Have we Got to the Bottom of this Mystery?

A correspondent sent me the link to THIS ARTICLE on the BBC website. It is based on THIS ACADEMIC PAPER, two of whose authors are at Bristol University.

Saccorhytus coronarius has been known for some time but has proved difficult to place in a family. It is early Cambrian in age and microscopic in size. The fossils studied come from China. It was thought to be a deuterostome but is now classified as a ecdysozoan. To quote "Saccorhytus testifies to the remarkable morphological disparity and ecological diversity of early Cambrian ecdysozoans and presents another case of secondary absence of the anus in ecdysozoans."

I do not pretend to understand the arguments for the creatures classification. But I am amazed at the quality of the illustrations which use both scanning electron microscopy (SEM) and synchrotron radiation X-ray tomographic microscopy (SRXTM).

Anatomy of S. coronarius. a,b, He22-45, with a single large protuberance. a, Lateral view. b, Close-up view of sixth lateral body cone. c–e, He22-94, SRXTM images. c, Surface model, lateral view. d,e, Virtual sections through body cones as denoted in c. f–h, He22-57, with two large protuberances. f, Apertural view. g, Virtual section through radial folds as denoted in f, bisecting a circumapertural protuberance. h, Virtual section through radial folds as denoted in f. Scale bars: 200 μm (a,c,f), 110 μm (b), 55 μm (d), 80 μm (e), 50 μm (g,h)

Anatomy of S. coronarius. a–e, UMCU2020021. a, Lateral view. b, Right view. c–e, Detail of body cones tilted approximately 40° from a,b, showing remnant of apical spine. f,h, UMCU2016008. f, Lateral view. h, Detail of fourth lateral body cone adpressed against body wall. g,i, UMCU2016010. g, Abapertural view. i, Detail of small abapertural spines adpressed against body wall. j,k, UMCU2018012. j, Right view. k, Detail of fifth right body cone adpressed against body wall. l, UMCU2019018, abapertural lateral view. Scale bars: 200 μm (a,b,f,g,j,l), 60 μm (c–e,h,i,k).