Brissus exiguus Cotteau, 1875
Plate: BrEx-10
Series: Oligocene Group: Catahoula Formation: Anahuac (Heterostegina Reef Zone)
Locale: Damond Mound County: Brazoria Stage: Chattian
Length: 47.0 mm Width: 35.8 mm Height: 21.7 mm
Specimen in photo: NPL 3858
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM 328246 (formerly listed in Guppy Collection) — National Museum of Natural History, Smithsonian Institution (Jackson, 1922; Kieran, 1997)
Locality: Anguilla, West Indies (Cotteau, 1875)
Stratigraphy: Anguilla Formation, Lower Miocene (Jackson, 1922)
Systematic Paleontology
CLASS: ECHINOIDEA Leske, 1778
SUBCLASS: EUECHINOIDEA Bronn, 1860
INFRACLASS: IRREGULARIA Latreille, 1825
SUPERORDER: ATELOSTOMATA Zittel, 1879
ORDER: SPATANGOIDA L. Agassiz, 1840
FAMILY: BRISSIDAE Gray, 1855
GENUS: BRISSUS Gray, 1825
SPECIES: Brissus exiguus Cotteau, 1875
TYPE SPECIES: Spatangus brissus var. unicolor Leske, 1778
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Catahoula
Formations: Anahuac Formation (Heterostegina Reef Zone)
Stratigraphic Units: Oligocene (Chattian) to Lower Miocene (Aquitanian) (Jackson, 1922)
Counties: Brazoria County, Texas ; Also reported from Anguilla and Trinidad (Jackson, 1922)
DESCRIPTION
TOP: Length, width, height: 47.0 mm × 35.8 mm × 21.7 mm
Top shape: Elongate, narrow and rounded anteriorly; subtruncate posteriorly (Jackson, 1922)
Top domed: Upper face swollen; subcarinate posteriorly (Jackson, 1922)
SIDE: Side shape: Lower face regularly elevated; depressed in front of the peristome (Jackson, 1922)
AMB: Amb shape: Anterior ambulacrum (III) straight, elongate, narrow; anterior furrow wholly wanting (Jackson, 1922)
Amb primary tubercles: Large tubercles present on Amb III (Jackson, 1922)
Paired Ambs: Wide, subflexuous, very unequal. Anterior pair (II and IV) nearly transverse (angle ~180°), little rounded at ends. Posterior pair (I and V) longer, straighter, a little deeper, and much less divergent (acute angle ~40°) (Jackson, 1922)
Amb primary zones: Poriferous areas wide; pores elongate, narrow, equal. Half-areas approach one another so closely as to leave no interporiferous area (Jackson, 1922)
INTERAMB: Interamb primary tubercles: Well developed dorsally near the apical disk (Jackson, 1922)
PORE PAIRS: Shape: Elongate, narrow (Jackson, 1922)
Density variation: Pores in Amb III widely separated and scarcely visible (Jackson, 1922)
FASCIOLE: Fasciole: Peripetalous fasciole subflexuous; does not limit the large tubercles of the dorsal side (Jackson, 1922)
APICAL SYSTEM: Location: Very excentric anteriorly (Jackson, 1922)
Shape: Small, compact, granular (Jackson, 1922)
Genital pores: Typically 4 (Jackson, 1922 notes the Holotype had an atrophied madreporite pore, but this is considered abnormal)
PERISTOME (MOUTH): Shape: Semicircular (Jackson, 1922)
Location: Very excentric anteriorly (Jackson, 1922)
SPECIMENS STUDIED & CONDITION
Specimen condition: Partial test, in situ .
ETYMOLOGY: From the Latin exiguus, meaning "small," "scanty," or "meager," referring to the small size of the type specimen compared to other Brissus species.
REMARKS & COMPARISONS
Remarks: The Texas specimen (NPL 3858) is significantly larger (47 mm) than the type specimen described by Cotteau (approx. 17 mm). Jackson (1922) noted a larger specimen in the Guppy collection (34 mm) that was broader anteriorly but retained essential characters, suggesting shape changes with ontogeny.
Comparisons: Brissus exiguus differs from the extant Brissus unicolor (B. unicola in text) by being longer and narrower, dorsally more carinate at the posterior end, and having paired ambulacra with poriferous zones that touch (no interporiferous area) (Jackson, 1922).
Data Note: The Texas specimen found in the Anahuac Formation (Oligocene) represents a significant range extension from the Caribbean Miocene type locality.
