The New Zealand Gastrotricha fauna is effectively unknown (Table 10.1; Fig. 10.1). The total number of recorded taxa from the Aotearoa New Zealand region is four genera and four undescribed species from the order Macrodasyida, and one undescribed specimen from the order Chaetonotida (fam., genus et sp. indet.; Table 10.1). In addition, there are over 330 specimens of unidentified Gastrotricha collected from New Zealand. The discovery rate, rate of description, and increase in our knowledge of gastrotrich diversity for New Zealand waters has remained unchanged during the last two decades (since Sterrer 2009). A checklist of New Zealand Gastrotricha is provided

Todaro M. Antonio

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10M. Antonio TodaroKingdom Animalia, phylum Gastrotricha hairy-bellied wormsAotearoa New ZealandtheofMarine BiotaNIWA Biodiversity Memoir136 2023CHAPTER 10To cite this article: Todaro, M.A. (2023) Chapter 10. Kingdom Animalia, phylum Gastrotricha (hairy-bellied worms). Pp. 187–191 in: Kelly, M., Mills, S., Terezow, M., Sim-Smith, C., Nelson, W. (Eds) The Marine Biota of Aotearoa New Zealand. Updating our marine biodiversity inventory. NIWA Biodiversity Memoir 136, 494 pp. https://docs.niwa.co.nz/library/public/NIWAbm136-ch10.zip18810Kingdom Animalia, phylum Gastrotricha (hairy-bellied worms) M. Antonio TodaroDepartment of Life Sciences, University of Modena and Reggio Emilia, Via G. Campi 213/D, 41125 Modena, Italy     antonio.todaro@unimore.it; https://orcid.org/0000-0002-6353-7281IntroductionThe phylum Gastrotricha includes microscopic (0.08–3.5 mm body length), free-living, aquatic worms, char-acterised by a meiobenthic life style. The name Gastro-tricha, effectively meaning ‘hairy stomach,’ refers to the dense ciliation that covers the ventral surface of these worms, and which they use to glide on the substrate. In marine habitats, gastrotrichs are mainly interstitial, whereas in fresh waters they are a common component of benthos, periphyton, and also of the plankton. The ecological role of the gastrotrichs is important within the microphagous, detritivorous, benthic community. Gastrotrichs ingest microalgae, bacteria and small pro-tists by aspiration, with their potent, triradiated, myo-epithelial pharynx, and in turn, they are preyed upon by small macrofauna, carnivorous ciliates, and free- living flatworms (Balsamo & Todaro 2002; Kieneke & Schmidt-Rhaesa 2015).These tiny worms have an acoelomate body organisation and are considered to be phylogenetically closely allied to the Platyhelminthes, with which they form the clade Rouphozoa, within the protostome lineage Spiralia (e.g. Struck et al. 2014; Egger et al. 2015).Gastrotrichs are unique among metazoans in their possession of a cuticle that envelopes the entire body, cilia included. The cuticle is composed of two layers and gives rise to external ornamentations such as plates, scales or spines, mostly seen in chetonotidans and in members of some macrodasyidan families (e.g., Thaumastodermatidae and Lepidodasyidae) (e.g. Ruppert 1991).The body of a gastrotrich is generally elongated, dorsoventrally flattened, transparent and colourless, though the ingested food may colour the digestive tract. Gastrotrichs are characterised by an anterior mouth, a long muscular pharynx, a straight gut, a ventral anus, and adhesive tubes by which they attach to sand grains or debris (Todaro et al. 2019; Balsamo et al. 2020). Excretion and osmoregulation are performed by protonephridia. Sensorial organs are in the form of tactile cilia and bristles, eye spots, and flap-like or piston-pit chemoreceptors. Marine gastrotrichs are primarily hermaphroditic, with paired gonads, and in many species, glandular or muscular reproductive organs; most such species engage in mutual cross-fertilisation, though traumatic insemination is also possible.  