Henicocystinae Jell, 1983

Nardin, Elise & Bohatý, Jan, 2013, A new pleurocystitid blastozoan from the Middle Devonian of the Eifel (Germany) and its phylogenetic importance, Acta Palaeontologica Polonica 58 (3), pp. 533-544 : 534-535

Subfamily Henicocystinae Jell, 1983

Emended diagnosis.—Pleurocystitids with trapezoidal to subpyriform thecal outline with no posterior lobe and flattened thecal flanges; periproct large with no anal lobe; one relatively compressed pectinirhomb at L3/L4; two uniserial feeding appendages (emended from Jell 1983: 212).

Remarks.— Jell (1983) considered the family Pleurocystitidae as an order (Pleurocystitida) within the rhombiferans and erected the new family Henicocystidae to classify the atypical genus Henicocystis Jell, 1983 . Pleurocystitids are here ranked as a family; we propose to lower the henicocystids into a subfamily rank. The Henicocystinae differs from the other subfamilies by having apparent uniserial feeding appendages and a single rhomb located at the L3/L4 suture. The re−examination of the specimens of Regulaecystis Dehm, 1932 and the fragments of feeding appendage preserved in Coopericystis Parsley, 1970 (USNM 114198a) suggest uniserial plating, which justify their assignment to the Henicocystinae .

In blastozoans, “each ambulacral complex […] is spatially subdivided into the ambulacral zone extending directly along the thecal surface and the brachioles” ( Rozhnov 2002: S604). The feeding appendages of the Henicocystinae possess all characteristics of brachioles (food−gathering, free and erect unbranched exothecal structures), except for the biserial plating. The ambulacral zone is strongly reduced and shows an atomous branching pattern (sensu Nardin et al. 2010). Modifications of the typical biserial brachiolar plating to biserial opposite and apparent uniserial plating are relatively common within the blastozoans, such as in some eocrinoids (e.g., Haimacystis , rhipidocystids; Sprinkle 1973; Sumrall et al. 2001; Rozhnov 2002), paracrinoids ( Regnéll 1945; Parsley and Mintz 1975), and some diploporans (e.g., asteroblastids; Rozhnov 2002). Typical brachioles show biserial alternate plating ( Sprinkle 1973). The secondary uniserial plating of the brachioles of the Henicocystinae might have resulted from an abnormal or displaced growth pattern leading to a pseudo−uniserial plating or to a biserial opposite plating altered during the fossilisation process. Those hypotheses have been suggested for the rhipidocystid eocrinoids and the paracrinoids; Sprinkle 1973; Sumrall et al. 2001; Rozhnov 2002; Guensburg et al. 2010).

Stratigraphic and geographic range.—Members of the Henicocystinae are known from the Middle Ordovician ( Coopericystis , Regulaecystis ) to the Middle Devonian ( Coopericystis , Henicocystis , Pleurocystitidae gen. et sp. indet. A, B, C and Regulaecystis ) of North America, Europe, and Australia.