Echinocyamus, van Phelsum, 1774

Ceranka, Tomasz, 2007, Symmetry disorders of the test of the Miocene echinoid Echinocyamus from Poland, Acta Palaeontologica Polonica 52 (3), pp. 503-518 : 504-505

Echinocyamus test

The typically developed test of the three examined Miocene Echinocyamus species is small (length from 1 to 10 mm, typically 3 mm), oval or pentagonal in outline ( Fig. 1A 1, B 1 ). The anterior part is often higher and narrower. Test shape is loaf−like to conical, with the culmination always at the apical system, on which the hydropore (equivalent of the madreporite), five ocular pores, and four gonopores occur ( Fig. 1C ). The petaloid area comprises five ambulacral petals ( Fig. 1A 2 ). Each petal consists of two columns, of which each is represented as two rows of pores. The pore pair of one respiratory tube foot is composed of pores diagonal to the structure's length. Each petaloid column may comprise up to 7–8 pore pairs, on average 3–4. Pores are round, and their diameter increases with the growth of the corresponding ambulacral tube foot. In side view profile, the test margin (ambitus) forms an arc, which is more acute in less arched forms. The oral side is flat or slightly concave with a centrally placed, round or pentagonal peristome ( Fig. 1B ). The round or transversely oval ( E. pusillus ), transversely oval or lenticular ( E. calariensis ) periproct is located halfway between the mouth opening and the test margin ( E. pusillus , E. calariensis ) or marginally ( E. apicatus )—in the latter case its margin lies in the plane oblique or almost perpendicular to the oral side ( Fig. 1B ). The periproct is situated always between the first and second pair of interambulacral plates (counting outward from the mouth, not counting the unpaired basicoronal).

The described symmetry deformations cause crucial changes of test and peristome shape. Therefore, the location and shape of the periproct are in practice the only features distinguishing the three species.

Figures

Fig. 1. Correctly developed test of fibulariid echinoid Echinocyamus apicatus Mortensen, 1948 (MWG/E/0) from Korytnica, Badenian. A. Aboral side. B. Oral side. C. Close−up of apical system. A1, B1, C1, photos of the specimen; A2, B2, C2, explanatory drawings of the same. I–V, growth zone; O, ocular pore; G, gonopore (genital pore); H, hydropore.

Fig. 2. Deformed test of Echinocyamus apicatus Mortensen, 1948 (MWG/E/1) from Korytnica, Badenian. L+ anomaly (6−ray symmetry). A. Aboral side. B. Oral side. C. Close−up of apical system. A1, B1, C1, photos of the specimen; A2, B2, C2, explanatory drawings of the same. I–V growth zone; O, ocular pore; G, gonopore (genital pore); H, hydropore.