Bryozoans from the Early Cambrian Cambrian Xiannüdong Formation of Shaanxi Province, China.

Molecular clock studies have suggested that the Phylum Bryozoa, or Moss Animals, first appeared in the Early Cambrian, which is consistent with the appearance of nearly all other Animal phyla at this time. However, for a long time the earliest known fossil Bryozoans came from the Early Ordovician, at which point six of the eight known orders of Bryozoans appear abruptly. Several putative Cambrian Bryozoan fossils, such as Pywackia, Archaeotrypa, and Marcusodictyon, were described, but none of these was universally accepted as a Bryozoan. In 2021 a more plausible Brozoan, Protomelission gatehousei, was described from the Early Cambrian of Australia and South China. In this it was possible to identify several Brozoan traits, including monomorphic zooid capsules, modular construction, organic composition, and a simple linear budding growth geometry, leading to the conclusion that this was probably a stem-group Bryozoan.

Protomelission gatehousei from the Cambrian Wirrealpa Limestone, South Australia. (a)–(g) Holotype, SADME 10470. (a) Front side of the colony showing the seven series of zooids. Top box corners indicate the area shown in (f); bottom box corners show the broken-off part in (c). (b) The top broken part of (a). (c) The lower broken part of (a). (d) Oblique lateral view of the bilaminate colony. (e) Enlarged view of (d) showing the staggered budding pattern and the curved basal walls of the two back-to-back layers (arrows and tailed arrows) in the bifoliate colony. (f) Quincuncial arrangement of sub-hexagonal zooids with broken frontal walls. (g) Lateral view of uncovered zooids; note the minute spoon-shaped structure (arrow) at the proximal end of basal wall extending backwards underneath the distal part of the parent zooid. (h), (i) SADME 10470-2. (h) Lateral view of a broken colony, showing the largely broken frontal walls (tailed arrows) and basal walls of opposite layer (arrows). (i) Enlarged view of three adjacent zooids. Note the dome shape of the distal part of frontal wall (tailed arrows), and almost circular orifice of zooid. Abbreviations: B, basal wall; F, frontal wall. Zhang et al. (2021).

However, while Protomelission gatehousei shows enough Bryozoan-like features that most palaeontologists have accepted it to be at least a stem group Bryozoan, the specimens used to describe the species lacked the definitive Bryozoan soft-tissue anatomy and diagnostic skeletal microstructure which would be necessary for complete conformation, leaving the identity of these fossils open to challenge.

In a paper published in the journal Nature on 3 June 2026, Baopeng Song (宋宝鹏) and Zhifei Zhang (张志飞) of the Department of Geology at Northwest University, Luke Strotz, also of the Department of Geology at Northwest University and also of the Department of Earth Sciences at Utrecht University, Timothy Topper, again of the Department of Geology at Northwest University, and of the Department of Palaeobiology at the Swedish Museum of Natural History, Andrej Ernst of the Institut für Geologie at Universität Hamburg, Zhiliang Zhang of the Department of Geology at Northwest University, and the Institut für Geologie at Universität Hamburg, Mei Luo (罗梅), again of the Department of Geology at Northwest University, Lars Holmer, again of the Department of Geology at Northwest University, and of the Department of Earth Sciences at Uppsala University, Yue Liang (梁悦), Yazhou Hu (胡亚洲), Caibin Zhang (张彩彬), and Yanlong Chen (陈延龙), all of the Department of Geology at Northwest University, and Glenn Brock, once again of the Department of Geology at Northwest University, and of the School of Natural Sciences at Macquarie University, describe new specimens of Protomelission gatehousei from the Early Cambrian Xiannüdong Formation of southern Shaanxi Province, China, as well as a second new species of Bryozoan from the same formation.

Notably, these fossils preserve soft-tissue features in exceptional fidelity, including internal moulds of membranous sacs in the zooid chambers, which allow the unequivocal placement of these taxa within the Phylum Bryozoa. The presence of two separate Bryozoan taxa within these Early Cambrian deposits pushes the origin of the group still earlier, confirming that this group appeared during the Cambrian explosion.

