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First complete holothurian skeletons from Poland (Early Kimmeridgian, Bełchatów, Central Poland)

Boczarski A.

Volumina Jurassica

2006

Vol. 4, no. 1

231-232

First complete holothurian skeletons (scleritome) and sclerite aggregates from the Early Kimmeridgian of Poland (Bełchatów, Central Poland) were described in this paper. The sclerites (hard parts) of the living holothurians are connect only by soft tissues. These tissues decompose after death of the animals very quickly, and the skeletons undergo quick dispersion in the sediment. Complete specimens of Holothurioidea are extremely rare finds (Boczarowski 2001). The scleritome is an association of all types of skeletal elements of single species (Bengtson 1985). Well-preserved holothurian remains were found in two marly limestone samples coming from boreholes Bełchatów 126 GP (depth 135.2 m) and Szczerców PS 68 (depth 219.8 m). Six complete or almost complete holothurian skeletons (Achistrum sp.), 35 skeletal aggregates (Achistrum sp., Hemisphaeranthos sp., Priscularites sp.) and thousands of isolated sclerites were found (Figs 1-2). Many recent species belonging to order Apodida Brandt, 1835 live buried in muddy or sandy sediments (Boczarowski 2001). These holothurians are able to very quickly dig itself in sediment through co-ordinating the action of tentacles and the cramps of the body. Achistrum Etheridge, 1881 emend. Frizzel & Exline 1955 and Hemisphaeranthos Terquem & Berthelin, 1875 emend. Frizzel & Exline 1955 probably lived as funnel-feeders (digging the tentacles into the sediment and making funnel shaped depression). Sclerite assemblages of Priscularites Deflandre-Rigaud, 1962 are very similar to scleritome of molpadid holothurians (order Molpadida Haeckel, 1896), especially to representatives of family Eupyrgidae Semper, 1868 and mostly to genus Eupyrgus Lutken, 1857. The representatives of this genus occur in most of seas of the northern hemisphere at present time. Thousands of them buried in the soft sediment. They are conveyor belt-feeders (digging the tentacles into the sediment and transferring them to the mouth permanently). Specimens found in marly limestones of Be.chatów probably lived on soft bottom, in the sediment as infaunal or semiinfaunal animals (Achistrum sp., Hemisphaeranthos sp. and Priscularites sp.). After the death their body quickly decayed, however the remains did not undergo the dispersion in sediments.