Washitaster riovistae (Adkins, 1920)
Plate: WaRi-10
Series: Lower Cretaceous Group: Washita Formation: Upper Weno
Locale: Rio Vista County: Johnson Stage: Albian
Length: 26.9 mm Width: 24.2 mm Height: 14.2 mm
Specimen in photos: BEG 21491 Holotype
Collector: (Not specified)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 21491 (Adkins, 1920).
Locality: Locality 720; one mile southeast of Rio Vista, Johnson County, Texas.
Stratigraphy: Top of Weno Formation (marl facies).
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: WASHITASTER Lambert, 1927
Species: Washitaster riovistae (Adkins, 1920)
TYPE SPECIES: Hemiaster riovistae Adkins, 1920
DIAGNOSIS
According to Adkins (1920): A Washitaster characterized by a low, elliptical test with a broadly truncated posterior. Distinguished from W. bravoensis by having pore pairs in the unpaired ambulacrum that are all similar (not alternating long and short) and separated by a transversely elongate tubercle. Lateral surfaces bear fascicle-like bands of crowded granules.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Weno Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Johnson.
Abundance: Rare.
DESCRIPTION (Based on Adkins, 1920)
TOP: Length, width, height: 26.9 mm L × 24.2 mm W × 14.2 mm H. Top shape: Elliptical in general outline; notched at the anterior ambitus. Rounded laterally with three distinct angulations. Top domed: Low; slope forward from apical system is gentle and almost straight. Highest point is on the low posterior median carina, about one-fifth the length from the posterior end (Adkins, 1920).
SIDE: Ambitus: Sharply rounded. Side shape: Anteriorly wedge-shaped; tallest point is posterior (three-fourths the way back). Profile: Mid-line curves sharply posteriorly from the highest point to the top of the truncated posterior end.
BOTTOM: Bottom shape: Peristome lies in a deep depression. Elevated median tuberculated area present (Adkins, 1920).
AMB: Amb shape: Unpaired anterior ambulacrum (III) is long and shallow with nearly straight sides, making a shallow notch at the ambitus. Paired Anterolaterals (II & IV): Diverge at 180°, turn forward at ~47°, then diverge to cross the ambitus far anteriorly. Paired Posterolaterals (I & V): Short, rather wide, bulging in the center; axes straight, diverging at ~115° (Adkins, 1920).
PORE PAIRS: Unpaired Amb: about 32 pairs of transverse slit-like pores. Distinctive feature: Pores are similar (not alternating long/short); separated by a conspicuously elevated, transversely elongate tubercle. The ten nearest the apex show a graduation in size; others are equal (Adkins, 1920).
TUBERCLES: Distribution: Margins are coarsely tuberculated. Around each tubercle is a circle of small tubercles (Adkins, 1920).
GRANULES: Distribution: Fine granules irregularly scattered in intervening spaces. Ambulacral plates have a double row of small granules (Adkins, 1920).
FASCIOLE: Marginal/Peripetalous: "Laterally the test bears several fascicle-like bands each consisting of three crowded rows of the smallest sized granules" (Adkins, 1920).
INTERAMB: Shape: Oval projections of posterolateral ambulacra consist of large smooth elongate plates.
APICAL SYSTEM: Location: Posterior; situated slightly more than two-thirds the length of the mid-line from the anterior notch. Genital pores: 4 genital plates; posterior pair slightly farther apart. Plating: Right anterior plate is the elongated madreporite (Adkins, 1920).
PERIPROCT (ANUS): Shape: Transversely oval; inferior margin slightly bulged downward. Location: Situated high on the posterior truncated surface (two-thirds the way up).
PERISTOME (MOUTH): Shape: Transversely oval. Lip: Posterior lip elevated into a blunt high tip or carina; slightly emarginate (Adkins, 1920).
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 21491.
ETYMOLOGY
Named for the town of Rio Vista, Texas, near the type locality.
REMARKS & COMPARISONS
Remarks: This is the Type Species for the genus Washitaster. Lambert separated this genus from Enallaster (now Heteraster) based on the presence of the fasciole-like bands described by Adkins.
Comparisons (per Adkins, 1920):
Plate: WaRi-10
Series: Lower Cretaceous Group: Washita Formation: Upper Weno
Locale: Rio Vista County: Johnson Stage: Albian
Length: 26.9 mm Width: 24.2 mm Height: 14.2 mm
Specimen in photos: BEG 21491 Holotype
Collector: (Not specified)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 21491 (Adkins, 1920).
