A, Riemann O, Ahlrichs WH (2008) Novel implications for the basal internal relationships of Gastrotricha revealed by an analysis of morphological characters. Zoologica Scripta 37: 429-460. https://doi.org/10.1111/j.1463-6409.2008.00334.x
  » https://doi.org/10.1111/j.1463-6409.2008.00334.x
• Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168.
• Lee J (2012) Marine gastrotrichs: Phylum Gastrotricha. NIBR, National Institute of Biological Resources, Incheon, 85 pp.
• Minowa AK, Kieneke A, Campos A, Balsamo M, Plewka M, et al. (2025) New branch on the Tree of Life of Gastrotricha: Establishment of a new genus for limno-terrestrial species. Zoological Journal of the Linnean Society 2: zlae166. https://doi.org/10.1093/zoolinnean/zlae166
  » https://doi.org/10.1093/zoolinnean/zlae166
• Naidu KV, Rao GC (2004) The fauna of India and the adjacent countries Gastrotricha. Biogeographia - The Journal of Integrative Biogeography 24: 131-160.
• Rao GC, Clausen C (1970) Planodasys marginalis gen. et sp. nov. and Planodasyidae fam. nov. (Gastotricha Magrodasyoidea). Sarsia 42: 73-82.
• Remane A (1925) Organisation und systematische Stellung der aberranten Gastrotrichen. Verhandlungen der deutschen zoologischen Gesellschaft 30: 121-128.
• Remane A (1927) Beitrage zur Systematik der Süsswassergastrotrichen. Zoologische Jahrbücher Abteilung für Systematik. Oekologie und Geographie der Tiere 53: 268-320.
• Ruppert EE (1977) Zoogeography and speciation in marine Gastrotricha. Mikrofauna Meeresbodens 61: 231-251.
• Ruppert EE (1978) The Reproductive System of Gastrotrichs. III. Genital organs of Thaumastodermatinae subfam. n. and Diplodasyinae subfam. n. with discussion of reproduction in Macrodasyida. Zoologica Scripta 7: 93-114. https://doi.org/10.1111/j.1463-6409.1978.tb00592.x
  » https://doi.org/10.1111/j.1463-6409.1978.tb00592.x
• Schratzberger M, Ingels J (2018) Meiofauna matters: the roles of meiofauna in benthic ecosystems. Journal of Experimental Marine Biology and Ecology 502: 12-25. https://doi.org/10.1016/j.jembe.2017.01.007
  » https://doi.org/10.1016/j.jembe.2017.01.007
• Sørensen MV, Araújo TQ, Macheriotou L, Braeckman U, Smith CR, Ingels J (2025) A new gastrotrich, Musellifer leasiae sp. nov. (Paucitubulatina: Muselliferidae), from Antarctica - the first record of the family from the deep-sea and the Southern Hemisphere. Zootaxa. 5647(4): 359-370. https://doi.org/10.11646/zootaxa.5647.4.3
  » https://doi.org/10.11646/zootaxa.5647.4.3
• Souid A, Gammoudi M, Saponi F, El Cafsi M, Todaro MA (2025) First investigation of the marine gastrotrich fauna from the waters of North Tunisia, with the description of a new species of Halichaetonotus (Gastrotricha, Chaetonotida). Diversity 17: 17. https://doi.org/10.3390/d17010017
  » https://doi.org/10.3390/d17010017
• Todaro MA, Rocha CEF (2004) Diversity and distribution of marine Gastrotricha along the northern beaches of the state of São Paulo (Brazil), with description of a new species of Macrodasys (Macrodasyida, Macrodasyidae). Journal of Natural History 38: 1605-1634. https://doi.org/10.1080/0022293031000156169
  » https://doi.org/10.1080/0022293031000156169
• Todaro MA, Rocha CEF (2005) Further data on marine gastrotrichs from the State of São Paulo and the first records from the State of Rio de Janeiro (Brazil). Meiofauna Marina 14: 27-31.
• Todaro MA, Hummon WD (2008) An overview and a dichotomous key to genera of the phylum Gastrotricha. Meiofauna Marina 16: 3-20.
• Todaro MA, Matinato L, Balsamo M, Tongiorgi P (2003) Faunistics and zoogeographical overview of the Mediterranean and Black Sea marine Gastrotricha. Biogeographia - The Journal of Integrative Biogeography 24: 131-160. https://doi.org/10.21426/B6110169
  » https://doi.org/10.21426/B6110169
• Todaro MA, Kånneby T, Zotto MD, Jondelius U (2011) Phylogeny of Thaumastodermatidae (Gastrotricha: Macrodasyida) Inferred from Nuclear and Mitochondrial Sequence Data. PLOS One 6: e17892. https://doi.org/10.1371/journal.pone.0017892
  » https://doi.org/10.1371/journal.pone.0017892
• Trokhymchuk R, Kieneke A (2024a) New records of deep-sea Gastrotricha and Tardigrada from Iberian and Canary Basins (Northeast Atlantic) with comments on abyssal meiofauna composition and the meiofauna paradox. The Journal of V. N. Karazin Kharkiv National University, Series Biology 43: 66-84. https://doi.org/10.26565/2075-5457-2024-43-6
  » https://doi.org/10.26565/2075-5457-2024-43-6
• Trokhymchuk R, Kieneke A (2024b) Novel distribution records of marine Tardigrada from abyssal sediments of the Northwest Atlantic Ocean. Organisms Diversity & Evolution 25: 13-28. https://doi.org/10.1007/s13127-024-00641-2
  » https://doi.org/10.1007/s13127-024-00641-2

ADDITIONAL NOTES

• ZooBank register
  https://zoobank.org/45A530E4-5499-4370-AB17-0761EDB1716D
• Data Availability Statement
  All data generated and/or analyzed are included in this article.
• Funding
  This study was financed in part by the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 478826/2013-7 to IB, and 141482/2021-4 to AKM), by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) - Finance Code 001 (CAPES/PrInt 88887.716041/2022-00 to AKM), by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP 2011/50317-5; 2014/23856-0; 2018/10313-0 to ARSG; 2025/14491-3 to AKM), and by FAEPEX-UNICAMP (2031/15 to ARSG).
• Ethical Statement
  Field activities were conducted under collection permits issued by Instituto Chico Mendes de Conservação da Biodiversidade - ICMBio (permit no. 99637-1).
• AI Statement
  Artificial intelligence tools were used solely to assist with language editing and grammar.
• How to cite this article
  Minowa AK, Guidi L, Garraffoni ARS, Bosco I (2026) A new species of Acanthodasys (Macrodasyida: Thaumastodermatidae) from the northern coast of São Paulo, Brazil. Zoologia 43: e25100. https://doi.org/10.1590/S1984-4689.v43.e25100
• Published by
  Sociedade Brasileira de Zoologia at Scientific Electronic Library Online - https://www.scielo.br/zool

Edited by

• Editorial responsibility
  Walter A.P. Boeger

Data availability

All data generated and/or analyzed are included in this article.

Publication Dates

• Publication in this collection
  20 July 2026
• Date of issue
  2026

History

• Received
  16 Oct 2025
• Accepted
  16 Mar 2026