Specimen of Protomelission gatehousei from the Xiannüdong Formation in which the membranous sacs are preserved (ELI DYCX 8-001). (a) Front side of the colony. The outlined area is magnified in (h). (b) Back side of the colony. The outlined area is magnified in (j). (c) Lateral view of the bifoliate colony. (d) Oblique lateral view of the bifoliate colony showing the hollow arched mesotheca (arrow). (e) Partial enlargement of (c) showing the staggered budding pattern. (f), (g) X-ray tomographic microscopy images showing the longitudinal section of the colony and the orifice of autozooids (arrowheads) (f, oblique lateral view; (g) lateral view). (h) Quincuncial arrangement of sub-hexagonal membranous sacs with elliptical orifice. Note the 10-μm gap present between adjacent membranous sacs, indicating the loss of skeletal walls during the taphonomic processes. The outlined area is the membranous sac magnified in (i). (i) Enlarged view of a membranous sac showing the orifice (asterisk), circular fibres (arrow) and longitudinal fibres (arrowhead). These features suggest muscle preservation in the membranous sac. (j) Enlarged view of a zooid. Note that the aperture is coated with secondary phosphate. (k) Enlarged view of a zooid. Note that the secondary phosphate coating of the aperture is partially stripped away. (l), (m) Enlarged view of the membranous sac showing the longitudinal fibres in (l) arrowhead, and circular fibres in (m), arrow. These features suggest muscle preservation in the membranous sac. Scale bars, 500 μm (a)–(d), 50 μm (e), (i)–(k), 200 μm (f), 150 μm (g), 100 μm (h) and 30 μm (l), (m). Song et al. (2026).

These new specimens show Protomelission gatehousei as forming upright colonies with two curved lamellar sheets of zooids back-to-back, with the largest colonies being 1-2 mm in width and about 3 mm high, tapering towards their tip. Each of these lamellae has six-to-eight rows of zooids, with budding originating from a planar mesotheca.

Soft-tissue preservation of Protomelission gatehousei. (a)–(e) ELI DYCX 8-005. (a) Front side of the colony, box corners indicate the area shown in (d). (b) The back side of the colony. (c) Lateral view of the bifoliate colony. (d), (e) Enlarged view of elongated hexagonal zooids. Note the longitudinally neatly arranged cylindrical structures on the both sides of the ridge-like orifice, which are possible secondary coatings of protective shields. (f) Protective shields developed in an extant Cheilostome Bryozoan, Valdemunitella sp. photographed by Dennis Gordon (Wellington). Song et al. (2026).

The new species described is named Dayingomelission hexaclitia, where 'Dayingomelission' means 'honeycomb from Daying' and 'hexaclitia' means 'six slopes' in reference to the sloped, hexagonal apertures of its autozooids. Colonies of Dayingomelission hexaclitia form a sheet-like grown covering the substrate. This sheet is interpreted as having spread by linear branching, with a single row of zooids diverging to form two new rows. Each autozooid is hexagonal and box-like, between 200 µm to 400 µm in diameter, and separated from its neighbours by a double-walled structure. All vertical walls show this double-walled structure, while the basal wall is planar, sometimes showing a slight curvature. 

Specimens of Dayingomelission hexaclitia from the Xiannüdong Formation showing the colony and cystids. (a), (b) ELI ZJBX 10-001 (holotype). (a) Oblique view of the front side of a unilaminate colony form clearly showing the regular hexagonal, compactly arranged, honeycomb-shaped cystids. The outlined area is shown in (b). (b) Hexagonal cystid with vertical wall and ring septa clearly evident (arrow). (c)–(e) ELI ZJBX 10-002. (c) Front side of a unilaminate colony form. The bottom outlined area shows the cystids magnified in (d); whereas the top outline shows the cystids magnified in (e). (d) Enlarged view of adjacent cystids. Note the hexagonal vertical wall (arrow) and the basal exterior wall of cystids (arrowheads). (e) Row bifurcation showing change in zooid width along rows. (f)–(i) ELI ZJBX 3-001. (f) Front side of a unilaminate colony form with styles indenting the zooidal chambers. (g) Oblique view showing hexagonal cystids with styles. (h) Oblique view of colony surface. Note that the styles arise in the endozone and extend through most of exozone. (i) Enlarged view of the vertical wall with planar spherulitic fabric. Scale bars, 500 μm (a), (c), 80 μm (b), 100 μm (d), 200 μm (e), 300 μm (f), (g), 100 μm (h) and 25 μm (i). Song et al. (2026).

