Pelanechinus

Lore & Background

Pelanechinus corallina, the type species, was originally described from a single fossilised specimen from Yorkshire, England, preserving only the oral part of the test. In this species, the plates are fused in groups of three—a central large plate with two half-sized ones on either side—and these groups overlap like roof tiles. A large tubercle appears on every second or third central plate. A later incomplete specimen from the coral rag at Calne, England, had a test diameter of 85 mm, was somewhat dorso-ventrally flattened, and preserved a single ambulacral area and most of two interambulacral areas, with distinct mouthparts and teeth surrounded by small overlapping plates in the peristomal area.

Pelanechinus oolithicum, known from Schinznach, Switzerland, also has plates fused in groups of three in the ambulacral area, but with three tubercles per set (the central one largest) and pore pairs in groups of three. Its interambulacral areas are about three times as wide as the ambulacral areas, with one perforated primary and several secondary tubercles on each plate, and its spines are slender and filled with a spongy material.

Pelanechinus triceps, from the Jura Mountains, has a type specimen diameter of 34 mm and height of 17.5 mm, with perforated and smooth primary tubercles. This species was originally described as Leptocidaris triceps, but Leptocidaris is now considered a junior synonym of Pelanechinus.

Reader's Guide

Pelanechinus is significant as a stem-group echinoid within the order Echinothurioida, a group known for flexible tests. Its fossil record spans the Middle Jurassic (Bajocian) to Late Jurassic (Oxfordian), with species described from England, Switzerland, and the Jura Mountains. The genus illustrates taxonomic revision: Pelanodiadema oolithicum and Leptocidaris triceps were later synonymized under Pelanechinus, reflecting evolving understanding of echinoid relationships. The flexible test structure, with overlapping plate groups and fused triads, is a key characteristic of the Echinothurioida and is well-documented in P. corallina and P. oolithicum. The preservation of mouthparts, teeth, and peristomal plates in P. corallina provides insight into the oral anatomy of these extinct urchins. The spongy-filled spines of P. oolithicum and the perforated, smooth primary tubercles of P. triceps add to the morphological diversity within the genus. As a stem-group echinoid, Pelanechinus helps clarify the early evolution of sea urchins, particularly the transition to flexible tests seen in modern echinothurioids.

Did You Know?

• Pelanechinus corallina was originally described from a single fossilised specimen preserving only the oral part of the test.
• The plates of Pelanechinus corallina are fused in groups of three and overlap like roof tiles.
• Pelanechinus oolithicum has slender spines filled with a spongy material.