Coenholectypus nanus Cooke, 1955
Plate: CoNa-10
Series: Lower Cretaceous Group: Washita Formation: Del Rio
Locale: Waco County: McLennan Stage: Cenomanian
Length: 4.83 mm Height: 2.5 mm
Specimen in photo: Collection of Ed Elliott
Repository: Private Collection
HOLOTYPE INFO:
Holotype: USNM 108714 — National Museum of Natural History, Smithsonian Institution (Cooke, 1955)
Locality: Road cut north of Glengarden Country Club swimming pool, Fort Worth, Tarrant County, Texas (Cooke, 1955)
Stratigraphy: Main Street Limestone (Cooke, 1955); Paratypes from Pawpaw Formation.
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 nanus Cooke, 1955
TYPE SPECIES: Discoidea depressa L. Agassiz, 1839
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita (Cooke, 1955; Thompson, 2016)
Formations: Del Rio Clay ; Main Street Limestone, Pawpaw Formation (Cooke, 1955)
Stratigraphic Units: Lower Cretaceous (Albian) to Upper Cretaceous (Cenomanian) (Cooke, 1955)
Counties: McLennan ; Tarrant, Val Verde (Cooke, 1955)
DESCRIPTION
TOP: Length, height: 4.83 mm L × 2.5 mm H
Top shape: Horizontal outline circular to subpentagonal (Cooke, 1955)
Top domed: Upper surface moderately tumid (Cooke, 1955)
SIDE: Ambitus: Rounded (Cooke, 1955)
BOTTOM: Bottom shape: Slightly concave around the peristome (Cooke, 1955)
SIZE: Largest / Smallest: Test small, rarely exceeding 10 mm in diameter (Cooke, 1955)
AMB: Amb primary zones: Poriferous zones straight, continuous (Cooke, 1955)
PORE PAIRS: Arrangement: Uniserial (Cooke, 1955)
Conjugate vs Nonconjugate: Zygopores oblique (Cooke, 1955)
TUBERCLES: Primary tubercles: Small, far apart; arranged in vertical rows, two rows in each area (Cooke, 1955)
APICAL SYSTEM: Genital pores: Five genital pores (Cooke, 1955)
PERIPROCT (ANUS): Shape & Size: Large (Cooke, 1955)
Location: Submarginal; well separated from the peristome (Cooke, 1955)
Visibility: Indents the ambitus; barely visible from above (Cooke, 1955)
PERISTOME (MOUTH): Size: Rather small (Cooke, 1955)
Location: Central (Cooke, 1955)
Lip: Moderately notched (Cooke, 1955)
SPINES: Shape: Short, acicular (Cooke, 1955)
SPECIMENS STUDIED & CONDITION: Specimen CoNa-10 in collection of Ed Elliott. Cooke (1955) noted types were covered with a ferruginous coating obscuring details.
ETYMOLOGY: From the Latin nanus, meaning "dwarf," referring to the very small size of the test (Cooke, 1955).
REMARKS & COMPARISONS
Remarks: Coenholectypus nanus is characterized by its very small size (<10mm) and submarginal periproct that indents the ambitus (Cooke, 1955).
Comparisons: Most closely resembles Coenholectypus planatus (Roemer) but is much smaller. The periproct in C. nanus is farther from the peristome and turned obliquely upward, indenting the ambitus. The decoration differs significantly: C. nanus has fewer tubercles arranged in vertical rows, whereas C. planatus has tubercles arranged transversely. The arrangement suggests that of Discholectypus meslei (Gauthier), though that species is much larger with a proportionately smaller periproct (Cooke, 1955).
Plate: CoNa-10
Series: Lower Cretaceous Group: Washita Formation: Del Rio
Locale: Waco County: McLennan Stage: Cenomanian
Length: 4.83 mm Height: 2.5 mm
Specimen in photo: Collection of Ed Elliott
Repository: Private Collection
HOLOTYPE INFO:
Holotype: USNM 108714 — National Museum of Natural History, Smithsonian Institution (Cooke, 1955)
Locality: Road cut north of Glengarden Country Club swimming pool, Fort Worth, Tarrant County, Texas (Cooke, 1955)
Stratigraphy: Main Street Limestone (Cooke, 1955); Paratypes from Pawpaw Formation.
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 nanus Cooke, 1955
TYPE SPECIES: Discoidea depressa L. Agassiz, 1839
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita (Cooke, 1955; Thompson, 2016)
Formations: Del Rio Clay ; Main Street Limestone, Pawpaw Formation (Cooke, 1955)
Stratigraphic Units: Lower Cretaceous (Albian) to Upper Cretaceous (Cenomanian) (Cooke, 1955)
Counties: McLennan ; Tarrant, Val Verde (Cooke, 1955)
DESCRIPTION
TOP: Length, height: 4.83 mm L × 2.5 mm H
Top shape: Horizontal outline circular to subpentagonal (Cooke, 1955)
Top domed: Upper surface moderately tumid (Cooke, 1955)
SIDE: Ambitus: Rounded (Cooke, 1955)
BOTTOM: Bottom shape: Slightly concave around the peristome (Cooke, 1955)
SIZE: Largest / Smallest: Test small, rarely exceeding 10 mm in diameter (Cooke, 1955)
AMB: Amb primary zones: Poriferous zones straight, continuous (Cooke, 1955)
PORE PAIRS: Arrangement: Uniserial (Cooke, 1955)
Conjugate vs Nonconjugate: Zygopores oblique (Cooke, 1955)
TUBERCLES: Primary tubercles: Small, far apart; arranged in vertical rows, two rows in each area (Cooke, 1955)
APICAL SYSTEM: Genital pores: Five genital pores (Cooke, 1955)
PERIPROCT (ANUS): Shape & Size: Large (Cooke, 1955)
Location: Submarginal; well separated from the peristome (Cooke, 1955)
Visibility: Indents the ambitus; barely visible from above (Cooke, 1955)
PERISTOME (MOUTH): Size: Rather small (Cooke, 1955)
Location: Central (Cooke, 1955)
Lip: Moderately notched (Cooke, 1955)
SPINES: Shape: Short, acicular (Cooke, 1955)
SPECIMENS STUDIED & CONDITION: Specimen CoNa-10 in collection of Ed Elliott. Cooke (1955) noted types were covered with a ferruginous coating obscuring details.
ETYMOLOGY: From the Latin nanus, meaning "dwarf," referring to the very small size of the test (Cooke, 1955).
REMARKS & COMPARISONS
Remarks: Coenholectypus nanus is characterized by its very small size (<10mm) and submarginal periproct that indents the ambitus (Cooke, 1955).
Comparisons: Most closely resembles Coenholectypus planatus (Roemer) but is much smaller. The periproct in C. nanus is farther from the peristome and turned obliquely upward, indenting the ambitus. The decoration differs significantly: C. nanus has fewer tubercles arranged in vertical rows, whereas C. planatus has tubercles arranged transversely. The arrangement suggests that of Discholectypus meslei (Gauthier), though that species is much larger with a proportionately smaller periproct (Cooke, 1955).
