|Basic info||Taxonomic history||Classification||Relationships|
|Morphology||Ecology and taphonomy||External Literature Search||Age range and collections|
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|M. R. Smith and J. -B. Caron 2010||Dorso-ventrally flattened, non-segmented body, lacking a mineralized shell; with a small head bearing a pair of eyes and tentacles, a hollow tubular element on the ventral surface of a short neck, a large, open axial cavity containing paired gills, and wide lateral fins.
Nectocaris is flat in lateral view (Fig. 1f and Supplementary Fig. 2) and rhomboid in dorso-ventral aspect; con- tinuous lateral fins taper towards the posterior (Fig. 1c, d and Supplementary Fig. 3). The body comprises a torso, a tubular ‘funnel’ protruding from the ventral side of a short neck (Fig. 1a, b, f and Supplementary Figs 2–4), and a small, eye-bearing head with a pair of non-segmented frontal projections (‘tentacles’ herein; Fig. 1a, b, f and Supplementary Figs 2–6). The body length averages 37 mm (further measurements in Supplementary Table 2).
The flexible tentacles extend from the anterior of the head; abrupt variations in their width, owing to rotations, indicate that they are flattened and presumably C-shaped in cross-section (Supplementary Figs 3, 5). Each tentacle margin is delineated by a narrow dark line that sometimes bears small repeated lobate projections (Supplementary Figs 5, 6). A squat triangular projection occurs at the base of each tentacle (Fig. 1b and Supplementary Figs 5, 7). A symmetrical dark region is sometimes evident at the anterior end of the head, between the tentacles (Supplementary Figs 5, 8); its position suggests a feeding apparatus.
Two large eyes are attached by short stalks to the latero-ventral surface of the head (Fig. 1a, b, f and Supplementary Figs 2–8). Unlike probable compound eyes in the Burgess Shale, which preserve in the same fashion as body tissue (that is, as carbon coated by diagenetic aluminosilicates8,9), the eyes of Nectocaris preserve as a conspicuous carbon film that envelopes a thick layer of bedding-perpendicular muscovite crystals (Supplementary Fig. 8). These crystals are evidence that a structure or a void within the eyes was replaced during diagenesis, consistent with a camera-type construction.
The external portion of the funnel widens away from the neck (Fig. 1a, b, f and Supplementary Figs 2–4, 7) and is preserved in various orientations (for example, Fig. 1a, b), indicating original flexibility. The internal portion widens laterally towards the posterior (Fig. 1b and Supplementary Fig. 7). A channel, which narrows in a constricted zone in the neck and often widens towards the funnel’s aperture, follows the midline of the funnel (for example, Fig. 1b and Supplementary Figs 4, 7) and opens into an axial ovoid cavity that occupies the full length of the body. Sediment often fills the channel and the cavity, indicating that the cavity opened to the environment through the funnel. Ovoid sediment-filled regions on either side of the funnel (Fig. 1b and Supplementary Fig. 7) may have been asso- ciated with openings of the axial cavity. The axial cavity’s width does not correlate with body width (r2 5 0.00015, P 5 0.952), consistent with the former being variable during life.
A black structure comprising serially repeated blade-like elements lines each side of the axial cavity, tapering to the front and rear (Fig. 1a and Supplementary Figs 3, 4 and 9). These structures, interpreted to represent gills, are connected to the cavity wall along their entire lateral length, as suggested by the homogeneous nature of the struc- tures and the interleaving of sediment between gill-blades on the lumen side (Fig. 1e and Supplementary Fig. 9). Each gill-blade is connected to its neighbours along a lateral axis in a zigzag fashion (Supplementary Fig. 9). The axis of some specimens bears a dark stain, narrower than the axial cavity, that tapers towards the rear of the body (Fig. 1c), suggestive of a digestive tube.
The animal’s fins run from the base of the neck to the rear end of the animal, with their maximal width occurring towards the anterior of the body (Fig. 1a, d). Repeated bar-like elements cross the entire width of the fins at regular intervals. A longitudinal element extends sole (Fig. 2). The presence of a constriction within the base of the funnel indicates that water flow might have been controlled by a valve. Thus, during life, water entered the axial cavity through openings near the funnel’s base and was expelled through the funnel (Supplementary Fig. 11), which could flex to direct any resultant motive force. This exhalent jet was probably subsidiary to the large fins in generating propulsion. Nectocaridids were probably predators or scavengers, feeding on small soft-bodied animals. The length, shape, flexibility and marginal projections of the tentacles probably facilitated the manipulation of small food items.
Collections (6 total)
|Time interval||Ma||Country or state||Original ID and collection number|
|Atdabanian||China (Yunnan)||Petalium latus (96869) Vetustovermis planus (86929)|
|Botomian||Australia (South Australia)||Vetustovermis planus (187498)|
|Delamaran||Canada (British Columbia)||Nectocaris pteryx (121962 121963 121964)|