Body plan features
The uniformly ciliated (Mandal, 2012) body has three regions (figure 2): an anterior tongue-like proboscis (protosome), a thick collar (mesosome), and an extended trunk (metasome)(Mertz 2004).
Figure 2 - Body regions of
Balanoglossus sp (Ferreira, undated)
The proboscis is a conical muscular structure and the proboscis stalk iskind of covered by the collar, part known as collarette (Mandal, 2012). The mouth is ventral, located inside of thecollarette and its lips are ventral boundaries of the collar region (Mandal,2012). The collar is the region between the proboscis and the trunk and itsexternal part is marked by elevations, depressions and circular grooves(Mandal, 2012). It is cylinder and generally shorter than the proboscis (BotRejectsInc., 2007). The trunk is divided intobranchiogenital region, with two rows of bronchial pores that are located inthe lateral sides, and the abdominal region that is an intestinal regionextending to the terminal anus (Marques, undated). The subsequent trunk might have perceptiblesacculations where the hepatic portion of the intestine displays superficially (BotRejectsInc., 2007).
There is a primitive structure in the collar that is verymuch like to a notochord, the stomochord, that in the beginning was deliberated to behomologous; however, these structures have different endodermal origin (Ruppert and Barnes 1994).
Above there are two images showing Balanoglossus sp external and internal structures (figure 3 and 4).
Figure 3 - A: External strucuture of Balanoglossus sp; B: Internal strucutures of Balanoglossus sp (Mandal, 2012).
Figure 4 - Both external and internal structures of
Balanoglossus sp (Kshitij Education India, 2014)