Early Jurassic “worm holothurians” (Echinodermata) as faecal traces of a worm-like holothurian-eater reflecting the consumed species

Abstract

“Worm holothurians” from a sequence of Early Liassic (Hettangian) shales at Gottingen (Germany) are string- and strip-shaped relics of faeces of a worm-like holothurian-eater. They consist of three typical associations of morphotypes of microscopic calcitic ossicles of the body wall skeletons of holothurians: (1) mostly buttons and a few larger hooks; (2) polyperforate spectacles and many tiny hooks; or, rarely, (3) sieve platelets only. The faeces were discarded by the predator partly as it rapidly advanced, leaving an elongated, irregularly curved string at the sediment surface, but mostly during its slow creeping and crawling at and below the sediment/water interface, when it left a narrowly meandering string in its moulded or tunnel-like trail. The elongated strings are generally well preserved, whereas the meandering ones are generally totally disintegrated, possibly due to ventilating activities of the predator. Upon the collapse of the trail wall, the biostratinomic state of disintegration was fixed as a strip of ossicles. Such a strip, therefore, represents the faecally documented part of a creeping or crawling trace in or just below the sediment surface. All holothurian calcareous ring segments found in some of the two kinds of strip-shaped ossicle associations with hooks belong to the same new type of ring form. According to a feasible scenario for the predator–prey relationship, this form should be defined as a new genus of chiridotid Apodida that contains the ossicle associations with hooks as two biological species. The strings of concentrated sieve platelets should also be interpreted as a biological species from a new genus within the Dendrochirotida.