''Rosella'' is a genus of glass sponges in the family

Rossellidae Rossellidae is a family of glass sponges belonging to the order Lyssacinosa. The family has a cosmopolitan distribution and is found at a large range of depths (, and likely deeper). Description The body is usually a cup-like structure. In sta ...

. It is found in the

Antarctic The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...

and

sub-Antarctic The sub-Antarctic zone is a region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region includes many islands ...

regions.

Description

Species are thick-walled saccular sponges. Calycocomes (six rayed

spicules Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

with secondary rays emanating from a solid calyx) are always present. They are often accompanied by spherical discohexactines (six rayed spicules with secondary rays ending as small discs), mesodiscohexasters (microscleres with primary rays that are rearranged by fusion to form eight compound primary rays situated at the corners of a cube. Secondary rays end as small discs) and microdiscohexasters (smaller forms of mesodiscohexasters). Dermalia (outer spicules of any size class) are usually pentactines, sometimes with stauractines (cross-like spicules with four perpendicular rays) and hexactines. Prostalia lateralia (large protruding spicules), when present, are monaxons (spicules with a single axis) and sometimes pentactines. The hypodermal pentactine spicules (spicules with five rays) may be differentiated into spicules with claw-like ends, serving as a means of attachment to the substrate the sponge is growing on. They commonly have paratropal and orthotropal tangential rays. The choanosomal skeleton is made of diactines (two rayed

spicule Spicules are any of various small needle-like anatomical structures occurring in organisms Spicule may also refer to: *Spicule (sponge), small skeletal elements of sea sponges *Spicule (nematode), reproductive structures found in male nematodes ( ...

with rays aligned on the same axis), and rarely hexactines (spicule with six perpendicular rays). Atralia (spicules associated with the atrial cavity) are mainly hexactines, rarely with pentactines or diactines.

Ecology

''Rossella'' species are abundant on the Antarctic shelf, where they may cover as much as half of the sea floor. As such, they play an important role in forming the benthic communities of this region. They form biogenic structures, increasing the structural complexity of the sea floor of this region. This more heterogeneous space can be utilised by other species. A wide variety of invertebrate species also live within the sponge structure, including

foraminiferans Foraminifera (; Latin for "hole bearers"; informally called "forams") are single-celled organisms, members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an ...

polychaetes Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are mad ...

amphipods Amphipoda is an order of malacostracan crustaceans with no carapace and generally with laterally compressed bodies. Amphipods range in size from and are mostly detritivores or scavengers. There are more than 9,900 amphipod species so far descri ...

isopods Isopoda is an order of crustaceans that includes woodlice and their relatives. Isopods live in the sea, in fresh water, or on land. All have rigid, segmented exoskeletons, two pairs of antennae, seven pairs of jointed limbs on the thorax, an ...

, tanaids,

copepods Copepods (; meaning "oar-feet") are a group of small crustaceans found in nearly every freshwater and saltwater habitat. Some species are planktonic (inhabiting sea waters), some are benthic (living on the ocean floor), a number of species have p ...

ostracods Ostracods, or ostracodes, are a class of the Crustacea (class Ostracoda), sometimes known as seed shrimp. Some 70,000 species (only 13,000 of which are extant) have been identified, grouped into several orders. They are small crustaceans, typical ...

acari Mites are small arachnids (eight-legged arthropods). Mites span two large orders of arachnids, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari, but genetic analysis does not show clear evid ...

pycnogonids Sea spiders are marine arthropods of the order Pantopoda ( ‘all feet’), belonging to the class Pycnogonida, hence they are also called pycnogonids (; named after ''Pycnogonum'', the type genus; with the suffix '). They are cosmopolitan, fou ...

gastropods The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. Ther ...

bivalves Bivalvia (), in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bival ...

, and

nematodes The nematodes ( or grc-gre, Νηματώδη; la, Nematoda) or roundworms constitute the phylum Nematoda (also called Nemathelminthes), with plant-parasitic nematodes also known as eelworms. They are a diverse animal phylum inhabiting a broa ...

. A sponge may host thousands of specimens and tens of species per 100 ml.

Species

The relationships between the species in this genus are not particularly well understood. The species composition has changed dramatically over the years, depending on which criteria are used. The external forms of this genus are highly variable, even within a single species. There is strong genetic evidence for a species flock in this genus, that is an accumulation of a large number of closely related species confined to a small area. These typically represent a rapid evolution of a dominant (and endemic) group in a region, resulting in many similar species. The current evidence suggests that this genus contains two clades corresponding to the well-defined species ''R. antarctica'', and the diverse assemblage of species that has been termed the ''R. racovitzae'' flock. More research is needed to understand how many species fall in this genus and how they are related. The following species are, however, currently (October 2021) recognised:

References

{{Taxonbar, from=Q4137505 Sponge genera Hexactinellida Hexactinellida genera