Most freshwater species reproduce by thelytokous parthenogenesis. In the latter case, two egg types are produced: thin-walled eggs, which hatch one to two days after deposition, and thick-walled resting eggs (e.g. Kieneke & Schmidt-Rhaesa 2015). The phylum is global in distribution and currently counts approximately 860 accepted species distributed in two orders: Macrodasyida (377 species almost all SummaryThe New Zealand Gastrotricha fauna is effectively unknown (Table 10.1; Fig. 10.1). The total number of recorded taxa from the Aotearoa New Zealand region is four genera and four undescribed species from the order Macro-dasyida, and one undescribed specimen from the order Chaetonotida (fam., genus et sp. indet.; Table 10.1). In addition, there are over 330 specimens of unidentified Gastrotricha collected from New Zealand. The discov-ery rate, rate of description, and increase in our knowledge of gastrotrich diversity for New Zealand waters has remained unchanged during the last two decades (since Sterrer 2009). A checklist of New Zealand Gastro- tricha is provided.Table 10.1. Summary of gastrotrich diversity in the Aotearoa New Zealand region expressed as total numbers and percentage change. Data for 2009 are derived from Sterrer et al. (2009: p. 136). OTU = Operational Taxonomic Unit. Chaetonotida Macrodasyida      Total                  % change 2009 2023 2009 2023 2009 2023 Total species diversity 1 1 4 4 5 5 0Described extant species 0 0 0 0 0 0 0Undescribed extant species (OTU) 1 1 4 4 5 5 0189Figure 10.1. Gastrotrich species in orders Macrodasyida and Chaetonotida similar to taxa recorded from New Zealand to date: Order Macrodasyida. A. Macrodasys sp. (family Macrodasyidae), scale = 200 μm; B. Thaumastoderma sp. (family Thaumastodermatidae), scale = 100 μm; C. Paraturbanella sp. (family Turbanellidae), scale = 200 μm; D. Turbanella sp. (family Turbanellidae), scale = 200 μm. Order Chaetonotida. E. Xenotrichula sp. (family Xenotrichulidae), scale = 100 μm; F. Chaetonotus sp. (family Chaetonotidae), scale = 100 μm. marine, distributed across 10 families and 37 genera) and Chaetonotida (132 marine and 353 freshwater species, distributed across eight families and 32 genera) (Todaro et al., 2021; Kieneke & Todaro 2021). Most macrodasyidan gastrotrichs lack a distinctive head, though sensorial organs can be well-defined; the sides of the body are parallel and bear from few to numerous adhesive tubes; the body ranges from short and broad to long and strap-like; the posterior body end is forked, rounded, or drawn out into a tail. In contrast, the body of most chaetonotidans includes a well-defined head lobe, a neck constriction, a slightly swollen trunk, and a forked posterior end at whose apexes are the only two, rarely four, adhesive tubes (Todaro et al. 2019).The New Zealand gastrotrich fauna is, to all intents and purposes, still unknown. Sterrer (2009) highlighted this, stating: “Gastrotricha have never been studied in this country and despite the fact that these worms are ubiquitous components of marine and freshwater meiofaunal systems, not a single species has ever been named”. Twelve years later, the situation remains unchanged, with only five putative taxa known for the New Zealand Exclusive Economic Zone. Records of marine gastrotrich taxa from New Zealand include: Riser (1984), who found Turbanella sp. (Macrodasyida: Turbanellidae) (see Fig. 10.1D), along with specimens of the family Thaumastodermatidae, in almost all the sampled beaches of the east coast of New Zealand, 190between Paihia in the North Island and Nugget Point, Southland, South Island; yet, chaetonotid gastrotrichs (Order Chaetonotida) were found only at Taylor’s Mistake and Okains Bay on Banks Peninsula in the South Island. Sterrer (2009) refers to Macrodasys sp. (family