Marine Tardigrades Research Articles

Intertidal and shallow subtidal marine tardigrades from the British Virgin Islands with a description of a new Batillipes (Heterotardigrada: Batillipedidae)

This is the first survey of marine tardigrades from the British Virgin Islands, though two species were previously reported from St. Croix, U.S. Virgin Islands. In June 2016, we collected subtidal and intertidal sand samples from various locations throughout the British Virgin Islands. We found 602 tardigrades in 18 of 21 samples, and these included 12 taxa, one of which, Batillipes wyedeleinorum sp. nov., is new to science and described here. We compared abundance and species diversity in intertidal and subtidal samples and found significantly greater abundance in intertidal habitats but no significant difference in the number of observed species between the two habitats. We calculated Chao 1 species richness, which indicated higher estimated richness in intertidal habitats and 15 ± 3.7 species (x̅ ± SD) in both habitats combined. Non-metric Multidimensional Scaling revealed differences in species composition between the two habitats with some species showing clear preferences for one or the other.

A new marine tardigrade species (Heterotardigrada: Batillipedidae) from the southeast coast of India

A new marine tardigrade species, Batillipes chandrayaani sp. nov. is described from the sandy mid littoral region of the southeast coast of India. This novel species can be distinguished from all its congeners by the presence of a dorsal indentation in the anterior cephalic region, shape of primary clavae, presence of secondary clavae, segmented dorsal body due to the presence of transverse cuticle folds, shape of leg IV sensory organ with the presence of two van der Land’s organs, long hook shaped lateral body projections on the caudal segment and the presence of a semi-circular cuticular projection on the coxal region of leg II and leg III.

Evolution of egg deposition strategies, exaptations of exuvia, and thanatochresis in tardigrades

AbstractThe cuticle is the tardigrade exoskeleton that, limiting animal growth, needs to be periodically shed. New cuticles must be formed (within the old ones) before getting rid of the obsolete exoskeletons at the end of moulting process. After ecdysis (the release of the old cuticle), the exuvia has different destinies according to tardigrade evolutionary lines. In the marine tardigrades (Heterotardigrada), the exuvia is lost and useless, while in the other taxa, it acquires interesting uses to be considered exaptations, since the cuticle previously shaped by natural selection for a function (i.e. as exoskeleton) is coopted for new adaptive scopes. These are related to egg deposition, parental care, mating, and diapause. Egg deposition within the exuvia is one of the three different egg deposition strategies developed by tardigrades: smooth eggs can be laid freely or within the exuvia, while ornamented eggs are laid freely. A new scenario for the evolution of such egg deposition strategies is characterised by five schematic steps: smooth eggs laid freely (ancestral state), synchronization of egg maturation with moulting (developed in tardigrade ancestor in sea), use of the exuvia for oviposition (for enhanced mechanical and physiological egg protection), acquisition of egg ornamentation, and ornamented eggs laid freely (related to a risk-spreading strategy). An interesting thanatochresis case related to the release of free eggs in crustaceans exuviae, convergently developed in two distant taxa of eu- and heterotardigrades, is presented and discussed.

Novel distribution records of marine Tardigrada from abyssal sediments of the Northwest Atlantic Ocean

Novel distribution records of marine Tardigrada from abyssal sediments of the Northwest Atlantic Ocean

A new species of Batillipes (Arthrotardigrada: Batillipedidae) from the mid littoral zone of the southeast coast of India.

Studies of marine tardigrades from Indian waters is very limited and relatively obscure. A new species of marine tardigrade is described from the southeast coast of India as part of an effort to better understand the marine tardigrade biodiversity of the Indian subcontinent. Batillipes kalami sp. nov. described from the sandy sediments of the mid littoral zone can be differentiated from all its congeners by the presence of unconstricted primary clavae, two pairs of lateral body projections between leg II and leg III, long and blunt ended lateral body projections between leg III and leg IV, shape of leg IV sensory organs and the presence of dorsal indentations in its head.

