Practice question

Among four major cnidarian classes Hydrozoa Scyphozoa Cubozoa and Anthozoa Anthozoa including sea anemones Order Actiniaria stony corals Scleractinia soft corals Alcyonacea and sea pens Pennatulacea display purely polypoidal organization throughout life cycle lacking free-swimming medusa stage. Polyps solitary or colonial with internal mesenteries partitioning gastrovascular cavity radially septa bearing muscles and gonads pedal disc attachment. Sexual reproduction via broadcast spawning or brooding planula settles. Absence medusa considered derived secondary loss emphasizing specialization for benthic sessile habit extensive reef building by scleractinians and zooxanthellae whereas Hydrozoa retain both forms Scyphozoa and Cubozoa dominant medusa with reduced polyp.