Retractor muscles: :Longitudinal muscle of the mesentery that is responsible for the shortening of the column (Stephenson, 1928: p. 36). The degree of the muscle concentration is taxonomically important; the types are referred to as circumscript, restricted and diffuse retractor muscles.

Images of Retractor Muscles: (species names are linked to the Hexacorallian database)

Species: Haliactis arctica

Caption: Transverse section of a perfect mesentery in the reproductive tract.

Species: Edwardsia finmarchica

Caption: Transverse section of pennon in the reproduction tract.

Species: Condylanthus aucklandicus

Caption: Transverse section of pennon at the oral disk.

Species: Telmatactis australiensis

Caption: Transverse section of mesentery of first cycle at level of lower part of actinopharynx.

Species: Edwardsia callianthus

Caption: A transverse section of a retractor muscle in the upper part of the fertile region of Edwardsia callianthus. (The mesogloea is shown as black and the fertile and cnidoglandular areas are stippled.)

 

Species: Iosactis vagabunda

Caption: Figure 5. *Iosactis vagabunda* gen. nov., sp. nov. Musculature, semi-schematic (mesogloea in black). The longitudinal section to the left shows the strong circular musculature (CM) of the body wall, the tiny marginal sphincter (MS), and the tentacle sphincter (TS). The dotted line indicates the partly destroyed actinopharynx (Ph), and AP denotes the pit in the aboral pole. The cross-sections (A-E) to the right show the septal musculature in one of the 24 septa along their longitudinal extension, whereby the circular musculature (CM) of the body wall is indicated in stippled lines. (A) Septum with weak diffuse retractor (R). (B-C) The tiny parietal muscle (P) enlarges together with the outer part of the retractor. (D-E) Below the actinopharynx there are only strong parietal muscles along the body wall. Reprinted with permission of Cambridge University Press.