Q. Type specimen of class enteropneusta?
Examine the specimen and note the following features:
1. Balanoglossus has a soft, elongated, worm-like body which has a ciliated surface.
2. Body length reaches 10-50 cms and is divided into short conical proboscis, , collar and long trunk.
3. Proboscis is cylindrical, tapering and muscular. Near the base is a proboscis pore which is the opening of the coelom (present within the proboscis) to the exterior.
4: Collar is a short, cylindrical, muscular band enclosing a pair of coelomic cavities (collar coelom). The collar opens by a pair of collar pores on the dorsal ; surface. The rim of the collar encloses the mouth which is permanently open. ,
5. The trunk is superficially ringed and divided into 3 parts (a) anterior branchiogenital part containing genital ridge that carry gonads. This part can , be demarcated from the outside as it has gill-slits but the contents cannot be seen without dissection. (b) hepatic region. (c) the posterior end which is the trunk region.
6. The mouth lies at the base of proboscis and is encircled by the edge of the collar.
7. In the hepatic region are present double rows of hepatic caeca.
8. Alimentary canal is straight and anus is at the end of the trunk. (Sexes are separate and fertilization is external. Development includes a free swimming pelagic larva called tornaria larva.)