This is Mazon Monday post #278.  What’s your favorite Mazon Creek fossil?  Tell us at email:esconi.info@gmail.com.

---

Lacking hard parts, jellyfish are rare in the fossil record. Mazon Creek has a few species of them.  One of the most common animal fossils found in Mazon Creek is Essexella asherae, which only recently was reclassified as a sea anemone (see Fossil Friday #188).  Today, we are looking at one of the rare Mazon Creek jellies, Anthracomedusa turnbulli, which is a box jelly.  A. turnbulli was described by Ralph Johnson and Eugene Richardson, Jr. in 1968 in the paper “Pennsylvanian Invertebrates of the Mazon Creek Area, Illinois: The Essex Fauna and Medusae”, which appeared in Fieldiana.

The namesake for Anthracomedusa turnbulli, is James Turnbull.  Turnbull was one of Eugene Richardson’s assistants in the field during the 1960s.  He found multiple specimens of A. turnbulli in Pit 11 in 1965. Those specimens were donated to the Field Museum and became the holotype and the paratypes in the Field’s collection. Here’s how Richardson described Jim’s finds in “Jellyfish in them thar hills”, which appeared in the October 1968 edition of the Field Museum Bulletin (see Mazon Monday #158).

A few years ago, one of the collectors cooperating with the Museum, Jim Turnbull of Libertyville and the U. S. Marines, dropped in to see us with a perfectly fine jellyfish in one of the familiar ironstone concretions. Recognizing its significance, Jim kindly gave it to the Museum for permanent deposit. We jokingly ordered some more. He returned to the strip mines, to the hill where he had found that one, and the following week was back with two more, which he also deposited with us.

Jim’s jellyfish are large and splashy specimens, four or five inches across the bell, with groups of tentacles almost that long hanging from four corners. Faint dark lines crossing the bell correspond to certain structures known as septa that similarly divide the bell of some modern jellyfish into four areas. When Professor Ralph Johnson saw the specimens, he recognized them as being very clearly members of a living group, the Order Carybdeida, but a species new to science.

Description

Holotype. FMNH no. PE 10500, one-half of a large concretion. collected in 1965 by James Turnbull from Pit 11 of the Peabody Coal Co., Essex, Illinois (fig. 57).

Paratypes. FMNH nos. PE 10501 (fig. 58), collected by James Turnbull, and PE 10951 both from Pit 11 of the Peabody Coal Co. Essex, Illinois.

Remarks. More than 20 well-preserved specimens have been ex-amined. The bell width varies from 28 to 100 mm. and the maximum tentacle length is 100 mm. Except for the general outline, there is little detail shown by the fossils. The holotype exhibits two faint lines running to each bell corner that probably represent septa. The cuboidal form and the cluster of tentacles borne at bell corners place Anthracomedusa in the order Carybdeida (Cubomedusae).

According to Hyman (1940) the Carybdeida are the most primi-tive of the Recent schyphozoans. Modern carybdeids are small and characteristically occur in warm, shallow waters. Anthracomedusa is the oldest known member of the order and may be the oldest known member of the subclass Scyphomedusae. Three imperfectly known genera from the lower Cambrian have been tentatively re-ferred to this subclass (Harrington and Moore, 1965).

The trivial name is proposed in honor of Mr. James Turnbull who collected the holotype and one of the paratypes and donated them to the Museum.

From Jack Wittry’s “The Mazon Creek Fossil Fauna”.

Anthracomedusa turnbulli Johnson and Richardson, 1968

Anthracomedusa turnbulli shares the same nickname as its present-day descendants, the Sea Wasps, suggesting the possible danger swimmers are in when encountering members of this group. Modern sea wasps are known for the extremely potent venom pro-duced by some species and are among the most venomous creatures in the world. Stings are extremely painful and sometimes fatal to humans.

A. turnbulli has a cube-like bell with four flattened sides, much like its extant class members, the Box Jellies. Each surface corner has one thick, short pedalium from which the smaller pedalia give rise to 24-30 tentacles. Larger animals may have up to 120 ten-tacles. In a good specimen, septa can be seen leading to four sub-umbrellar funnels which end in the coelenteron, or stomach.

Specimens tend to be very flat. Often the corner tentacles fold in on themselves, or the concretion reveals only part of the tentacle bundles. Of the sea jellies described in this section, A. turnbulli was the least frequent Essex animal in a sample of 2,500 animal concretions, with only five specimens found.

Specimens

Holotype – FMNH PE 10500 – Collected by James Turnbull

Paratype – FMNH PE 10501 – Collected by James Turnbull

FMNH 32364 – Collected by Jerry Herdina

Francis Tully specimen from the original paper “Pennsylvanian Invertebrates of the Mazon Creek Area, Illinois: The Essex Fauna and Medusae”

From ESCONI member Ben Riegler in Fossil Friday #270