Both species have hexagonal zooids with a box-shaped profile and a non-porous phosphatized or silicified skeleton. These are more-or-less uniform in size, and angled at 30-75° to the median lamina or basal exterior wall. They have preserved phosphatized internal structures interpreted as membranous sacks, the outer end of which comprises an elliptical orifice surrounded by an undulating fold. These are made up of densely packed circular and longitudinal fibres interpreted as annular and longitudinal muscles. Longitudinally aligned cylindrical structures, possibly representing protective shields or a broad operculum are present in some specimens. In others sac is attached to the cystid wall in the inner part of the zooid cell.

Membranous sacs preserved in situ in the autozooid cystids of Protomelission gatehousei and Dayingomelission hexaclitia and colonial growth reconstruction of Protomelission gatehousei . (a), (b) Protomelission gatehousei  ELI DYCX 8-016. (a) Front side of a bifoliate colony showing the eight series of zooids. The outlined area is magnified in (b). (b) Enlarged view of a zooid. Note that the membranous sac (arrow) is preserved in the cystid (arrowhead). (c)–(g) Dayingomelission hexaclitia ELI DYCX 8-004. (c) Front side of a unilaminate colony, with ten series of zooids, all with membranous sacs and cystids. The outlined area is magnified in (g). (d) Back side of the colony showing the membranous sacs of the zooids and the gap between the sacs. The outlined area is magnified in (e). (e) Enlarged view showing capsule￾like membranes and gaps. (f) X-ray tomographic microscopy image showing the longitudinal section of zooids with membranous sacs and cystids. (g) Enlarged view highlighting that the membranous sacs (arrow) are captured in the cystids (arrowhead), and the membranous sacs are in contact with the cystids 20 μm from the apertures (ligamentous attachment, asterisks). (h) Three-dimensional reconstruction of a Bryozoan zooid with protruding lophophore. (i) Longitudinal section of reconstructed Bryozoan zooid. Greyish white, cystid; translucent white, membranous sac and tentacles; pink, polypide excluding tentacles. (j) Reconstruction of Protomelission gatehousei , front surface view. Scale bars, 500 μm (a), (c), (d), 40 μm (b), 200 μm (e), (f) and 100 μm (g). Song et al. (2026).

Both Protomelission gatehousei and Dayingomelission hexaclitia show most of the key features associated with Palaeozoic Bryozoans, including  aspects of their colony morphology, their skeletal architecture,  the presence of soft-tissue structures such as membranous sacs, as well as annular and longitudinal musculature. Notably they contain a number of features associated with the Class Stenolaemata, including styles and  a free-walled colony organisation, which would make both species crown-group Brozoans. This makes it more likely that they were biomineralized in life, although it is impossible to determine the initial composition of their skeletons. Brozoans are known to have undergone a number of independent biomineralization events, with a molecular clock analysis indicating that the first of these was likely to have happened in the Early Cambrian. These results also imply that the common ancestor of the organic￾walled Gymnolaemata and the mineralized Stenolaemata probably originated in the early Cambrian (Terreneuvian) or even perhaps in the Ediacaran Period.

Phylogenetic relationships of Bryozoans. A 50% majority-rule consensus phylogenetic tree inferred using morphological characters and Bayesian analysis based on a matrix of 22 taxa and 50 characters. Node values are Bayesian posterior probability support values. Coloured areas indicate the three taxonomic classes that comprise the Bryozoa along with outgroups, with Protomelission and Dayingomelission belonging to Stenolaemata. Song et al. (2026).

The presence of two species of Bryozoan in the Early Cambrian Xiannüdong Formation of Shaanxi Province, as well as one of these species being present in the lower Wirrealpa Limestone of South Australia makes it likely that Bryazoans had already diversified and become widespread in the Early Cambrian. This lends support to the idea that the tentative mineralised Bryomorphs from the Lower Cambrian of Nevada recently described by Pruss et al. (2022) are also Bryozoans, and that Moss Animals were therefore widespread in shallow Cambrian seas, particularly Archaeocyath reef-associated carbonate platform settings. 

