Trachymedusae
Trachymedusae are a group of jellyfish belonging to the class Hydrozoa. Unlike most other hydrozoans, trachymedusae lack a polyp stage in their life cycle and are entirely free-living. They are found in a wide range of marine environments, from coastal waters to the open ocean.
Common Names
Trachymedusae are often referred to as "trachyline hydromedusae" or simply "trachylines."
Characteristics
Trachymedusae are characterized by several distinctive features:
- Lack of polyp stage: Unlike most hydrozoans, trachymedusae lack a sessile polyp stage in their life cycle. They are entirely free-living.
- Mesoglea: They have a thick, gelatinous mesoglea, the layer between the epidermis and gastrodermis, which gives them their characteristic bell shape.
- Tentacles: Trachymedusae usually have numerous tentacles that are often branched and can be quite long.
- Statocysts: They possess statocysts, sensory organs that help them maintain balance and orientation in the water column.
- Gonads: Their gonads are located on the manubrium, the central stalk of the bell.
Environments
Trachymedusae are found in various marine environments, including:
- Coastal waters: Some species inhabit shallow coastal waters.
- Open ocean: Many trachymedusae are found in the open ocean, some even in the deep sea.
- Tropical and temperate waters: They are found in both tropical and temperate waters.
References
For more information on trachymedusae, you can consult the following reliable references: