Seek and you shall find: new species of the rare genus Ornamentula (Gastrotricha: Chaetonotida) and first record outside of type-locality

Axell K. Minowa André R.S. Garraffoni About the authors

ABSTRACT

Ornamentula Kisielewski, 1991 is a monospecific genus in Order Chaetonotida. The sole species, O. paraensis Kisielewsk, 1991, is a semiplanktonic gastrotrich found in a single pond in the Amazon region of Brazil. Herein we describe a new species of the genus Ornamentula, collected in a small urban lagoon in the Atlantic Forest of southeast Brazil. Ornamentula miyazakii sp. nov. resembles O. paraensis, but it shows differences in the ornamented trunk scales and spinal spines distribution, sufficient to proposte it as it’s a new species.

KEY WORDS:
Atlantic rainforest; semiplanktonic gastrotrich; taxonomy; urban lagoon

INTRODUCTION

Gastrotricha are free-living microinvertebrates found in benthic and epiphytic as well as periphytic biotopes in marine and freshwater habitats around the world (Balsamo et al. 2008Balsamo M, JL d’Hondt, 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-...
, 2014Balsamo M, Grilli P, Guidi L, d’Hondt JL (2014) Gastrotricha: Biology, ecology and systematics. Families Dasydytidae, Dichaeturidae, Neogosseidae, Proichthydiidae. Backhuys Publishers, Weikersheim-Germany, 187 pp., Kieneke and Schmidt-Rhaesa 2015Kieneke A, Schmidt-Rhaesa A (2015) Gastrotricha. Handbook of Zoology. Gastrotricha, Cycloneuralia and Gnathifera, 3: 1-134., Todaro et al. 2019Todaro MA, Sibaja-Cordero JA, Segura-Bermúdez OA, Coto-Delgado G, Goebel-Otárola N, Barquero JD, Cullell-Delgado M, Dal Zotto M (2019) An Introduction to the Study of Gastrotricha, with a Taxonomic Key to Families and Genera of the Group. Diversity 11(7): 117. https://doi.org/10.3390/d11070117
https://doi.org/10.3390/d11070117...
). The phylum is divided in two orders (Macrodasyida Remane, 1925, Chaetonotida Remane 1925Remane A (1925) Organisation und systematische Stellung der aberranten Gastrotrichen. Verhandlungen der Deutschen zoologischen. Gesellschaft. 30: 121-128.), 18 families, 69 genera and more than 860 species (Balsamo et al. 2014Balsamo M, Grilli P, Guidi L, d’Hondt JL (2014) Gastrotricha: Biology, ecology and systematics. Families Dasydytidae, Dichaeturidae, Neogosseidae, Proichthydiidae. Backhuys Publishers, Weikersheim-Germany, 187 pp., 2015Balsamo M, d’Hondt JL, Kisielewski J, Todaro MA, Tongiorgi P, Guidi L, de Jong Y (2015). Fauna Europaea: Gastrotricha. Biodiversity Data Journal 3: e5800. https://doi.org/10.3897/BDJ.3.e5800
https://doi.org/10.3897/BDJ.3.e5800...
, Garraffoni et al. 2017Garraffoni ARS, Araújo TQ, Lourenço AP, Guidi L, Balsamo M (2017) A new genus and new species of freshwater Chaetonotidae (Gastrotricha: Chaetonotida) from Brazil with phylogenetic position inferred from nuclear and mitochondrial DNA sequences. Systematics and Biodiversity 15(1): 49-62. https://doi.org/10.1080/14772000.2016.1214189
https://doi.org/10.1080/14772000.2016.12...
, Todaro et al. 2019Todaro MA, Sibaja-Cordero JA, Segura-Bermúdez OA, Coto-Delgado G, Goebel-Otárola N, Barquero JD, Cullell-Delgado M, Dal Zotto M (2019) An Introduction to the Study of Gastrotricha, with a Taxonomic Key to Families and Genera of the Group. Diversity 11(7): 117. https://doi.org/10.3390/d11070117
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).

