Pseudodiadema whitneyi (Ikins, 1940)
Plate: LoWh-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: Austin County: Travis Stage: Albian
Length: 11.8 mm Height: 4.9 mm
Specimen in photo: Collection of Ed Elliott
Repository: Private Depository
Plate: LoWh-20
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: Leander County: Williamson Stage: Albian
Length: 12.84 mm Height: 5.64 mm
Specimen in photo: UT4051A Holotype
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
Plate: LoWh-30
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Member: Cedar Park Member
Locale: Austin County: Travis Stage: Albian
Length: 7.2 mm Height: 2.7 mm
Specimen in photo: Collection of Kevin Durney
Repository: Private Depository
HOLOTYPE INFO:
Holotype: UT 4051-A (Ikins, 1940).
Locality: 2 miles west of Leander, Williamson County, Texas (Ikins, 1940).
Stratigraphy: Walnut Clay, Fredericksburg Group.
SYNONYMY
Cooke’s transfer was based on misinterpretation of the apical system; the holotype lacks the bilaterally elongated, star‑shaped, or posteriorly projecting apical disc diagnostic of Loriolia.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Order Hemicidaroida Beurlen, 1934
Family Pseudodiadematidae Pommel, 1883
Genus Pseudodiadema Desor, 1855
Species: Pseudodiadema whitneyi (Ikins, 1940)
TYPE SPECIES: Pseudodiadema versipora (Agassiz, 1840)
DIAGNOSIS
Small, circular, low hemispherical test with flat to slightly depressed upper and lower surfaces. Ambulacra straight and narrow, bearing two rows of perforate, crenulate primary tubercles. Interambulacra wider, with two rows of larger primary tubercles. Granulation fine and abundant across the test. Apical system large, subpentagonal to oval, lacking posterior elongation or bilateral modification. Peristome small and decagonal, with ten shallow branchial incisions.
This diagnosis matches Ikins’ original description and the morphology of Pseudodiadema versipora, not Loriolia.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Walnut Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Williamson (Type), Travis.
Abundance: Rare.
DESCRIPTION
TOP
The test is circular in outline with a low, depressed profile. The adoral surface is nearly flat but shows a slight central depression near the peristome. The aboral surface is gently convex, lacking any anterior–posterior asymmetry or elongation. The apical system occupies a large subpentagonal to oval area but remains equidimensional, with no posterior projection or bilateral modification.
SIDE
The ambitus lies approximately 40% of the height from the base, giving the test a low hemispherical form. The sides are smoothly curved and evenly inflated, with no flattening or anterior–posterior distortion. The overall profile is depressed, consistent with Ikins’ original description.
BOTTOM
The adoral surface is flat. The peristome is centrally located, slightly depressed, and decagonal in outline, with ten shallow branchial incisions. Buccal notches are present at the interambulacral margins.
AMBULACRAL
The ambulacra are straight and narrow, widening gradually from ~1 mm at the apical system to ~2.5 mm at the ambitus, then narrowing again toward the peristome. Each ambulacrum consists of two rows of alternating plates, each plate subdivided into three pore‑bearing elements. Two rows of perforate, crenulate primary tubercles extend from the apical system to the peristome, with approximately ten tubercles per row. Poriferous zones are wide.
PORE PAIRS
Pores are round and uniserial from the apical system to the peristome. Near the peristome, the uniserial arrangement becomes slightly irregular, as described by Ikins.
INTERAMBULACRAL
Interambulacra are 1.8–2.3 times wider than the ambulacra. Each interambulacrum consists of two rows of alternating plates, with approximately eleven plates per row. Each plate bears a single large, scrobiculate, perforate, crenulate primary tubercle. Plate margins carry scattered granules.
TUBERCLES
Primary tubercles are perforate, crenulate, and scrobiculate, with large, well‑defined areoles. Only one primary tubercle occurs per plate in both ambulacra and interambulacra. No secondary rows are present — a condition consistent with Pseudodiadema and matching Ikins’ holotype.
GRANULATION
Fine, abundant miliary granules cover the test, concentrated along plate margins and forming well‑defined hexagonal areolae around the primary tubercles. This granulation pattern is characteristic of Pseudodiadematids.
