Holaster nanus Cragin, 1893
Plate: HoNa-10
Series: Lower Cretaceous Group: Washita Formation: "Vola bed" (Main Street/Grayson equivalent
Locale: Bells County: Grayson Stage: Albian
Length: 22.9 mm Width: 21.3 mm Height: 10.2 mm
Specimen in photo: BEG 40555 Holotype
Collector: J. A. Taff Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 40555 (Texas Memorial Museum).
Locality: Denison-Bonham Road, Choctaw Creek, Grayson County, Texas.
Stratigraphy: "Vola bed" (Main Street/Grayson equivalent) per Cragin (1893
SYNONYMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Holasteroida Durham, 1957
Family: Holasteridae Pictet, 1857
Genus: HOLASTER L. Agassiz, 1836
Species: Holaster nanus Cragin, 1893
TYPE SPECIES: Spatangus nodulosus Goldfuss, 1829
DIAGNOSIS
Test small, low, and broadly ovate; flattened below and evenly low-arched above. Unpaired ambulacrum pores are very oblique and dot-like. Paired ambulacra are gently flexuous with compressed, subequal pores (Cragin, 1893).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: “Vola bed" (Main Street/Grayson equivalent (Cragin, 1893).
Stratigraphic Units: Lower Cretaceous, Albian
Counties: Grayson
Abundance: Rare; only a single specimen collected (Cragin, 1893).
DESCRIPTION
TOP: Length, width, height: 22.9 mm L × 21.3 mm W × 10.2 mm H.
Top shape: Broadly ovate (Cragin, 1893); cordate (Book Author). Widest part is 40% from the anterior margin.
Top domed: Evenly low-arched above; posteriorly obtusely subcarinate (Cragin, 1893).
SIDE: Ambitus: Ambitus at midpoint.
Side shape: Inflated; posterior end truncated and anterior end curved.
Profile: Low and depressed.
BOTTOM: Bottom shape: Flattened below (Cragin, 1893); flat.
AMB: Amb shape: Lanceolate. All five ambulacra are about equal in length.
Amb arrangement: Unpaired ambulacrum (III) has a shallow anteoral furrow that becomes obsolete on the summit region; moderately conspicuous near the apical disc but rapidly becomes inconspicuous anteriorly. Paired ambulacra are gently flexuous (Cragin, 1893).
PORE PAIRS: Arrangement: Unpaired amb pores are dot-like, arranged in very oblique pore pairs whose interspaces increase rapidly centrifugally; outer pores dot-like, inner ones slightly compressed and subvertical.
Paired ambs: Pores are compressed, dot-like to hyphen-like (not dash-like); pore pairs are subequal (Cragin, 1893).
TUBERCLES: Distribution: Small, round tubercles. More numerous around the periproct, ambulacra, and on the bottom surface.
GRANULES: Distribution: Heavier in areas with dense tuberculation.
FASCIOLE: Not specified.
APICAL SYSTEM: Location: Central. Type: Compact.
PERIPROCT (ANUS): Shape: Longitudinally oval.
Location: Located on the truncated posterior face, approximately 1/3 from the bottom.
PERISTOME (MOUTH): Shape: Large, transversely oval.
Location: Set far forward (20% from anterior margin).
Sunken: Depressed.
Visibility: Visible from anterior end.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 40555. Collected by Mr. J. A. Taff.
ETYMOLOGY
From the Latin nanus, meaning "dwarf," referring to the small size of the species.
REMARKS & COMPARISONS
Remarks: Cooke (1946) considered Holaster nanus to be a synonym of Holaster laevis (Brongniart), noting the variability in Texas populations. Cragin noted that the dimensions of the holotype might represent a depressed individual and not the typical proportions of the species.
Comparisons:
Plate: HoNa-10
Series: Lower Cretaceous Group: Washita Formation: "Vola bed" (Main Street/Grayson equivalent
Locale: Bells County: Grayson Stage: Albian
Length: 22.9 mm Width: 21.3 mm Height: 10.2 mm
Specimen in photo: BEG 40555 Holotype
Collector: J. A. Taff Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: BEG 40555 (Texas Memorial Museum).
