Pliotoxaster inflatus (Smiser, 1936)
Plate: PlIn-10
Series: Lower Cretaceous Group: Washita Formation: Duck Creek
Locale: County: Grayson Stage: Albian
Length: 48.4 mm Width: 45.0 mm Height: 32.7 mm
Specimen in photo: NPL 83033 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 20645 (Smiser, 1936).
Locality: 2.5 miles north of Denison, Grayson County, Texas (Smiser, 1936).
Stratigraphy: Duck Creek Formation, Washita Group.
SYNONYMY
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: Toxasteridae Lambert, 1920
Genus: PLIOTOXASTER Fourtau, 1907
Species: Pliotoxaster inflatus (Smiser, 1936)
TYPE SPECIES: Spatangus collegnii Sismonda, 1844
DIAGNOSIS
Test medium-sized, cordate, and highly inflated. Characterized by a deep anterior sulcus, depressed paired petals, and a vertically truncated posterior. Distinguished from P. whitei by its greater inflation and broader shape (Smiser, 1936).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Duck Creek Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson.
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 48.4 mm L × 45.0 mm W × 32.7 mm H. Top shape: Cordate with angular shoulders; wider anteriorly, narrowing posteriorly. Widest point is about 40% from the anterior margin. Top domed: Bulbous appearance from the anterior end. Small keel present on top of the unpaired interambulacrum.
SIDE: Ambitus: Positioned about 45% of height from the bottom. Side shape: Very inflated (Smiser, 1936). Profile: Posterior end features a sloping truncation; periproct visible from aboral view.
BOTTOM: Bottom shape: Somewhat curved (convex).
AMB: Amb shape: All five ambulacra are sunken (Smiser, 1936). Unpaired ambulacrum (III) is the shortest. Amb arrangement: Anterior paired petals are 50% longer than the unpaired ambulacrum. Posterior paired petals are about 30% longer than the unpaired ambulacrum. Paired ambulacra are broad with open ends.
PORE PAIRS: Shape: Unpaired amb: Slit-like pores arranged en chevron. Paired ambs: Numerous elongated slits (Smiser, 1936).
TUBERCLES: Distribution: Tubercles are perforated and evenly cover the test.
GRANULES: See Tubercles.
FASCIOLE: Absent.
APICAL SYSTEM: Location: Anterior of center ("1/3rd above from center"); subcentral (Smiser, 1936). Plating: Small with a large madreporite. Genital pores: 4.
PERIPROCT (ANUS): Shape: Longitudinally oval; points upward. Size: Small; about equal in size to the peristome. Location: Situated high on the posterior truncation (about 60% from the adoral surface). Visibility: Visible from the aboral view.
PERISTOME (MOUTH): Shape: Transversely pentagonal. Location: Anterior (about 20% from anterior margin). Sunken: Yes. Plastron: Large.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83033. Collected by William R. Thompson, Jr.
ETYMOLOGY
From the Latin inflatus (swollen), referring to the highly convex profile of the test (Smiser, 1936).
REMARKS & COMPARISONS
Remarks: Smiser (1936) originally described this species as Toxaster inflatus, noting its similarity to Toxaster elegans (Macraster elegans) but distinguishing it by the pore arrangement. The species is assigned here to Pliotoxaster based on the petal arrangement and lack of a distinct peripetalous fasciole.
Plate: PlIn-10
Series: Lower Cretaceous Group: Washita Formation: Duck Creek
Locale: County: Grayson Stage: Albian
Length: 48.4 mm Width: 45.0 mm Height: 32.7 mm
Specimen in photo: NPL 83033 Hypotype
Collector: William R. Thompson, Jr.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 20645 (Smiser, 1936).
Locality: 2.5 miles north of Denison, Grayson County, Texas (Smiser, 1936).
Stratigraphy: Duck Creek Formation, Washita Group.
SYNONYMY
- Toxaster inflatus Smiser, 1936
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: Toxasteridae Lambert, 1920
Genus: PLIOTOXASTER Fourtau, 1907
Species: Pliotoxaster inflatus (Smiser, 1936)
TYPE SPECIES: Spatangus collegnii Sismonda, 1844
DIAGNOSIS
Test medium-sized, cordate, and highly inflated. Characterized by a deep anterior sulcus, depressed paired petals, and a vertically truncated posterior. Distinguished from P. whitei by its greater inflation and broader shape (Smiser, 1936).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Duck Creek Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Grayson.
Abundance: Uncommon.
DESCRIPTION
TOP: Length, width, height: 48.4 mm L × 45.0 mm W × 32.7 mm H. Top shape: Cordate with angular shoulders; wider anteriorly, narrowing posteriorly. Widest point is about 40% from the anterior margin. Top domed: Bulbous appearance from the anterior end. Small keel present on top of the unpaired interambulacrum.
SIDE: Ambitus: Positioned about 45% of height from the bottom. Side shape: Very inflated (Smiser, 1936). Profile: Posterior end features a sloping truncation; periproct visible from aboral view.
BOTTOM: Bottom shape: Somewhat curved (convex).
AMB: Amb shape: All five ambulacra are sunken (Smiser, 1936). Unpaired ambulacrum (III) is the shortest. Amb arrangement: Anterior paired petals are 50% longer than the unpaired ambulacrum. Posterior paired petals are about 30% longer than the unpaired ambulacrum. Paired ambulacra are broad with open ends.
PORE PAIRS: Shape: Unpaired amb: Slit-like pores arranged en chevron. Paired ambs: Numerous elongated slits (Smiser, 1936).
TUBERCLES: Distribution: Tubercles are perforated and evenly cover the test.
GRANULES: See Tubercles.
FASCIOLE: Absent.
APICAL SYSTEM: Location: Anterior of center ("1/3rd above from center"); subcentral (Smiser, 1936). Plating: Small with a large madreporite. Genital pores: 4.
PERIPROCT (ANUS): Shape: Longitudinally oval; points upward. Size: Small; about equal in size to the peristome. Location: Situated high on the posterior truncation (about 60% from the adoral surface). Visibility: Visible from the aboral view.
PERISTOME (MOUTH): Shape: Transversely pentagonal. Location: Anterior (about 20% from anterior margin). Sunken: Yes. Plastron: Large.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Hypotype NPL 83033. Collected by William R. Thompson, Jr.
ETYMOLOGY
From the Latin inflatus (swollen), referring to the highly convex profile of the test (Smiser, 1936).
REMARKS & COMPARISONS
Remarks: Smiser (1936) originally described this species as Toxaster inflatus, noting its similarity to Toxaster elegans (Macraster elegans) but distinguishing it by the pore arrangement. The species is assigned here to Pliotoxaster based on the petal arrangement and lack of a distinct peripetalous fasciole.
