Musellifer leasiae: A new species of Gastrotrich from Antarctica.

The waters of the Southern Ocean, which surrounds Antarctica, are considered to be a hotspot for marine biodiversity, yet only their macrofauna has been extensively studied. The meiobenthos (bottom dwelling organisms larger than single-celled microbes, but still difficult or impossible to see with the naked eye) of this region has been particularly poorly studied, and almost all of the studies which have occurred have been of Nematodes or Crustaceans. To date, twenty species of Tardigrades have been described from the waters around Antarctica, two Gnathostomulids, one of which was only identified to family level, and five Kinorynchs (although a study which should be published later this year is expected to add to this) have been described from this region, but not a single Scalidophoran, Loriciferan, or meiobenthic Priapulid.

Gastrotrichs are a phylum of minute animals, generally less than a millimetre in length, found in interstitial spaces in sediments. Their small size meant that they went unnoticed until the event of microscopy, with the group not being discovered until the 1860s. Despite this unfamiliarity they seem to be ubiquitous in marine sediments, and are also often found in non-marine settings. To date, only a single Gastrotrich, Thaumastoderma antarctica, has been identified from Antarctic waters, although there have been several reports of unidentified Gastrotrichs.

In a paper published in the journal Zootaxa on 17 June 2025, Martin Sørensen of the Natural History Museum of Denmark at the University of Copenhagen, Thiago Araújo of the University of Massachusetts Lowell, Lara Macheriotou and Ulrike Braeckman of the Marine Biology Research Group at Ghent University, Craig Smith of the Department of Oceanography at the University of Hawai’i at Mānoa, and Jeroen Ingels of the Coastal and Marine Laboratory at Florida State University, and the National Institute for Water and Atmospheric Research in Wellington, New Zealand, describe a second species of Gastrotrich from Antarctic waters.

The new species is described from specimens collected in December 2015 and April 2016 from sediment cores collected from depths of between 532 and 701 m in Andvord Bay the west coast of Graham Land, and the Gerlache Strait, which separates the Palmer Archipelago from the Antarctic Peninsula. It is placed within the genus Musellifer, and given the specific name leasiae, in honour of marine biologist  Francesca Leasi in recognition of her numerous contributions to Gastrotrich taxonomy and morphology.

Map showing the sampling stations. (A) Overview of Antarctica, with the Antarctic Peninsula framed. (B) Antarctic Peninsula with sampling area framed. (C) Sampling area with stations. Red star indicates the type locality; yellow dots indicate additional stations with Musellifer leasiae. Sørensen et al. (2025).

Specimens of Musellifer leasiae are between 322 and 415 μm in length, and have a body with a pointed head, a weakly defined neck, a parallel-sided body, and a pair of tapering furcal branches ('tails'). This body is covered by approximately 26 columns of scales, with an average of 45 scales per column. The columns can be divided into eight dorsal columns, two sets of five ventral columns, and eight ventral columns. The ventral surface also has two rows of locomotory cilia.

Line art illustration of Musellifer leasiae, (A) Dorsal view. (B) Ventral view. (C) Close-ups of head scales, anterior-, and posterior trunk scales, and terminal furca scales. Sørensen et al. (2025).

Five species of Musellifer have been described previously; Musellifer delamarei and Musellifer profundus from the Mediterranean, Musellifer tridentatus from the Caribbean, Musellifer reichardti from the Atlantic coast of Florida, and Musellifer sanlitoralis from the San Juan Archipelago in Washington State. Only a single specimen has previously been described from the Southern Hemisphere, a possible specimen of Musellifer profundus, making Musellifer leasiae the first known species in the genus with a Southern Hemisphere, as well as the first species from the Antarctic.

Light micrographs showing overviews and details of holotype NHMD-1801023 (A)-(H) and paratype NHMD-1801024 (I) of Musellifer leasiae. (A) Ventral overview. (B) Body, anterior, U0-32, dorsal view. (C) Body, anterior, U0-32, ventral view. (D) Body, median, U26-55, dorsal view. (E) Body, median, U28-60, dorsal view. (F) Body, posterior, U54-84, dorsal view. (G) Body, posterior, U54-86, ventral view. (H) Caudal furca branches, U67-100, ventral view. (I) Body, posterior, U54-82, focused on adhesive glandular tissue. Abbreviations: agt, adhesive glandular tissue; lcf, locomotory ciliary field; vcb, ventral ciliary bands. Sørensen et al. (2025).

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Echinoderes semprucciae: A new species of Kinorhynch from a macerating Neptune Grass environment in the eastern Mediterranean.

