Question

Select the incorrect statement.

• A. Digestive system is complete in Aschelminthes and Echinodermata but not in Platyhelminthes.
• B. Segmentation is present in Annelida and Arthropoda but absent in Chordata.
• C. Organ system level of organisation is found in Aschelminthes and Annelida but not in Ctenophora.
• D. Circulatory system is absent in Platyhelminthes and Aschelminthes but present in Hemichordata.

Answer 1

Answer: (B)

Metameric segmentation is found in annelids, arthropods and chordates. In metameric segmentation, there is a linear repetition of body parts where each repeated unit is called somite (metamere).
In earthworms, the successive somites are essentially similar, but they are dissimilar in different body regions of a crayfish or insect. Metamerism is conspicuous both externally in annelids. It is mostly external in arthropods and internal in humans and in other chordates (vertebrate, body muscles, some blood vessels and nerves).