Although genera such as ChaetonotusEhrenberg, 1830Ehrenberg CG (1830) Organization, systematik und geographisches Verhältnis der Infusionsthierchen. Zwei Verträge. Abhandlungen der Königlichen Akademie der Wissenschaften zu Berlin. Kupfertafeln, Gelesen, 1828, 108 pp., TurbanellaSchultze, 1853Schultze M (1853) Über Chaetonotus und Ichthydium (Ehrb.) und eine neue verwandte Gattung Turbanella. Müller’s Archiv für Anatomie und Physiologie 6: 241-254., AspidiophorusVoigt, 1903Voigt M (1903) Eine neue Gastrotrichen species (Chaetonotus arquatus) aus dem Schlosspark Teiche zu Plön. Plöner Forschungsberichte 10: 90-93., TetranchyrodermaRemane, 1926Remane A (1926) Morphologie und Verwandtschaftsbeziehungen der aberranten Gastrotrichen I. Zeitschrift für Morphologie und Oekologie der Tiere 5: 625-754., and MacrodasysRemane, 1924Remane A (1924) Neue aberrante Gastrotrichen. I. Macrodasys buddenbrocki nov. gen. nov. spec. Zoologischer Anzeiger 61: 289-297. are considered highly specious with dozens of species, other genera, e.g. DendrodasysWilke, 1954Wilke U (1954) Mediterrane Gastrotrichen. Zoologische Jahrbücher 82: 497-550., CrasiellaClausen, 1968Clausen C (1968) Crasiella diplura gen. et sp. n. (Gastrotricha, Macrodasyoidea). Sarsia 33(1): 59-64. https://doi.org/10.1080/00364827.1968.10411130
https://doi.org/10.1080/00364827.1968.10...
, DiuronotusTodaro et al., 2005Todaro MA, Balsamo M, Kristensen RM (2005) A new genus of marine chaetonotids (Gastrotricha), with a description of two new species from Greenland and Denmark. Marine Biological Association of the United Kingdom. Journal of the Marine Biological Association of the United Kingdom 85(6): 1391-1400., BifidochaetusKolicka & Kisielewski, 2016Kolicka M, Dabert M, Dabert J, Kånneby T, Kisielewski J (2016) Bifidochaetus, a new Arctic genus of freshwater Chaetonotida (Gastrotricha) from Spitsbergen revealed by an integrative taxonomic approach. Invertebrate Systematics 30(4): 398-419. https://doi.org/10.1071/IS16001
https://doi.org/10.1071/IS16001...
, have very few species and some even consist of a single species, e.g. Ornamentula Kisielewski, 1991, HummondasysTodaro et al., 2014Todaro MA, Leasi F, Hochberg R (2014) A new species, genus and family of marine Gastrotricha from Jamaica, with a phylogenetic analysis of Macrodasyida based on molecular data. Systematics and Biodiversity 12(4): 473-488. https://doi.org/10.1080/14772000.2014.942718
https://doi.org/10.1080/14772000.2014.94...
, ThaidasysTodaro et al., 2015Todaro MA, Dal Zotto M, Leasi F (2015) An integrated morphological and molecular approach to the description and systematisation of a novel genus and species of Macrodasyida (Gastrotricha). Plos One 10(7): e0130278. https://doi.org/10.1371/journal.pone.0130278
https://doi.org/10.1371/journal.pone.013...
and CephalionotusGarraffoni et al., 2017Garraffoni ARS, Araújo TQ, Lourenço AP, Guidi L, Balsamo M (2017) A new genus and new species of freshwater Chaetonotidae (Gastrotricha: Chaetonotida) from Brazil with phylogenetic position inferred from nuclear and mitochondrial DNA sequences. Systematics and Biodiversity 15(1): 49-62. https://doi.org/10.1080/14772000.2016.1214189
https://doi.org/10.1080/14772000.2016.12...
.

Ornamentula is a monotypic genus belonging to Dasydytidae Daday, 1905Daday EV (1905) Untersuchungen über die Süsswasser mikrofauna paraguays. Zoologica 44: 72-86 (Chaetonotida). It was originally described by Kisielewski (1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168.) to accommodate the new species Ornamentula paraensis Kisielewsk, 1991, collected in a small pond from the Brazilian Amazon rainforest. Originally, Kisielewski (1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168.) spelled the species name as Ornamentula paraënsis, with a diacritic. However, the ICZN - Art. 32.5.2. states that: “A name published with a diacritic or other mark, ligature, apostrophe, or hyphen, or a species-group name published as separate words of which any is an abbreviation, is to be corrected.

Although most gastrotrich species are meiobenthic, O. paraensis has a semiplanktonic lifestyle, like few other gastrotrichs (Balsamo et al. 2014Balsamo M, Grilli P, Guidi L, d’Hondt JL (2014) Gastrotricha: Biology, ecology and systematics. Families Dasydytidae, Dichaeturidae, Neogosseidae, Proichthydiidae. Backhuys Publishers, Weikersheim-Germany, 187 pp., Kieneke and Schmidt-Rhaesa 2015Kieneke A, Schmidt-Rhaesa A (2015) Gastrotricha. Handbook of Zoology. Gastrotricha, Cycloneuralia and Gnathifera, 3: 1-134., Todaro et al. 2019Todaro MA, Sibaja-Cordero JA, Segura-Bermúdez OA, Coto-Delgado G, Goebel-Otárola N, Barquero JD, Cullell-Delgado M, Dal Zotto M (2019) An Introduction to the Study of Gastrotricha, with a Taxonomic Key to Families and Genera of the Group. Diversity 11(7): 117. https://doi.org/10.3390/d11070117
https://doi.org/10.3390/d11070117...
, Minowa and Garraffoni 2017Minowa AK, Garraffoni ARS (2017) A new species of Haltidytes Remane, 1936 (Gastrotricha: Chaetonotida: Dasydytidae) from an urban lagoon in Brazil with a phylogenetic reconstruction of the genus based on morphological data. Zoologischer Anzeiger 269: 100-109. https://doi.org/10.1016/j.jcz.2017.08.003
https://doi.org/10.1016/j.jcz.2017.08.00...
, 2020Garraffoni ARS, Araújo TQ (2020) Keys to Neotropical and Antarctic Fauna. In: Damborenea C, Rogers DC, Thorp JH (Eds) Phylum Gastrotricha. Academic Press, London, 125-143.). These species show various morphological adaptations such as the complete loss of posterior adhesive tubes, a system of ciliary bands in the head region and short diagonal ciliary bands or tufts on the ventral trunk, and lateral motile spines to perform saltatory movements in the water column (Kisielewski 1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168., Kieneke et al. 2008Kieneke A, Arbizu PM, Riemann O (2008) Body musculature of Stylochaeta scirtetica Brunson, 1950 and Dasydytes (Setodytes) tongiorgii (Balsamo, 1982) (Gastrotricha: Dasydytidae): A functional approach. Zoologischer Anzeiger 247: 147-158. https://doi.org/10.1016/j.jcz.2007.11.001
https://doi.org/10.1016/j.jcz.2007.11.00...
, Kieneke and Ostmann 2012Kieneke A, Ostmann A (2012) Structure, function and evolution of somatic musculature in Dasydytidae (Paucitubulatina, Gastrotricha). Zoomorphology 131(2): 95-114. https://doi.org/10.1007/s00435-012-0152-5
https://doi.org/10.1007/s00435-012-0152-...
).

