How will you distinguish between hydrozoan polyp and scyphozoan polyp?

Answer 1

The difference between most hydrozoans and most scyphozoans is that in hydrozoans, the polyp stage usually predominates, with the medusa small or sometimes absent.

Often, the medusa never breaks away from the parent polyp, and remains in a state of arrested development, although its gametes function. Such a medusa is referred to as a sporosarc.

In scyphozoans, the medusa stage is typically large and free-living, with the polyp stage small.

However, there are exceptions - certain hydrozoans known as the Trachylina never form a polyp stage. Free-living medusoid hydrozoans can be hard to tell from scyphozoans, but hydrozoan medusae generally have a muscular shelf, or velum, projecting inward from the margin of the bell.

This structure is not found in scyphozoans. Hydrozoans also lack cells in the mesoglea, the jelly layer found between the basic cell layers, whereas scyphozoans contain amoeboid cells in the mesoglea.

Another feature that is quite common in Hydrozoa but not typical of Scyphozoa is colonial organization.