Macrodasyidae) (see Fig. 10.1A) and Paraturbanella sp. (family Turbanellidae) (see Fig. 10.1C) from the intertidal sand at Porirua Inlet in the North Island, and Thaumastoderma sp. (Macrodasyida: Thaumastodermatidae) (see Fig. 10.1B) from subtidal sand in Dunedin Harbour (= Otago Harbour) in the South Island. Finally, Kamenev et al. (1993) reported about 330 gastrotrich specimens per square metre in waters 4–12 m deep at Whale Island in the Bay of Plenty.Provided one has a good, high-power microscope (differential interference contrast optics are recom-mended), most gastrotrichs are readily identifiable to genus, even by inexperienced observers, using several published dichotomous or pictorial keys (e.g., Kieneke & Schmidt-Rhaesa 2015; Todaro et al. 2019). For anyone who wishes to find and identify gastrotrichs, Todaro et al. (2019) is a primary text, providing a dichotomous and pictorial key to the genera of the phylum along with details of all the suitable techniques in the supplementary material. For the benefit of researchers working in the same areas of New Zealand that the available gastrotrich records come from, photomicrographs of non-New Zealand species belonging to the equivalent taxa reported for New Zealand are provided in Fig. 10.1. Finally, an updated list of accepted gastrotrich species/taxa may found in WoRMS (https://www.marinespecies.org/) and the Gastrotricha World Portal (https://www.gastrotricha.unimore.it), a free-access site entirely dedicated to these fascinating creatures.  Knowledge gaps, research progress and future prioritiesCurrently, there are over 500 marine gastrotrich species known from the world over, but none have been formal-ly described from New Zealand. Consequently, local re-search on these animals cannot depart from an initial assessment of the alpha-diversity. Taxonomy should be based on an integrative approach (morphology coupled with molecular data) to avoid misidentification and un-veil possible cases of cryptic speciation. New Zealand is rich in sandy beaches, the preferred habitat of these creatures, and a good start would be to focus the study on the gastrotrich fauna of the littoral and sublittoral sand of four to six beaches characterised  by different exposure. Geographic distance from other localities and the amenity of the sampling locations may grant exciting future scientific discoveries.AcknowledgementsThe author extends his gratitude to Daniel Leduc, NIWA, for giving him the opportunity to contribute to this work, and many thanks to Michelle Kelly, Editor of the NIWA Biodiversity Memoir Series, for the excel-lent editing work of the first draft of the manuscript. Suggestions by Prof. Rick Hochberg, University of Massachusetts Lowell, USA, and Prof. Maria Balsamo, University of Urbino, Italy, improved the readability of the article. This work was partially supported by a grant ‘Far attrezzare 2021’ from the University of Modena e Reggio Emilia, Italy.ReferencesReferences to the taxonomic authorities and dates for gastrotrich taxa in this chapter and the associated checklist can be located in WoRMS (https://www.ma-rinespecies.org/) and the Gastrotricha World Portal (https://www.gastrotricha.unimore.it).Balsamo, M., Artois, T., Smith, J.P.S., Todaro, M.A., Guidi, L., Leander, B.S., Van Steenkiste, N.W.L. (2020) The curious and neglected soft-bodied meiofauna: Rouphozoa (Gastrotricha and Platyhelminthes). Hydrobiologia 847: 2613–2644.  