Species of Ornamentula are characterized by a type of well-developed cuticular armature, unique among all Gastrotricha, that consists of a complex reticular ornamentation on the scales associated with thick and long spines (Kisielewski 1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168.). Kisielewski (1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168.) highlighted a possible proximity of Ornamentula’s lineage with those of Setopus and Haltidytes based on the presence of scales and bifurcated spines. This hypothesis was also accepted by Kånneby et al. (2013Kånneby T, Todaro MA, Jondelius U (2013) Phylogeny of Chaetonotidae and other Paucitubulatina (Gastrotricha: Chaetonotida) and the colonization of aquatic ecosystems. Zoologica Scripta 42(1): 88-105. https://doi.org/10.1111/j.1463-6409.2012.00558.x
https://doi.org/10.1111/j.1463-6409.2012...
) and Kånneby and Todaro (2015Kånneby T, Todaro MA (2015) The phylogenetic position of Neogosseidae (Gastrotricha: Chaetonotida) and the origin of planktonic Gastrotricha. Organisms Diversity and Evolution 15(3): 459-469. https://doi.org/10.1007/s13127-015-0223-9
https://doi.org/10.1007/s13127-015-0223-...
) based on a molecular analysis based on 3 genes, but it was not confirmed by studies based on morphological data (Kieneke et al. 2008Kieneke A, Arbizu PM, Riemann O (2008) Body musculature of Stylochaeta scirtetica Brunson, 1950 and Dasydytes (Setodytes) tongiorgii (Balsamo, 1982) (Gastrotricha: Dasydytidae): A functional approach. Zoologischer Anzeiger 247: 147-158. https://doi.org/10.1016/j.jcz.2007.11.001
https://doi.org/10.1016/j.jcz.2007.11.00...
, Kieneke and Ostmann 2012Kieneke A, Ostmann A (2012) Structure, function and evolution of somatic musculature in Dasydytidae (Paucitubulatina, Gastrotricha). Zoomorphology 131(2): 95-114. https://doi.org/10.1007/s00435-012-0152-5
https://doi.org/10.1007/s00435-012-0152-...
).

So far, our knowledge on the biology, life cycle and distribution of many semiplanktonic gastrotrichs is very limited, probably due to a lack of specialists, but especially to the rareness of Dasydytidae specimens and their difficult preparation and handling (Kieneke et al. 2008Kieneke A, Arbizu PM, Riemann O (2008) Body musculature of Stylochaeta scirtetica Brunson, 1950 and Dasydytes (Setodytes) tongiorgii (Balsamo, 1982) (Gastrotricha: Dasydytidae): A functional approach. Zoologischer Anzeiger 247: 147-158. https://doi.org/10.1016/j.jcz.2007.11.001
https://doi.org/10.1016/j.jcz.2007.11.00...
, Kieneke and Ostmann 2012Kieneke A, Ostmann A (2012) Structure, function and evolution of somatic musculature in Dasydytidae (Paucitubulatina, Gastrotricha). Zoomorphology 131(2): 95-114. https://doi.org/10.1007/s00435-012-0152-5
https://doi.org/10.1007/s00435-012-0152-...
). In order to contribute to the poor knowledge on semiplanktonic gastrotrichs in the Neotropical region (Kisielewski 1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168., Kånneby et al. 2013Kånneby T, Todaro MA, Jondelius U (2013) Phylogeny of Chaetonotidae and other Paucitubulatina (Gastrotricha: Chaetonotida) and the colonization of aquatic ecosystems. Zoologica Scripta 42(1): 88-105. https://doi.org/10.1111/j.1463-6409.2012.00558.x
https://doi.org/10.1111/j.1463-6409.2012...
, Kånneby and Todaro 2015Kånneby T, Todaro MA (2015) The phylogenetic position of Neogosseidae (Gastrotricha: Chaetonotida) and the origin of planktonic Gastrotricha. Organisms Diversity and Evolution 15(3): 459-469. https://doi.org/10.1007/s13127-015-0223-9
https://doi.org/10.1007/s13127-015-0223-...
, Minowa and Garraffoni 2017Minowa AK, Garraffoni ARS (2017) A new species of Haltidytes Remane, 1936 (Gastrotricha: Chaetonotida: Dasydytidae) from an urban lagoon in Brazil with a phylogenetic reconstruction of the genus based on morphological data. Zoologischer Anzeiger 269: 100-109. https://doi.org/10.1016/j.jcz.2017.08.003
https://doi.org/10.1016/j.jcz.2017.08.00...
, 2020Minowa AK, Garraffoni ARS (2020) Assessing biodiversity shortfalls of freshwater meiofauna from Atlantic Forest: new species, distribution patterns and first total evidence phylogeny of semiplanktonic Gastrotricha. Molecular Phylogenetics and Evolution 152: 106926. https://doi.org/10.1016/j.ympev.2020.106926
https://doi.org/10.1016/j.ympev.2020.106...
), herein we describe the second species of the genus Ornamentula found in an urban lagoon surrounded by Atlantic rainforest, in Southeast Brazil.

