Phymosoma mexicanum Bose, 1910
Plate: PhMe-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: Harker Heights County: Bell Stage: Albian
Length: 26.9 mm Height: 13.1 mm
Specimen in photos: Collection of Frank Crane
HOLOTYPE INFO:
Holotype: Originally described by Böse (1910). Repository: Instituto Geológico de México (IGM).
Locality: Cerro de Muleros, Chihuahua (near El Paso, Texas) (Böse, 1910).
Stratigraphy: Subdivision 2 (Fredericksburg Group equivalent).
SYNONYMY
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Calycina Gregory, 1900
Order: Phymosomatoida Mortensen, 1904
Family: Phymosomatidae Pomel, 1883
Genus: PHYMOSOMA Haime, 1853
Species: Phymosoma mexicanum (Böse, 1910)
TYPE SPECIES: Diadema priscum Agassiz, 1840
DIAGNOSIS
Test subcircular to subpentagonal and relatively thick (Böse, 1910). Ambulacra narrow adapically with biserial pore pairs extending almost entirely aborally. Distinguishing feature: Ambulacral tubercles in the two series alternate near the apical system (Adkins, 1928). Interambulacra feature four rows of tubercles (Böse, 1910). Tubercles are imperforate and crenulate.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Comanche Peak Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Bell, El Paso (Type area).
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 26.9 mm L × 13.1 mm H (Figured Specimen). Top shape: Subcircular to subpentagonal; round at ambitus (Böse, 1910). Top domed: Depressed above (Böse, 1910).
SIDE: Ambitus: Rounded; positioned low ("depressed down") (Böse, 1910). Side shape: Relatively thick in the middle (Böse, 1910).
BOTTOM: Bottom shape: Depressed around the peristome (Böse, 1910).
AMB: Amb shape: Narrow at the top and widest at the ambitus (Böse, 1910). Amb arrangement: Two sets of 12 to 13 thick, prominent tubercles (Böse, 1910). Tubercles of the two series alternate near the apical scar; this is less noticeable at the ambitus and lower face (Böse, 1910; Adkins, 1928).
PORE PAIRS: Shape: Oval with a small flange (Böse, 1910). Arrangement: Biserial almost entirely on the aboral surface; pores multiply/crowd near the peristome (Böse, 1910).
TUBERCLES: Primary Perforated: No (Imperforate) (Böse, 1910). Primary Crenulate: Yes (Böse, 1910). Mamelons: Strong/Thick (Böse, 1910). Interambulacral Tubercles: Four rows total. Two central rows (12–14 tubercles) reach the apex; two lateral rows extend just a little down from the apical scar (Böse, 1910). Scrobicular Tubercles: Granules tend to form circles around the tubercles (Böse, 1910).
GRANULES: Distribution: Numerous uneven granules in the narrow gap between tubercle series; often forming incomplete hexagons around each tubercle (Böse, 1910). Miliary area is relatively wide, smooth, and sunken above; covered with a few granules in ambitus and lower face (Böse, 1910).
FASCIOLE: Absent.
INTERAMB: Width: Fairly broad (Böse, 1910). Shape: Plates are much wider than high and slightly flexuous at the ambitus (Böse, 1910).
APICAL SYSTEM: Size: Quite large (indicated by scar) (Böse, 1910). Condition: Preserved in some specimens as a scar.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Quite large (Böse, 1910). Shape: Subcircular (Böse, 1910). Lip: Slight depression with recesses (notches); tube-lips are outgoing and wider than interambulacral lips (Böse, 1910).
SPINES: Shape: Small, elongated, sub-columnar; thicker at half-length. Ornamentation: Fine longitudinal grooves across the bottom; grooves disappear from half the length up. Collar (collaret) well developed (Böse, 1910).
SPECIMENS STUDIED & CONDITION: One specimen studied from the Collection of Frank Crane.
ETYMOLOGY
Named for the country of Mexico, where the type material was collected (Böse, 1910).
REMARKS & COMPARISONS
Remarks: This species is very similar to Phymosoma texanum (Roemer) (Cooke, 1953). However, it is retained as a distinct species based on the specific granulation pattern and tubercle arrangement described by Böse. Lambert & Thiéry (1914) validated the species under the genus Cyphosoma.
Comparisons:
Plate: PhMe-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Comanche Peak
Locale: Harker Heights County: Bell Stage: Albian
Length: 26.9 mm Height: 13.1 mm
Specimen in photos: Collection of Frank Crane
HOLOTYPE INFO:
Holotype: Originally described by Böse (1910). Repository: Instituto Geológico de México (IGM).
