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Sponge Organism Cell Connectome

A sponges organism only has about 20 cell types, which get together to perform various life processes. Therefore, in general these ~20 cell types can function as a unique cell connectome.

Overall, the sponges cell types are summarized in the following table (Ref: Musser et al., 2021):

Index Cell Type Name Code Cell Type Family Name from Weissenfels (1989) Description and explanation of naming
1 Archaeocytes Arc Archaeocytes and relatives Archaocyten Large mesenchymal cells with prominent nucleolus found throughout mesohyl. Principal stem cell in sponges and one of the most abundant cells in the mesohyl.
2 Sclerocytes Scl Archaeocytes and relatives Skleroblasten Elongate mesenchymal cells, often containing growing spicule.
3 Mesocytes l Mes1 Archaeocytes and relatives Medium-sized and irregularly-shaped mesenchymal cell with nucleolus that are relatively uncommon in mesohyl. Name refers to localization in mesohyl and relationship with two other novel mesenchymal cell types.
4 Mesocytes 2 Mes2 Archaeocytes and relatives Medium-sized egg-shaped mesenchymal cells with nucleolus, smaller than archaeocytes. May represent the collencytes referred to by Weissenfels (6). However, the term collencyte has also confusingly been used in other sponges to refer to a type of pinacocyte progenitor, and several authors recommend discontinuing its use (93). Name refers to localization in mesohyl and relationship with two other novel mesenchymal cell types.
5 Mesocytes 3 Mes3 Archaeocytes and relatives Very rare elongate or fusiform mesohyl cell. Distributional pattern within S. lacustris, beyond presence in the mesohyl, is unclear. Name refers to localization in mesohyl and relationship with two other novel mesenchymal cell types.
6 Incurrent Pinacocytes 1/2 incPin 1/2 Endymocytes Exopinacocyten, Prosendopinacocyten, Porocyten Epithelial cells forming external tent, outer layer of osculum, and lining subdermal lacunae and incurrent canals. Our single-cell analysis suggests exopinacocytes of the outer tent layer are genetically similar to prosendopinacocytes lining the vestibule and incurrent canals. In contrast, apendopinacocytes lining the excurrent canals and inner layer of the osculum are more distinct. Thus, the traditional term "endopinacocyte" that unites both proesndo- and apendo- pinacocytes appears to be inconsistent with our genetic findings in S. lacustris. Our name reflects the fact that these cells broadly coincide to the incurrent system in sponges.
7 Apendopinacocytes 1/2 apnPin1/2 Endymocytes Apendopinacocyten Epithelial cells lining excurrent channels and inner layer of osculum, sometimes ciliated. We observed ciliated cells in both the osculum as well as in excurrent channels near choanocyote apopyles.
8 Basopinacocytes basPin Endymocytes Exopinacocyten Epithelial cells forming layer adherent to substratum, which express spongin short-chain collagen and enwrap mature spicules, cementing them into the base of the sponge. Weissenfels (6) referred to both cells of the basal substratum and cells in the outer layer of the epithelial tent together as "exopinacocytes", which we find as genetically distinct. However, Weissenfels recognized that the cells along the basal substratum were responsible for producing spongin, similar to our findings and those of Nakayama (16). Whether basopinacocytes are synonymous with "spongocytes" described in other sponges to secrete spongin collagen and play a role in gemmule epithelial formation is unclear (93).
9 Sclerophorocytes Scp Endymocytes Begleitzellen Mesenchymal cells typically observed in contact with mature spicules, which function in spicule transport and skeletogenesis and described as "transport cells" in (16). Here, we propose a new Greek translation that honors previous names and recognizes their role in transporting spicules.
10 Lophocytes Lph Endymocytes Lophocyten Migratory cells with filopodia and elongate, asymmetric shape. Most prevalent near basopinacocytes and incurrent pinacocytes. Described across porifera as being important in collagen synthesis (93), consistent with our findings that they upregulate distinct collagens.
11 Metabaloyctes 1/2 Met1/2 Endymocytes Large, multipolar mesohyl cells lacking nucleolus. Relatively uncommon in mesohyl, although often found in proximity to baso- and incurrent pinacocytes. This cell type does not clearly correspond to any previously-defined morphological cell type in freshwater sponges, and its homology to mesenchymal cell types in other sponges is unclear. The name was chosen to reflect their apparent functional role as metabolic cells.
12 Choanoblasts 1/2 Chb1/2 Peptidocytes Choanoblasten Proliferative medium-size cells lacking collar and cilium that are progenitors of choanocytes and apopylar cels. Often found in the mesohyl in close proximity to choanocyte chambers
13 Choanocytes (Cellcard, Wiki) Cho Peptidocytes Choanocyten Mature choanocytes, small cells with collar and cilium that play a central role in feeding and driving water flow.
14 Apopylar Cells Apo Peptidocytes Konuszellen Cells forming the excurrent pore of mature choanocyte chamber. Cilium present but lacks microvilli collar.
15 Myopeptidocytes 1/2 Myp1/2 Peptidocytes Medium-sized mesechymal cells with prominent vacuoles and long projections forming cellular network, nucleolus absent. Their name reflects their expression profile, which combines both muscle contractile genes and genes involved in phagocytosis and digestion.
16 Amoebocytes Amb Amoeboid-Neuroid Amobocyten Small mesenchymal cells lacking nucleolus, observed engulfing other cells, similar to that noted by Weissenfels (6).
17 Neuroid Nrd Amoeboid-Neuroid Small, multipolar mesenchymal cells with thin projections, usually found in choanocyte chambers. Similar to the neuroid cells described by Pavans de Ceccatty (23), which he later termed "neuroid" cells (94). Also synonymous with central cells described by Reiswig and Brown (24). We use "neuroid" cell as it predates the term central cell and is a better functional description of these cells.
18 Granulocytes Grl Amoeboid-Neuroid Granulocyten Small mesenchymal cells with projections, scattered in mesenchyme but also often found in the tent and in proximity to pinacocytes.
19 Trophocyten Nutrient cells present during gemmule formation, not sampled in our study
20 Thesocyten (statocyten) Cells constituting the gemmule, not sampled in our study
21 Spermatogonien Sperm cells present during sexual maturity, not sampled in our study.
22 Oogonien Egg cells present during sexual maturity, not sampled in our study.

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