MATERIAL AND METHODS

The material for the research was collected in a small urban lagoon, São Paulo, Brazil, with an area of 0.05 km2 (22°79’S; 47°14’W), surrounded by fragments of Atlantic rainforest. The collection was carried out during an ongoing freshwater Gastrotricha sampling project, in which periodic biweekly collections have been carried out since 2017. The organisms were found in the samples from October 2017, from the upper 30 cm of the water surface, among floating vegetation roots, using 5 L buckets. The material was stored with constant aeration, with a temperature around 20 °C, and processed within seven days.

The sorting was carried out according to the protocol reported by Minowa and Garraffoni (2020Minowa AK, Garraffoni ARS (2020) Assessing biodiversity shortfalls of freshwater meiofauna from Atlantic Forest: new species, distribution patterns and first total evidence phylogeny of semiplanktonic Gastrotricha. Molecular Phylogenetics and Evolution 152: 106926. https://doi.org/10.1016/j.ympev.2020.106926
https://doi.org/10.1016/j.ympev.2020.106...
) using 500 ml water samples sieved through a 30 µm mesh, poured into Petri dishes, and observed under a Zeiss Stemi 2000 stereomicroscope, focusing on the water column searching for of semiplanktonic gastrotrichs.

Each individual was isolated, anesthetized with 2% MgCl2, mounted individually and digitally documented under a Zeiss Axio Imager M2 light microscope equipped with DIC and AxioCam MRC5 digital video camera. The images were recorded and measurements were taken using the ZEN lite 2.5 2018 image software.

TAXONOMY

Gastrotricha Metschnikoff, 1865Metschnikoff E (1865) Über einige wenig bekannte niedere Thierformen. Zeitschrift für wissenschaftliche Zoologie 15: 450-463.

Chaetonotida Remane, 1925Remane A (1925) Organisation und systematische Stellung der aberranten Gastrotrichen. Verhandlungen der Deutschen zoologischen. Gesellschaft. 30: 121-128. [Rao & Clausen, 1970Rao GC, Clausen C (1970) Planodasys marginalis gen. et sp. nov. and Planodasyidae fam. nov. (Gastrotricha Macrodasyoidea). Sarsia 42(1): 73-82. https://doi.org/10.1080/00364827.1970.10411164
https://doi.org/10.1080/00364827.1970.10...
]

Paucitubulatina d’Hondt, 1971d’Hondt JL (1971) Gastrotricha. Oceanography and Marine Biology Annual Review 9: 141-192.

Dasydytidae Daday, 1905Daday EV (1905) Untersuchungen über die Süsswasser mikrofauna paraguays. Zoologica 44: 72-86

OrnamentulaKisielewski, 1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168. (emended)

Dasydytidae of 106-132 μm in length. Body covered with very large and ornamented scales. Dorsal neck with one or two transversal rows of three spined scales. Dorsal trunk with two parallel columns of six large ornamented scales and a rearmost group made of three scales. Long cephalic and trunk dorsal spines present on all scales or just on anterior three. Each long spine provided with a single strong lateral denticle. Transverse band of cephalic cilia situated between large lateral plates. Four paired spines groups (ta-td) along the anterior trunk half, two pairs of rear spines (r1-r2) near the trunk end and in some cases a small pair of ventral rearmost spined scales. Posterior trunk half ventrally covered with fine ornamented and spined scales, oval or arrow-head in shape.

Two species: Ornamentula paraensisKisielewski, 1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168. (type species) and Ornamentula miyazakii sp. nov.

Ornamentula miyazakii sp. nov.

http://zoobank.org/33D78328-A59F-4468-8BD9-6999A90C9033

Figs 1-12, Tables 1, 2

Type material. Holotype. Photographs of one specimen (adult) collected from an urban lagoon in Paulínia, Brazil in October 2017 with floating vegetation. The specimen was examined alive with a compound microscope equipped with DIC, but due to the fragility of its body, it was destroyed and is no longer available (Garraffoni et al. 2019Garraffoni ARS, Kieneke A, Kolicka M, Corgosinho PH, Prado J, Nihei SS, Freitas AV (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...
). The holotype is illustrated in Figs 1-3 and photomicrographs in Figs 5-7 (Garraffoni et al. 2019) and its digital image data are available at the Museum of Zoology, Universidade Estadual de Campinas, Brazil, under the accession number ZUEC GCH 52; Paratypes: Photographs of two additional specimens (adult and juvenile) collected from the same sampling site, with digital image data available under accession numbers ZUEC GCH 53 to ZUEC GCH 54.

