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Notes on the Genera Euchitonia, Dictyocoryne and Hymeniastrum

Petrushevskaya and Kozlova (1972, p. 528) made the following taxonomic changes for part of the Family Spongodiscidae:

Genus RHOPALASTRUM Ehrenberg

Rhopalastrum Ehrenberg, 1847a, chart to p.385: Haeckel, 1887, p.526

Rhopalodictyum Ehrenberg, 1860b, p. 832: Haeckel, 1887, p. 589

Dictyocoryne Ehrenberg, 1860b, p. 830: Haeckel, 1887, p. 592

Dictyastrum Ehrenberg, 1860b, p. 830: Haeckel, 1887, p. 524

Euchitonia Ehrenberg, 1860b, p. 831: Haeckel, 1887, p. 532

Pteractis Ehrenberg, 1872a, p. 277

"Spongodiscidae with thin spongy central disc (where chambered rings may be sometimes seen), with three spongy arms and patagium between them."

It is not clear why the genus Hymeniastrum Ehrenberg was excluded from Petrushevskaya and Kozlova's synonymy.

It has already been noted by Ling (1966), Ling and Anikouchine (1967) and Nigrini (1967) that presence or absence of a patagium is of no generic or specific consequence. Ling (1972) is of the opinion that "the concerntric sponqy disc bears the taxonomic value for these spumellarians."

It is the present authors' opinion that:

1. Patagium is of no consequence taxonomically.

2. All the forms of this general type possess some degree of central spheroidal and/or discoidal structure, but this may be obscured by spongy material. The degree of visibility of the central structure may be of generic siqnificance.

3. Some forms exhibit bilateral symmetry while others have equiangular displacement between arms and this feature may be of generic significance.

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4. Species with bifurcating arms should be placed in different genera from those having simple arms.

For these reasons and because major taxonomic revision should involve a stratigraphic study, the following taxonomy, more conservative than that of Petrushevskaya and Kozlova (1972) is proposed.

Family Spongodiscidae Haeckel 1862, emend. Riedel, 1967

"Emended definition: Discoidal, spongy or finely-chambered skeleton, with or without surficial pore-plate, often with radiating arms or marginal spines. and without a large central phacoid shell." (from Riedel, 1971)

GENUS Euchitonia Ehrenberg, emend. Nigrini 1967

Euchitonia Ehrenberg, 1860b, p. 831; sens. emend. Haeckel, 1887, p. 532.

"Euchitoniidae with three simple, undivided, chambered (proximally, at least) arms, with or without terminal spines; triangular shell, bilateral, one unpaired and two paired arms. Patagium may or may not be present. The definition of this genus is emended herein to include forms with and without (1) terminal spines; and (2) a patagium." (from Nigrini, 1967)

The genus Rhopalastrum Ehrenberg, 1847, is similar to the above but has spongy rather than chambered arms and for that reason is not included. Species included:

1. Euchitonia elegans (Ehrenberg)

2. Euchitonia furcata Ehrenberg

3. Euchitonia sp. includes immature or broken specimens of the above, distinguishable by a strong and clearly visible central structure of 3 or 4 concentric spheroidal shells and strong bilateral symmetry. Species of Euchitonia possess a much coarser lattice than other genera.

4. Euchitonia cf. echinata - see remarks for Dictyocoryne truncatum.

GENUS Dictyocoryne Ehrenberg

Dictyocoryne Ehrenberg, 1860b, p. 830

Rhopalodictyum Ehrenberg, 1860b, p. 832

Spongodiscidae with three simple, undivided, spongy arms, with or without terminal spines, equally to bilaterally disposed. Patagium may or may not be Present. Central structure often obscured by spongy meshwork, but consisting

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of 5 to 10 or more concentric discoidal shells. Species included:

1. Dictyocoryne profunda Ehrenberg

2. Dictyocoryne truncatum Ehrenberg

GENUS Hymeniastrum Ehrenberg

Hymeniastrum Ehrenberg, 1847b, p. 54

Dictyastrum Ehrenberg, 1860b, p. 830

Spongodiscidae with three simple, undivided, chambered arms, with or without terminal spines; triangular shell, equiangular displacement between arms. Patagium may or may not be present. Central structure often obscured by spongy meshwork, but consisting of 4 to 5 concentric discoidal shells.

Species included:

1. Hymeniastrum euclidis Haeckel

NOTE: l. It is entirely possible that Dictyocoryne and Hymeniastrum are congeneric.

2. Riedel (1971) places Hymeniastrum in the Family Coccodiscidae.