Leniechinus, Kier, 1968

Mooi, Rich, Kroh, Andreas & Srivastava, Dinesh K., 2014, Phylogenetic re-evaluation of fossil and extant micro-echinoids with revision of Tridium, Cyamidia, and Lenicyamidia (Echinoidea: Clypeasteroida), Zootaxa 3857 (4), pp. 501-526 : 523-524

Leniechinus and Lenicyamidia

In the genus-level analysis based on the Kroh & Smith (2010) dataset, branching order within the fibulariids is poorly resolved. When Lenicyamidia was excluded, Leniechinus was recovered as a sister group to Fibularia + Tridium in an unresolved trichotomy with Cyamidia ( Fig. 3 ). However, in the species-level analysis, Leniechinus falls to the base of the fibulariid clade, below the nodes joining Echinocyamus and Mortonia to the more crownward fibulariids ( Fig. 5 ). The reason for this discrepancy is based on the observation that more features could be scored for the extant taxon Echinocyamus than for the incompletely known fossil taxon Leniechinus in the genus-level analysis. Moreover, in the species-level analysis several features that turn out to be relatively plesiomorphic within the Fibulariidae overall push Leniechinus more basally. For example, the relatively high number of pore pairs in the petaloids, along with the width of the interporiferous zones, tend to exclude Leniechinus from the more crownward fibulariids, making it plesiomorphically more similar to Mortonia .

Kier (1968) stated that Leniechinus was likely more closely related to Lenita than to other fibulariids such as Lenicyamidia , based at least in part on the presence of internal buttresses (which are lacking in Lenicyamidia ). Internal buttresses can be greatly reduced in paedomorphic scutellines so that they resemble those of fibulariids. Mooi (1990) excluded Lenita from his concept of the laganines. Nearly all the characters he listed as synapomorphies for the scutellines cannot be determined in Lenita . Nevertheless, Lenita is neither a laganine nor a clypeasterine, as it clearly lacks laganiform synapomorphies. In Lenita , the interambulacral columns plesiomorphically remain paired all the way to the apical system, the hydropores are numerous and scattered across the madreporite (seen in laganiforms only in taxa such as Peronella ), and the periproct is strongly aboral, separated from the peristome by at least three pairs of post-basicoronal plates. Lenita also expresses key features in the symmetry of the oral surface plating that are also very unlike those of laganiforms. In contrast, the present analysis firmly places Leniechinus among the laganiforms. For these reasons, Leniechinus cannot be considered closely related to Lenita . Similarities in oral tuberculation between Lenita and Leniechinus (the supposed locomotory tubercles) appear to be convergent.

Lenicyamidia compta , on the other hand, does have affinities with fibulariids. It possesses key features that place it crownward in the fibulariid clade, even above the nodes that join Leniechinus , Mortonia , and Echinocyamus to the family ( Fig. 5 ). It has reduced petaloids, narrow interporiferous zones, and completely lacks internal buttresses. Among all the fibulariids, the elongate periproct and test plate pattern places it with Cyamidia .

Figures

FIGURE 3. Phylogenetic relationships among clypeasteroid genera and relevant outgroups showing positions of Tridium (=Fibularia), Cyamidia, Lenicyamidia, and Leniechinus when these taxa are added to and coded for the matrix of Kroh & Smith (2010). Strict consensus tree of two MPTs. Numbers above branches indicate bootstrap values above 50%, those below indicate Bremer indices above 1 (all other nodes collapse one step away from the shortest tree).

FIGURE 5. Phylogenetic relationships among fibulariid species and relevant laganiforms showing positions of Tridium (= Fibularia), Cyamidia, Lenicyamidia, and Leniechinus. Numbers above branches indicate bootstrap values above 50%, those below indicate Bremer indices above 1 (all other nodes collapse one step away from the shortest tree).