Schizaster (Paraster) susana Zachos and Molineux, 2003
Plate: ScpSu-10
Series: Upper Eocene Group: Jackson Formation: Unknown
Locale: Manning County: Angelina Stage: Priabonian
Length: 23.6 mm Width: 22.6 mm Height: 16.6 mm
Specimen in photos: TX 886.2 Paratype Collector: (Not specified)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: TX 1993.5 (Zachos & Molineux, 2003).
Locality: Texas (Zachos & Molineux, 2003).
Stratigraphy: Caddell Formation, Jackson 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: Schizasteridae Lambert, 1905
Genus: SCHIZASTER L. Agassiz, 1836
Subgenus: PARASTER Pomel, 1869
Species: Schizaster (Paraster) susana Zachos & Molineux, 2003
TYPE SPECIES: Schizaster gibberulus L. Agassiz, 1847
DIAGNOSIS
A small Schizaster (subgenus Paraster) characterized by the presence of four genital pores. The test is high and inflated with a deep anterior sulcus. The anterior paired petals are less than twice the length of the posterior pair (Zachos & Molineux, 2003).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Jackson
Formations: Caddell Formation.
Stratigraphic Units: Paleogene, Upper Eocene (Priabonian).
Counties: Angelina, San Augustine.
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 23.6 mm L × 22.6 mm W × 16.6 mm H. Top shape: Cordate; angular shoulders and a slight posterior point. Widest point at the midpoint. Top domed: Very inflated. Deep, wide anterior sulcus cuts the margin.
SIDE: Ambitus: Positioned slightly posterior of the midpoint. Side shape: Rounded sides curve less above the ambitus to create a posterior peak (keel). Profile: The anterior sulcus is extremely deep, dropping approximately 7/8 of the test height. Anterior paired petals drop about 1/2 of the height; posterior pair drop about 1/7.
BOTTOM: Bottom shape: Not detailed, implied convex.
AMB: Amb shape: All paired ambulacra are petaloid and deeply sunken. Amb arrangement: Posterior paired petals are very short. Anterior paired petals are less than twice the length of the posterior pair. Interambulacra between the anterior and posterior petals form a 90-degree angle.
PORE PAIRS: Shape: Slightly elongated (slit-like).
TUBERCLES: Distribution: Fine and dense.
GRANULES: See Tubercles.
FASCIOLE: Peripetalous and latero-anal fascioles present in type description (Zachos & Molineux, 2003).
APICAL SYSTEM: Location: Small; positioned posterior of the midpoint. Genital Pores: Four (Diagnostic for Paraster).
PERIPROCT (ANUS): Shape: Small and round. Location: Situated high on the posterior face, above the midpoint.
PERISTOME (MOUTH): Shape: Reniform (kidney-shaped); wide and horizontally narrow. Location: Anterior (1/5 from anterior end). Lip: Pronounced; visible from the side.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Paratype TX 886.2.
ETYMOLOGY
Named for Susan Zachos (Zachos & Molineux, 2003).
REMARKS & COMPARISONS
Remarks: This species is assigned to the subgenus Paraster (often elevated to Genus) based on the presence of four genital pores; Schizaster sensu stricto possesses only two. Zachos & Molineux (2003) described this species from the Upper Eocene Caddell Formation.
Comparisons:
Plate: ScpSu-10
Series: Upper Eocene Group: Jackson Formation: Unknown
Locale: Manning County: Angelina Stage: Priabonian
Length: 23.6 mm Width: 22.6 mm Height: 16.6 mm
Specimen in photos: TX 886.2 Paratype Collector: (Not specified)
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: TX 1993.5 (Zachos & Molineux, 2003).
Locality: Texas (Zachos & Molineux, 2003).
Stratigraphy: Caddell Formation, Jackson 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: Schizasteridae Lambert, 1905
Genus: SCHIZASTER L. Agassiz, 1836
Subgenus: PARASTER Pomel, 1869
Species: Schizaster (Paraster) susana Zachos & Molineux, 2003
TYPE SPECIES: Schizaster gibberulus L. Agassiz, 1847
DIAGNOSIS
A small Schizaster (subgenus Paraster) characterized by the presence of four genital pores. The test is high and inflated with a deep anterior sulcus. The anterior paired petals are less than twice the length of the posterior pair (Zachos & Molineux, 2003).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Jackson
Formations: Caddell Formation.
Stratigraphic Units: Paleogene, Upper Eocene (Priabonian).
Counties: Angelina, San Augustine.
Abundance: Rare.
DESCRIPTION
TOP: Length, width, height: 23.6 mm L × 22.6 mm W × 16.6 mm H. Top shape: Cordate; angular shoulders and a slight posterior point. Widest point at the midpoint. Top domed: Very inflated. Deep, wide anterior sulcus cuts the margin.
SIDE: Ambitus: Positioned slightly posterior of the midpoint. Side shape: Rounded sides curve less above the ambitus to create a posterior peak (keel). Profile: The anterior sulcus is extremely deep, dropping approximately 7/8 of the test height. Anterior paired petals drop about 1/2 of the height; posterior pair drop about 1/7.
BOTTOM: Bottom shape: Not detailed, implied convex.
AMB: Amb shape: All paired ambulacra are petaloid and deeply sunken. Amb arrangement: Posterior paired petals are very short. Anterior paired petals are less than twice the length of the posterior pair. Interambulacra between the anterior and posterior petals form a 90-degree angle.
PORE PAIRS: Shape: Slightly elongated (slit-like).
TUBERCLES: Distribution: Fine and dense.
GRANULES: See Tubercles.
FASCIOLE: Peripetalous and latero-anal fascioles present in type description (Zachos & Molineux, 2003).
APICAL SYSTEM: Location: Small; positioned posterior of the midpoint. Genital Pores: Four (Diagnostic for Paraster).
PERIPROCT (ANUS): Shape: Small and round. Location: Situated high on the posterior face, above the midpoint.
PERISTOME (MOUTH): Shape: Reniform (kidney-shaped); wide and horizontally narrow. Location: Anterior (1/5 from anterior end). Lip: Pronounced; visible from the side.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Paratype TX 886.2.
ETYMOLOGY
Named for Susan Zachos (Zachos & Molineux, 2003).
REMARKS & COMPARISONS
Remarks: This species is assigned to the subgenus Paraster (often elevated to Genus) based on the presence of four genital pores; Schizaster sensu stricto possesses only two. Zachos & Molineux (2003) described this species from the Upper Eocene Caddell Formation.
Comparisons:
- Schizaster caddoensis: S. susana is distinguished from the Middle Eocene S. caddoensis by the number of genital pores (4 vs 2), stratigraphic position (Upper vs Middle Eocene), and petal proportions.
