Digestive System of Amphioxus

Digestive System of Amphioxus

In Branchiostoma the digestive system of amphioxus consists of alimentary canal and digestive glands.

Alimentary canal

The alimentary canal is straight complete tube like Structure running from mouth to anus. It has following parts.

Mouth

Mouth is large oval aperture present antero venterally below the rostrum it just bordered by frile like oral hood.

Oral hood and buccal cavity

The oral hood is formed by dorsal and lateral outgrowths of anterior end of trunk.

Buccal cirri

At the margin of oral hood has 10-12 pair of slender and ciliated oral cirri or buccal cirri. These bears sensory pappilae. The number of buccal cirri increasing according to age of animal. The buccal cirri and margin of hood supported by Skelton rod. The buccal cirri act as sieve or filter to entry of large particle with food current.

Vestibule or buccal cavity

The oral hood open into large cavity like Structure called buccal cavity or vestibule which opened into mouth.

Wheel organ

At the base of oral hood there are 6-8 pair fingure like fold called wheel organ or rotary organ or muller's organ. Each organ is surrounded by cilliated groove. The mid dorsal groove is largest which open into buccal cavity. At the upper surface of wheel organ there is a small depression called hatches pit and groove is called hatches groove. All these organs secrets mucous.

Velum 

Velum is circular ring like membrane present posterior side of vestibule. It has pore like structure called enterosome, which open into pharynx. The velum has some spineter which open and close the enterosome. There are about 10-12 slender like cilliated and sensory Structure present called veller tentacles. These help as strain the water current 

Pharynx

The pharynx is very large specious part of alimentary canal. It contains about one half anteriror part of the body. It has several part has pharyngeal wall and Gill's Slits, endosyle, epipharyngeal groove and peripharyngeal bends. The lateral wall of pharynx are perforated by 150 to 200 pairs of verticle opening called branchial aperture Gill's Slits or Gill's cleft. The gills Slits bear no Gill's and between two Gill's Slits present branchial lamella or Gill's bar. The gills are covered by cillia. These cillia are present in lateral cillia and fountal cillia. The gills bar of two type as primary and secondary. The primary Gill bar is also called P.gill rod. The P.gill bar connected with each other by synapticula.

Endostyle

The endostyler present ventrally on the floor of pharynx. It farm a shallow groove with four longitudinal tract of mucous secreating glands.

Digestive glands

These glands cell has five tract of cilliated cells. The cillia of median tract are longest. The endostyler is supported by to gelatinous skeltoal plates in higher animals the endostyler is connected into thyroid gland. This endostyler constracts iodine the epipharyngeal groove has cillia and present on the roof of pharynx. This groove runs to the oesophageal opening. The peripharyngeal bands are pair of narrow cilliated tract arising from endostyler. It has absence of Gill's Slits.