Stomechinus jordani Thompson, 2020
Plate: SiJo-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Edwards
Locale: Fluvanna County: Scurry Stage: Albian
Length: 29.1 mm Height: 20.8 mm
Collection: Dr. Steven Crane
Holotype NPL 94364
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 94364 .
Paratypes: NPL 94365 .
Locality: Fluvanna, Scurry County, Texas.
Stratigraphy: Edwards Formation, Fredericksburg Group.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Echinacea Claus, 1876
Order: Stomopneustoida Kroh & Smith, 2010
Family: Stomechinidae Pomel, 1883
Genus: STOMECHINUS Desor, 1856
Species: Stomechinus jordani Thompson, 2020
TYPE SPECIES: Echinus bigranularis Lamarck, 1816
DIAGNOSIS
A spherically shaped Stomechinus characterized by a hemicyclic apical system. Ambulacral plating is diadematoid with the lowest element not reaching the perradius. Pore pairs are trigeminate and arranged in offset triads forming a broad adradial band.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Edwards Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Scurry.
Abundance: Rare; fewer than ten specimens found.
DESCRIPTION
TOP: Length, width, height: 29.1 mm L × 20.8 mm H. Top shape: Round; slightly pentagonal with flush ambulacra. Top domed: Domed above.
SIDE: Ambitus: Positioned 47% of height from the adoral surface. Side shape: Globular, tall, with rounded sides.
BOTTOM: Bottom shape: Base flat.
AMB: Amb shape: Lanceolate; blunt at apical system, widest at ambitus, narrowing at peristome. Amb arrangement: Ambulacra are 40% the width of the interambulacra at the ambitus. Plating: Diadematoid plate compounding; lowest plate is the smallest and does not reach the perradius.
PORE PAIRS: Arrangement: Uniserial, trigeminate. Offset triads form a broad adradial band throughout; very offset nearing the peristome. Shape: Round.
TUBERCLES: Primary Perforated: No (Imperforate). Primary Crenulate: No Noncrenulate. Ambulacral Tubercles: 1 to 4 primary tubercles in the middle of each plate; fewer nearing poles. Interambulacral Tubercles: 1 to 8 primary tubercles on each plate; fewer nearing poles. Ambulacral and interambulacral tubercles are of similar size.
GRANULES: Distribution: Thick granulation and secondary tubercles present in both ambulacra and interambulacra.
FASCIOLE: Absent.
INTERAMB: Shape: Plates are 11 times wider than tall.
APICAL SYSTEM: Size: Diameter 6.2 mm. Shape: Hemicyclic; oculars I and V are insert. Plating: Oculars small; madreporite large. Flush with top of test.
PERIPROCT (ANUS): Shape: Irregularly oval.
PERISTOME (MOUTH): Size: Diameter 11.4 mm (39% of test diameter). Shape: Subpentagonal. Lip: Small notches.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 94364 and eight other specimens in the Frank Crane Collection.
ETYMOLOGY
Named in honor of Robert “Bob” Lewis Jordan of Fluvanna, Texas, a generous landowner who facilitated fossil collecting on his property.
REMARKS & COMPARISONS
Remarks: This species represents the genus Stomechinus in the Lower Cretaceous of Texas.
Comparisons:
Plate: SiJo-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Edwards
Locale: Fluvanna County: Scurry Stage: Albian
Length: 29.1 mm Height: 20.8 mm
Collection: Dr. Steven Crane
Holotype NPL 94364
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 94364 .
Paratypes: NPL 94365 .
Locality: Fluvanna, Scurry County, Texas.
Stratigraphy: Edwards Formation, Fredericksburg Group.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Echinacea Claus, 1876
Order: Stomopneustoida Kroh & Smith, 2010
Family: Stomechinidae Pomel, 1883
Genus: STOMECHINUS Desor, 1856
Species: Stomechinus jordani Thompson, 2020
TYPE SPECIES: Echinus bigranularis Lamarck, 1816
DIAGNOSIS
A spherically shaped Stomechinus characterized by a hemicyclic apical system. Ambulacral plating is diadematoid with the lowest element not reaching the perradius. Pore pairs are trigeminate and arranged in offset triads forming a broad adradial band.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Edwards Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Scurry.
Abundance: Rare; fewer than ten specimens found.
DESCRIPTION
TOP: Length, width, height: 29.1 mm L × 20.8 mm H. Top shape: Round; slightly pentagonal with flush ambulacra. Top domed: Domed above.
SIDE: Ambitus: Positioned 47% of height from the adoral surface. Side shape: Globular, tall, with rounded sides.
BOTTOM: Bottom shape: Base flat.
AMB: Amb shape: Lanceolate; blunt at apical system, widest at ambitus, narrowing at peristome. Amb arrangement: Ambulacra are 40% the width of the interambulacra at the ambitus. Plating: Diadematoid plate compounding; lowest plate is the smallest and does not reach the perradius.
PORE PAIRS: Arrangement: Uniserial, trigeminate. Offset triads form a broad adradial band throughout; very offset nearing the peristome. Shape: Round.
TUBERCLES: Primary Perforated: No (Imperforate). Primary Crenulate: No Noncrenulate. Ambulacral Tubercles: 1 to 4 primary tubercles in the middle of each plate; fewer nearing poles. Interambulacral Tubercles: 1 to 8 primary tubercles on each plate; fewer nearing poles. Ambulacral and interambulacral tubercles are of similar size.
GRANULES: Distribution: Thick granulation and secondary tubercles present in both ambulacra and interambulacra.
FASCIOLE: Absent.
INTERAMB: Shape: Plates are 11 times wider than tall.
APICAL SYSTEM: Size: Diameter 6.2 mm. Shape: Hemicyclic; oculars I and V are insert. Plating: Oculars small; madreporite large. Flush with top of test.
PERIPROCT (ANUS): Shape: Irregularly oval.
PERISTOME (MOUTH): Size: Diameter 11.4 mm (39% of test diameter). Shape: Subpentagonal. Lip: Small notches.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 94364 and eight other specimens in the Frank Crane Collection.
ETYMOLOGY
Named in honor of Robert “Bob” Lewis Jordan of Fluvanna, Texas, a generous landowner who facilitated fossil collecting on his property.
REMARKS & COMPARISONS
Remarks: This species represents the genus Stomechinus in the Lower Cretaceous of Texas.
Comparisons:
- Stomechinus tenuis & S. bigranularis: S. jordani is more globular, the pore pairs are not offset as much, and the periproct is smaller.
- Stomechinus polyporus: S. jordani has a smaller peristome, larger apical system, and lacks the sunken perradius and interradius seen in S. polyporus.
- Stomechinus herberti: S. jordani is more rounded and the ambulacra are less protruding.
