Contribution of soft-bodied meiofaunal taxa to Italian marine biodiversity

Abstract

Meiofauna includes an astonishing diversity of organisms, whose census is far from being complete. Most classic ecological studies have focused on hard-bodied Ecdysozoan taxa (notably Copepoda and Nematoda), whose cuticle allows determination at species-level after fixation, rather than soft-bodied, Spiralian taxa, which most often lose any diagnostic feature in fixed samples. Yet, metabarcoding studies have recently revealed a species-richness of softbodied taxa comparable, and in cases superior, to that of Copepoda and Nematoda together. However, given objective difficulties inherent to their study, which necessarily has to be performed on living individuals, and their limited utilisation for ecological and applicative research, taxonomic expertise on soft-bodied organisms has declined over the years, and diversity of these phyla in most areas of the world is presently completely unknown. Here we present an expert-based survey of current knowledge on the composition and distribution of soft-bodied meiofaunal taxa in Italy, with special references to the predominantly or exclusively meiobenthic phyla Gastrotricha, Gnathostomulida, Platyhelminthes, Rotifera, Xenacoelomorpha, and macrofaunal taxa with conspicuous meiofaunal representatives (Annelida, Mollusca and Nemertea). A total of 638 described species have been reported from Italian coasts; furthermore, the existence of a large number of undescribed species is mentioned. Knowledge of Annelida, Gastrotricha, and Rotifera appears particularly detailed, placing Italy among the best-known country worldwide. In contrast, knowledge of Platyhelminthes and Xenacoelomorpha appears patchy, and limited to few areas. Sampling effort has been uneven, with most species recorded from the Tyrrhenian Sea, while large sections of the Adriatic and Ionian seas have been poorly explored. Results highlight the role that Marine Biological Stations, notably the Zoological Station "Anton Dohrn" in Naples, have had in promoting the study of soft-bodied taxa in Italy.

First trait-based characterization of Arctic ice meiofauna taxa

“…Flexible and semi-flexible organisms possess an advantage in the narrow and twisting brine channel network. These traits are also common in organisms living in interstitial sediment habitats (Curini-Galletti et al 2020) and may be a reason why benthic organisms like Nematoda and Acoela thrive in the ice (Krembs et al 2000).…”

“…Most Nematoda, not typical inhabitants of the pelagic realm, are predictably either sympagic or sympagic-benthic (Moens et al 2013). The fact that all Acoela are only known from the ice may be influenced by their unknown taxonomic status (Janssen and Gradinger 1999;Friedrich and Hendelberg 2001) and the fact that Acoela in general -along with other soft-bodied meiofauna -often do not preserve well with common preservatives and frequently remain unidentified (Curini-Galletti et al 2020). Generally, however, Acoela and Platyhelminthes (again we note one of the ice Acoela may be a platyhelminth) are most prominent at the seafloor (Achatz et al 2013).…”

Antarctic Special Protected Area 161 as a Reference to Assess the Effects of Anthropogenic and Natural Impacts on Meiobenthic Assemblages

“…However, ciliates, as part of the complex detritus-bacteria-meiofauna system, might play an important role in the marine ecosystem functioning [4,11,83]. In addition, numerous worldwide investigations have recently documented the presence of a very small meiobenthic species, belonging to the Chaetognata genus Spadella, suggesting that meiobenthos may number more specialized forms than expected [84][85][86][87][88].…”

Biases and distribution patterns in hard‐bodied microscopic animals (Acari: Halacaridae): Size does not matter, but generalism and sampling effort do

“…Indeed, sampling bias, which hassles all biodiversity inventories (Barbosa et al, 2010; Boakes et al, 2010), becomes hefty for meiofauna due to the problems inherent to the study of minute animals (Fontaneto et al, 2012). Some microscopic animals, though, are more popular than others, as most conventional ecological studies on meiofauna have focused on hard‐bodied taxa rather than on groups with flimsy, soft bodies (Curini‐Galletti et al, 2020). This has been well documented in the literature and attributed to the fact that soft‐bodied taxa (e.g.…”