Kinorhynches are tiny (at most 3 mm) worm like
animals found in marine sediments, with segmented tube- or
barrel-shaped bodies, separate head and neck regions and evertable
pharynxes. They are relcated to Pripulid Worms (large unsegmented
Worms with evertable pharyxes and Loriciferas (small unsegmented
animals with cup-shaped rigid bodies and evertable pharynxes), the
three groups being grouped together as the Scalidophora. Molecular
clock estimates have suggested that the three groups diverged during
the Eidacaran, but while Priapulids are well documented from the
Cambrian onwards, and a large, Loricifera-like animal (Sirilorica)
is also known from the Cambrian, to date no Kinorhynches have been
found in the fossil record from any period.
In a paper published in the journal Nature:Scientific Reports on 26 November 2015, a team of scientists led by
Huaqiao Zhang of the Key Laboratory of Economic Stratigraphy and Palaeogeography of the Chinese Academy of Sciences, at the NanjingInstitute of Geology and Palaeontology, describe a series of
Kinorhynch fossils from the Early Cambrian Xinli Member of the
Dengying Formation in Nanjiang County in Sichuan Province, deposits
that form part of the Small Shelly Fauna at the beginning of the
Cambrian (the Small Shelly Fauna marks the beginning of the Cambrian
in deposits around the world; in these beds numerous small shells and
shell-elements are found, but not larger mineralized shells) and are
dated to about 535 million years ago.
Several of the best preserved specimens are
described together as Eokinorhynchus rarus, where
'Eokinorhynchus' means 'dawn-Kinorhynch' and 'rarus'
means 'rare', though Zhang et al.
record the presence of fragmentary specimens that apparently belong
to other species. Eokinorhynchus rarus is
essentially similar to modern Kinorhynches, with a segmented tubulaer
trunk, a neck region and head with an evertable pharyx, but while
modern Kinorhynches invariably have 11 segments, Eokinorhynchus
rarus appears to have a minimum
of 20.
SEM images of
Eokinorhynchus rarus.
(a–c) Dorsal, ventral, and left lateral views, respectively. (d–f)
Close-up views of zones 2 and 3 to show the arrangement pattern of
pharyngeal teeth (numbered in the two basal circlets), with white
arrows denoting the 3rd and black arrows denoting the 4th circlet of
pharyngeal teeth. Abbreviations: A1–A20, 1st to 20th trunk annulus;
an, anus; cs, caudal spine; hsc, head scalid; ls, large sclerite;
1ls–5ls, 1st to 5th pair of large sclerites; mg, midgut; nsc, neck
scalid; spl, small plate; ss, small spine; vls, ventral large
sclerite. Scale bar beneath (c) applies to (a–c), and scale bar
beneath (d) applies to (d–e). Zhang et al.
(2015).
The presence of
Eokinorhynchus rarus in
deposits dating to the earliest Cambrian supports the idea that the Scalidophoran groups diverged in the Ediacaran, but does not explain
the absence of Kinorhynch fossils from other deposits, particularly
notable Cambrian drposits such as the Burgess Shale, which preserve
numerous non-mineralized taxa. Zhang et al.
suggest that the microscopic size and interstitial lifestyle of
Kinorhynches makes them unsuitable for Burgess Shale type
preservation, but suitable for preservation as phosphatic
microfossils; a type of preservation that has only been discovered
and studied in recent years, as computerized scanning and modeling
methods have enabled palaeontologists to study fossils that would
either have been destroyed or overlooked using traditional
techniques.
Reconstruction of Eokinorhynchus rarus.
(a–c) Dorsal, ventral, and right lateral views, respectively.
Dinghua Yang in Zhang et
al. (2015).
See also...
Yuganotheca elegans: An Early Cambrian Lophophorate Animal with affinities to Brachiopods and Phoronids. Lophophorates are animals which feed using a filter called a...
Priapulid Worms from the Middle Cambrian of Canada. Priapulid Worms are a form of marine worms with denticle-covered
pharynxes which can be everted to form proboscises. They are a minor element of
modern marine faunas, largely restricted to deep marine...
A new species of Vetulicolian from the Early Cambrian of Kangaroo Island, South Australia. Vetulicolians are an enigmatic group of Cambrian fossils known from the
Chengjiang and Guanshan biotas of South China, Sirius Passet in...
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Yuganotheca elegans: An Early Cambrian Lophophorate Animal with affinities to Brachiopods and Phoronids. Lophophorates are animals which feed using a filter called a...Priapulid Worms from the Middle Cambrian of Canada. Priapulid Worms are a form of marine worms with denticle-covered
pharynxes which can be everted to form proboscises. They are a minor element of
modern marine faunas, largely restricted to deep marine...A new species of Vetulicolian from the Early Cambrian of Kangaroo Island, South Australia. Vetulicolians are an enigmatic group of Cambrian fossils known from the
Chengjiang and Guanshan biotas of South China, Sirius Passet in...Follow Sciency Thoughts on Facebook.