https://doi.org/10.1007/s10750-020-04287-xBalsamo, M., Todaro, M.A. (2002) Gastrotricha. Pp. 45–61 in: Rundle, S.D., Robertson, A.L., Schmid-Araya, J.M. (Eds) Freshwater meiofauna: Biology and Ecology. Backhuys Publishers, Leiden, 369 pp.Egger, B., Lapraz, F., Tomiczek, B., Müller, S., Dessimoz, C., Girst-mair, J., Skunca, N., Rawlinson, K.A., Cameron, C.B., Beli, E., Todaro, M.A., Gammoudi, M., Noreña, C., Telford, M.J. (2015) A transcriptomic-phylogenomic analysis of the evolutionary relationships of flatworms. Current Biology 25: 1347–1353. https://doi.org/10.1016/j.cub.2015.03.034Kamenev, G.M., Fadeev, V.I., Selin, N.I., Tarasov, V.G., Malakehov, V.V. (1993) Composition and distribution of macro- and meio-benthos around sublittoral hydrothermal vents in the Bay of Plenty, New Zealand. New Zealand Journal of Marine and Fresh-water Research 27: 407–418.  https://doi.org/10.1080/00288330.1993.9516582Kieneke, A., Schmidt-Rhaesa, A. (2015) Gastrotricha and Gnath- ifera. Pp. 1–134 in: Schmidt-Rhaesa, A. (Ed.) Handbook of Zool-ogy: Gastrotricha, Cycloneuralia and Gnathifera, Volume 3. Wal-ter de Gruyter GmbH, Berlin, 354 pp.Kieneke, A., Todaro, M.A. (2021) Discovery of two ‘chimeric’ Gas-trotricha and their systematic placement based on an integrative approach. Zoological Journal of the Linnean Society 192: 710–735. https://doi.org/10.1093/zoolinnean/zlaa117Riser, N.W. (1984) General observations on the intertidal interstitial fauna of New Zealand. Tane, Journal of the Auckland University Field Club 30: 239–250.Ruppert, E.E. (1991) Gastrotricha. Pp. 41–109 in: Harrison F.W., Ruppert R.R. (Eds) Microscopic Anatomy of Invertebrates, Vol-ume 4. Wiley-Liss, New York, 438 pp. Sterrer, W. (2009) Chapter 7. Gastrotricha. Pp. 134–136 in: Gor-don, D.P. (Ed.) New Zealand Inventory of Biodiversity Volume 1, Kingdom Animalia: Radiata, Lophotrochozoa, and Deuterosto-mia, Canterbury University Press, Christchurch, 566 pp.191Checklist of extant Gastrotricha known from the New Zealand EEZThe checklist is arranged according to the currently accepted systematics and classificatory scheme employed by the World Register of Marine Species, Gastrotricha (https://www.marinespecies.org/aphia.php?p=taxde-tails&id=2078). Endemic taxa are indicated by ‘E’. Non-indigenous species are indicated by ‘NI’. All other taxa are considered native by default, i.e. naturally occurring in New Zealand and elsewhere.Phylum GASTROTRICHA Order CHAETONOTIDA Chaetonotida sp. indet. Riser, 1984Order MACRODASYIDA  Family MACRODASYIDAE Macrodasys sp. indet. Sterrer, 2009Family THAUMASTODERMATIDAE Thaumastoderma sp. indet. Sterrer, 2009Family TURBANELLIDAE Paraturbanella sp. indet. Sterrer, 2009Turbanella sp. indet. Riser, 1984Struck, T.H., Wey-Fabrizius, A.R., Golombek A., Hering, L., Wei-gert, A., Bleidorn, C., Klebow, S., Iakovenko, N., Hausdorf, B., Petersen, M., Kuck, P., Herlyn, H., Hankeln, T. (2014) Platyzoan paraphyly based on phylogenomic data supports a noncoelo-mate ancestry of Spiralia. Molecular Biology and Evolution 31: 1833–1849. https://doi.org/10.1093/molbev/msu143Todaro, A., d’Hondt, J-L., Hummon, W. (2021) World Gastrotricha Database. Gastrotricha. Available from: https://www.marine-species.org/aphia.php?p=taxdetails&id=2078 (accessed 28 Sep-tember 2021).Todaro, M.A., Sibaja-Cordero, J.A., Coto-Delgado, G., Goeb-el-Otárola, N., Barquero, J.D., 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: 117. https://doi.org/10.3390/d11070117Zhang, Z.-Q. (2013) Animal biodiversity: An update of classifica-tion and diversity in 2013. Pp. 5–11 in: Zhang, Z.-Q. (Ed.) Ani-mal Biodiversity: An Outline of Higher-Level Classification and Survey of Taxonomic Richness (Addenda 2013). Zootaxa 3703: 1–82. https://doi.org/10.11646/zootaxa.3703.1.1This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/.All photographic images remain the copyright of the original credited photographers._______________________________________ISSN 1174-0043; 136ISBN 978–1–99–117447–5 (digital edition)Copyright NIWA 2023

Kingdom Animalia, phylum Gastrotricha (hairy-bellied worms)

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Kingdom Animalia, phylum Gastrotricha (hairy-bellied worms)

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