Locality: Denison-Bonham Road, Choctaw Creek, Grayson County, Texas.
Stratigraphy: "Vola bed" (Main Street/Grayson equivalent) per Cragin (1893
SYNONYMY
- Holaster laevis (Brongniart, 1822) (fide Cooke, 1946)
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Atelostomata Zittel, 1879
Order: Holasteroida Durham, 1957
Family: Holasteridae Pictet, 1857
Genus: HOLASTER L. Agassiz, 1836
Species: Holaster nanus Cragin, 1893
TYPE SPECIES: Spatangus nodulosus Goldfuss, 1829
DIAGNOSIS
Test small, low, and broadly ovate; flattened below and evenly low-arched above. Unpaired ambulacrum pores are very oblique and dot-like. Paired ambulacra are gently flexuous with compressed, subequal pores (Cragin, 1893).
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Washita
Formations: “Vola bed" (Main Street/Grayson equivalent (Cragin, 1893).
Stratigraphic Units: Lower Cretaceous, Albian
Counties: Grayson
Abundance: Rare; only a single specimen collected (Cragin, 1893).
DESCRIPTION
TOP: Length, width, height: 22.9 mm L × 21.3 mm W × 10.2 mm H.
Top shape: Broadly ovate (Cragin, 1893); cordate (Book Author). Widest part is 40% from the anterior margin.
Top domed: Evenly low-arched above; posteriorly obtusely subcarinate (Cragin, 1893).
SIDE: Ambitus: Ambitus at midpoint.
Side shape: Inflated; posterior end truncated and anterior end curved.
Profile: Low and depressed.
BOTTOM: Bottom shape: Flattened below (Cragin, 1893); flat.
AMB: Amb shape: Lanceolate. All five ambulacra are about equal in length.
Amb arrangement: Unpaired ambulacrum (III) has a shallow anteoral furrow that becomes obsolete on the summit region; moderately conspicuous near the apical disc but rapidly becomes inconspicuous anteriorly. Paired ambulacra are gently flexuous (Cragin, 1893).
PORE PAIRS: Arrangement: Unpaired amb pores are dot-like, arranged in very oblique pore pairs whose interspaces increase rapidly centrifugally; outer pores dot-like, inner ones slightly compressed and subvertical.
Paired ambs: Pores are compressed, dot-like to hyphen-like (not dash-like); pore pairs are subequal (Cragin, 1893).
TUBERCLES: Distribution: Small, round tubercles. More numerous around the periproct, ambulacra, and on the bottom surface.
GRANULES: Distribution: Heavier in areas with dense tuberculation.
FASCIOLE: Not specified.
APICAL SYSTEM: Location: Central. Type: Compact.
PERIPROCT (ANUS): Shape: Longitudinally oval.
Location: Located on the truncated posterior face, approximately 1/3 from the bottom.
PERISTOME (MOUTH): Shape: Large, transversely oval.
Location: Set far forward (20% from anterior margin).
Sunken: Depressed.
Visibility: Visible from anterior end.
SPINES: Unknown.
SPECIMENS STUDIED & CONDITION: Holotype BEG 40555. Collected by Mr. J. A. Taff.
ETYMOLOGY
From the Latin nanus, meaning "dwarf," referring to the small size of the species.
REMARKS & COMPARISONS
Remarks: Cooke (1946) considered Holaster nanus to be a synonym of Holaster laevis (Brongniart), noting the variability in Texas populations. Cragin noted that the dimensions of the holotype might represent a depressed individual and not the typical proportions of the species.
Comparisons:
- H. completus: H. nanus has a less conspicuous unpaired ambulacrum anteriorly and very oblique pore pairs, whereas H. completus has crowded, slightly oblique pores and straight paired ambulacra (Cragin, 1893).
- H. simplex: H. nanus has paired ambulacra with subequal pores (dot-like or hyphen-like), whereas H. simplex has unequal pores (thin, dash-like/slit-like) and more remote pores in the unpaired ambulacrum (Cragin, 1893).