APICAL SCAR (APICAL SYSTEM)
The apical system is large, occupying 36–41% of the test diameter. It is subpentagonal to oval, with a smooth margin and no posterior groove, projection, or elongation. The shape is radially symmetrical and equidimensional, consistent with Pseudodiadema and inconsistent with Loriolia.
PERISTOME
The peristome is small to moderate in size (39–47% of test diameter), decagonal, and slightly depressed. Ten moderately developed branchial incisions are present. Weak phyllodes occur at the ambulacral margins. Buccal notches present at interambulacral margins.
SPINES
Unknown.
SPECIMENS STUDIED & CONDITION:
ETYMOLOGY
Named in honor of Professor Francis Luther Whitney (1878–1962) of the University of Texas (Ikins, 1940).
REMARKS & COMPARISONS
Remarks
Ikins (1940) correctly placed the species in Pseudodiadema. Cooke’s (1946) reassignment to Loriolia was based on the presence of uniserial pores and a large apical system, but the holotype lacks the defining apical modifications of Loriolia (bilateral elongation, posterior projection, star‑shaped outline). The holotype instead exhibits the equidimensional, subpentagonal apical system typical of Pseudodiadema.
Comparison
With Loriolia rosana: Superficially similar in size and general outline, but L. rosana possesses a distinctly elongated, bilaterally modified apical disc and a higher tubercle density. P. whitneyi lacks these features.
With Loriolia abilenensis: Differs in apical system shape (elongate in L. abilenensis, subpentagonal in P. whitneyi) and overall test profile.
Conclusion: The holotype morphology is fully consistent with Pseudodiadema and inconsistent with Loriolia. The correct combination is Pseudodiadema whitneyi Ikins, 1940.
Plate: LoWh-10
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: Austin County: Travis Stage: Albian
Length: 11.8 mm Height: 4.9 mm
Specimen in photo: Collection of Ed Elliott
Repository: Private Depository
Plate: LoWh-20
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Locale: Leander County: Williamson Stage: Albian
Length: 12.84 mm Height: 5.64 mm
Specimen in photo: UT4051A Holotype
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
Plate: LoWh-30
Series: Lower Cretaceous Group: Fredericksburg Formation: Walnut
Member: Cedar Park Member
Locale: Austin County: Travis Stage: Albian
Length: 7.2 mm Height: 2.7 mm
Specimen in photo: Collection of Kevin Durney
Repository: Private Depository
HOLOTYPE INFO:
Holotype: UT 4051-A (Ikins, 1940).
Locality: 2 miles west of Leander, Williamson County, Texas (Ikins, 1940).
Stratigraphy: Walnut Clay, Fredericksburg Group.
SYNONYMY
- Pseudodiadema whitneyi Ikins, 1940
- Loriolia whitneyi (Ikins) Cooke, 1946 – misassigned
Cooke’s transfer was based on misinterpretation of the apical system; the holotype lacks the bilaterally elongated, star‑shaped, or posteriorly projecting apical disc diagnostic of Loriolia.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Carinacea Kroh & Smith, 2010
Order Hemicidaroida Beurlen, 1934
Family Pseudodiadematidae Pommel, 1883
Genus Pseudodiadema Desor, 1855
Species: Pseudodiadema whitneyi (Ikins, 1940)
TYPE SPECIES: Pseudodiadema versipora (Agassiz, 1840)
DIAGNOSIS
Small, circular, low hemispherical test with flat to slightly depressed upper and lower surfaces. Ambulacra straight and narrow, bearing two rows of perforate, crenulate primary tubercles. Interambulacra wider, with two rows of larger primary tubercles. Granulation fine and abundant across the test. Apical system large, subpentagonal to oval, lacking posterior elongation or bilateral modification. Peristome small and decagonal, with ten shallow branchial incisions.
This diagnosis matches Ikins’ original description and the morphology of Pseudodiadema versipora, not Loriolia.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Fredericksburg
Formations: Walnut Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Williamson (Type), Travis.
Abundance: Rare.