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Malformations in Trilobites from the Silurian and Devonian of Europe.

Malformations in fossils, such as pathologies caused by infections, scars left by recovered injuries, or teratologies caused by developmental problems, can tell us a lot about how extinct organisms grew and interacted with their environments, although when analysing these is clearly preferable to have access to non-malformed examples of the same species, or at least a close relative.

Trilobites were a diverse and abundant group of Arthropods which appeared early in the Cambrian, and survived until the End Permian Extinction. Their dorsal exoskeleton was heavily biomineralized, and was shed periodically to allow the animals to grow. This has lead to an extensive fossil record with Trilobites being extremely common in many Palaeozoic marine deposits. This abundant fossil record makes Trilobites an excellent candidate group for the study of malformations.

In a paper published in the journal Acta Palaeontologica Polonica on 22 April 2025, Russell Bicknell of the Division of Paleontology (Invertebrates) at the American Museum of Natural History, and the Palaeoscience Research Centre at the University of New England, Patrick Smith of the Palaeontology Department at the Australian Museum Research Institute, and the Department of Biological Sciences at Macquarie University, Lisa Amati of Paleontology at the New York State Museum, and Melanie Hopkins, also of the Division of Paleontology (Invertebrates) at the American Museum of Natural History, describe malformations in European Silurian and Devonian Trilobite specimens from the collections of the Natural History Museum in London and the New York State Museum.

The first specimen examined by Bicknell et al., NYSM 19739, is an isolated cephalon (head part) from a Harpetid Trilobite, Lioharpes venulosus, from the Early Devonian Koněprusy Limestone of the Czech Republic, in the collection of the New York State Museum. The cephalon is 26.2 mm long and 22.3 mm wide with a u-shaped indentation on its right marginal rim. This indentation is 5.6 mm long and extends 1.9 mm towards the midline. The marginal rim is covered in small circular pits, which around the indentation are irregular, ovate, and occasionally fused into larger pits.

Malformed Harpetid Trilobite Lioharpes venulosus, NYSM 19739 from the Koněprusy Limestone, Pragian, Lower Devonian, Koněprusy, Czech Republic. (A₁) complete cephalon; (A₂) close up showing U-shaped indentation (arrow). Specimen coated in ammonium chloride sublimate. Bicknell et al. (2025).

Bicknell et al. note that malformations to the cephalic fringes of Harpetid Trilobites have been recorded before, and that these are usealy attributed to injuries, an analysis with which they concur. However, they also observe that injuries can happen in a variety of ways, with fringe injuries having previously attributed to problems during moulting, failed predation attempts, or unknown causes. They suggest that a moulting injury is the most likely explanation for the injury to the Koněprusy specimen, with the delicate fringe likely torn during moulting, and the enlarged and fused pits being a result of fusion of the torn margin during healing. Various purposes have been suggested for the cephalic fringes of Harpetid Trilobites, including filtering for food, sensory roles, sediment ploughing, hydrostatic support, cephalic reinforcement, burrowing, and enhancing hydrodynamic efficiency. Whatever the purpose of this organ, an injury to it is likely to have been detrimental to the living Trilobite, and presumably repairing this injury would have been a priority during subsequent moults.

The second specimen, NHMUK PI In 65061, looked at is a Phacopid Trilobite, Calymene blumenbachii, from the Early Silurian Much Wenlock Limestone Formation of Shropshire, England, in the collection of the Natural History Museum. This specimen comprises a partial cephalon, thorax, and pygidium, with a total length of 92.9 mm and a width of 48.6 mm. The second thoracic axial ring (middle part of the second segment of the thorax) of this specimen is covered by a structure with closely spaced openings, which has an elevated round crater at its right extremity, with an opening 1.7 mm across.

Bicknell et al. interpret this as an encrusting Trepostome Bryozoan covering the 3rd thoracic tergite, with the larger opening being an ovate zoarium (specially modified zooid which produced eggs). The restriction of the encrustation to one tergite strongly suggests that this happened while the Trilobite was alive, and that the Bryozoan colony was therefore unable to overgrow the articulations between tergites.

