Plinthosella magna, Pisera, 2000

Pisera, Andrzej, 2000, New species of lithistid sponges from the Paleogene of the Ukraine, Zoosystema 22 (2), pp. 285-298 : 293-296

Plinthosella magna n. sp.

( Figs 2L ; 6 )

MATERIAL. — Holotype, the only specimen in the collection NHM ZN3.

ETYMOLOGY. — The species name magna , in Latin “great”, refers to relatively large size of this species.

DIAGNOSIS. — Club-shaped sponge with shallow depression at the upper pole in which a cluster of rounded openings of short canals occurs. Desmas are tripodial strongly tuberculated with the upper conical ray bearing no articulation. Desmas articulation nonterminal. No dermalia have been observed.

DESCRIPTION

Club-like specimens about 7.5 cm high and 4 cm thick maximum bearing slightly depressed and excentrically located shallow depression about 1.5 cm in diameter at the upper pole. Numerous very densely spaced and 0.5 mm in diameter round canal openings occur on the bottom. These canals continue first vertically, then diverge outward and extend in irregular manner through the sponge. Outer surface smooth, bearing only very loosely spaced canal openings 0.5-0.8 mm in diameter. Skeleton dense and composed of heavy desmas, measuring 600 × 500-600 µm. They are completely covered with numerous large (58 µm across) mushroom-shaped and round tubercles. Young desmas nearly smooth and measure 500 µm in width and 400 µm in height. Desmas have tetractine geometry and are tripodial, i.e. only three inner (directed toward the sponge interior) rays display articulations, while the outer ray (directed toward the sponge surface) has no articulation and is developed in the form of a high narrow cone. Also on the young desmas there is no indication of any articulation on the outer conical ray. No dermal skeleton has been observed. Articulation of desmas is strictly non terminal.

REMARKS

This must be the specimen which was erroneously considered by Oakley (1942) as rhizomorine Jereica clavaeformis Pomel.

The Cretaceous lithistids with tripodial tuberculated desmas, having one ray conical and without articulation, are attributed to the family Plinthosellidae Schrammen, 1910 , which has siliceous plates as dermalia. No dermalia are preserved in the investigated material, but desmas are very similar to those occurring in the Upper Cretaceous Plinthosella Zittel (see Zittel 1878; Schrammen 1910; Moret 1926; Hurcewicz 1966). My specimen differs from the Cretaceous forms in larger size and club shape, in canalization, as well as in details of desma morphology. Similar tripodial desmas occur in some Cretaceous tetracladines, but then they are limit- ed only to the outermost layer of choanosomal skeleton, the rest being composed of typical tetraclones. In the investigated specimen, the whole skeleton is built of the same type of tripodial desmas.

Among Recent demosponges, morphologically close desmas occur in Desmanthus Topsent, 1893 (see Lévi & Lévi 1989), which is, however, encrusting in habit and composed of one layer of desmas that are accompanied by styles or tylostyles.

Figures

FIG. 2. — Habit of the investigated sponges; A-D, Theonella ukrainica n. sp.; A, NHM ZN10D; B, holotype NHM ZN5A; C, NHM ZN5E; D, NHM ZN5F; E-H, Chenendopora piaskovskii n. sp.; E, F, paratype NHM ZN11 in lower side (E) and upper side (F) views; G, H, holotype NHM ZN1 in upper (G) and lower side (H) views; I-K, Lerouxia digitata n. sp.; I, NHM ZN4; J, holotype, NHM ZN7; K, paratype, NHM ZN8; L, Plinthosella magna n. sp., holotype NHM ZN3, oblique view. Scale bars: A-D, G, H, L, 1 cm; E, F, I-K, 2 cm.

FIG. 6. — Plinthosella magna n. sp., holotype NHM ZN3; A, B, loose young, still smooth tripodial desmas in top and side views; C, D, typical tripodial strongly tuberculated desmas in top (C) and lateral (D) views; E, details of adult desmas to show character of tuberculation; F, G, choanosomal skeleton in top (F) and lateral (G) views to show its very dense character and nonterminal articulation of desmas. Scale bars: A, B, 100 µm; C, D, 200 µm; E, 50 µm; F-G, 500 µm. All SEM photographs.