DESCRIPTION
TOP
The test is circular in outline with a low, depressed profile. The adoral surface is nearly flat but shows a slight central depression near the peristome. The aboral surface is gently convex, lacking any anterior–posterior asymmetry or elongation. The apical system occupies a large subpentagonal to oval area but remains equidimensional, with no posterior projection or bilateral modification.
SIDE
The ambitus lies approximately 40% of the height from the base, giving the test a low hemispherical form. The sides are smoothly curved and evenly inflated, with no flattening or anterior–posterior distortion. The overall profile is depressed, consistent with Ikins’ original description.
BOTTOM
The adoral surface is flat. The peristome is centrally located, slightly depressed, and decagonal in outline, with ten shallow branchial incisions. Buccal notches are present at the interambulacral margins.
AMBULACRAL
The ambulacra are straight and narrow, widening gradually from ~1 mm at the apical system to ~2.5 mm at the ambitus, then narrowing again toward the peristome. Each ambulacrum consists of two rows of alternating plates, each plate subdivided into three pore‑bearing elements. Two rows of perforate, crenulate primary tubercles extend from the apical system to the peristome, with approximately ten tubercles per row. Poriferous zones are wide.
PORE PAIRS
Pores are round and uniserial from the apical system to the peristome. Near the peristome, the uniserial arrangement becomes slightly irregular, as described by Ikins.
INTERAMBULACRAL
Interambulacra are 1.8–2.3 times wider than the ambulacra. Each interambulacrum consists of two rows of alternating plates, with approximately eleven plates per row. Each plate bears a single large, scrobiculate, perforate, crenulate primary tubercle. Plate margins carry scattered granules.
TUBERCLES
Primary tubercles are perforate, crenulate, and scrobiculate, with large, well‑defined areoles. Only one primary tubercle occurs per plate in both ambulacra and interambulacra. No secondary rows are present — a condition consistent with Pseudodiadema and matching Ikins’ holotype.
GRANULATION
Fine, abundant miliary granules cover the test, concentrated along plate margins and forming well‑defined hexagonal areolae around the primary tubercles. This granulation pattern is characteristic of Pseudodiadematids.
APICAL SCAR (APICAL SYSTEM)
The apical system is large, occupying 36–41% of the test diameter. It is subpentagonal to oval, with a smooth margin and no posterior groove, projection, or elongation. The shape is radially symmetrical and equidimensional, consistent with Pseudodiadema and inconsistent with Loriolia.
PERISTOME
The peristome is small to moderate in size (39–47% of test diameter), decagonal, and slightly depressed. Ten moderately developed branchial incisions are present. Weak phyllodes occur at the ambulacral margins. Buccal notches present at interambulacral margins.
SPINES
Unknown.
SPECIMENS STUDIED & CONDITION:
- Holotype UT 4051-A: Williamson County.
- Specimen 2: Collection of Ed Elliott (Plate LoWh-10). Length 11.8 mm. Travis County.
- Specimen 3: Collection of Kevin Durney (Plate LoWh-30). Length 7.2 mm. Travis County
ETYMOLOGY
Named in honor of Professor Francis Luther Whitney (1878–1962) of the University of Texas (Ikins, 1940).
REMARKS & COMPARISONS
Remarks
Ikins (1940) correctly placed the species in Pseudodiadema. Cooke’s (1946) reassignment to Loriolia was based on the presence of uniserial pores and a large apical system, but the holotype lacks the defining apical modifications of Loriolia (bilateral elongation, posterior projection, star‑shaped outline). The holotype instead exhibits the equidimensional, subpentagonal apical system typical of Pseudodiadema.
Comparison
With Loriolia rosana: Superficially similar in size and general outline, but L. rosana possesses a distinctly elongated, bilaterally modified apical disc and a higher tubercle density. P. whitneyi lacks these features.
With Loriolia abilenensis: Differs in apical system shape (elongate in L. abilenensis, subpentagonal in P. whitneyi) and overall test profile.
Conclusion: The holotype morphology is fully consistent with Pseudodiadema and inconsistent with Loriolia. The correct combination is Pseudodiadema whitneyi Ikins, 1940.