Figures 1-3
Schematic drawing of Ornamentula miyazakii sp. nov.: (1) dorsal view; (2) lateral view; (3) ventral view. at: anterior ciliary tuft, ca: cephalic long spine, cs: cephalic spines, fs: fish-shaped scale, gs: granular scale, ps: posterior spine, pt: posterior ciliary tuft, r1: rear spine 1, r2: rear spine 2, sb: sensory long bristle, sr: scales transverse row, ta-td: groups of trunk ventrolateral long spines, tlb: transversal lateral band, vs: ventral scales. Scale bar: 50 µm.

Figures 4-8
Ornamentula miyazakii sp. nov. photomicrographs of mature specimens: (4) paratype, lateral view; (5) holotype, dorsal view; (6) holotype, ventral view; (7) holotype, dorsal cephalic view; (8) paratype, ventral trunk view. ca: cephalic long spine, cs: cephalic spines, ds1-5: dorsal scales, fs: fish-shaped scale, gs: granular scale ps: posterior spine, r1: rear spine 1, r2: rear spine 2, sb: sensory long bristle, sr: ta-td: groups of trunk ventrolateral long spines, vs: ventral scales. Scale bars: 4-6 = 50 µm, 7-8 = 10 µm.

Diagnosis. Ornamentula species 101-193 μm in body length (126-227 μm posterior spines included). Cone-shaped head, small cephalion. Two pairs of extremely long cephalic sensory bristles. Trunk dorsally covered by two columns each made of six large, ornamented scales each with a single spine. Ventral trunk side with small spined scales between ciliary tufts. Posterior end truncated; two pairs of dorsal terminal scales each with a thick spine and a similar terminal ventral scale with a thick spine.

Species-specific characters. A pair of extremely long, lateral cephalic sensory bristles inserted adjacent to the posterior cephalic ciliary tufts. Neck with one transversal row of three spined ornamented scales. Fish-shaped (oval scale with a posterior shallow constriction, and with convexe end) lateral ornamented scale (U44), immediately posterior to the tb spines group. An additional pair of dorsolateral rear spines, inserted on small ornamented scales. All dorsal scales with long, thick slightly curved spines with prominent denticles.

Description. Description based on characters and measurements of two adults (holotype and paratype) (Table 1).

Table 1
Morphometric features of Ornamentula miyazakii sp. nov. and O. paraensisKisielewski, 1991Kisielewski J (1991) Inland-water Gastrotricha from Brazil. Annales Zoologici 43: 1-168.. All measures in μm. x = average (without the juvenile measures in O. miyazakii sp. nov); n: number of specimens; ca: cephalic spine; ta, tb, tc, td: groups of trunk ventrolateral long spine; r1-2: rear spines; d1-3: spines on dorsal scales; s1-7: dorsal scales.

Ornamentula of 101-193 μm length (spines excluded); 126-227 μm (spines included). Elongated-oval dorsoventrally flattened body, with distinct cone-shaped head, and well developed lobes (31 μm wide), with a short and narrow neck region. Sub-terminal mouth ring (8.4 μm diameter), with short tentacle-like projections around the mouth ring. Cephalion 18 μm wide (U04), pleura absent, and hypostomion not observed (Figs 1, 11). Narrow cylindrical pharynx (62 μm long) (Figs 6, 9). Intestine with maximum width at its middle (127 μm long, 44 μm wide, U62,) (Figs 4-9). Truncated posterior end with two thick caudal spines (r1-r2) inserted on dorsolateral scales (U85; U90).

Cephalic ciliation consists of two pairs of lateral tufts (anterior one adjacent to the mouth, U04; posterior one medio-lateral, U06) and a pair of cephalic ciliary transversal bands (U10), bordering the cephalic lateral plates, interrupted in the dorsal and ventral medial region (Figs 1-3, 9-12). A pair of cephalic sensory bristles extremely long (4.3 μm; U03) inserted between the second lateral cephalic ciliary tuft and lateral cephalic transversal ciliary bands, anteriorly to granular lateral scales (U10) (Figs 1, 10, 11). Trunk ventral ciliation consists of three paired tufts (U43-U45, U59-U61, U86-U90) associated to lateral trunk spines tb1-3, tc1-2 and r2, respectively (Figs 3-4).

Figures 9-12
Ornamentula miyazakii sp. nov., photomicrographs of a juvenile in dorsal view. at: anterior ciliary tuft, ce: cephalion, pt: posterior ciliary tuft sb: sensory long bristle, sr: scales of the transverse row, tlb: transversal lateral band. Scale bars: 9 = 100 µm, 10-12 = 50 µm.