Preliminary studies of the tardigrada communities from a polymetallic nodule area of the deep South China Sea

Knowledge about marine tardigrades from the South China Sea is very scarce, with only four species from shallow waters recorded to date. The present study investigated the structure and diversity of tardigrade communities from the deep sea (1517-1725 m) at 8 stations in a polymetallic nodule area of the northern South China Sea. A total of 151 arthrotardigrades were collected belonging to 11 genera (Angursa, Batillipes, Coronarctus, Euclavarctus, Exoclavarctus, Halechiniscus, Moebjergarctus, Raiarctus, Rhomboarctus, Tanarctus and Tholoarctus), representing 17 species. Two Angursa species (Angursa sp. 4 and Angursa sp. 3) were the most abundant (25.2% and 14.6%, respectively), followed by Moebjergarctus sp. (13.9%). Specimens were mostly (90.7%) distributed in the upper layer of the sandy-mud sediment (0-1 cm). The SIMPROF test showed that the composition of tardigrade communities at all stations was not significantly different. At different stations, the number of species, Shannon-Wiener diversity index and Pielou’s evenness index ranged from 4 to 10, 1.94 to 2.87, and 0.75 to 1.00, respectively. The average taxonomic distinctness (Δ+) ranged from 72.50 to 90.00, and the variation in taxonomic distinctness (Λ+) ranged from 316.67 to 1181.25. This study provides some basic information about the biodiversity of the marine tardigrade community in the South China Sea.

New Records of Marine Tardigrades (Arthotardigrada) from the Iberian Peninsula: Biogeographical Implications

Biogeography patterns of marine tardigrades are poorly studied. Many species of marine tardigrades are considered endemic, but this high number may be an artifact resulting from skewed knowledge about marine tardigrade diversity in different regions of the world. On the other hand, some species of marine tardigrades are considered cosmopolitan. Most of these were described many years ago. Unfortunately, these early descriptions are very incomplete and omit many characteristics with diagnostically relevant value, thus, resulting in many types of these records of these species worldwide. The objective of this study is to report, for the first time, the presence of three species of marine tardigrades in the Atlantic shores of the Iberian Peninsula. These three species were previously described from other regions of the world and the biogeographic consequences of their presence on the study area are discussed. These records provide valuable insights about the biogeography of marine tardigrades in this region.

First record of a deep-sea tardigrade from the South China Sea, Halechiniscus janus sp. nov. (Arthrotardigrada: Halechiniscidae).

The knowledge of marine tardigrades in the South China Sea (Western Pacific Ocean) is very scarce, with only four species from shallow waters recorded until now. The first deep-sea (15301624 m bsl) tardigrade species from this sea, Halechiniscus janus sp. nov. (Arthrotardigrada: Halechiniscidae), is described here. Specimens of the new species have four wrinkled digits without peduncles on each leg, terminated by simple crescent-shaped claws, and primary clavae clearly shorter than cirri A, both inserted on a common cirrophore, as typical for the genus Halechiniscus Richters, 1908. The new species differs from all other Halechiniscus species by its cylindrical body and conical head; by the presence of semispherical secondary clavae, and by sensory organs on legs IV consisting of a short cirrophore followed by a short papilla terminated in a peculiar short bipartite tip. The discovery of this new bathyal species, with its peculiar morphological traits, brings new insights not only to the biogeography and ecology of tardigrades, but also to the understanding of the only partially resolved systematics of the diversified family Halechiniscidae.

