Coenholectypus planatus (Roemer, 1852)
Plate: CoPl-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Bulverde County: Comal Stage: Albian
Length: 18.4 mm Height: 8.4 mm
Specimen in photo: NPL 82999 (Hypotype)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: Original types described by Roemer (1849, 1852) from "Fredericksburg, Texas." Likely housed in the Roemer Museum (Germany) or University of Bonn.
Locality: Fredericksburg, Texas (Roemer, 1852)
SYNONYMY
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 planatus (Roemer, 1852)
TYPE SPECIES: Discoidea depressa L. Agassiz, 1839
DIAGNOSIS: Test subcircular, subcorneal, flattened on the under surface. Ambulacra narrow, straight, and somewhat lanceolate, with six irregular rows of tubercles; poriferous zones somewhat straight, narrow, unigeminal. Interambulacra wide, plates numerous and narrow, each with a nearly horizontal row of small tubercles. Apical system small, the madreporite large. Peristome small, subcircular. Periproct large. (Clark & Twitchell, 1915)
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity ; Fredericksburg, Washita (Clark & Twitchell, 1915)
Formations: Glen Rose Formation Walnut, Comanche Peak, Goodland, Georgetown (Cooke, 1946)
Stratigraphic Units: Lower Cretaceous, Albian (Cooke, 1946; Smith & Rader, 2009)
Counties: Comal,Travis, Pecos, Tarrant (Cooke, 1946)
DESCRIPTION
TOP: Length, width, height: 18.4 mm L × 8.4 mm H Range 12–70 mm width (Clark & Twitchell, 1915)
Top shape: Subcircular, subconical to dome-shaped; some pentagonal (Clark & Twitchell, 1915; Cooke, 1946)
Top domed: Upper surface distinctly elevated at center with slightly tumid sides (Clark & Twitchell, 1915)
SIDE: Ambitus: Rounded to sharp (Clark & Twitchell, 1915)
Side shape: Subconical to domed (Cooke, 1946)
BOTTOM: Bottom flat: Flat and slightly depressed in the vicinity of the peristome (Clark & Twitchell, 1915)
Bottom shape: Concave around peristome (Cooke, 1946)
AMB: Amb shape: Narrow, straight, somewhat lanceolate; increasing in width toward ambitus (Clark & Twitchell, 1915)
Amb width: About half as wide as interambulacra (Cooke, 1946)
Amb primary tubercles: Six rows of small tubercles in broader portion; reduced to four toward apex/peristome (Clark & Twitchell, 1915)
Amb primary zones: Poriferous zones narrow (Clark & Twitchell, 1915)
INTERAMB: Interamb width: About three times the width of ambulacra at ambitus (Clark & Twitchell, 1915)
Interamb plating: Plates numerous and narrow (Clark & Twitchell, 1915)
Interamb primary tubercles: Horizontal rows of small tubercles, 5 or 6 per row at ambitus (Clark & Twitchell, 1915)
PORE PAIRS: Arrangement: Unigeminal (Clark & Twitchell, 1915)
TUBERCLES: Primary tubercles: Cover greater portion of plates; larger on lower surface (Clark & Twitchell, 1915)
Primary Perforated: Yes (Clark & Twitchell, 1915)
Primary Crenulate: Yes (Clark & Twitchell, 1915)
Primary Areola shape: Small circular areola (Clark & Twitchell, 1915)
Secondary tubercles: Minute granules interspersed between primary tubercles (Clark & Twitchell, 1915)
APICAL SYSTEM: Size / Location: Small (Clark & Twitchell, 1915)
Genital pores: Five perforated genital plates (Cooke, 1946)
Madreporite: Large; indistinctly separated from other plates (Clark & Twitchell, 1915)
PERIPROCT (ANUS): Shape & Size: Large, oval to pyriform (Clark & Twitchell, 1915; Cooke, 1946)
Location: Infra-marginal; extends from vicinity of mouth (peristome) to the ambitus (Clark & Twitchell, 1915)
PERISTOME (MOUTH): Size: Small (Clark & Twitchell, 1915)
Shape: Subcircular to decagonal (Clark & Twitchell, 1915)
Lip: Slight incisions give a decagonal margin (Clark & Twitchell, 1915)
SPECIMENS STUDIED & CONDITION: Hypotype NPL 82999 .