Kinorhynchs are tiny (generally less than 1 mm) worm like Animals largely found in marine sediments, for which reason they are sometimes known as 'Mud Dragons'. They appear to be ubiquitous members of the interstitial meiofauna (Animals that live between sediment grains) in shallow marine habitats, but have been studied in relatively few locations. However, not all Kinorhynchs are sediment-dwellers, with members of the group having been found living on a wide range of Algae, marine Plants, and Animals.

In a paper published in The Eutopean Zoological Journal on 3 February 2024, Adele Cocozza di Montanara of the Department of Science and Technology at the Parthenope University of Naples, Alberto González-Casurrubios of the Department of Biodiversity, Ecology and Evolution at the Complutense University of Madrid, and Diego Cepeda of the Centre for Research on Biodiversity and Global Change at the Autonomous University of Madrid, and the Department of Life Sciences at Alcalá University, describe a new species of Kinorhynch from a macerating Neptune Grass environment off the coast of Ischia Island in the western Mediterranean Sea.

Neptune Grass, Posidonia oceanica, is a form of Seagrass endemic to the Mediterranean, where it forms vast meadows in the photic parts of the sea (i.e. those areas where sufficient sunlight penetrates to allow photosynthesis). Seagrasses are important habitat-forming organisms, and a wide range of Animals, including Kinorhynchs are adapted to life in these meadows. However, as well as meadows, Seagrasses also form areas called 'macerating Seagrass detrital bottoms', where large volumes of decomposing leaves and rhizomes accumulate, typically below the photic zone, forming an important marine carbon sink. Whilst these environments have been known since the 1950s, very little attention has been paid to them or the fauna which live there, to which end Cocozza di Montanara et al. have begun a project to study the fauna of the macerating Seagrass detrital bottom environment of the Regno di Nettuno Marine Protected Area, along the coast of Ischia Island off the western coast of Italy.

Study area at 65–80 m depth along the northwestern area of Ischia Island (western Mediterranean Sea). Cocozza di Montanara et al. (2025).

The new species is placed in the genus Echinoderes, and given the specific name semprucciae, in honour of Federica Semprucci of the University of Urbino Carlo Bo, for acting as co-supervisor for Adele Cocozza di Montanara's PhD and supporting and guiding her research on meiofauna. The species is described from two specimens, both collected on 19 June 2020 near Ischia Island, an adult female, collected at a depth of 80 m, and an adult male collected at a depth of 70 m.

Line art illustrations of Echinoderes semprucciae. (a) Ventral view of a female based on holotype (NHMD-1177723). (b) Dorsal view of a female based on holotype (NHMD-1177723). (c) Dorsal view of segments 10–11 of a male based on paratype (NHMD-1177722). Abbreviations: ac, acicular spine; gcoI, type 1 glandular cell outlet; LA, lateral accessory; LD, laterodorsal; ltas, lateral terminal accessory spine; lts, lateral terminal spine; LV, lateroventral; MD, middorsal; ML. midlateral; ne, nephridiopore; pa. papilla; PD. paradorsal; ps, penile spines; SD, subdorsal; ss, sensory spot; t, tube; Vl, ventrolateral; VM, ventromedial; number in abbreviations indicates the corresponding segment. Cocozza di Montanara et al. (2025).

The two known specimens of Echinoderes semprucciae are 202 μm (female) and 193 μm (male) in length, with a retractable mouth cone surrounded by oral styles. This retractable mouth is mounted on an organ called the introvert, which has six concentric rings of scalids and 10 longitudinal sectors defined by the arrangement of primary spinoscalids. Behind the head is a neck section, then a trunk comprising eleven segments, with spines on segments four, six, eight, nine, and eleven; the two spines on segment eleven being elongated to form a pair of tail-like structures.

Light micrographs of female holotype (NHMD-1177723) (a)-(d), (g) and male paratype (NHMD-1177722) (e), (f) of Echinoderes semprucciae. (a) Ventral overview. (b) Head, dorsal view. (c) Head, ventral view. (d) Ventral view of segments 5–6. (e) Lateral view of segments 5–8. (f) Detail of penile spines. (g) Ventral view of segment 11. ltas, lateral terminal accessory spine; lts, lateral terminal spine; lvs, lateroventral spine; lvt, lateroventral tube; pa, papillae; ps, penile spines; te, tergal extension, number after abbreviation indicates the corresponding segment, sensory spots are marked with dashed circles and type 1 glandular cell outlets with closed circle. Cocozza di Montanara et al. (2025).

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