A trans-isthmus survey of marine tardigrades from Costa Rica (Central America) with descriptions of seven new species

ABSTRACT The Central American Isthmus has had profound effects on the evolution and distribution of larger marine organisms, but the impacts on meiobenthic animals have received little attention. Tardigrades are microscopic metazoan lobopodians that are ubiquitous in benthic communities worldwide, but little is known about marine tardigrades in Central America. Only two marine tardigrades have been identified to species level in all of Central America, and these came from a single sample of barnacles from El Salvador collected in 1953. Additionally, multiple haplotypes of Echiniscoides were reported from Costa Rica and Panama, but species names were not assigned. Here we report an extensive survey of both intertidal and subtidal marine tardigrades from both the Caribbean and Pacific coasts of Costa Rica. We found 701 individuals in 65 samples. There was a total of 19 taxa, including seven species with a sufficient quality and quantity of specimens to describe here as new to science. The new species are Archechiniscus murilloi sp. nov., Batillipes homocercus sp. nov., Batillipes ichthyocercus sp. nov., Echiniscoides costaricensis sp. nov., Echiniscoides ritavargasae sp. nov., Styraconyx vargasi sp. nov. and Tanarctus breedyae sp. nov. Ten taxa were found only in the Caribbean, six were found only in the Pacific, and three were found on both coasts. We discuss the three species with trans-isthmus distributions and note two additional candidate geminate species pairs that warrant further investigation.

The Genus Milnesium Doyère, 1840 in Mexico with Description of a New Species

Knowledge of the diversity and distribution of tardigrades in Mexico is limited. Up to now 79 taxa of limno-terrestrial, freshwater and marine tardigrades were reported (including three species of Milnesium) from the country. We examined a total of 73 specimens of the genus Milnesium collected from mosses and lichens in northeastern Mexico. The analysed specimens represent four species, of which one was previously unknown, and is described in this paper. Milnesium fridaesp. nov. has eyes, claw configuration (CC) [3–3] - [3–3], a wide and short buccal tube (standard width on average 64% of its length), and cuticle with very small pseudopores visible under high magnifications. It differs from other Milnesium species by various morphometric characteristics specified in the paper. Moreover, the ontogenetic variability of CC in new species was followed, observing that there is no variability in this character. In addition, distribution of the Milnesium species in Mexico is also discussed.

Marine tardigrades from Lützow-Holm Bay, East Antarctica with the description of a new species

Marine tardigrades in the Antarctic and sub-Antarctic regions are poorly understood. During the 59th Japan Antarctic Research Expedition, a sediment sample was collected from Lutzow-Holm Bay, East Antarctica. The sediment sample yielded three species of marine tardigrades belonging to the family Styraconyxidae Kristensen & Renaud-Mornant, 1983: Angursa antarctica Villora-Moreno, 1998, Styraconyx cf. qivitoq Kristensen & Higgins, 1984, and S. takeshii sp. nov. The new species resembles S. nanoqsunguak Kristensen & Higgins, 1984 by the overall morphology, but the new species has thick seminal receptacle ducts that do not terminate in typical, swelled vesicles, in contrast to S. nanoqsunguak’s narrow seminal receptacle ducts that terminate in small vesicles. The presence of the undivided mouth papilla and the larger body further differentiates the new species from S. nanoqsunguak. We also report a young adult female with a gonopore, but lacking seminal receptacles in the new species. As well as morphological information, we provided the sequences of the new species’ nuclear 28S rRNA and mitochondrial cytochrome c oxidase subunit I fragments. Using the former molecular data, phylogenetic analyses of Styraconyxidae were conducted and polyphyly of Styraconyx was suggested. The biogeography of marine tardigrades in the Antarctic and sub-Antarctic regions are also discussed.

Final Note of Special Issue “Tardigrades Taxonomy, Biology and Ecology”

Tardigrada (water bears) are microscopic invertebrates inhabiting aquatic (freshwater and marine) and terrestrial habitats. They are thriving in almost all Earth ecosystems from deepest oceans to highest mountains, from tropics to polar regions. Water bears are probably most famous for their cryptobiotic abilities, which allow them to survive a broad spectrum of extreme environmental conditions. The Special Issue on tardigrades was launched to popularize research on these fascinating microinvertebrates. The published papers were focused on (a) marine and terrestrial tardigrades diversity, (b) interpopulation variability of Antarctic eutardigrade Paramacrobiotus fairbanksi, (c) encystment in freshwater eutardigrade Thulinius ruffoi and (d) use of a metabarcoding approach to community structures studies in microenvironments.