Abnormal Calymenid Trilobites Calymene blumenbachii from the Much Wenlock Limestone Formation, Homerian, Wenlock, Silurian, England, UK. (A) NHMUK PI In 65061, (A₁) complete specimen; (A₂) close up showing the large bryozoan growth. (B) NHMUK PI In 19857 showing pygidial ribs that terminate early (white arrows) and are fused proximal to the medial lobe (black arrow).  Bicknell et al. (2025).

The next specimen examined, NHMUK PI In 19857, is another example of Calymene blumenbachii from the Much Wenlock Limestone. This specimen is a partial pygidium (tail part) 13.2 mm long and 18.2 mm wide. On the right side of this specimen the pygidial ribs are disrupted and irregular, with two ribs terminating 1.6 mm short of the pygidial margin, while another two fuse 1.2 mm from the pygidial axis.

Bicknel et al. observe that similar deformations to the pygidia have been observed in a wide range of other Trilobites, including Dalmanities pleuroptyx, Dechenella macrocephalus, Niobina sp., and Prionopeltis archiaci. They attribute these deformations to genetic or developmental issues, but suggest that the limited disruption to the pygidium they caused did not represent a major handicap.

Specimen NYSM 19740 is an Acastid Trilobite, Treveropyge sp., from the early Devonian Saint Céneré Formation of Mayenne in northwest France. this specimen is another isolated pygidium, s 11.6 mm long and 17.9 mm wide. It has a deformation to the axial lobe, which is asymmetric, with two of the axial rings malformed and curving to the right.

Malformed Acastid Trilobite Treveropyge sp., NYSM 19740 from the Saint Céneré Formation, Lochkovian, Lower Devonian, Mayenne, France. (A₁) Complete pygidium; (A₂) close up showing asymmetrical axial lobe and incomplete axial ring (arrows). Specimen coated in ammonium chloride sublimate. Bicknell et al. (2025).

Again, Bicknell et al. note that similar deformations have been seen in other Trilobites, such as Calliops marginatus, Dolicholeptus licticallis, and Sceptaspis lincolnensis. They suggest that these malformations are caused by genetic deformations, leading to incomplete development or non-functional somites.

The final specimen examined, NHMUK PI I 1108, is an external impression of a partial pygidium belonging to the Styginid Trilobite Scutellum (Scutellum) pardalios, from the Middle Devonin Barton Limestone Member of Devon, England. This impression is t is 59.5 mm long and 44.0 mm wide. On the right side of this impression (i.e. on the left side of the Trilobite) two ribs fuse into a single rib 29.1 mm from the pygidial axis. This single rib then terminates 4.8 mm from the pygidial margin.

Malformed Styginid Trilobite Scutellum (Scutellum) pardalios, NHMUK PI I 1108 from the Barton Limestone Member, Torquay Limestone Formation, Givetian, Middle Devonian, England, UK. (A₁) Pygidium preserved as external impression; (A₂) close up showing fused pygidial pleurae (arrows). Bicknell et al. (2025).

Bicknell et al. note that the surface of the pygidium was covered with ornamentation, with no visible break in this, which appears to  rule out the malformation having been formed by an unsuccessful predation attempt, or similar injury. Recovery from injury is the most commonly sited reason for malformations seen in Styginid Trilobites, followed by parasitic infections during early development, which seems equally unlikely. Bicknell et al. suggest instead that this deformity might be the result of a difficult moult, or possibly a genetic aberration. They do not believe this minor deformity would have significantly affected the living Trilobite.

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Aethozoon flavum: An in-faunal solitary Bryozoan found in deep sea sediments from Mayotte Island.

Bryozoans are a phylum of suspension feeding Lophotrochozoans found in all aquatic environments from lakes and rivers to the deep oceans. Bryozoans have a simple bodyplan, with a ciliated tentacle crown called a lophophore, which is used to collect food, and a u-shaped digestive tract, all of which is contained within a thick body wall, the cystid, which is often mineralized. The majority of Bryozoans are colonial with linked cystids, often forming elaborate structures, as well as connected digestive tracts, which enable them to share food. 

