Pionodema

Classification
Phylum: Brachiopoda
Class: Rhynchonellata
Order: Orthida
Family: Draboviidae
Genus: Pionodema Foerste, 1912
Cincinnatian Species: Pionodema bellula

Geologic Range
Late Ordovician

Common Paleoecology
Pionodema is an extinct genus of stationary epifaunal suspension feeders

Identification in Hand Sample:

  • Transversely semioval, dorsibiconvex valves
  • Short, curved ventral interarea
  • Orthocline dorsal interarea
  • Ventral interior with extended muscle scar bisected by median ridge
  • Dorsal interior with small, lobate cardinal process and thin shaft on low notothyrial platform
  • Brachiophores plates converge anteriorly onto median ridge

Geographic Occurrences

		

Published Description

Treatise on Invertebrate Paleontology, Part H, Vol. 3 (2000):

  • Transversely semioval, dorsibiconvex valves with short, curved ventral interarea and orthocline dorsal interarea; ventral interior with extended muscle scar bisected by median ridge; dorsal interior with small, lobate cardinal process and thin shaft on low notothyrial platform; brachiophores plates converge anteriorly onto median ridge.

Cooper (1930) :

  • Group A. Black River puncatate shells. Inside the ventral valve of this group, there are prominent teeth supported by well-defined, discrete, and widely divergent dental plates, whose anterior ends are continued forward as low elevations along the lateral margins of the muscular field.The adductor track is generally more or less elevated and bears lanceolate adductor scars; the diductor scars (including the adjustor scars) are subflabellate and their front ends are extended anteriorly to the termination of the adductor track for a short distance but never enclose it. In front of the adductor scars, there is commonly a low elevation or median ridge extended forward for a short distance. In the apex of the delthyrium
    there is a small plate, probably a pedicle attachment, filling the posterior of the apex flush with the area but sloping forward or bevelled at its front end, and showing concentric lines of growth. The front or bevelled portion of the plate is attached to the inner surface of the thickened delthyrial margin formed by the progressive growth-track of the teeth. Such a plate has been seen in Schizophoria, Enteletes, and a few species of dalmanellids but never in the impunctate shells discussed below. (See pl. 35, fig. 3.)
  • In the dorsal valve (pl. 35, fig. 4) the cardinal process, although small in size, has an expanded myophore or muscular attachment, is distinctly bilobed, and is dalmanelloid in every respect. The crural bases are long, somewhat curved, and shaped like the tusk of a boar.The crural base supports are widely divergent, discrete plates which attach directly to the valve. In one species (P. subaequata) their anterior ends are produced forward as low ridges which curve inward toward the median ridge. The sockets are defined by small concave plates, here termed fulcral plates. These unite the outside face of the crural base with the inside wall of the valve. The median ridge is a low elevation extending forward to the middle of the shell, dividing the adductor scars into a right and left set. The posterior adductor scars are the smaller; each scar of the anterior pair appears to be composed of two units, a larger inner scar, and a smaller outer scar. This duplex character of the anterior adductors appears in many orthoid shells, especially in Schizophoria and Orthotichia. The outer, extra set may represent dorsal adjustors.
  • Group B. Black River impunctate shells. In this group the delthyrium is completely open; the teeth are strong, with deep crural fossettes; the muscular field is suboval and divisible into three elements, the adductor, diductor, and adjustor scars. The first are hemi-elliptical impressions situated on each side of a low median ridge; the diductor impressions are elongate, expanded in front, and do not extend anteriorly to the end of the adductor track; the adjustor scars are situated at the base of the dental plates and partially on their sides. The whole field is surrounded by a low elevation of adventitious shell substance. The entire inner surface of the shell is marked by low radial ridges and elongate
    pustules, the latter being interrupted ridges. (P1. 35, fig. 7.)
  • In the dorsal valve, the cardinal process is a simple, thick ridge,
    having a compressed myophore. The crural bases are long but blunt,
    their supporting plates converge, and unite beneath the cardinal process
    to form a shallow sessile cruralium. Concave fulcral plates are present
    exactly as in the punctate division. The median ridge extends to the
    middle of the valve and bisects a quadripartite adductor field.
  • Group C. Chazy impunctate shells. In the ventral valve of these shells the dental plates are discrete and are continued directly to the floor of the valve. They are bent slightly inward near their contact with the floor and mark off deep umbonal cavities. The muscular field is strongly trilobed in front; the adductor track expands in its forward growth. The diductor tracks are widely divergent and their anterior extremities extend in front of the end of the adductor track. Pallial markings are prominent. Two main trunks are given off from the anterior ends of each of the diductor impressions. Each trunk divides and sends a branch postero-laterally and one antero-medially. The former subdivides into two subsidiary trunks and the branches directed anteromedially likewise bifurcate. These bifurcations are repeated more rapidly until the main sinuses are broken up completely into innumerable subsidiary rami. The two inner trunks bound a central heart-shaped area. (P1. 35, figs. II, I5.)
  • The dorsal valve of this group is characterized by convergent crural base supports which form a sessile cruralium somewhat deeper than is usual in the previously discussed group. The cardinal process is thin and septum-like but has a compressed, crenulated myophore. Fulcral
    plates are present on the outside of the crural bases and the median ridge
    is thin. (P1. 35, fig. 12.)

P. bellula