Moebjergarctus clarionclippertonensis, a new abyssal tardigrade (Arthrotardigrada, Halechiniscidae, Euclavarctinae) from the Clarion-Clipperton Fracture Zone, North-East Pacific.

A new marine tardigrade, Moebjergarctus clarionclippertonensis sp. nov., is described based on specimens collected from a manganese nodule area in the Clarion-Clipperton Fracture Zone of the abyssal North-eastern Pacific. The new species is a member of the bathyal/abyssal subfamily Euclavarctinae Renaud-Mornant, 1983. Within the Euclavarctinae, the genus Moebjergarctus Bussau, 1992, with only one described species, M. manganis Bussau, 1992, is characterised by simple claws, club-shaped and anteriorly bent primary clavae, well-developed spherical secondary clavae and cephalic cirri separated into three parts: short cirrophore, long and annulated scapus, and a short flagellum. Moebjergarctus clarionclippertonensis sp. nov. can be distinguished from M. manganis by the morphology of cephalic cirri which have scapi annulated only in the proximal part and by the presence of a caudodorsal bulge covered by a crescent-shaped cuticular thickening.

A new marine tardigrade genus and species (Arthrotardigrada, Styraconyxidae) with unique pockets on the legs

A marine heterotardigrade Cyaegharctus kitamuraigen. et sp. nov. (Arthrotardigrada, Styraconyxidae) is described from Daidokutsu, a submarine cave off Iejima island, Okinawa Islands, Ryukyu Archipelago, Japan. It is easily distinguished from all other styraconyxids by its pocket organs (putative sensory structures) on all legs in addition to the usual leg sensory organs. Its combination of other character states, such as the dorso-ventrally flattened body, ovoid primary clavae, conical secondary clavae, large terminal anus, internal digits with proximal pads and peduncles, external digits with developed peduncles and all digits with three-pointed claws in adult female, supports the erection of a new genus and species.

Marine Tardigrada from the Mexican Caribbean with the description of Styraconyx robertoi sp. nov. (Arthrotardigrada: Styraconyxidae).

Marine tardigrades were sampled at three sites on Mexico's Caribbean coast. Eleven taxa were collected, one of which is described as a new species. Styraconyx robertoi sp. nov. is characterized by: asymmetric primary clavae; dorsal cuticle with a grid-like sculpture; claws with reduced accessory hooks; females with peduncles on only two digits (the external) of legs I-IV; males with peduncles only on the external digits of legs I-III and peduncles on all four digits of leg IV. Styraconyx robertoi sp. nov. is most similar toS.craticuliformis Chang Rho, 1998 and S. kristenseni Renaud-Mornant, 1981 by having asymmetric primary clavae but differs from S. craticuliformis mainly by the number of peduncles and from S. kristenseni mainly by the presence of a grid-like dorsal sculpture. Additionally, a comparison of material collected from the same region, but reported previously only as genus level records, was carried out in order to produce a refined list of the known Mexican marine tardigrade species.

The Deep-Sea Genus Coronarctus (Tardigrada, Arthrotardigrada) in Brazil, South-Western Atlantic Ocean, with the Description of Three New Species

Three new marine tardigrade species from the deep-sea genus Coronarctus are described from the South-Western Atlantic Ocean: Coronarctus dissimilis sp. nov., C. neptunus sp. nov., and C. yurupari sp. nov. These, and C. laubieri Renaud-Mornant, 1987, are the first records of deep-sea tardigrades from this marine region. Specimens of those species were collected from two localities of the Brazilian continental slope (Potiguar and Campos basins) at depths comprised between 150 and 3000 m. Specimens of the three new species have short cephalic appendages and heteromorphic claws, belonging to the, here designated, C. tenellus group of species. Each of the new species can be distinguished from all the other species of the group by their peculiar-shaped secondary clavae and claws. The most relevant morphological characters used for the taxonomy of the genus: shape of cephalic cirri, shape of secondary-clavae, size and number of accessory spines on claws, and shape of seminal receptacles, are discussed and an identification key to all ten known Coronarctus species is provided.