In a paper published in the journal Marine Biodiversity on 21 February 2024, Thomas Schwaha of the Department of Evolutionary Biology at the University of Vienna, Daniela Zeppilli of Biologie et Écologie des Ecosystèmes marins Profonds at the University of Brest, Alberto González‑Casarrubios of the Department of Biodiversity, Ecology and Evolution at the Complutense University of Madrid, and Diego Cepeda of the Department of Biology and Research Centre for Biodiversity and Global Change at the Autonomous University of Madrid, describe a new species of solitary Bryozoan from the sediments around Fani Maoré, a recently discovered submarine volcano off eastern Mayotte, a French overseas department in the Comoros Islands of the southern Indian Ocean.

Visible fauna was not present around Fani Maoré, but sediment samples recovered from the site were found to be rich in meiofauna (small benthic Invertebrates), with an unknown Aethozoid Bryozoan being the most abundant non-Nematode species. 

Aethozoids are a small and poorly understood group of non-mineralized, usually solitary, Bryozoans, with only five previously described species in four genera; Aethozoon pellucidum, from the northeast Atlantic, and recently the deep Kuril-Kamchatka Trench at depths of greater that 7000 m, Aethozooides uraniae from the deep-sea hypersaline anoxic Urania basin of the eastern Mediterranean, Franzenella limicola from the shallow Baltic, and Solella radicans and Solella monniotae from the deep North Atlantic.

The new species is placed in the genus Aethozoon and given the specific name flavum, the Latin word for yellow, in reference to the colour of the examined specimens. These are between 1787 μm and 2996 μm in length (average length 2281 μm), with a wider basal section 295 μm to 392 μm in length which contains the containing gonads, digestive tract, retractor muscles and funicular system. Two types of appendage are present at the base, kenozooidal cystid appendages, which appear tp be used for asexual reproduction; with examined specimens having a budding stages attached, and the related Aethozooides uraniae also produces buds from kenozooidal cystid appendages. Aethozoon flavum is also apparently capable of sexual reproduction, with all examined specimens being similtaneous hermaphrodites. Not all specimens of Aethozoon flavum had kenozooidal cystid appendages, while some had two. The other type of appendages are known as non-kenozooidal cystid appendages, and are less clear in purpose, but may be remnants of former attachment to a parent zooid.

Details of single zooids of Aethozoon flavum. (a) Holotype (MNHNIB-2017-723) showing long, non-kenozooidal cystid appendages; (b) Paratype (MNHN-IB-724) showing shorter cystid appendages including two shorter kenozooidal ones; (c) Paratype (MNHN-IB-725) showing zooid devoid of polypide and kenzooidal cystid appendage with distal bud; (d) Schematic drawing. Abbreviations: alt, anal tube; am, apertural muscles; b, bud; bdb, basal duplicature band; ca, cardia; cae, caecum; db, duplicature band; fg, foregut; fuc, funicular cords; kca, kenozooidal cystid appendage; int, intestine; nca, nonkenozooidal cystid appendage; ply, polypide; py, pylorus; o, orifice; rm, retractor muscles;  v, vestibulum; vw, vestibular wall. Schwaha et al. (2024).

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Freshwater Bryozoans from Cuba.

Bryozoans, or Moss Animals, are colonial lophophorates, which is to say animals that feed using a lophophore, a horseshoe-shaped structure bearing ciliated tentacles around the mouth, that form encrusting or weed-like colonies. The individual 'animals' are on average about 0.5 mm in length, and live inside a protective covering from which they extend a crown of cilia-covered tentacles called a lophophore. These are not true individuals though as they develop as buds on the colony and share nutrients; for this reason they are referred to as 'zooids'. Bryozoans are widespread globally, but are often overlooked because they are small and the colonies resemble plants. Members of the Class Phylactolaemata are found only in freshwater environments. Unlike other Bryozoans they do not have separate reproductive zooids not capable of feeding, rather all of the zooids in a colony are capable of feeding and reproducing, being simultaneous hermaphrodites. The colonies can also reproduce asexually, by producing special zooids called statoblasts, which are entirely enclosed within chitinous, bivalved shells, which either remain adhered to the colony or sink to the bottom (or in some cases float, in which case they are known as floatoblasts), remaining dormant through periods of adverse conditions, before opening and growing into new colonies.

