Table 1.
List of investigated species and literature data.
Fig 1.
A: Heart of Limulus polyphemus (lateral view, μCT). B: Heart of Hottentotta hottentotta (dorsal view, cLSM). C: Ostium and proximal part of cardiac artery of Euscorpius tergestrinus (lateral view, cLSM; red cyan anaglyph, use goggles), arrowhead indicates longitudinal fibers of the epicard. D: Ostium and proximal part of cardiac artery of Lasiodora parahybana (lateral view, cLSM), arrowhead indicates longitudinal fibers of the epicard. aa: anterior aorta; ca: cardiac artery; os: ostium; pa: posterior aorta.
Fig 2.
A: Part of the heart of Scutigera coleoptrata (dorsal view, cLSM), asterisk indicates narrowed region under the overlap of two consecutive tergites. B: Part of the heart of Geophilus flavus (dorsal view, cLSM) between the longitudinal trunk musculature (purple), tracheae are located near the ostia. C: Part of the heart of Polydesmus complanatus (dorsal view, cLSM), arrowhead indicates the origin of a cardiac artery which was ripped off during preparation. D: Part of the heart of Glomeris marginata (lateral view, μCT) in an unrolled specimen. ca: cardiac artery; ost: ostium; ter: tergite; tra: trachea.
Fig 3.
Hearts of some non-malacostracan crustaceans.
A: Heart of Hutchinsoniella macracantha, location in the body (ventral view, cLSM). B: Heart of H. macracantha (dorsal view, cLSM). C: Heart of Daphnia magna (lateral view, anterior is right, cLSM), arrowhead indicates anterior opening of the heart. D: Heart of Pseudodiaptomus pelagicus, location in the body (lateral view, cLSM). E: Heart of Centropages typicus (dorsal view, cLSM, red cyan anaglyph, use goggles). aa: anterior aorta; aav: anterior aortic valve; h: heart; ost: ostium.
Fig 4.
Hearts of malacostracan crustaceans.
Heart of Nebalia herbstii (lateral view, fluo). B, C: Myocard and ostium of Anaspides tasmaniae (B: lateral view of exterior, C: interior, μCT), arrowhead indicates double layer of myofibers running in opposite directions. D: Heart of Apseudes spinosus (ventral view, cLSM). E: Ostia and origins of cardiac arteries of A. spinosus (ventral view, cLSM). F: Heart of Neomysis integer (ventral view, cLSM). G: Heart of Munida sarsi (dorsal view, μCT), dorsal surface virtually clipped to show bundles of myofibers running through the heart lumen. aav: anterior aortic valve; ca: cardiac artery; ost: ostium; pa: posterior aorta.
Fig 5.
The heart of Xibalbanus tulumensis („Crustacea“: Remipedia;).
All tiles are red cyan anaglyphs, use goggles to see images correctly. A: Volume rendering of the heart in the mid-posterior trunk segments (dorsolateral view, μCT); thinner regions at the border between two consecutive segments are visible beneath the overlap of the two respective tergites. B, C: Shadow projection of the outer (B) and inner (C) view of the heart in the anterior portion of the segment (lateral/medial view, μCT), arrowhead indicates longitudinal fibers of the epicard overlapping the semicircular cardiomyocytes. ca: cardiac artery; ost: ostium.
Fig 6.
A: Heart of Petrobius brevistylis (ventral view, fluo), location of the heart between the longitudinal musculature. B: Unpaired excurrent opening in the ventral median line of the heart of P. brevistylis (dorsal view of the interior, ventral portion of the myocard, cLSM). C: Heart of Procloeon bifidum, location of the heart between the longitudinal musculature (ventral view, cLSM). D: Ostium of P. brevistylis (dorsal view, cLSM), arrowhead indicates the dorsal median line where cardiomyocytes are attached to each other. E: Epicard (grey) and myocard (red) of the heart of Blaptica dubia (dorsolateral view, cLSM). alm: alary muscle; ec: epicard; h: heart; mc: myocard; ost: ostium; ov: ostial valve; ueo: unpaired excurrent opening.
Fig 7.
Schematic representations of the arrangement of cardiomyocytes in the myocard (character 5 and character 7).
A: meshwork around the lumen, most cells perpendicular to longitudinal axis (5:0). B: single layer of semicircular cells without helical shift (5:1, 7:0). C: single layer of semicircular cells with helical shift (5:1, 7:1). D: two distinct layers of fibers with helical shift in opposite directions (5:4, 7:1). E: meridional with dorsal and ventral knots (5:2). F: meshwork without dominant orientation and bundles running across the lumen (5:3).
Fig 8.
Exemplar for the character states of character 9.
A: state 0, only a slit visible from the outside, muscular valves protrude deep into the lumen (example from Euscorpius tergestrinus, lateral view, cLSM). B: state 1: deep V-shaped (horizontal section) trench; valves which are made up of several myofibers only protrude a little way into the lumen (example from Pseudodiaptomus pelagicus, dorsal view, cLSM) red cyan anaglyph, use goggles; C: state 2: shallow (almost flat) trench, most of the valve visible from outside (example from Nebalia herbstii, lateral view, cLSM). D: state 3: origin of ostial valves extruded; V-shaped trench of medium depth (example from Leucon nasica, ventrolateral view, 3D visualized from histological sections).
Fig 9.
Relationships between components of character statements (sensu Sereno [58]) and RDF triplets describing character states.
This scheme illustrates the differences between the definition of “character” sensu Sereno [58] and “character” sensu Hennig [59]. A: transformational characters (example: character 2). B: neomorphic characters (example: character 4).
Fig 10.
Parsimony-based reconstruction of the evolutionary transformation of character 5.
5: Heart, myocard, cardiomyocytes, arrangement: white: meshwork around the lumen, most cells perpendicular to longitudinal axis (0); blue: single layer of semicircular cells (1); green: meridional with dorsal and ventral knots (2); yellow: meshwork without dominant orientation and bundles running across the lumen (3); black: two distinct layers of fibers (4). The pictograms show schematic cross sections of the myocard to illustrate the respective character states. This is one of the most parsimonious reconstructions, for ambiguities see S1 File.
Fig 11.
Parsimony-based reconstruction of the evolutionary transformation of character 9.
9: Heart, ostia, shape: white: only a slit visible from the outside, muscular valves protrude deep into the lumen (0); light blue: deep V-shaped (horizontal section) trench; valves made up of several myofibers only protrude a little way into the lumen (1); green: shallow (sometimes almost flat) trench, most of the valve visible from outside (2); black: origin of ostial valves extruded; V-shaped trench of medium depth (3). The pictograms show schematic horizontal sections of the ostia to illustrate the respective character states. This is one of the most parsimonious reconstructions, for ambiguities see S1 File.
Fig 12.
Schematic representation of the impact of a thick, incompressible myocard on relative volume reduction via constriction during systole in tubular hearts (adapted from Vogel [86] for spherical hearts).
(*calculation based on the original scale of the drawing with a luminal diameter of 15 mm and myocard thickness of 6 mm during diastole).