Table 1 Summary of characteristics of the five types of coelom formation described for enteropneusts according to literature
|  | Characteristics accord. to literature | Taxon | Source | Author’s commentary |
|---|---|---|---|---|
Type I (Figure 14A) | Mesocoela & metacoela form as separated, epithelial outpocketings from the middle and posterior gut regions | S. kowalevskii (harrimaniidae) | Bateson (1884)[44] present study | Confirmed by ultrastructural investigations (present study) |
Type II (Figure 14B) | A single anterior coelomic sac pinches off from the archenteron and subdivides posterolateral into mosocoel & metacoel | S. puillus (harrimaniidae) | Davis (1908)[47] | Limited light microscopical resolution. TEM study warranted |
Type III (Figure 14C) | Mesocoela and metacoela form from separated, but solid masses of cells from the middle and posterior gut regions | New England Tornaria unknown species (Ptychoderidae) | Morgan (1891)[45] | Misenterpretation of the term solid, originally described as epithelial enterocoela |
Type IV (Figure 14D) | Meso-and mrtacoela originate from a single outpacketing from the posterior gut region that later subdivides | Glandiceps sp. (Spengelidae) | Rao (1953)[56] | Origin of mesocoela is not documented in original literature. |
B.clavigerus (Ptychoderidae) | Bourne (1889)[55] | Origin of metacoela only described convincingly | ||
Stiasny (1914)[48] | ||||
Spengel (1893)[41] | ||||
Type V (Figure 14E) | meso-and metacoela originate from multiple clusters of mesenchymatic cells within the blastocoel | tentaculated Tornaria (Ptychoderidae) | Morgan (1894)[46] | Limited light microscopical resolution. TEM study warranted |