Mellita costabilei Thompson, 2016
Plate: MeCo-10
Series: (Pleistocene) Group: unsure Formation: unsure
Locale: Aqua Fria Draw County: Brewster Stage: Calabrian
Length: 22.4 mm Width: 21.9 mm Height: 3.0 mm
Specimen in photo: NPL 73956 Holotype
Collector: James Costabile
University of Texas Non-vertebrate Paleo. Lab.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 73956.
Locality: Agua Fria Draw, Brewster County, Texas.
Stratigraphy: Pleistocene terrace deposits (study area often associated with Green Valley/Agua Fria alluvium).
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Clypeasteroida A. Agassiz, 1872
Family: Mellitidae Stefanini, 1912
Genus: MELLITA L. Agassiz, 1841
Species: Mellita costabilei Thompson, 2016
TYPE SPECIES: Echinodiscus quinquiesperforatus Leske, 1778
DIAGNOSIS
A Mellita from the Pleistocene of West Texas characterized by an apex positioned slightly anterior of center. The paired anterior lunules are eye-shaped and slope forward from the center. The posterior lunule is long and narrow.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Undifferentiated Quaternary
Formations: Terrace deposits / Alluvium.
Stratigraphic Units: Pleistocene (Calabrian/Rancholabrean).
Counties: Brewster.
Abundance: Rare; known from only one locality in Study Butte/Agua Fria area.
DESCRIPTION
TOP: Length, width, height: 22.4 mm L × 21.9 mm W × 3.0 mm H.
Top shape: Subcircular; slightly longer than wide. Notches present at the anterior margin and at each of the 4 ambulacral lunules.
Top domed: Flat to gently domed; apex positioned slightly anterior of center.
SIDE: Side shape: Margins thin and sharp.
BOTTOM: Bottom shape: Flat.
AMB: Amb shape: Petaloid; petals are equal in size and open distally.
Amb arrangement: Anterior paired petals (II & IV) contain 22 sets of pores. Posterior paired petals (I & V) contain 28 sets of pores; they are slightly longer and narrower than the anterior pair and flex posteriorly/downward.
LUNULES: Arrangement: Five lunules present.
Anterior Paired (II & IV): Eye-shaped; positioned closer to the margin than the petals; slope forward from the center.
Posterior Paired (I & V): Larger than anterior lunules; ends are less pointed (more rounded), especially the marginal end. Positioned closer to the margin than the petals.
Anal (Unpaired) Lunule: Located on the posterior interambulacrum (5); half is located between the posterior paired ambulacra and half below. Narrow and long.
PORE PAIRS: Shape: Inner pores tiny and round; outer pores elongated. Separated by a long furrow.
Arrangement: Closely spaced within each set.
TUBERCLES: Distribution: Thickly and evenly cover the entire test. Largest tubercles are found at the margin, adorally, and adorally on interambulacra 1 and 4.
Features: Small, crenulate; areoles sunken.
GRANULES: See Tubercles section.
FASCIOLE: Absent.
APICAL SYSTEM: Location: Central.
Genital pores: 4 genital pores.
Plating: Madreporite is large and star-shaped.
PERIPROCT (ANUS): Shape: Vertically elongated.
Size: Smaller than the peristome.
Location: Oral (bottom); located at the center margin of the first pair of post-basicoronal plates, halfway between the peristome and the unpaired lunule.
PERISTOME (MOUTH): Shape: Round.
Location: Central.
Features: Food grooves are shallow, branching away from five nodes at the peristome. Grooves extend from the margin and from each outer lunule to the peristome.
SPINES: Shape: Small, tapered; widest at the collar.
Distribution: Preserved on the holotype at the peristome and along food grooves.
SPECIMENS STUDIED & CONDITION: Two specimens studied. Holotype NPL 73956.
ETYMOLOGY
Named after James Costabile, who discovered the echinoid with his son.
REMARKS & COMPARISONS
Remarks: This species represents a unique inland occurrence of a marine clypeasteriod in West Texas, likely deposited during a marine incursion or reworked into Pleistocene terrace deposits.
Comparisons:
Remarks (01-2026): Group and Formation unsure. Texas Pleistocene terrace deposits are difficult to stage precisely without radiometric dating; retained "Pleistocene" in general (Moon, 1953).
Plate: MeCo-10
Series: (Pleistocene) Group: unsure Formation: unsure
Locale: Aqua Fria Draw County: Brewster Stage: Calabrian
Length: 22.4 mm Width: 21.9 mm Height: 3.0 mm
Specimen in photo: NPL 73956 Holotype
Collector: James Costabile
University of Texas Non-vertebrate Paleo. Lab.