Do marine sponges host epizoic tardigrades?

Just over 200 species of marine tardigrades have been described, and most of these have been collected in sand and other sediments. However, several species are known to associate with other invertebrates such as barnacles, bryozoans, and holothurians. It is possible that many epizoic tardigrade species remain to be discovered, since surveys of tardigrades on other potential animal hosts are very rare. Sponges, with extensive cavities, constant water flow, and protective secondary compounds, are known to harbour a highly diverse epizoic community, but there are no published studies indicating that marine tardigrades are among this community, and there is only one published record of tardigrades from freshwater sponges. We collected 30 samples of marine sponges, consisting of 12 species, from the central Bahamas. We processed these for tardigrades and other meiofauna using the freshwater shock technique. One unusual non-tardigrade in our samples was Loxosomella sp., an entoproct which is a known commensal on sponges. Here we also provide the first record of marine tardigrades associated with marine sponges. However, we found only one species, Archechiniscus bahamensis, which is the most common species occurring free-living in Bahamian subtidal sand. Therefore, we conclude that marine sponges, at least in the Bahamas, do host epizoic marine tardigrades, but they may not be a unique or important host for marine tardigrades.

First records of marine tardigrades of the genus Coronarctus (Tardigrada, Heterotardigrada, Arthrotardigrada) from Mexico

Deep-water sampling in the Perdido Fold Belt, Gulf of Mexico, Mexican Economic Exclusive Zone yielded five specimens of tardigrades belonging to the genus Coronarctus Renaud-Mornant, 1974. The specimens represent the first records of the genus for Mexico. Two two-clawed larvae and two four-clawed larvae of Coronarctus mexicus Romano, Gallo, D’Addabbo, Accogli, Baguley & Montagna, 2011 and a single four-clawed larval specimen of an undescribed Coronarctus species were identified. Taxonomic analysis of the specimens contributed to the knowledge of deep-sea and Mexican marine tardigrades, two data-poor areas of study.

Latitudinal gradients in body size in marine tardigrades

AbstractHomeotherms and many poikilotherms display a positive relationship between body size and latitude, but this has rarely been investigated in microscopic animals. We analysed all published records of marine Tardigrada to address whether microscopic marine invertebrates have similar ecogeographical patterns to macroscopic animals. The data were analysed using spatially explicit generalized least squares models and linear models. We looked for latitudinal patterns in body size and species richness, testing for sampling bias and phylogenetic constraints. No latitudinal pattern was detected for species richness, and sampling bias was the strongest correlate of species richness. A hump-shaped increase in median body size with latitude was found, and the effect remained significant for the Northern Hemisphere but not for the Southern. The most significant effect supporting the latitudinal gradient was on minimum body size, with smaller species disappearing at higher latitudes. Our results suggest that biogeographical signals were observed for body size, albeit difficult to detect in poorly studied groups because of swamping from biased sampling effort and from low sample size. We did not find a significant correlation with the latitudinal pattern of body size and ecologically relevant net primary productivity.

Batillipes pennaki Marcus, 1946 (Arthrotardigrada: Batillipedidae): deciphering a species complex.

Batillipes pennaki has been considered a common and a cosmopolitan marine tardigrade species. However, the original diagnosis of this species is very incomplete, and consequently there is a high probability of incorrect records. Therefore, a comparative analysis of quantitative and qualitative morphological characters among eight different populations from the Atlantic basin was done in this study to investigate if B. pennaki is a complex of similar species, each with a restricted distribution range. The result of discriminant analyses showed clear morphometric differences between populations that were arranged into three main groups, distinguishing Western Atlantic populations, Eastern Atlantic populations and a Mediterranean population. Furthermore, the result of analyses of morphological structures revealed peculiarities of some traits with taxonomic relevance, such as leg IV sensory organs and primary clavae, consistent with the clusters revealed by quantitative data, allowing us to distinguish three different pseudocryptic species and supporting the hypothesis that B. pennaki is a species complex.