Palhemiaster krohi Thompson, 2016
Plate: PaKo-10
Series: Lower Cretaceous Group: Washita Formation: Boracho
Locale: Kent County: Culbertson Stage: Cenomanian
Length: 59.3 mm Width: 58.9 mm Height: 31.0 mm
Specimen in photo: NPL 82991 Holotype
Collector: Frank Crane
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 82991.
Locality: Kent, Culberson County, Texas.
Stratigraphy: Boracho Formation, Washita Group.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Hemiasteridae H. L. Clark, 1917
Genus: PALHEMIASTER Lambert, 1915
Species: Palhemiaster krohi Thompson, 2016
TYPE SPECIES: Hemiaster comanchei Clark, 1915
DIAGNOSIS
A very large Palhemiaster characterized by a depressed, low profile and a trapezoidal lateral outline. Both the anterior and posterior ends are truncated.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Boracho Formation.
Stratigraphic Units: Lower Cretaceous, Cenomanian.
Counties: Culberson.
Abundance: Rare; only two specimens known.
DESCRIPTION
TOP: Length, width, height: 59.3 mm L × 58.9 mm W × 31.0 mm H. Top shape: Oval, cordate; almost as wide as long. Widest point is anterior of center. Top domed: Flat aborally; aboral surface is domed from end view.
SIDE: Ambitus: Rounded; positioned low (25% of height from adoral surface). Side shape: Trapezoidal profile; flat aborally, convex below. Profile: Both anterior and posterior ends are truncated.
BOTTOM: Bottom shape: Adoral surface slopes downward toward a rounded keel. Plastron: Very large, protruding, and pronounced.
AMB: Amb shape: Unpaired ambulacrum (III) sits in a sulcus and is open-ended. Paired ambulacra are only slightly sunken, petaloid, weakly bowed, and open-ended.
PORE PAIRS: Unpaired Amb: Outer pores are slit-shaped; inner pores are only slightly elongated. Paired Ambs: In the anterior pair, anterior pore pairs are small, slightly elongated, and en chevron; posterior pore pairs resemble those of the unpaired amb. In the posterior pair, both sets of pore pairs resemble those of the unpaired amb.
TUBERCLES: Distribution: Small, perforated tubercles; more plentiful near the petals and along the margin. Areolas: Sunken.
FASCIOLE: Peripetalous: Very pronounced and wide around the posterior 2/3 of the test; missing anteriorly.
APICAL SYSTEM: Location: Anterior of center. Type: Ethmophract. Genital pores: 4 gonopores. Size: Very small.
PERIPROCT (ANUS): Shape: Transversely oval. Location: Situated high above the center on the posterior face. Visibility: Visible from above.
PERISTOME (MOUTH): Shape: Reniform ("renal shaped"). Size: Small. Orientation: Facing downward.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 82991 and one other specimen in the Frank Crane Collection.
ETYMOLOGY
Named after Dr. Andreas Kroh (Natural History Museum, Vienna) in recognition of his many contributions to echinoid paleontology.
REMARKS & COMPARISONS
Remarks: Palhemiaster krohi is distinguished from Palhemiaster comanchei and Palhemiaster peroni by its test shape; the latter species are very inflated with an overall rounded lateral profile, whereas P. krohi is depressed and trapezoidal. Additionally, the apical system is central in P. comanchei and P. peroni, but anterior in P. krohi. The pore pair morphology in the unpaired and anterior paired ambulacra also differs.
Plate: PaKo-10
Series: Lower Cretaceous Group: Washita Formation: Boracho
Locale: Kent County: Culbertson Stage: Cenomanian
Length: 59.3 mm Width: 58.9 mm Height: 31.0 mm
Specimen in photo: NPL 82991 Holotype
Collector: Frank Crane
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 82991.
Locality: Kent, Culberson County, Texas.
Stratigraphy: Boracho Formation, Washita Group.
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Spatangoida L. Agassiz, 1840
Family: Hemiasteridae H. L. Clark, 1917
Genus: PALHEMIASTER Lambert, 1915
Species: Palhemiaster krohi Thompson, 2016
TYPE SPECIES: Hemiaster comanchei Clark, 1915
DIAGNOSIS
A very large Palhemiaster characterized by a depressed, low profile and a trapezoidal lateral outline. Both the anterior and posterior ends are truncated.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Boracho Formation.
Stratigraphic Units: Lower Cretaceous, Cenomanian.
Counties: Culberson.
Abundance: Rare; only two specimens known.
DESCRIPTION
TOP: Length, width, height: 59.3 mm L × 58.9 mm W × 31.0 mm H. Top shape: Oval, cordate; almost as wide as long. Widest point is anterior of center. Top domed: Flat aborally; aboral surface is domed from end view.
SIDE: Ambitus: Rounded; positioned low (25% of height from adoral surface). Side shape: Trapezoidal profile; flat aborally, convex below. Profile: Both anterior and posterior ends are truncated.
BOTTOM: Bottom shape: Adoral surface slopes downward toward a rounded keel. Plastron: Very large, protruding, and pronounced.
AMB: Amb shape: Unpaired ambulacrum (III) sits in a sulcus and is open-ended. Paired ambulacra are only slightly sunken, petaloid, weakly bowed, and open-ended.
PORE PAIRS: Unpaired Amb: Outer pores are slit-shaped; inner pores are only slightly elongated. Paired Ambs: In the anterior pair, anterior pore pairs are small, slightly elongated, and en chevron; posterior pore pairs resemble those of the unpaired amb. In the posterior pair, both sets of pore pairs resemble those of the unpaired amb.
TUBERCLES: Distribution: Small, perforated tubercles; more plentiful near the petals and along the margin. Areolas: Sunken.
FASCIOLE: Peripetalous: Very pronounced and wide around the posterior 2/3 of the test; missing anteriorly.
APICAL SYSTEM: Location: Anterior of center. Type: Ethmophract. Genital pores: 4 gonopores. Size: Very small.
PERIPROCT (ANUS): Shape: Transversely oval. Location: Situated high above the center on the posterior face. Visibility: Visible from above.
PERISTOME (MOUTH): Shape: Reniform ("renal shaped"). Size: Small. Orientation: Facing downward.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype NPL 82991 and one other specimen in the Frank Crane Collection.
ETYMOLOGY
Named after Dr. Andreas Kroh (Natural History Museum, Vienna) in recognition of his many contributions to echinoid paleontology.
REMARKS & COMPARISONS
Remarks: Palhemiaster krohi is distinguished from Palhemiaster comanchei and Palhemiaster peroni by its test shape; the latter species are very inflated with an overall rounded lateral profile, whereas P. krohi is depressed and trapezoidal. Additionally, the apical system is central in P. comanchei and P. peroni, but anterior in P. krohi. The pore pair morphology in the unpaired and anterior paired ambulacra also differs.
