Stercomata (or stercomes) are extracellular pellets of waste material produced by some groups of

foraminifera 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 (cell biology), ectoplasm for catching food and ot ...

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xenophyophorea Xenophyophorea is a clade of foraminiferans. Members of this class are multinucleate unicellular organisms found on the ocean floor throughout the world's oceans, at depths of . They are a kind of foraminiferan that extract minerals from their s ...

ns and

komokiacea The Komokiacea are a small group of amoeboid protozoa, considered to be foraminifera, though there have been suggestions that they are a separate group, closely related to foraminifera. Komokiacea are rather large organisms, often exceeding 300 m ...

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Gromia ''Gromia'' is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. ''Gromia'' are ameboid, producing filose pseudopodia that extend out from the ce ...

'', and

testate amoebae Testate amoebae (formerly thecamoebians, Testacea or Thecamoeba) are a polyphyletic group of unicellular amoeboid protists, which differ from naked amoebae in the presence of a test that partially encloses the cell, with an aperture from which the ...

. The pellets are ovoid (egg-shaped), brownish in color, and on average measure from 10-20 µm in length. Stercomata are composed of small mineral grains and undigested waste products held together by strands of

glycosaminoglycans Glycosaminoglycans (GAGs) or mucopolysaccharides are long, linear polysaccharides consisting of repeating disaccharide units (i.e. two-sugar units). The repeating two-sugar unit consists of a uronic sugar and an amino sugar, except in the case ...

. The term “sterkome” was first used Schaudinn in 1899 to describe the balls of undigested food remains produced by the testate amoeba ''Trichosphaerium sieboldi'', the foraminiferan ''Saccammina sphaerica'', and the gromiid ''Gromia dujardinii''. Schaudinn conducted feeding experiments on live individuals of ''Trichosphaerium sieboldi'' kept in culture dishes to confirm that stercomata were accumulations of waste material produced as a byproduct of feeding.

Taxonomic distribution

Foraminifera

Stercomata are produced by members of several different subclades of Foraminifera that possess organic-walled or agglutinated tests, including: single-chambered taxa with spherical organic-walled tests (e.g., ''Bathyallogromia'' and other undescribed species), single-chambered taxa with sac-like agglutinated tests (e.g., ''Saccammina'' and ''Leptammina''), single-chambered taxa with tubular agglutinated tests (e.g., ''Bathysiphon''), multi-chambered taxa with organic-walled tests (e.g., ''Nodellum'' and ''Resigella''), taxa with complex agglutinated tests composed of delicate branching tubes (Komokioidea), and deep-sea taxa with large, complex tests agglutinated tests (Xenophyophorea).

Saccamminid foraminiferans

Komokiaceans

Xenophyophores

In xenophyophores, the stercomata are contained within an organic tubes called stercomare.

Multichambered, organic-walled foraminiferans

Gromiida

Gromiida is a subclade of

Endomyxa Endomyxa is a subphylum of Rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are a ...

, a clade that branches within the more inclusive group

Rhizaria The Rhizaria are an ill-defined but species-rich supergroup of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus Paulinella in the phylum Cercozoa, they are all non-photosynthethic, but many foramini ...

, a clade that encompasses a diverse array free-living and parasitic single-celled eukaryotes that possess branching or anastomosing pseudopodia and complex life cycles. In ''

'', the only described genus of Gromiida, stercomata are spherical to ovoid in shape and range in color from brown to gray to orange. Individual stercomes range in size from <5 µm (''G. psammophila'') to 15-30 µm (''G. saoirsei''). Stercomata consist of the undigested remains of ingested food and may include mineral grains, sponge spicules and diatoms, which are held together by

. Unlike the stercomata in foraminiferans, the stercomata in gromiids are retained in the cytoplasm and not stored outside of the cell body; however, after the release of flagellated gametes during sexual reproduction, the stercomata remain in the interior of the test.

Testate Amoebae

References

Biology {{biology-stub