In a paper published in the journal ZooKeys on 12 March 2020, Rafael Carballeira of the Departamento de Ciencias da Terra and the Centro de Investigacións Científicas Avanzadas at the Universidade da Coruña, Cosme Romay of the Grupo de Investigación en Bioloxía Evolutiva and Centro de Investigacións Científicas Avanzadas at the Universidade da Coruña, and Atocha Ramos of the Grupo de investigación Química Analítica Aplicada and Centro de Investigacións Científicas Avanzadas at the Universidade da Coruña, report the first known occurence of Freshwater Bryozoans in Cuba.

The freshwater Bryozoan fauna of the insular Caribbean has been mainly studied in the Leeward Islands (Aruba, Bonaire, Klein Bonaire and Curaçao), with three known species from the study of colonies and floatoblasts (statoblast buoyant with the annulus composed of gas chambers): Plumatella agilis, Plumatella casmiana, and Plumatella longigemmis. In addition, Plumatella repens has been reported in Puerto Rico. Unidentified Plumatella colonies and floatoblasts were reported on the islands of Cuba and Trinidad in the 1940s.

Knowledge of the distribution of Freshwater Bryozoans in the Caribbean is scarce despite the great biogeographical interest of this area. It constitutes a complex island system located between two large continental biogeographic regions: Nearctic and Neotropical. 

The La Niña Bonita Reservoir is located in the council of Bauta (Artemisa Province, Cuba). This water body is a freshwater wetland with an area of 12 000 m² and a maximum depth of 10 m. This reservoir dams the Jaimanitas River, with a basin of 9.2 km² dominated by limestone rocks, and is used mainly for irrigation and Fish farming. 

Ciénaga de Zapata Swamp is located in the Zapata Peninsula (Matanzas Province, Cuba). This wetland is the largest (2600 km²) and best conserved marsh swamp in the insular Caribbean, as well as the one with the greatest biodiversity. It has been declared a national conservation area by the government of Cuba and has been internationally recognized as a Ramsar Site. The shallow marshes show an important accumulation of organic matter and the lithology is dominated by limestones and dolomites with seeping underground waters (cenotes). The waters are bicarbonated-calcic with a great spatial heterogeneity depending on the input of groundwater seeps or marine intrusions. Also, there is a great salinisation of groundwater as a consequence of the exploitation of freshwater aquifers.

(A) Location map. (1) La Niña Bonita Reservoir and (2) Ciénaga de Zapata Swamp (B) Aerial photograph of the La Niña Bonita Reservoir (ESRI World Imagery, ArcGIS 10.0) C Aerial photograph of the Ciénaga de Zapata Swamp (ESRI World Imagery, ArcGIS 10.0). Carballeira et al. (2020).

In shallow wetland areas, samples of 2 cm³ of surface sediment were collected in the La Niña Bonita Reservoir and in the Ciénaga de Zapata Swamp. Sediment samples were screened through a 50 μm mesh; the larger fractions were examined under a stereoscopic microscope, and floatoblasts were collected with a pipette. Floatoblasts were treated with 2% sodium hydroxide for 1 minute under agitation at room temperature, then subjected to an ultrasonic bath for 15 seconds, and finally washed in deionised water. Floatoblasts for scanning electron microscopy were mounted on aluminium stubs, sputtered with platinum/palladium (15 nm) for 1 min using a Cressington Sputter Coater 208HR SEM, and studied with a JEOL Field Emission SEM JSM 7200F operated at 15 kV in the University of Coruña’s Research Support Service.

The morphometry of the examined floatoblasts showed that they belong to the species Plumatella repens. The shape of the floatoblast is broadly oval, both valves are equally convex in lateral view, and the floatoblast annulus is smooth, without tubercles. Floatoblast measurements were 318.5–350.2 μm in total length and 217.3–252.6 μm in total width. The fenestra of floatoblasts is rounded oval in dorsal view and oval in ventral view, covered with rounded tubercles and a relatively intense reticulation.

