Atelecrinidae Bather, 1899

Messing, Charles G., 2013, A revision of the genus Atelecrinus PH Carpenter (Echinodermata: Crinoidea), Zootaxa 3681 (1), pp. 1-43 : 4-5

Family Atelecrinidae Bather, 1899

Emended diagnosis. Articulate crinoids with centrodorsal conical (usually taller than wide across the base); adoral rim with five interradial depressions, sockets or deep pits; centrodorsal cavity broad and deep, with no adoral lip. Cirrus sockets in 10 or 15 columns, bearing weak to strong, lateral articular tubercles arising from socket rim. Basals wedge-shaped, forming an externally visible ring (rarely as separated triangles) with a small central canal and with a pair of interior curved projections that may form a rosette-like structure. Rays divided once at primibrachial 2. Proximal syzygies at 3+4, and usually 6+7, 9+10 (unknown beyond 3+ 4 in Sibogacrinus ). Proximal pinnules absent. Arms terminating in a long filament composed of slender, elongated brachials lacking pinnules (unknown in Adelatelecrinus and Sibogacrinus ) (modified from Hess and Messing 2011).

Type genus. Atelecrinus PH Carpenter, 1881.

Remarks. Bather (1900) erected Atelecrinidae for Atelecrinus after first mentioning the family name without comment ( Bather 1899). Three genera have subsequently been variously added or removed. AH Clark (1912) added monotypic Atopocrinus sibogae based on its tall conical centrodorsal, socket fulcral ridges, and similar proximal brachials, though he also noted similarities with the comatulids Zenometra and Psathyrometra [then in Antedonidae ; now in Zenometridae ( Messing and White 2001) ]. Atopocrinus also has five undivided rays similar to those of the comatulid Pentametrocrinus AH Clark, 1908 ( Pentametrocrinidae ), and a complete complement of pinnules. AH Clark (in Clark and Clark 1967) added Sibogacrinus for Atelecrinus anomalus AH Clark, 1912, which led AM Clark (in Clark and Clark 1967) to diagnose the family with few uniting features and numerous exceptions, e.g., 10 arms or (in Atopocrinus ) 5 arms; centrodorsal with cirrus sockets flanked by “prominent elevations” [p. 811] sometimes forming a horseshoe-shaped ridge (except in Sibogacrinus ); pinnules absent from the first 12 or more brachials (except in Atopocrinus ).

Gislén (1924) transferred Upper Cretaceous Atelecrinus belgica (Jaekel 1901) to a new genus, Jaekelometra, and removed it to the fossil family Conometridae . Rasmussen and Sieverts-Doreck (1978) returned the genus to Atelecrinidae (see also Jagt 1999) but recognized only one feature common to the then four included genera ( Atelecrinus , Atopocrinus , Sibogacrinus, Jaekelometra ): cirrus sockets with a distinct fulcral ridge or pair of tubercles and a more or less prominent edge. Messing (2003) removed Jaekelometra and Sibogacrinus from the family, because the tall thin basals of J. belgica (Jaekel, 1902) and J. columnaris Gislén, 1924, differed completely from the flattened wedge-shaped ossicles of Atelecrinus , and the tall basals of Sibogacrinus (only known at the time in external view) appeared similar to those of Jaekelometra. He also cited the basals of J. meijeri Rasmussen, 1961, as flattened and wedge-shaped, but small, without interior processes, and nestled within a much smaller central cavity than in Atelecrinus ; however, these were actually broken portions of typical Jaekelometra basals ( Jagt 1999) and possibly an extreme form of J. group of concava (Schlüter, 1878) (Hess, in Hess and Messing, 2011). Messing (2003) treated both Sibogacrinus and Jaekelometra as incertae sedis.

Most recently, new material of Atopocrinus from Japan has revealed a small rather than cavernous centrodorsal cavity, and five tongue-like basal rays instead of a complete basal ring (Messing, unpublished). Messing (in Hess and Messing, 2011) placed the genus in the new family Atopocrinidae without superfamilial assignment. In Jaekelometra, atelecrinid socket tubercles appear to be absent, the basals are tall and thin rather than wedgeshaped, and the oral surface of the centrodorsal varies widely, e.g., in J. group of concava, it may be flat with shallow interradial grooves or bear five large radial pits resembling those of the comatulid Notocrinus virilis Mortensen, 1917 (Notocrinidae) ( Jagt 1999). Hess (in Hess and Messing, 2011) erected the new family Jaekelometridae for this genus, also without superfamilial assignment.

Reexamination of the unique but now deteriorated type specimen of S. anomalus (Messing, unpublished) has revealed thick, wedge-shaped basals more similar to those of Atelecrinus than Jaekelometra. The cirrus sockets also bear weak triangular fulcral processes. As a result, Hess and Messing (2011) retained Sibogacrinus within Atelecrinidae , although its centrodorsal cavity is much less spacious than in the other atelecrinid genera.

Within the Atelecrinidae , relationships among the four genera included in this paper appear to be ( Sibogacrinus ( Atelecrinus ( Adelatelecrinus + Paratelecrinus )). The latter three share a cavernous centrodorsal cavity, distinctive projecting fulcral tubercles, thin rather than thick basals, and much longer cirri with more elongated segments. Adelatelecrinus and Paratelecrinus group together on the basis of their common possession of 5 hollow, interradial buttresses in the centrodorsal cavity that open adorally as deep, ring-shaped pits, whereas Atelecrinus has shallow interradial depressions (see also Messing 2003). Table 1 provides a tabular key to all named species in Atelecrinidae .