Scyphocrinus elegans (Sea lily) — The Shane Bodimer Collection

The Sea Lily

Crinoids are animals, not plants, although the name means "lily-like." They belong to the phylum Echinodermata, alongside sea stars and sea urchins, and share the five-part symmetry and calcium carbonate skeleton of those groups. A crinoid has a cup of plates holding the organs, with five arms rising from it. Fine side branches called pinnules carry tube feet that flick drifting plankton into a groove, and cilia carry the food to the mouth.

Scyphocrinitids were camerate crinoids of the latest Silurian and Early Devonian. They had a crown of about 40 centimeters on a stem of up to about 3 meters, ending in a chambered bulb commonly 10 to 20 centimeters across. The drawing shows the animal as recent work reconstructs it, with the stem lying along the sea floor and the crown raised high above it, in the highest tier of Paleozoic sea-floor life.

Fig. 1 A scyphocrinitid crinoid with its stem lying along the sea floor and the lobolith at its endDrawing by Magdalena Łukowiak, after Gorzelak and others (2020), via Wikimedia Commons · CC BY 4.0

The Specimen

This slab of reddish-brown rock carries a single crinoid, or sea lily, from Morocco. The animal is preserved as dark grey calcite against the red matrix. Its crown, the cup and the fan of feeding arms, lies flat on the surface. The arms spread upward and to the left from the cup, packed side by side, and toward the right they lie in close parallel rows. The stem runs from the base of the cup toward the lower edge, surrounded by loose stem segments called columnals, each a short cylinder like a stacked coin.

Judging by the ruler in the dealer photograph, the slab measures roughly 20 centimeters (about eight inches) across. The label reads Scyphocrinus elegans, but Scyphocrinites elegans Zenker, 1833 was described from Bohemia, and in 1986 Rudolf Prokop and Václav Petr concluded that North African scyphocrinitids published under that name are probably not the same species. A cautious identification is "scyphocrinitid crinoid, Morocco."

Fig. 2 A scyphocrinitid slab from the Erfoud region, MoroccoPhoto by Géry Parent via Wikimedia Commons · CC BY-SA 4.0

The Lobolith

The bulb at the end of a scyphocrinitid stem is called a lobolith. Isolated bulbs were named Camarocrinus by James Hall in 1879, and Frank Springer's 1917 Smithsonian monograph treats the genus Scyphocrinus and its bulbous root Camarocrinus. The lobolith is hollow and divided into chambers, built in some forms of branching rods and in others of thin plates. Loboliths are rarely found attached to crowns.

Its function has been argued for more than a century. The buoyancy reading, set out in Reimund Haude's 1972 study, held that the chambers were gas-filled: the bulb floated, the crown hung below it, and the crinoid drifted with the currents as a "buoy sea lily." Two previous editions of the Treatise adopted it.

In 2020 Gorzelak and colleagues re-examined it in Paleobiology, using the microscopic structure of the skeleton and a mechanical model. They found no features in the lobolith wall that would keep gas in or seawater out, and calculated that a drifting scyphocrinitid would have been a poor filter feeder. They proposed instead that the lobolith was a modified holdfast, with the stem lying along the sea floor and the lobolith possibly acting as a drag anchor. The 2025 Treatise revision says that, on current knowledge, it seems scyphocrinitids lived on the bottom and their loboliths served as holdfasts. The wording is cautious, and the buoyancy interpretation has not disappeared from the literature.

Fig. 3 Loboliths (*Camarocrinus*), from Frank Springer's 1917 monographDrawing by K. M. Chapman via Wikimedia Commons

Crinoids Today

About 650 to 700 species of crinoid are alive today. More than 5,000 fossil species have been described, and the class reached its peak diversity roughly 300 million years ago. Living crinoids occupy habitats from shallow coral reefs to the floors of oceanic trenches. The deepest-dwelling species known, Bathycrinus kirilli, was described in 2019 from the Izu-Bonin Trench in the western Pacific, at 9,715 to 9,735 meters.

Popular accounts divide living crinoids into stalked "sea lilies" and unstalked "feather stars." The division is useful but informal. Sea lilies keep a stalk as adults. Feather stars lose it while still very small and keep only the top segment, which bears hooked appendages called cirri for clinging to the bottom. Because the stalk has been lost and regained more than once in crinoid history, neither group is a tidy branch of the family tree. In today's seas the stalked forms no longer live in shallow water: the shallowest known species, Metacrinus rotundus, lives at about 100 meters off Japan. Feather stars range from just below the tide line to great depth.

The animal in the photograph below is a feather star on a reef. It has no stalk, but it shows the crown form that all crinoids share: a cup with many feathered arms.

Fig. 4 A living feather star on a reef at Batu Moncho IslandPhoto by Alexander Vasenin via Wikimedia Commons · CC BY-SA 3.0

The Silurian–Devonian Boundary

The International Commission on Stratigraphy's 2024 chart places the start of the Silurian Period at 443.1 million years ago and its end, which is also the start of the Devonian Period, at 419.62 million years ago. The boundary is defined at Klonk, in the Czech Republic, by the first appearance of the graptolite Uncinatograptus uniformis. The Devonian, named for Devon in southwest England, ran until 358.86 million years ago.

Scyphocrinitids lived across the boundary, and their loboliths have been used to help recognize it in places such as Xinjiang in northwest China and southern Turkey.

Fig. 5 The world about 420 million years ago, at the end of the Přídolí EpochMap by Christopher R. Scotese and colleagues via Wikimedia Commons · CC BY 4.0

Scyphocrinitids in Morocco

Moroccan scyphocrinitid slabs are collected in the Tafilalt region of southeastern Morocco, near Erfoud and Taouz. The crinoids occur in the Scyphocrinites limestones, layers and lenses a few centimeters to a few decimeters thick set in much thicker sequences of shale. Most of the limestone is crinoid debris, though some layers hold whole scyphocrinoids, and loboliths are abundant.

In 2014 Maria Corriga, Carlo Corradini and colleagues published conodont studies of three measured sections showing that the Scyphocrinites limestones span the Silurian–Devonian boundary. The more primitive cirrus-type loboliths occur through the Přídolí; plate-type loboliths and Camarocrinus appear at the top of the Přídolí and in the basal Lochkovian.

Taken together, the sources support an age of about 420 million years for the Moroccan beds, to within a few million years. Which genus the animal on this slab represents cannot be told from the photograph.

Fig. 6 A slab of scyphocrinoid crowns on display at the Geoscience Museum of the University of GöttingenPhoto by Illustratedjc via Wikimedia Commons · CC BY-SA 4.0

Provenance

This specimen was bought in March 2024 from The Stones & Bones Collection, a fossil dealer. The locality recorded for the piece is Morocco. A more specific find site, horizon or collecting date is not recorded here.