Body dorsum mostly covered with enormous scales with ornamentations described originally as scale reinforcements, probably due to their exaggerated size (Figs 1, 4-6). Cephalic cuticular armature: Two pairs of anterior lateral cephalic plates on the head (U10), slightly folded in its margin, with finely granulated surface, (Fig. 7), different from the scales of the trunk. These plates are positioned at both sides of lateral cephalic transverse bands (Figs 1-3). Several pairs of small rounded scales, each with a fine barbed spine, with fine barbed spines (U08-U12) on the cephalic dorsal space between granulated plates (Figs 1, 10, 11). Anterior cephalic spines short (3.7 μm, 1.5x the length of inserted scale), lengthen gradually to the posterior longer ones (7 μm, 2.4x the length of inserted scale) (Fig. 1). The lateral cephalic spines (ca) are inserted anteriorly adjacent to the granular plate (17.7 μm long, U03), much thicker at the base and gradually getting thinner distally, until the denticle, where it gets thinnest (Figs 1-3, 7).

Trunk cuticular armature: Single dorsal anteriormost transversal row with three simple spined scales (U21). The dorsal trunk is covered with two parallel column of six scales each (U24, U30, U43, U58, U76, U90), with varying sizes (Table 2), each scale bears a long, straight, thick, and barbed spine at 4/5 of its length. Laterally, three scales positioned posterior to each spine group (U35, U50, U64), first rounded between ta and tb spine groups; followed by fish-shaped scale, posterior to tb spine group (i.e. rounded anterior half, with middle portion slightly constricted, and posterior half concave, with two pointed edges); posteriormost rounded scale lodged on the concavity of fish-shaped scale. Two pairs of rearmost ventrolateral scales (U67, U96) with r1 and r2 spines inserted, followed by a ventral triangular scale (Figs 2, 3, 8) with short curved spine (U99).

Table 2
Comparison of several morphological structures between Ornamentula miyazakii sp. nov. and O. paraensis.

Ventrolateral trunk with thick and straight spines organized in four groups (ta, tb, tc, td) arranged in 5-3-2-1 spines each (U27, U43, U61, U68), with a conspicuous denticle at 4/5 of its length, and inserted on triangular scales (Figs 2-3, 8). The ta group is the most laterally inserted, with ta1-2 spines dorsolateral (Fig. 2).

Ventral trunk anteriorly smooth in interciliar space, and posterior region with 15 small rounded scales (U55-70) between tb, tc, and td spine groups. Anterior scales with longer spines (3.4 μm, 1.5x the length of inserted scale) followed by posterior ones shorter spines (1.7 μm, 1.5x the length of inserted scale) (Fig. 8).

Sexuality unknown, as we could not observe any specimen with eggs, nor the sexual organs.

Etymology. Species dedicated to animation director Hayao Miyazaki, a highly notorious animator and filmmaker. He animated the fantasy film “Princess Mononoke”, and illustrated the character Forest Spirit (1h01’20” in the original film), that at nighttime turns to Daidarabocchi, resembling the specimen drawn in Fig. 1.

Ecology. Freshwater, periphytic and semiplanktonic among roots of floating vegetation mainly composed by Eichhornia sp.

Remarks. Although the body plan of the taxon Ornamentula seems to be different from other members of Dasydytidae, it shows some common characteristics with other semiplanktonic species. Like its counterparts, Ornamentula species are characterized by a tenpin-shaped body, with evident head and neck constriction, cephalic ciliature arranged by discontinuous tufts and/or bands and body with paired groups of ventrolateral single-barbed spines.

Both Atlantic and Amazonian Ornamentula species share several unique morphological features characteristic of the taxon bauplan, such as: i) two parallel columns of dorsal ornamented scales forming a rigid armature, ii) two pairs of lateral cephalic plates (granular scales) on both sides of cephalic transverse ciliary bands, iii) a pair of lateral cephalic spines, iv) two pairs of ventrolateral cephalic ciliary tufts followed by the transverse band, and three ventral ciliary tufts on the trunk, v) four groups of movable ventrolateral spines with a conspicuous denticle inserted on ornamented scales and organized in 5-3-2-1 (ta-tb-tc-td) and vi) two pairs of terminal ventral spines with denticles (r1 and r2).

However, the new species can be distinguished from O. paraensis by some remarkable differences:

1. The dorsolateral cephalic spines (ca) thicker and curved, followed by a pair of long cephalic bristles adjacent to the second cephalic tuft, absent in former species.

2. The group of dorsal cephalic scales provided with spines with prominent denticles, in contrast to simple and shorter spines in former species.

3. The absence of second dorsal transverse rows of scales on the neck, present in O. paraensis.

4. The lateral trunk scale, posterior to tb spine group, fish-like shaped, in contrast to the rounded scale of O. paraensis.

5. Ventral spined scales with rounded uniform shape through the ventrum, unlike O. paraensis, with rounded in anterior portion and posteriorly triangular shaped.

6. A third terminal ventral scale with a short, simple and curved spine, much shorter than r1 and r2 spines, absent in O. paraensis.