Locality: Cerro de Muleros, Chihuahua (near El Paso, Texas) (Böse, 1910).
Stratigraphy: Subdivision 2 (Fredericksburg Group equivalent).
SYNONYMY
- Phymosoma mexicana Böse, 1910 (Original orthography)
- Cyphosoma mexicanum (Böse) Lambert & Thiéry, 1914
- Phymosoma mexicanum (Böse) Cooke, 1953
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Superorder: Calycina Gregory, 1900
Order: Phymosomatoida Mortensen, 1904
Family: Phymosomatidae Pomel, 1883
Genus: PHYMOSOMA Haime, 1853
Species: Phymosoma mexicanum (Böse, 1910)
TYPE SPECIES: Diadema priscum Agassiz, 1840
DIAGNOSIS
Test subcircular to subpentagonal and relatively thick (Böse, 1910). Ambulacra narrow adapically with biserial pore pairs extending almost entirely aborally. Distinguishing feature: Ambulacral tubercles in the two series alternate near the apical system (Adkins, 1928). Interambulacra feature four rows of tubercles (Böse, 1910). Tubercles are imperforate and crenulate.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Comanche Peak Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Bell, El Paso (Type area).
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 26.9 mm L × 13.1 mm H (Figured Specimen). Top shape: Subcircular to subpentagonal; round at ambitus (Böse, 1910). Top domed: Depressed above (Böse, 1910).
SIDE: Ambitus: Rounded; positioned low ("depressed down") (Böse, 1910). Side shape: Relatively thick in the middle (Böse, 1910).
BOTTOM: Bottom shape: Depressed around the peristome (Böse, 1910).
AMB: Amb shape: Narrow at the top and widest at the ambitus (Böse, 1910). Amb arrangement: Two sets of 12 to 13 thick, prominent tubercles (Böse, 1910). Tubercles of the two series alternate near the apical scar; this is less noticeable at the ambitus and lower face (Böse, 1910; Adkins, 1928).
PORE PAIRS: Shape: Oval with a small flange (Böse, 1910). Arrangement: Biserial almost entirely on the aboral surface; pores multiply/crowd near the peristome (Böse, 1910).
TUBERCLES: Primary Perforated: No (Imperforate) (Böse, 1910). Primary Crenulate: Yes (Böse, 1910). Mamelons: Strong/Thick (Böse, 1910). Interambulacral Tubercles: Four rows total. Two central rows (12–14 tubercles) reach the apex; two lateral rows extend just a little down from the apical scar (Böse, 1910). Scrobicular Tubercles: Granules tend to form circles around the tubercles (Böse, 1910).
GRANULES: Distribution: Numerous uneven granules in the narrow gap between tubercle series; often forming incomplete hexagons around each tubercle (Böse, 1910). Miliary area is relatively wide, smooth, and sunken above; covered with a few granules in ambitus and lower face (Böse, 1910).
FASCIOLE: Absent.
INTERAMB: Width: Fairly broad (Böse, 1910). Shape: Plates are much wider than high and slightly flexuous at the ambitus (Böse, 1910).
APICAL SYSTEM: Size: Quite large (indicated by scar) (Böse, 1910). Condition: Preserved in some specimens as a scar.
PERIPROCT (ANUS): (Unknown).
PERISTOME (MOUTH): Size: Quite large (Böse, 1910). Shape: Subcircular (Böse, 1910). Lip: Slight depression with recesses (notches); tube-lips are outgoing and wider than interambulacral lips (Böse, 1910).
SPINES: Shape: Small, elongated, sub-columnar; thicker at half-length. Ornamentation: Fine longitudinal grooves across the bottom; grooves disappear from half the length up. Collar (collaret) well developed (Böse, 1910).
SPECIMENS STUDIED & CONDITION: One specimen studied from the Collection of Frank Crane.
ETYMOLOGY
Named for the country of Mexico, where the type material was collected (Böse, 1910).
REMARKS & COMPARISONS
Remarks: This species is very similar to Phymosoma texanum (Roemer) (Cooke, 1953). However, it is retained as a distinct species based on the specific granulation pattern and tubercle arrangement described by Böse. Lambert & Thiéry (1914) validated the species under the genus Cyphosoma.
Comparisons:
- Phymosoma texanum: P. mexicanum is distinguished by having ambulacral tubercles that alternate near the apical system (Adkins, 1928), whereas they are typically opposite in P. texanum. Additionally, P. mexicanum features an "incomplete hexagon" granulation pattern around the tubercles (Böse, 1910).