SIZE
ETYMOLOGY: From the Latin planatus, meaning "flattened," referring to the flat oral surface (Roemer, 1852).
REMARKS & COMPARISONS
Remarks: Coenholectypus planatus is the most common holectypoid in the Texas Cretaceous. Cooke (1946) and Smith & Kroh (2011) list Coenholectypus adkinsi (Smiser) as a synonym, considering it a juvenile form. Smith & Kroh also list C. engerrandi as a synonym, though Thompson (2016) argues for its validity based on morphological differences (pentagonal shape). The original description by Roemer (1852) established the flattened base and large infra-marginal periproct as key characters.
Comparisons: Adult forms in the Washita Group are typically larger than those in the Trinity/Fredericksburg. Connecting forms exist between C. planatus, C. charltoni, and C. transpecosensis (Clark & Twitchell, 1915).
Remarks (1-2025): I am placing Holectypus cf. planus Giebel, 1853 as a Synonymy after studying the images and seeing that the 5th pore is clogged.
Remarks (6-2026): Three large specimens (90-110 mm diameter) have been found in north Comal County. Large and small Coenholectypus planatus occur together in the Salenia‑zone limestones of the Glen Rose Formation. Their identical morphology and shared stratigraphic position indicate a single population exhibiting wide ontogenetic size variation. The giant forms represent fully mature individuals rather than a separate taxon or facies morphotype.
Plate: CoPl-10
Series: Lower Cretaceous Group: Trinity Formation: Glen Rose
Locale: Bulverde County: Comal Stage: Albian
Length: 18.4 mm Height: 8.4 mm
Specimen in photo: NPL 82999 (Hypotype)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: Original types described by Roemer (1849, 1852) from "Fredericksburg, Texas." Likely housed in the Roemer Museum (Germany) or University of Bonn.
Locality: Fredericksburg, Texas (Roemer, 1852)
SYNONYMY
- Holectypus cf. planus Giebel, 1853
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 planatus (Roemer, 1852)
TYPE SPECIES: Discoidea depressa L. Agassiz, 1839
DIAGNOSIS: Test subcircular, subcorneal, flattened on the under surface. Ambulacra narrow, straight, and somewhat lanceolate, with six irregular rows of tubercles; poriferous zones somewhat straight, narrow, unigeminal. Interambulacra wide, plates numerous and narrow, each with a nearly horizontal row of small tubercles. Apical system small, the madreporite large. Peristome small, subcircular. Periproct large. (Clark & Twitchell, 1915)
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Trinity ; Fredericksburg, Washita (Clark & Twitchell, 1915)
Formations: Glen Rose Formation Walnut, Comanche Peak, Goodland, Georgetown (Cooke, 1946)
Stratigraphic Units: Lower Cretaceous, Albian (Cooke, 1946; Smith & Rader, 2009)
Counties: Comal,Travis, Pecos, Tarrant (Cooke, 1946)
DESCRIPTION
TOP: Length, width, height: 18.4 mm L × 8.4 mm H Range 12–70 mm width (Clark & Twitchell, 1915)
Top shape: Subcircular, subconical to dome-shaped; some pentagonal (Clark & Twitchell, 1915; Cooke, 1946)
Top domed: Upper surface distinctly elevated at center with slightly tumid sides (Clark & Twitchell, 1915)
SIDE: Ambitus: Rounded to sharp (Clark & Twitchell, 1915)
Side shape: Subconical to domed (Cooke, 1946)
BOTTOM: Bottom flat: Flat and slightly depressed in the vicinity of the peristome (Clark & Twitchell, 1915)
Bottom shape: Concave around peristome (Cooke, 1946)
AMB: Amb shape: Narrow, straight, somewhat lanceolate; increasing in width toward ambitus (Clark & Twitchell, 1915)
