Ventral surface without a sucker; tentacles when present of nuchal type; dorsal surface not papillate; eyes in tentacular, cerebral and frontal clusters and in sub-marginal and marginal areas of the body; eyes rarely absent; marginal eyes present; marginal band of eyes limited to clusters over the brain region or in and around tentacles; marginal eyes present; marginal band of eyes completely encircling body; with or without nuchal tentacles; with prominent nuchal tentacles.

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