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Reduced thorax and pygidium; smoothed cephalon; downward projecting spines; facies independence
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Light, streamlined body allows fast swimming. Spines prohibit effective movement on the sediment surface. Distribution controlled by water column characteristics rather than sediment characteristics.
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Pelagic lifestyle/swimming
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Smooth exterior, broad & flat axial lobe
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Reduce friction
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Burrowing
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Larger muscle attachments
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Stronger limb motions to move sediments
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Eyes reduced or absent
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Darker conditions, less need/no need for keen eyesight
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Living in deep water
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Wide bodies, genal spines
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Added support for soupy substrate
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Well-developed limbs, flexible hypostome, Cruziana feeding traces
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Food passed anteriorly towards the mouth during the course of movement, flexible hypostome used as a scoop.
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Particle feeding
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Unusual occipital angle, pitted fringe
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Pits allow water to flow through cephalon from leg-generated currents
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Filter feeding
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Rigid, strongly braced hypostome; forked hypostome projections
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Ability to process relatively large food particles
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Predatory, feeding on soft bodied worms
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