Circeaster mandibulum
Deep-sea starfish from New Caledonia with jaw-like pedicellariae.
Circeaster mandibulum, a deep-sea starfish belonging to the family Goniasteridae, inhabits waters off New Caledonia. Its name comes from the Latin *mandibulum* (“jaw”), a reference to the pedicellariae found on its adambulacral plates.
This species can be separated from *Circeaster loisetteae* by two key traits: it bears 8 to 15 flattened, blade-like furrow spines arranged in a palmate pattern (whereas *C. loisetteae* has 7 to 8 spines that are square in cross-section), and its superomarginal plates only meet at the very tip of each arm (in *C. loisetteae*, these plates begin abutting right from the arm base near the disk). It differs from *Circeaster pullus* in that *C. pullus* has bivalve pedicellariae with nearly smooth valves and smooth, blunt furrow spines, while *C. mandibulum* lacks bivalve pedicellariae and has roughened, bristle-like tips on its furrow spines. The species most closely resembles *Circeaster sandrae* in also lacking bivalve pedicellariae, but it is distinguished by having 8 to 15 triangular to square furrow spines with rough tips, compared to *C. sandrae*’s 4 to 8 flattened, blunt, and smooth furrow spines.
The body is stout and star-shaped, with an arm length about 2.8 to 3.3 times the disk radius. The arms are elongate, triangular, and rounded at the tips. Abactinal plates are flat and mostly bare, each bearing 10 to 15 widely spaced round granules; plates on the arms grow larger than those on the disk. There are 36 to 38 superomarginal plates and 38 to 40 inferomarginal plates (at a radius of 4.0 to 5.0). The superomarginals form a prominent border, accounting for 13 to 17 percent of the disk radius, and meet over the midline for the 10 to 15 plates at the arm tip. Marginal plate surfaces are mostly bare but carry 20 to 30 coarse, round granules. Nearly every actinal intermediate plate holds a single palm-like pedicellaria with wide valves, each bearing 3 to 5 serrations. Furrow spines number 8 to 15, are flattened and blade-like, and are arranged in a straight or palmate row. Subambulacral spines are absent, but each adambulacral plate has 1 or 2 palmate or clam-shaped pedicellariae.
The species is known only from New Caledonia, at depths between 320 and 470 meters.
Quick Facts
- Genus
- Circeaster
- Species
- mandibulum
Facts from the source article.
Lore & Background
The species epithet mandibulum is Latin for 'jaw', alluding to the pedicellariae present on the adambulacral plates. Circeaster mandibulum is distinguished from Circeaster loisetteae by having 8 to 15 flattened, blade-like furrow spines in a palmate arrangement, versus 7 to 8 quadrate spines in C. loisetteae, and by having abutted superomarginal plates only at the distalmost tip of the arm, rather than from the arm base. It differs from Circeaster pullus, which possesses bivalve pedicellariae with nearly smooth valves and smooth, blunt furrow spines, whereas C. mandibulum lacks bivalve pedicellariae and has roughened, bristle-like furrow spine tips. It shows closer resemblance to Circeaster sandrae in lacking bivalve pedicellariae, but differs by having 8 to 15 triangular to quadrate furrow spines with roughened tips, compared to C. sandrae's 4 to 8 flattened, blunt, and smooth furrow spines.
Reader's Guide
Circeaster mandibulum contributes to the understanding of deep-sea starfish diversity in the Goniasteridae family, particularly in the waters of New Caledonia. Its morphological features, such as the jaw-like pedicellariae and the specific arrangement of furrow spines, provide key taxonomic characters for distinguishing it from congeners like Circeaster loisetteae, Circeaster pullus, and Circeaster sandrae. The species' description, including the number and form of marginal plates and the presence of palm-like pedicellariae on actinal intermediate plates, adds to the known variation within the genus. Its known depth range of 320 to 470 meters highlights the deep-sea habitat of this starfish. The detailed comparison with related species underscores the importance of careful morphological analysis in deep-sea taxonomy, where subtle differences in spine shape and plate arrangement define species boundaries.
Did You Know?
- The species epithet mandibulum is Latin for 'jaw', referring to the pedicellariae on the adambulacral plates.
- Circeaster mandibulum lacks bivalve pedicellariae, unlike Circeaster pullus.
- This species is known only from New Caledonia at depths of 320 to 470 meters.
Frequently Asked Questions
What is Circeaster mandibulum?
It is a deep-sea starfish in the family Goniasteridae, found in the waters surrounding New Caledonia. The species is named for jaw-like pedicellariae that sit on its adambulacral plates.
At what depth can you find Circeaster mandibulum?
This starfish occupies a depth band of roughly 320 to 470 meters off the coast of New Caledonia, placing it firmly in the deep-sea zone.
What does the name 'mandibulum' actually refer to?
The species epithet comes from the Latin word for 'jaw,' a nod to the distinctive pedicellariae on the adambulacral plates that give the organism a jaw-like appearance.
How is Circeaster mandibulum distinguished from Circeaster loisetteae?
C. mandibulum carries 8 to 15 flattened, blade-shaped furrow spines arranged palmately, while C. loisetteae has only 7 to 8 spines with a square cross-section. Additionally, the superomarginal plates of C. mandibulum only converge at the very tip of each arm, whereas in C. loisetteae they begin touching near the base.
What are the notable body proportions of Circeaster mandibulum?
Its arms extend to roughly 2.8 to 3.3 times the radius of its central disk, and it typically bears 36 to 38 superomarginal plates alongside 38 to 40 inferomarginal plates.
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