DISCUSSION

It is well known in the literature how difficult the identification process is for meiofauna species (Fonseca et al. 2018Fonseca G, Fontaneto D, Di Domenico M (2018) Addressing biodiversity shortfalls in meiofauna. Journal of Experimental Marine Biology and Ecology 502: 26-38. https://doi.org/10.1016/j.jembe.2017.05.007
https://doi.org/10.1016/j.jembe.2017.05....
, Garraffoni et al. 2019Garraffoni ARS, Kieneke A, Kolicka M, Corgosinho PH, Prado J, Nihei SS, Freitas AV (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...
) and how remarkably poor the biodiversity knowledge is of these microscopic organisms compared to other groups of animals (Appeltans et al. 2012Appeltans W, Ahyong ST, Anderson G, Angel MV, Artois T, Bailly N, et al. (2012) The magnitude of global marine species diversity. Current Biology 22(23): 2189-2202. https://doi.org/10.1016/j.cub.2012.09.036
https://doi.org/10.1016/j.cub.2012.09.03...
, Fonseca et al. 2018Fonseca G, Fontaneto D, Di Domenico M (2018) Addressing biodiversity shortfalls in meiofauna. Journal of Experimental Marine Biology and Ecology 502: 26-38. https://doi.org/10.1016/j.jembe.2017.05.007
https://doi.org/10.1016/j.jembe.2017.05....
). Consequently, accurate diagnosis and meiofaunal species delimitation are difficult to access, leading to shortfalls (sensu Hortal et al. 2015Hortal J, de Bello F, Diniz-Filho JAF, Lewinsohn TM, Lobo JM, Ladle RJ (2015) Seven shortfalls that beset large-scale knowledge of biodiversity. Annual Review of Ecology, Evolution, and Systematics 46: 523-549. https://doi.org/10.1146/annurev-ecolsys-112414-054400
https://doi.org/10.1146/annurev-ecolsys-...
) regarding identity, distribution and evolution of meiofaunal taxa.

As pointed out by Fonseca et al. (2018Fonseca G, Fontaneto D, Di Domenico M (2018) Addressing biodiversity shortfalls in meiofauna. Journal of Experimental Marine Biology and Ecology 502: 26-38. https://doi.org/10.1016/j.jembe.2017.05.007
https://doi.org/10.1016/j.jembe.2017.05....
), to overcome these shortfalls it is highly recommended that meiofaunologists use the available microscopical techniques (optical, scanning, transmission, and confocal microscopy) as much as possible to better describe the external morphology and internal anatomy of new species. Thus, we are aware of the risk of conducting a nomenclatural act based on morphological information obtained only with the use of light microscopy with DIC gathered from two adult specimens. However, our decision to designate a new species is grounded in practical and philosophical standpoints that supported us to consider O. paraensis and O. miyazakii sp. nov. as two distinct evolutionary entities, or two distinct explanatory hypotheses for the intrinsic or relational properties of organisms that can be accounted for reproductive events (Fitzhugh 2005Fitzhugh K (2005) The inferential basis of species hypotheses: the solution to defining the term ‘species’. Marine Ecology 26(3-4): 155-165. https://doi.org/10.1111/j.1439-0485.2005.00058.x
https://doi.org/10.1111/j.1439-0485.2005...
, 2009Fitzhugh K (2009) Species as explanatory hypotheses: refinements and implications. Acta Biotheoretica 57(1-2): 201-248. https://doi.org/10.1007/s10441-009-9071-3
https://doi.org/10.1007/s10441-009-9071-...
).

In some cases due to environmental remoteness, sampling depth (e.g. deep sea), or rarity of some taxa, only one or very few meiofaunal specimens are collected and can be used to observe a sufficient number of morphological features to identify and delimit the species. In the last five years, we have been continuously sampling the lagoon where O. miyazakii sp. nov. was found and we were able to find many specimens of three unknown species of semiplanktonic gastrotrich (two of them were described by Minowa and Garraffoni 2017Minowa AK, Garraffoni ARS (2017) A new species of Haltidytes Remane, 1936 (Gastrotricha: Chaetonotida: Dasydytidae) from an urban lagoon in Brazil with a phylogenetic reconstruction of the genus based on morphological data. Zoologischer Anzeiger 269: 100-109. https://doi.org/10.1016/j.jcz.2017.08.003
https://doi.org/10.1016/j.jcz.2017.08.00...
, 2020Minowa AK, Garraffoni ARS (2020) Assessing biodiversity shortfalls of freshwater meiofauna from Atlantic Forest: new species, distribution patterns and first total evidence phylogeny of semiplanktonic Gastrotricha. Molecular Phylogenetics and Evolution 152: 106926. https://doi.org/10.1016/j.ympev.2020.106926
https://doi.org/10.1016/j.ympev.2020.106...
) and at least five unknown benthic gastrotrich (one of them described by Garraffoni and Melchior 2015Garraffoni ARS, Melchior MP (2015) New species and new records of freshwater Heterolepidoderma (Gastrotricha: Chaetonotidae) from Brazil with an identification key to the genus. Zootaxa 4057(4): 551-568. https://doi.org/10.11646/zootaxa.4057.4.5
https://doi.org/10.11646/zootaxa.4057.4....
). However, until October 2019, this was the only sampling moment we found specimens belonging to O. miyazakii sp. nov. Thus, taking into account these specificities and the ontological status of species taxa as a species-as-individuals hypothesis (e.g. Coleman and Wiley 2001Coleman KA, Wiley EO (2001) On species individualism: a new defense of the species-as-individuals hypothesis. Philosophy of Science 68(4): 498-517. https://doi.org/10.1086/392939
https://doi.org/10.1086/392939...
, Fitzhugh 2009Fitzhugh K (2009) Species as explanatory hypotheses: refinements and implications. Acta Biotheoretica 57(1-2): 201-248. https://doi.org/10.1007/s10441-009-9071-3
https://doi.org/10.1007/s10441-009-9071-...
), we agree with Kieneke and Nikoukar (2017Kieneke A, Nikoukar H (2017) Integrative morphological and molecular investigation of Turbanella hyalina Schultze, 1853 (Gastrotricha: Macrodasyida), including a redescription of the species. Zoologischer Anzeiger 267: 168-186. https://doi.org/10.1016/j.jcz.2017.03.005
https://doi.org/10.1016/j.jcz.2017.03.00...
) and interpret the description of new species based on very few specimens as “primary species hypothesis”. In this case, the use of “primary” is only an indication of the initial essay for species delimitation, because O. miyazakii sp. nov. or Thaumastoderma antarcticaKieneke, 2010Kieneke A (2010) A new species of Thaumastoderma (Gastrotricha: Macrodasyida) from the Antarctic deep sea with a phylogenetic analysis of the whole genus. Journal of the Marine Biological Association of the United Kingdom 90: 575-584. https://doi.org/10.1017/S002531540900085X
https://doi.org/10.1017/S002531540900085...
(among many other examples in gastrotrichs) were hypothesized as entities that have unique common evolutionary origins and are spatiotemporally located (Rieppel 2009Rieppel O (2009) Species as a process. Acta biotheoretica 57(1-2): 33-49. https://doi.org/10.1007/s10441-008-9057-6
https://doi.org/10.1007/s10441-008-9057-...
), in the same way that any taxonomist would do if they had many specimens to analyze.