Plumatella repens, floatoblast from La Niña Bonita Reservoir and the Ciénaga de Zapata Swamp (Cuba), scanning electron micrographs: (A) View of dorsal valve. (B) View of ventral valve. (C) Suture between valves is a single cord with a row of low tubercles on either side. (D) Section of the annulus showing the connection between gas chambers, with circular pores with filiform extensions along the border. Scale bars: 50 µm (A), (B); 10 µm (C); 5 µm (D). Carballeira et al. (2020).

The length of the dorsal fenestra is larger than half the total length of the floatoblast. The annulus is smooth, without tubercles, occasionally with moderate nodulation and some large tubercles on the periphery, around the fenestrae especially on the ventral side. The measurements of the dorsal fenestra are 130.9–176.4 μm in length and 105.5–163.7 μm in width, while the ventral fenestra measures 187.5–247.3 μm in length and 141.2–188.7 μm in width. The suture between the valves is a single cord with tubercles on both sides. A section of the annulus shows circular pores with filiform projections connecting the gas chambers.

These new records of Plumatella repens are the first certain record of a Freshwater Bryozoan species in Cuba; only Plumatella sp. was reported on the island previously, without specifying a locality. This extends the distribution range of the species in the Caribbean area, with a single record in Puerto Rico so far. The presence of Plumatella repens on the island of Cuba is consistent with the existence of records of the species in the insular Caribbean and the cosmopolitan distribution of this species.

The ecology of Plumatella repens in Cuba and Puerto Rico is associated with permanent freshwater ecosystems and coastal wetlands with highly mineralized waters caused by the predominant limestone lithology, and influenced by seawater mixing within an oligohaline range (0.5–5‰). The species also experiences a wide range of nutrient concentrations (nitrates, phosphates) and high levels of dissolved organic matter.

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Ophiacantha scissionis: A fissiparous six-armed Brittle Star from from Jeju Island, Korea.und

Brittle Stars, Ophiuroidea, are five-limbed Echinoderms related to Starfish and having a similar body-plan. However while the five limbs of the Starfish are rigid extensions of the central disk, and movement is achieved by means of tube-feet on the underside of the animal, the limbs of Brittle Stars are fully articulated and used for locomotion. The fossil record of Brittle Stars goes back to at least the Early Ordovician, though these Palaeozoic Brittle Stars have not been extensively studied. Brittle Stars are the largest extant Echinoderm group, with over 2100 described species, 131 of which are placed in a single genus, Ophiacantha, though it is likely that some of these species should be separated out to form new genera.

In a paper published in the journal Zoological Studies on 24 May 2019, Taekjun Lee of the Department of Life Sciences at Korea University, Sabine Stöhr of the Department of Invertebrate Zoology at the Swedish Museum of Natural History, Yeon Jae Bae of the Department of Environmental Science and Ecological Engineering at Korea University, and Sook Shin of the Department of Chemistry Life Science at Sahmyook University, describe a new species of Ophiacantha from Jeju Island, Korea.

The new species is named Ophiacantha scissionis, where 'scissionis' derives from the Latin term scissio, meaning 'split'. The central disks of the observed specimens of this species are 1.3–2.2 mm in diameter, the arms generally less than 10 mm in length. Almost all of the specimens examined had six limbs, rather than five, with the majority having an incomplete central disk, three fully developed arms, and three arms at the same stage of regrowth. This is taken by Lee et al. to indicate that this species reproduces primarily by fission, splitting in two, rather than sexually.

Ophiacantha scissionis in (top) dorsal, and (bottom) ventral views. Lee et al. (2019).

Ophiacantha scissionis was found at depths of between 32.8 and 35.7 m in the waters around Munseom Island, a small island of the southern coast of Jeju Island, Korea. All specimens found were living on the colonial Bryozoan Bantariella bocki. This Bryozoan is currently found from the Bonin Islands of Japan (near Taiwan) in the south, north as far as Jeju Island, but is apparently spreading further north as the climate warms.

Ophiacantha scissionis, regenerating specimens with six arms, stereo-microscopic images. Arrow mark, split points for disk division. Lee et al. (2019).

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