Acanthambonia sp. A

Holmer, Lars E. & Biernat, Gertruda, 2002, Urban and Peri-urban small and medium-size Enterprise Development for sustainable Vegetable Production and Marketing Systems, Acta Palaeontologica Polonica 47 (1), pp. 141-156 : 148

Acanthambonia sp. A

Fig. 5A–E.

Helmersenia cf. ladogensis ( Jeremejew, 1856) ; Biernat 1973: 110, pl. 33: 1–7, fig. 40.

Material.—Total of 9 ventral valves. Figured ventral valves: RM Br133786, RM Br133787.

Description.—See Biernat (1973: 110).

Remarks.—Only ventral valves of this rare and poorly known species were recovered in this study, but Biernat (1973) also described and illustrated the dorsal valve. It was then tentatively considered to represent juveniles of Helmersenia ladogensis , but restudy of this taxon (e.g., Holmer and Popov 2000: 143, fig. 79: 3) indicates that Helmersenia is clearly different in the size and shape of the pedicle opening as well as in lacking an interior pedicle tube. The Polish species is most similar to species of Acanthambonia in having a minute apical foramen, which is continued internally as a pedicle tube along the valve floor ( Biernat 1973: pl. 33: 1, fig. 40). Acanthambonia sp. A is the first record of the genus from Tremadoc strata, but it described under open nomenclature in view of the poor preservation of the few available specimens.