Plate: BrEx-10
Series: Oligocene Group: Catahoula Formation: Anahuac (Heterostegina Reef Zone)
Locale: Damond Mound County: Brazoria Stage: Chattian
Length: 47.0 mm Width: 35.8 mm Height: 21.7 mm
Specimen in photo: NPL 3858
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: USNM 328246 (formerly listed in Guppy Collection) — National Museum of Natural History, Smithsonian Institution (Jackson, 1922; Kieran, 1997)
Locality: Anguilla, West Indies (Cotteau, 1875)
Stratigraphy: Anguilla Formation, Lower Miocene (Jackson, 1922)
Systematic Paleontology
CLASS: ECHINOIDEA Leske, 1778
SUBCLASS: EUECHINOIDEA Bronn, 1860
INFRACLASS: IRREGULARIA Latreille, 1825
SUPERORDER: ATELOSTOMATA Zittel, 1879
ORDER: SPATANGOIDA L. Agassiz, 1840
FAMILY: BRISSIDAE Gray, 1855
GENUS: BRISSUS Gray, 1825
SPECIES: Brissus exiguus Cotteau, 1875
TYPE SPECIES: Spatangus brissus var. unicolor Leske, 1778
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Catahoula
Formations: Anahuac Formation (Heterostegina Reef Zone)
Stratigraphic Units: Oligocene (Chattian) to Lower Miocene (Aquitanian) (Jackson, 1922)
Counties: Brazoria County, Texas ; Also reported from Anguilla and Trinidad (Jackson, 1922)
DESCRIPTION
TOP: Length, width, height: 47.0 mm × 35.8 mm × 21.7 mm
Top shape: Elongate, narrow and rounded anteriorly; subtruncate posteriorly (Jackson, 1922)
Top domed: Upper face swollen; subcarinate posteriorly (Jackson, 1922)
SIDE: Side shape: Lower face regularly elevated; depressed in front of the peristome (Jackson, 1922)
AMB: Amb shape: Anterior ambulacrum (III) straight, elongate, narrow; anterior furrow wholly wanting (Jackson, 1922)
Amb primary tubercles: Large tubercles present on Amb III (Jackson, 1922)
Paired Ambs: Wide, subflexuous, very unequal. Anterior pair (II and IV) nearly transverse (angle ~180°), little rounded at ends. Posterior pair (I and V) longer, straighter, a little deeper, and much less divergent (acute angle ~40°) (Jackson, 1922)
Amb primary zones: Poriferous areas wide; pores elongate, narrow, equal. Half-areas approach one another so closely as to leave no interporiferous area (Jackson, 1922)
INTERAMB: Interamb primary tubercles: Well developed dorsally near the apical disk (Jackson, 1922)
PORE PAIRS: Shape: Elongate, narrow (Jackson, 1922)
Density variation: Pores in Amb III widely separated and scarcely visible (Jackson, 1922)
FASCIOLE: Fasciole: Peripetalous fasciole subflexuous; does not limit the large tubercles of the dorsal side (Jackson, 1922)
APICAL SYSTEM: Location: Very excentric anteriorly (Jackson, 1922)
Shape: Small, compact, granular (Jackson, 1922)
Genital pores: Typically 4 (Jackson, 1922 notes the Holotype had an atrophied madreporite pore, but this is considered abnormal)
PERISTOME (MOUTH): Shape: Semicircular (Jackson, 1922)
Location: Very excentric anteriorly (Jackson, 1922)
SPECIMENS STUDIED & CONDITION
Specimen condition: Partial test, in situ .
ETYMOLOGY: From the Latin exiguus, meaning "small," "scanty," or "meager," referring to the small size of the type specimen compared to other Brissus species.
REMARKS & COMPARISONS
Remarks: The Texas specimen (NPL 3858) is significantly larger (47 mm) than the type specimen described by Cotteau (approx. 17 mm). Jackson (1922) noted a larger specimen in the Guppy collection (34 mm) that was broader anteriorly but retained essential characters, suggesting shape changes with ontogeny.
Comparisons: Brissus exiguus differs from the extant Brissus unicolor (B. unicola in text) by being longer and narrower, dorsally more carinate at the posterior end, and having paired ambulacra with poriferous zones that touch (no interporiferous area) (Jackson, 1922).
Data Note: The Texas specimen found in the Anahuac Formation (Oligocene) represents a significant range extension from the Caribbean Miocene type locality.
