Formerly: Heterocrinus simplex
Map point data provided by iDigBio.
- C2 Sequence (Fairview: Fairmount, Mount Hope)
- C1 Sequence (Clays Ferry/Kope: McMicken, Southgate, Economy/Fulton)
- Ten arms bearing slender ramules from opposite sides every second brachial
- Small, smooth, conical aboral cup
- Average cup dimensions of 6 mm high and 5 mm wide
- Average stem dimensions of 300 mm long and 3 mm in diameter
Ectenocrinus simplex from the Waynesville Formation of Waynesville, Ohio (OUIP 1533)
- A complete small adult specimen (cup height 2.5 mm) of E. simplex from the Galena Group of Minnesota has a stalk 25.5 cm long (Brower, 1992b). A larger specimen (cup height 8.5 mm) from the Cincinnatian also has 25 cm of stalk attached with no evidence of a distal termination.
- Ectenocrinus also has ten arms bearing slender ramules from opposite sides every second brachial. The ramules are unbranched and become shorter distally (Brower, 1992b). Brower (1992b, fig. 13) reconstructed the feeding posture and filtration fan of E. simplex.
- Remarks. –Ectenocrinus simplex is represented by about 20 specimens, mostly aboral cups, from the Elgin, Clermont, and Fort Atkinson Members of the Maquoketa Formation of northern Iowa and southern Minnesota. The complex nomenclature of this crinoid has been reviewed by Warn and Strimple (1977) and Brower (1992b). The Maquoketa specimens of E. simplex were originally described as E. raymondi by Slocom (1924, p. 337, pl. 29, figs. 5-9) because of the ridges and grooves along the sides of the main arms. These features can also be seen in Middle Ordovician specimens from the Galena Group of Iowa and Minnesota and the Trenton Group of New York; thus, E. raymondi is clearly a junior synonym of E. simplex. The ridges and grooves are an adaptive feature and they interlock the adjacent arms together when the crown is closed. Geographic variation and allometry within the aboral cups of Ectenocrinus simplex is discussed later in this paper.
- Discussion of the homocrinid Ectenocrinus simplex also provides useful information. Obviously, the homocrinid symmetry plane is present in the radial circlets of the aboral cup. Although not well preserved, the base of the cup bears pentagonal basals with a pentagonal opening for the axial nerve cords and associated structures; the resultant symmetry is pentagonal. The sutures of the unusual trimeric stem of E. simplex are located in the B ray, E ray, and CD interray; the pentalobate or pentagonal axial canal has lobes or points directed interradially (Warn and Strimple, 1977, p. 86, 87; Brower, 1992b, p. 980). This arrangement produces another symmetry plane ranging from the CD interray through the A ray which corresponds to the crinoidal symmetry plane of many camerates and some cladids (Moore, 1962).
Fossils of Ohio (1996):
- A small, smooth, conical aboral cup and only 10 Primary arms. The 10 arms bear very slender branches (ramules) on every second brachial. Columnals are circular.
- 10 Primary arms have numerous very thin branches on every second brachial; columnals circular.
- The one form that did not disappear was the round form with the pentagonal lumen and well-fused trimeres. This had been the most “progressive” of all the variants and also the one apparently best adapted to shallow waters. This form had appeared first in the shallow shelf facies 9 m above the base of the Denley Limestone at Deer River (Figure 8). It soon became very abundant and expanded its range into still shallower water throughout the rest of the Denley (Figure 8). In the upper Denley Limestone it was thus able to survive while all the other clinal forms disappeared. This form was Ectenocrinus simplex.
- All Ectenocrinus specimens with round columnals and pentagonal lumina are classified as belonging to E. simplex.
- Warn and Strimple (1977) found lichenocrinid holdfasts associated with E. simplex
- Diagnosis. -Ectenocrinus with round, trimeric columnal; lumen pentagonal. See Warn and Strimple (1977) for diagnosis and description of crown.
- Descriptions of stem and column. -Columnals round, trimeric; lumina sharply pentagonal or pentagonal with rounded comers; near crown columnals thin, nearly same size as their neighbors; distally columnals enlarge, heteromorphic, with short, narrow forms alternating with tall, wide ones; columnal and lumen shape appear uniform through entire length of stem; holdfasts unknown.
- Collections. -Seven crowns have been found in the lower Steuben Limestone. Columnals are extremely abundant and are among the chief components of Steuben Limestone encrinites.
- Occurrence. – Throughout the shallow-water facies of the Denley Limestone and through all facies of the Steuben and Hillier Limestones (heavy stipples on Figure 8).
- The Ordovician crinoid Ectenocrinus simplex (Hall) from the Cincinnatian Series of Ohio and vicinity provides a typical example. Assuming average dimensions (cup 6 mm high and 5 mm wide; stem at least 300 mm long and 3 mm in diameter) gives a cup colume (calcite and tissues) for this crinoid of approximately 3.9 X 10^-2 cubic cm and total volume, including arms, cup, anal tube, and stem, of about 2.3 cubic cm.