 amiskwia is a genus of large, soft-bodied invertebrate of unknown affinity known from fossils of the middle cambrian lagerstÃ¤tten both in the burgess shale formation in british columbia and the maotianshan shales of yunnan province, china. thumb|left|amiskwia sagittiformis very few specimens of this organism have been found, only eighteen of the burgess shale species, a. sagittiformis, and a single specimen of the maotianshan species, a. sinica â which may be a reflection of its genuine rarity, but is more likely to be due to taphonomic (preservational) or behavioural factors. the fossils reach  in length. the head is rounded, tipped with two tentacles, and appears to contain a four-ganglion brain; the body flattens out and broadens in the trunk, which appears to have been fairly muscular. where the trunk meets the head there is a small tubular opening, which can be interpreted as the mouth; the gut terminates where the trunk narrows and meets the tail, which is broad and paddle shaped. the body morphology suggests a free energetic swimmer, which may be consistent with the dearth of fossils (in other words, a free-swimming animal would be able to avoid being buried alive in a mudflow on a regular basis, compared to a benthic animal). amiskwia was originally categorized by paleontologist charles walcott. walcott thought he saw three buccal spines in the fossils, and therefore categorized amiskwia as a chaetognath worm (arrow worm). however, amiskwia appears to lack the characteristic grasping spines and teeth of other burgess fossil arrow worms. later scientists suggested an affinity with the nemerteans (ribbon worms), but the evidence for this was somewhat inadequate. conway morris, on re-examining of the burgess shale fauna in the 1970s, described it as being the single known species in an otherwise unknown phylum, given that it has two tentacles near its mouth, rather than the characteristic single tentacle of true nemerteans. (nemerteans do not have a single tentacle. however, a pair of antero-lateral tentacles is present in 2 of the many genera of pelagic nemerteans. nemerteans do have a single eversibleânormally internalâproboscis, which when everted could re
Burgess_Shale_fossils Cambrian_animals Invertebrate_incertae_sedis Maotianshan_shales_fossils