Laffonia, Heer, 1877

Laffonia is neither a ctenophore, an actinarian nor a holothurian

Te affinity of Laffonia has never been clarified unequivocally since its discovery (Heer, 1877; Reich, 2015; Ziegler, 1991). Laffonia and its probable junior synonym Pseudocaudina were described as morphologically resembling extant diploblastic animals including ctenophores (comb jelly) and anthozoans (sea anemones). Laffonia was most recently regarded as the closest to the Beroida, a ctenophore group that lacks a pair of tentacles (Ziegler, 1991). Te presumed similarity is based mainly on the presence of striated bands in Laffonia , which supposedly are reminiscent of the ciliabearing comb rows in extant ctenophores (Ziegler, 1991). However, the identification of comb rows in Laffonia is only tentative at best ( Conway Morris & Collins, 1996). Ctenophore comb rows are composed of numerous independent ctenes that are serially arranged on the external body surface along an oral-aboral axis and each ctene includes a basal cushion plate that carries numerous macrocilia used for swimming (Tamm, 2014). Te striated bands of Laffonia are only visible along the inferred lateral edges of the capsule, indicating they are apparently restricted to this region. Te transverse striations are densely arranged along the band with no distinctly raised bars ( Fig. 4D, E View Fig ), which is inconsistent with the cushion plates of extant ctenophores or the cushion-like structures in well-preserved ctenophore fossils ( Conway Morris & Collins, 1996; Ou et al., 2015; Parry et al., 2021; Stanley & Stürmer, 1983, 1987; Zhao et al., 2019). In addition, Pseudocaudina was once compared to an actinarian based on potential similarities in the column-like body (Heding, 1932). However, the presence of lateral striated bands and the lack of reliable anthozoan characters such as mesentery, pedal disc, and circumoral tentacles in Laffonia and Pseudocaudina make this inference suspect.

Pseudocaudina was initially interpreted as a holothurian ( Broili, 1926). Te transverse striations visible at the inferred anterior end of Pseudocaudina were interpreted as the transverse muscles that presumably surround the body with no interruption at the inferred ambulacra, which is a typical characteristic of synaptid holothuroids ( Synaptidae View in CoL ) ( Broili, 1926). While a holothurian identification was subsequently cited several times following its description ( Croneis & McCormack, 1932; Frizzell & Exline, 1966), this assignment was nevertheless still disputed (Heding, 1932; Hess, 1973; Reich, 2015; Smirnov, 2012; Ziegler, 1991). Te suggested muscle system in Pseudocaudina is questionable for several reasons. Te appearance of this system was likely created by the compression of its dorsal and ventral sides during fossilisation and is inconsistent with the preservation in the three-dimensionally preserved Laffonia (Ziegler, 1991) . Neither Pseudocaudina nor Laffonia exhibit other diagnostic traits of holothurians such as a perioral ring of calcareous sclerites at their anterior ends, sclerites in their dermis, and radially arranged ambulacra (Reich, 2015). Laffonia and Pseudocaudina can therefore not be assigned to holothurians.