Repository: Non-vertebrate Paleo. Lab., Univ. of Texas
HOLOTYPE INFO:
Holotype: NPL 73956.
Locality: Agua Fria Draw, Brewster County, Texas.
Stratigraphy: Pleistocene terrace deposits (study area often associated with Green Valley/Agua Fria alluvium).
SYSTEMATIC PALEONTOLOGY – TAXONOMY
Class: Echinoidea Leske, 1778
Subclass: Euechinoidea Bronn, 1860
Infraclass: Irregularia Latreille, 1825
Superorder: Neognathostomata Smith, 1981
Order: Clypeasteroida A. Agassiz, 1872
Family: Mellitidae Stefanini, 1912
Genus: MELLITA L. Agassiz, 1841
Species: Mellita costabilei Thompson, 2016
TYPE SPECIES: Echinodiscus quinquiesperforatus Leske, 1778
DIAGNOSIS
A Mellita from the Pleistocene of West Texas characterized by an apex positioned slightly anterior of center. The paired anterior lunules are eye-shaped and slope forward from the center. The posterior lunule is long and narrow.
STRATIGRAPHICAL OCCURRENCE & DISTRIBUTION
Group: Undifferentiated Quaternary
Formations: Terrace deposits / Alluvium.
Stratigraphic Units: Pleistocene (Calabrian/Rancholabrean).
Counties: Brewster.
Abundance: Rare; known from only one locality in Study Butte/Agua Fria area.
DESCRIPTION
TOP: Length, width, height: 22.4 mm L × 21.9 mm W × 3.0 mm H.
Top shape: Subcircular; slightly longer than wide. Notches present at the anterior margin and at each of the 4 ambulacral lunules.
Top domed: Flat to gently domed; apex positioned slightly anterior of center.
SIDE: Side shape: Margins thin and sharp.
BOTTOM: Bottom shape: Flat.
AMB: Amb shape: Petaloid; petals are equal in size and open distally.
Amb arrangement: Anterior paired petals (II & IV) contain 22 sets of pores. Posterior paired petals (I & V) contain 28 sets of pores; they are slightly longer and narrower than the anterior pair and flex posteriorly/downward.
LUNULES: Arrangement: Five lunules present.
Anterior Paired (II & IV): Eye-shaped; positioned closer to the margin than the petals; slope forward from the center.
Posterior Paired (I & V): Larger than anterior lunules; ends are less pointed (more rounded), especially the marginal end. Positioned closer to the margin than the petals.
Anal (Unpaired) Lunule: Located on the posterior interambulacrum (5); half is located between the posterior paired ambulacra and half below. Narrow and long.
PORE PAIRS: Shape: Inner pores tiny and round; outer pores elongated. Separated by a long furrow.
Arrangement: Closely spaced within each set.
TUBERCLES: Distribution: Thickly and evenly cover the entire test. Largest tubercles are found at the margin, adorally, and adorally on interambulacra 1 and 4.
Features: Small, crenulate; areoles sunken.
GRANULES: See Tubercles section.
FASCIOLE: Absent.
APICAL SYSTEM: Location: Central.
Genital pores: 4 genital pores.
Plating: Madreporite is large and star-shaped.
PERIPROCT (ANUS): Shape: Vertically elongated.
Size: Smaller than the peristome.
Location: Oral (bottom); located at the center margin of the first pair of post-basicoronal plates, halfway between the peristome and the unpaired lunule.
PERISTOME (MOUTH): Shape: Round.
Location: Central.
Features: Food grooves are shallow, branching away from five nodes at the peristome. Grooves extend from the margin and from each outer lunule to the peristome.
SPINES: Shape: Small, tapered; widest at the collar.
Distribution: Preserved on the holotype at the peristome and along food grooves.
SPECIMENS STUDIED & CONDITION: Two specimens studied. Holotype NPL 73956.
ETYMOLOGY
Named after James Costabile, who discovered the echinoid with his son.
REMARKS & COMPARISONS
Remarks: This species represents a unique inland occurrence of a marine clypeasteriod in West Texas, likely deposited during a marine incursion or reworked into Pleistocene terrace deposits.
Comparisons:
- Mellita isometra: M. costabilei closely resembles M. isometra but possesses shorter lunules.
- Mellita quinquiesperforata: The posterior lunule in M. costabilei is narrower and longer than that of M. quinquiesperforata.
Remarks (01-2026): Group and Formation unsure. Texas Pleistocene terrace deposits are difficult to stage precisely without radiometric dating; retained "Pleistocene" in general (Moon, 1953).
