In Nature Communications a paper showing the oldest arthropod cardiovascular system in the organism Fuxianhuia protensa. The fossil dates from about 520 MYA, in the early Cambrian.
The figure caption for the top figure:
(a) Image of whole cardiovascular system showing broad heart (H) extending between thoracic tergites T7–T14. The CVS tapers from the level of T13 to become reduced to a single vessel at abdominal tergite Ab3 that fades to invisibility at level of Ab4. Cerebral (ce) and post-cerebral (p ce) CVS stem from paired frontal arteries (f a, bracketed upper right) that are connected by a stout heterolateral vessel (arrowed 1); (b) energy-dispersive X-ray spectroscopy (EDX) showing CVS represented by a carbon film; (c) EDX resolves Fe at the level of T13–T17; (d) enlargement of EDX between T10 and T12 demonstrating intense puncta (arrowheads) flanked by fine collateral, together interpreted as ventral projecting vessels; (e) enlargement of heart and lateral vessels between T7 and T11 demonstrating broad origins (asterisks) of lateral vessels bifurcating into main flanking arteries (at arrowheads); and (f) CVS at T11–T13 showing well preserved traces of main flanking arteries (arrowheads). Scale bar, 2 mm.
The Figure caption for the lower figure:
(a) Cardiovascular system (red) shown in relation to the brain and central nervous system (blue); (b) whole reconstruction, with brain and segmental ganglia (blue) shown in relation to serial arrangements of tergites. The reconstruction of the vascular system assumes that posterior abdominal extensions of the dorsal vessel are likely present although these are not defined by carbon traces in the fossil. The reconstruction of the nervous system infers that paired nerves are associated with the telson. As described elsewhere1, 2, 6, tergites do not reflect true metamerism, there being >1 ganglion coincident with each tergite from T7. Likewise, lateral vessels occur one per tergite frontally in the thorax but are more crowded further towards the rear; (c) cardiovascular system (red) in relation to the gut (green).