Besides, hypotheses of homology between characteristics of species of distinct lineages are as important as the hypotheses of species themselves. Highlighting the existence of the pairs of granular transverse scales on both species of Ornamentula, inserted on both sides of the head, arranged in such a way that the transverse ciliary band lies between them. However, these granular scales, despite the similar relative positions on the head, are not homologous to the cephalic pleura present in other Paucitubulatina (Kieneke and Schmidt-Rhaesa 2015Kieneke A, Schmidt-Rhaesa A (2015) Gastrotricha. Handbook of Zoology. Gastrotricha, Cycloneuralia and Gnathifera, 3: 1-134.). This statement is supported by the position relative to the ciliary arrangement, as such structures are arranged adjacent to the cephalion, and each ciliary cephalic tuft is inserted ventrally (Minowa and Garraffoni 2020Minowa AK, Garraffoni ARS (2020) Assessing biodiversity shortfalls of freshwater meiofauna from Atlantic Forest: new species, distribution patterns and first total evidence phylogeny of semiplanktonic Gastrotricha. Molecular Phylogenetics and Evolution 152: 106926. https://doi.org/10.1016/j.ympev.2020.106926
https://doi.org/10.1016/j.ympev.2020.106...
) on benthic representatives. Even compared with the semiplanktonic species, the cephalic reinforcement (pleura) is inserted anteriorly to the ciliary band, in contrast with the posterior insertion of the second scale in the Ornamentula species.

Garraffoni and Araújo (2020Garraffoni ARS, Araújo TQ (2020) Keys to Neotropical and Antarctic Fauna. In: Damborenea C, Rogers DC, Thorp JH (Eds) Phylum Gastrotricha. Academic Press, London, 125-143.) provided a taxonomic key for Neotropical Gastrotricha species, which we updated here with the Ornamentula identification and included the new species.

Gastrotricha: Chaetonotida: Dasydytidae: Ornamentula

1a. Cephalic spined scaled simple; dorsal scales arranged in two parallel columns of six scales each, three anterior with long barbed spines, three posterior spineless, dorsal neck with two transversal rows of three spined scales .................... Ornamentula paraensis

1b. Cephalic spined scaled barbed; dorsal scales arranged in two parallel columns of six scales each, all of them with long barbed spines, dorsal neck with single transversal row of three spined scales .................... Ornamentula miyazakii sp. nov.

ACKNOWLEDGEMENTS

We are grateful to the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP 2014/23856-0, 2017/20312-8, and 2019/01955-0) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (Capes Finance Code 001) for the financial support. We are grateful to Rick Hochberg and an anonymous reviewer for their constructive criticism that greatly improved the first version of the manuscript. Additional thanks to Yasmina Shah Esmaeili for editing the English text.

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Publication Notes

  • Available online:

    February 26, 2021
  • Zoobank Register:

    http://zoobank.org/62A0E65E-E8CD-4122-AA6B-FCD54A0638C0
  • Publisher:

    © 2021 Sociedade Brasileira de Zoologia. Published by Pensoft Publishers at https://zoologia.pensoft.net

Publication Dates

  • Publication in this collection
    12 Mar 2021
  • Date of issue
    2021

History

  • Received
    21 July 2020
  • Accepted
    13 Dec 2020
  • Published
    26 Feb 2021
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