Locality: Locality 720; one mile southeast of Rio Vista, Johnson County, Texas.
Stratigraphy: Top of Weno Formation (marl facies).
SYNONYMY
- Enallaster riovistae Adkins, 1920
- Washitaster riovistae (Adkins) Lambert, 1927
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: WASHITASTER Lambert, 1927
Species: Washitaster riovistae (Adkins, 1920)
TYPE SPECIES: Hemiaster riovistae Adkins, 1920
DIAGNOSIS
According to Adkins (1920): A Washitaster characterized by a low, elliptical test with a broadly truncated posterior. Distinguished from W. bravoensis by having pore pairs in the unpaired ambulacrum that are all similar (not alternating long and short) and separated by a transversely elongate tubercle. Lateral surfaces bear fascicle-like bands of crowded granules.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: Weno Formation.
Stratigraphic Units: Lower Cretaceous, Albian.
Counties: Johnson.
Abundance: Rare.
DESCRIPTION (Based on Adkins, 1920)
TOP: Length, width, height: 26.9 mm L × 24.2 mm W × 14.2 mm H. Top shape: Elliptical in general outline; notched at the anterior ambitus. Rounded laterally with three distinct angulations. Top domed: Low; slope forward from apical system is gentle and almost straight. Highest point is on the low posterior median carina, about one-fifth the length from the posterior end (Adkins, 1920).
SIDE: Ambitus: Sharply rounded. Side shape: Anteriorly wedge-shaped; tallest point is posterior (three-fourths the way back). Profile: Mid-line curves sharply posteriorly from the highest point to the top of the truncated posterior end.
BOTTOM: Bottom shape: Peristome lies in a deep depression. Elevated median tuberculated area present (Adkins, 1920).
AMB: Amb shape: Unpaired anterior ambulacrum (III) is long and shallow with nearly straight sides, making a shallow notch at the ambitus. Paired Anterolaterals (II & IV): Diverge at 180°, turn forward at ~47°, then diverge to cross the ambitus far anteriorly. Paired Posterolaterals (I & V): Short, rather wide, bulging in the center; axes straight, diverging at ~115° (Adkins, 1920).
PORE PAIRS: Unpaired Amb: about 32 pairs of transverse slit-like pores. Distinctive feature: Pores are similar (not alternating long/short); separated by a conspicuously elevated, transversely elongate tubercle. The ten nearest the apex show a graduation in size; others are equal (Adkins, 1920).
TUBERCLES: Distribution: Margins are coarsely tuberculated. Around each tubercle is a circle of small tubercles (Adkins, 1920).
GRANULES: Distribution: Fine granules irregularly scattered in intervening spaces. Ambulacral plates have a double row of small granules (Adkins, 1920).
FASCIOLE: Marginal/Peripetalous: "Laterally the test bears several fascicle-like bands each consisting of three crowded rows of the smallest sized granules" (Adkins, 1920).
INTERAMB: Shape: Oval projections of posterolateral ambulacra consist of large smooth elongate plates.
APICAL SYSTEM: Location: Posterior; situated slightly more than two-thirds the length of the mid-line from the anterior notch. Genital pores: 4 genital plates; posterior pair slightly farther apart. Plating: Right anterior plate is the elongated madreporite (Adkins, 1920).
PERIPROCT (ANUS): Shape: Transversely oval; inferior margin slightly bulged downward. Location: Situated high on the posterior truncated surface (two-thirds the way up).
PERISTOME (MOUTH): Shape: Transversely oval. Lip: Posterior lip elevated into a blunt high tip or carina; slightly emarginate (Adkins, 1920).
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 21491.
ETYMOLOGY
Named for the town of Rio Vista, Texas, near the type locality.
REMARKS & COMPARISONS
Remarks: This is the Type Species for the genus Washitaster. Lambert separated this genus from Enallaster (now Heteraster) based on the presence of the fasciole-like bands described by Adkins.
Comparisons (per Adkins, 1920):
- Washitaster bravoensis: W. riovistae differs by having similar pore pairs in the unpaired ambulacrum (vs. alternating long and short in bravoensis) and a broader, less deeply excavated posterior truncation.
- Macraster wenoensis: W. riovistae has a more posterior apical system, a broader posterior truncation (vs. sharply excavated vertical groove in wenoensis), and fasciole bands.