Amb width: About half as wide as interambulacra (Cooke, 1946)
Amb primary tubercles: Six rows of small tubercles in broader portion; reduced to four toward apex/peristome (Clark & Twitchell, 1915)
Amb primary zones: Poriferous zones narrow (Clark & Twitchell, 1915)
INTERAMB: Interamb width: About three times the width of ambulacra at ambitus (Clark & Twitchell, 1915)
Interamb plating: Plates numerous and narrow (Clark & Twitchell, 1915)
Interamb primary tubercles: Horizontal rows of small tubercles, 5 or 6 per row at ambitus (Clark & Twitchell, 1915)
PORE PAIRS: Arrangement: Unigeminal (Clark & Twitchell, 1915)
TUBERCLES: Primary tubercles: Cover greater portion of plates; larger on lower surface (Clark & Twitchell, 1915)
Primary Perforated: Yes (Clark & Twitchell, 1915)
Primary Crenulate: Yes (Clark & Twitchell, 1915)
Primary Areola shape: Small circular areola (Clark & Twitchell, 1915)
Secondary tubercles: Minute granules interspersed between primary tubercles (Clark & Twitchell, 1915)
APICAL SYSTEM: Size / Location: Small (Clark & Twitchell, 1915)
Genital pores: Five perforated genital plates (Cooke, 1946)
Madreporite: Large; indistinctly separated from other plates (Clark & Twitchell, 1915)
PERIPROCT (ANUS): Shape & Size: Large, oval to pyriform (Clark & Twitchell, 1915; Cooke, 1946)
Location: Infra-marginal; extends from vicinity of mouth (peristome) to the ambitus (Clark & Twitchell, 1915)
PERISTOME (MOUTH): Size: Small (Clark & Twitchell, 1915)
Shape: Subcircular to decagonal (Clark & Twitchell, 1915)
Lip: Slight incisions give a decagonal margin (Clark & Twitchell, 1915)
SPECIMENS STUDIED & CONDITION: Hypotype NPL 82999 .
SIZE
- Holotype Size: Diameter 58 mm (Roemer, 1852). From Fredericksburg Group.
- Size Range: Diameter 25 mm to 70 mm (Clark & Twitchell, 1915).
- Average Size: Diameter ~45 mm to 55 mm. From Fredericksburg Group.
- Average Size: Diameter ~25 mm to 35 mm. From Glenrose Formation.
- Largest Known: Diameter 70 mm (Clark & Twitchell, 1915). From Fredericksburg Group.
ETYMOLOGY: From the Latin planatus, meaning "flattened," referring to the flat oral surface (Roemer, 1852).
REMARKS & COMPARISONS
Remarks: Coenholectypus planatus is the most common holectypoid in the Texas Cretaceous. Cooke (1946) and Smith & Kroh (2011) list Coenholectypus adkinsi (Smiser) as a synonym, considering it a juvenile form. Smith & Kroh also list C. engerrandi as a synonym, though Thompson (2016) argues for its validity based on morphological differences (pentagonal shape). The original description by Roemer (1852) established the flattened base and large infra-marginal periproct as key characters.
Comparisons: Adult forms in the Washita Group are typically larger than those in the Trinity/Fredericksburg. Connecting forms exist between C. planatus, C. charltoni, and C. transpecosensis (Clark & Twitchell, 1915).
Remarks (1-2025): I am placing Holectypus cf. planus Giebel, 1853 as a Synonymy after studying the images and seeing that the 5th pore is clogged.
Remarks (6-2026): Three large specimens (90-110 mm diameter) have been found in north Comal County. Large and small Coenholectypus planatus occur together in the Salenia‑zone limestones of the Glen Rose Formation. Their identical morphology and shared stratigraphic position indicate a single population exhibiting wide ontogenetic size variation. The giant forms represent fully mature individuals rather than a separate taxon or facies morphotype.
