Bairdoppilata collaevata, Maddocks, 2025

Bairdoppilata collaevata , sp. nov.

(Graphs 1, 6; Figures 2A–B View FIGURE 2 ; 3E–S View FIGURE 3 ; 4A–B, G–H, K View FIGURE 4 ; 5E–K, N–P View FIGURE 5 ; 6K–Z View FIGURE 6 ; 32 View FIGURE 32 AA–CC; 33CC–DD)

1974 Bairdoppilata sp. —Maddocks, p. 209 (part; not Pl. 2, figs. 4–7, 18 = Ba. floreana ).

Derivation of Name: Collaevatus, -a, -um, adjectival past participle of the Latin verb collaevo, collaevare: to make entirely smooth, to quell; referring to the almost smooth surface with inconspicuous puncta.

Material Examined: 20 specimens.

Types: Holotype specimen 4169 LV, USNM 1751239 . Paratype specimens 4168R, USNM 1751240 ; 4192Car, 1751241; illustrated specimens1751242–1751245 .

Type Locality: Stetson Bank, UH 2019, on the continental shelf of Texas, Northwest Gulf of Mexico, about 80 miles south by east of Galveston , Texas ; 28 o 10’N, 94 o 18’W, water depth 90 m.

Occurrence: Cuba, the Flower Gardens, Stetson Bank ( Table 1).

Dimensions: Holotype specimen 4169 LV, L 0.985 mm, H 0.640 mm . Paratype specimen 4168 RV, L 0.929 mm, H 0.528 mm . Paratype specimen 4192Car, L 1.054 mm, W 0.523 mm. Also see Graph 1.

Diagnosis: Carapace long, high, medially inflated, with curved flanks in dorsal outline; surface weakly punctate to nearly smooth; opaque patch pattern filigreed with lobose central patch.

Description: Carapace broadly and symmetrically domed; greatest height just anterior to mid-length; substantial dorsal overreach; evenly arched dorsal margin, steep anterodorsal and posterodorsal slopes, level to gently convex ventral margin, and bluntly rounded, weakly caudate posterior end ( Figure 5J View FIGURE 5 ). Caudal process short, thick, bluntly terminated; swollen but not ridged ( Figure 6R–S View FIGURE 6 ). Diamond-shaped with curved lateral margins in dorsal and ventral outline, tapering to narrowly rounded anterior and acutely pointed posterior ends ( Figure 5N–O View FIGURE 5 ). Surface minutely dimpled to almost smooth with delicate leathery texture ( Figures 5H, J–K View FIGURE 5 ; 6X–Z View FIGURE 6 ). Slightly swollen anterior angle and caudal process, which in combination with marginal opaque spots give illusion of rippled marginal band ( Figure 6T–W View FIGURE 6 ).

Opaque patch pattern filigreed, complex, variable, consisting of swirls and lobes outlining circular transparent fields; approximately symmetrical in both valves ( Figures 3E–I View FIGURE 3 ; 5I–J View FIGURE 5 ). Central patch an inverted triangle with irregular edges, anterodorsal lobe, and higher posterodorsal lobe; connected to dark dorsal surface by broad, irregular stripe, which may enclose circular transparent area. Anterior and posterior spots circular, not ventrally extended; separate marginal opaque spots at mid-anteroventral, mid-ventral, and mid-posteroventral locations; smaller opaque streaks and loops in anterolateral and posterolateral fields, of variable shapes but sharply outlined, which may enclose transparent circles; total effect as if large transparent circles were cut out of formerly continuous opaque regions.

Hinge with well-developed ligamental striation ( Figure 6M–O View FIGURE 6 ). Supplemental dentition sharply executed, conspicuous ( Figure 6I–L, P–Q View FIGURE 6 ). ZC broad, vestibules narrow or non-existent; selvages gently curved, subparallel to valve edge, edged with chitin thread; nodular zones of narrow to moderate width ( Figures 3E–F View FIGURE 3 ; 5P View FIGURE 5 ; 6N–O View FIGURE 6 ). LV anterior margin smooth; LV posteroventral margin smooth or with small, irregular marginal nodes or spines; RV anterior margin smooth or with narrow irregular edging; RV posterior margin smooth or with nodular spines ( Figures 3J–O, R–S View FIGURE 3 ; 5J View FIGURE 5 ; 6O, R–S View FIGURE 6 ).

Juvenile A-1 instars with dense, crisply incised puncta and reduced transparency ( Figure 4A–B View FIGURE 4 ). Opaque patch pattern filigreed, as in adults; with two end spots and three peripheral spots along ventral margin. Juvenile A-1 LV anteroventral and posteroventral margins smooth; RV with anteroventral frill and posteroventral nodular spines ( Figure 4A–B View FIGURE 4 ).

Remarks: Ba. collaevata is similar to Ba. diatreta in shape and opaque patch pattern; it differs in its larger size and nearly smooth surface with a leathery texture. The population is variable, and a few specimens approach Ba. diatreta in size and punctate texture. In a few specimens, the honeycomb structure underlying the punctate texture is a barely visible relict pattern, as if the puncta were filled by a mosaic of small crystallites. The patch pattern has the same design as in Ba. diatreta , but it is more lobose with thicker connecting bands.

The narrow, irregular to nodular edging on the anteroventral and posteroventral margins margin of some adult RV and LV ( Figures 3D, J–N View FIGURE 3 ; 6O, R–S View FIGURE 6 ) does not display the sharply incised, transverse fluting of a frill. It might represent a slight overgrowth of the exterior layer of punctate surface ornamentation beyond the valve edge, although not to such extent as to be termed a velum. The juvenile A-1 RV has a more characteristic, striate frill on the anteroventral margin and nodular spines on the posteroventral margin ( Figure 4A View FIGURE 4 ). How the juvenile condition transforms into (or is replaced by) the adult condition after the final molt is a mystery that requires more investigation.

In Graph 1, the LV cluster is offset (up and to the right) relative to the RV cluster (down and to the left), by the usual magnitude. The RV cluster overlaps with the RV cluster for Ba. diatreta , but there is no overlap of the LV clusters. Because of the small number of specimens at each locality ( Table 1), it is difficult to assess sexual dimorphism.

Maddocks (1974) reported Bairdoppilata sp. from the Flower Gardens, but four species were included in the material: Ba. collaevata , Ba. diatreta , Ba. fithianae , and Ba. floreana . The illustrations are of Ba. floreana . The statement that the species is living in Bermuda applies only to Ba. fithianae .