Coenholectypus sp. Pomel, 1883
Plate: CoSp-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Canyon Lake County: Comal Stage: Albian
Length: 3.8 mm Height: 2.0 mm
Specimen in photo: NPL 83000 (Hypotype)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
Systematic Paleontology
CLASS: ECHINOIDEA Leske, 1778
SUBCLASS: EUECHINOIDEA Bronn, 1860
INFRACLASS: IRREGULARIA Latreille, 1825
SUPERORDER: GNATHOSTOMATA Zittel, 1879
ORDER: HOLECTYPOIDA Duncan, 1889
FAMILY: COENHOLECTYPIDAE Smith & Wright, 1999
GENUS: COENHOLECTYPUS Pomel, 1883
SPECIES: Coenholectypus sp.
TYPE SPECIES: Discoidea depressa L. Agassiz, 1839
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation
Stratigraphic Units: Lower Cretaceous, Albian
Counties: Comal County
DESCRIPTION
TOP: Length, height: 3.8 mm L × 2.0 mm H
Top shape: Round, slightly pentagonal
Flatness: Top flat for 50% of top surface
SIDE: Side shape: Evenly rounded sides
BOTTOM: Bottom flat: Flat, large
AMB: Amb primary tubercles: Two rows of tubercles
Amb granules: Many granules
INTERAMB: Interamb width: Twice the size of ambulacra
Interamb primary tubercles: Four rows of tubercles
TUBERCLES: Primary tubercles: Many large tubercles
Granulation: Thick granulation
APICAL SYSTEM: Size: Large; diameter about 20% of diameter of test
PERIPROCT (ANUS): Shape & Size: Huge; pointed at top and rounded on bottom
Location: Marginal; cuts into margin with 2/3rds positioned above the ambitus
PERISTOME (MOUTH): Size: Diameter 50% of diameter of test
Shape: Round
Lip: 10 tiny notches
SPECIMENS STUDIED & CONDITION: Specimen NPL 83000; Juvenile/Micro-echinoid .
REMARKS & COMPARISONS
Remarks: This specimen is identified as a juvenile, likely of Coenholectypus planatus (Roemer), which is common in the Glen Rose Formation. The marginal position of the periproct (cutting the margin and extending supramarginally) is characteristic of juvenile Holectypoids, where the periproct migrates to the oral surface (infra-marginal) in adulthood.
Comparisons: The spacing of the buccal notches and the shape of the periproct are identical to C. planatus. The very large relative size of the peristome (50% of test) and periproct are consistent with ontogenetic traits of juvenile echinoids.
Plate: CoSp-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Canyon Lake County: Comal Stage: Albian
Length: 3.8 mm Height: 2.0 mm
Specimen in photo: NPL 83000 (Hypotype)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
Systematic Paleontology
CLASS: ECHINOIDEA Leske, 1778
SUBCLASS: EUECHINOIDEA Bronn, 1860
INFRACLASS: IRREGULARIA Latreille, 1825
SUPERORDER: GNATHOSTOMATA Zittel, 1879
ORDER: HOLECTYPOIDA Duncan, 1889
FAMILY: COENHOLECTYPIDAE Smith & Wright, 1999
GENUS: COENHOLECTYPUS Pomel, 1883
SPECIES: Coenholectypus sp.
TYPE SPECIES: Discoidea depressa L. Agassiz, 1839
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity
Formations: Glen Rose Formation
Stratigraphic Units: Lower Cretaceous, Albian
Counties: Comal County
DESCRIPTION
TOP: Length, height: 3.8 mm L × 2.0 mm H
Top shape: Round, slightly pentagonal
Flatness: Top flat for 50% of top surface
SIDE: Side shape: Evenly rounded sides
BOTTOM: Bottom flat: Flat, large
AMB: Amb primary tubercles: Two rows of tubercles
Amb granules: Many granules
INTERAMB: Interamb width: Twice the size of ambulacra
Interamb primary tubercles: Four rows of tubercles
TUBERCLES: Primary tubercles: Many large tubercles
Granulation: Thick granulation
APICAL SYSTEM: Size: Large; diameter about 20% of diameter of test
PERIPROCT (ANUS): Shape & Size: Huge; pointed at top and rounded on bottom
Location: Marginal; cuts into margin with 2/3rds positioned above the ambitus
PERISTOME (MOUTH): Size: Diameter 50% of diameter of test
Shape: Round
Lip: 10 tiny notches
SPECIMENS STUDIED & CONDITION: Specimen NPL 83000; Juvenile/Micro-echinoid .
REMARKS & COMPARISONS
Remarks: This specimen is identified as a juvenile, likely of Coenholectypus planatus (Roemer), which is common in the Glen Rose Formation. The marginal position of the periproct (cutting the margin and extending supramarginally) is characteristic of juvenile Holectypoids, where the periproct migrates to the oral surface (infra-marginal) in adulthood.
Comparisons: The spacing of the buccal notches and the shape of the periproct are identical to C. planatus. The very large relative size of the peristome (50% of test) and periproct are consistent with ontogenetic traits of juvenile echinoids.
