Pentremites meganae Atwood & Sumrall, 2012 - blastoid in the Mississippian of Kentucky USA.

Blastoids are an extinct group of echinoderms. They resemble crinoids in having a head, or theca, perched atop a long stem of stacked columnals composed of calcite (see pictures of a complete specimen elsewhere in this photo album). Crinoids and blastoids are pelmatozoans - stalked echinoderms. Both groups are sessile, benthic, filter-feeding organisms. The overall structure and morphology of crinoid heads and blastoid heads are quite different. Blastoid heads have pentaradial symmetry and somewhat resemble closed flower buds or nuts. They have 5 ambulacral grooves extending outward and downward from the summit of the theca. During life, many thin, delicate brachioles extended from the ambulacral grooves - these structures captured tiny particles of food from seawater as the blastoid engaged in filter feeding.

Two pyriform Pentremites blastoids have been reported from the Glen Dean Formation of Kentucky - Pentremites pyriformis and Pentremites meganae. Pyriformis has concave ambulacra (best seen in summit view). Meganae has flat to convex ambulacra. The specimen shown above is consistent with Pentremites meganae (see Atwood & Sumrall, 2012).

Classification: Animalia, Echinodermata, Blastozoa, Blastoidea, Spiraculata, Pentremitidae

Stratigraphy: Glen Dean Formation, Chesterian Series, Upper Mississippian

Locality: Wax South Outcrop - Rt. 88 roadcut south of the town of Wax & immediately south of Nolin Reservoir/Lake, west-northwest of the town of Cub Run, far-western Hart County, west-central Kentucky, USA (37° 20' 10.88” North latitude, 86° 07’ 35.03” West longitude)

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