Bairdoppilata fimbriata, Maddocks, 2025

Bairdoppilata fimbriata sp. nov.

(Graphs 2, 6; Figures 2E–F View FIGURE 2 ; 7A–O View FIGURE 7 ; 8A–Y View FIGURE 8 ; 9A–S View FIGURE 9 ; 10A View FIGURE 10 –AA; 32R–V; 33S–X)

? 1966 Bairdia bradyi Bold.–Bold , p. 45, Pl. 1, figs. 5a–c. Derivation of name: Latin adjective fimbriatus, -a, -um, meaning fringed; in reference to the prominent posteroventral comb of spines on the LV.

Material Examined: 59 specimens.

Types: Holotype specimen 4174Car, USNM 1751254 ; Paratype specimens 4147 LV, USNM 1751255 ; 4148 RV, USNM 1751261 ; 4149 RV, USNM 1751262 ; 4238Car, USNM 1751263 ; illustrated specimens USNM 1751256– 1751260 , 1751264–1751265 .

Type Locality: UH 2962, Roatan , Bay Islands , Honduras. Big and Little French Keys area. 16 o 21’N, 86 o 27’W, water depth 5 feet GoogleMaps .

Occurrence: Belize, Roatan ( Table 1).

Dimensions: Holotype 4174Car, L 0.848 mm, H 0.487 mm. Paratype specimen 4147 LV, LV L 0.846 mm, LV H 0.482 mm . Paratype specimen 4148 RV, RV L 0.886 mm, RV H 0.462 mm . Paratype specimen 4238Car, L 0.834 mm, W 0.473 mm. See also Graph 2.

Diagnosis: Carapace short, relatively low; normal overreach (LV>RV); LV with prolonged posteroventral marginal region, carrying a comb of up to 9 long, thick, blunt spines; mid-lateral surface inflated, marginal region somewhat abruptly compressed.

Description: LV broadly and almost symmetrically arched, greatest height anterior to mid-length, moderate dorsal overreach, no posterodorsal break in slope, anteroventral margin weakly curved to nearly straight; mid-ventral margin level, between projecting anteroventral lip and posteroventral fringe of LV; posteroventral margin broadly extended with fringe of thick spines; ( Figures 7B–C, E–F, H–I View FIGURE 7 ; 9B, D, F–G View FIGURE 9 ). LV somewhat abruptly swollen centrally in AMS region; RV less inflated, more nearly flat; compressed marginal brim with rounded edges ( Figures 7A–I View FIGURE 7 ; 9A–G View FIGURE 9 ). Caudal process extended, bluntly terminated, slightly swollen but not ridged; thin edge penetrated by 6 or more hair-thin, diverging RPC ( Figures 7A–K View FIGURE 7 ; 8A, C, E, H, J–K, N, R, S, V View FIGURE 8 ; 9H, K–L View FIGURE 9 ). Posteroventral marginal region of LV flat, projecting conspicuously; edged by comb of up to 9 thick, straight, blunt spines, separated by U-shaped spaces of equal width; spines arise distal to nodular zone, are hollow at base but not tip, not penetrated by RPC, and have no associated sensilla; spines extend along posteroventral margin just to (but not along) caudal process ( Figures 7B–C, E–F, H–I View FIGURE 7 ; 8H, J, N, P, V View FIGURE 8 ; 9B, D, K–L View FIGURE 9 ). Slender in dorsal view, only slightly swollen centrally; anterior end tapering evenly, posterior end more abruptly constricted; with moderate overreach by LV ( Figure 9R–S View FIGURE 9 ).

Opaque patch pattern similar in both valves; consisting of darker central spot, surrounded by broad, lighter circular area, which narrows anterodorsally, then widens to join cloudy dorsal region; no anterior or posterior spot ( Figure 7A–K View FIGURE 7 ).

Hinge with ligamental striation; valve wall with granular texture, well-developed supplemental dentition ( Figure 10A–E, M–U, X View FIGURE 10 –AA). ZC broad, vestibules of variable depth; selvages nearly straight, nodular zones of moderate width ( Figures 7A–K View FIGURE 7 ; 8A–V View FIGURE 8 ; 10F–L View FIGURE 10 ). LV anteroventral margin smooth or with remnants of velum ( Figure 8G, I, M, O, Q, U View FIGURE 8 ); LV posteroventral margin with long blunt spines, or eroded bases of spines ( Figures 8H, J, N, P, R, V View FIGURE 8 ; 9G, K–L View FIGURE 9 ; 10A, D–E, I–O View FIGURE 10 ). RV anteroventral margin smooth or with remnants of velum ( Figures 8B, D, F, L, T View FIGURE 8 ; 9I View FIGURE 9 ; 10G–H View FIGURE 10 ); RV posteroventral margin has narrow, nodular velum resembling piecrust edging, or eroded remnants ( Figures 8A, C, E, K, S View FIGURE 8 ; 9H View FIGURE 9 ; 10T–U View FIGURE 10 ).

A–1 instar more angular in outline than adult, with more extended, narrowly pointed caudal process; opaque patch pattern consists of central cloudy region with sinuous contours, resembling adult, which occupies much of central area and merges with dorsal streak; no anterior or posterior spots ( Figure 7M–Q View FIGURE 7 ). Juvenile A–1 LV has anteroventral margin with frill; posteroventral margin with broken bases of spines ( Figure 7M, O–Q View FIGURE 7 ). Juvenile A–1 RV with smooth anteroventral and posteroventral margins ( Figure 7N, R View FIGURE 7 ).

Remarks: Bold (1966, Pl. 1, figs. 5a–c) illustrated a species from a sediment core in Colon Harbour, Panama, which he identified as Bairdia bradyi , without any taxonomic discussion, description, or measurements. The LV illustrated in his Figure 5a View FIGURE 5 (reproduced here as Figure 1W View FIGURE 1 ) has a spinose posteroventral fringe, resembling that of Ba. fimbriata , although the spines are eroded or perhaps merged at their bases. That valve is rather high in proportion to length (perhaps female), and it has a nodular or spinose anterior edging that has not been seen in Ba. fimbriata . The LV and RV illustrated in his Figures 5b–c View FIGURE 5 (reproduced here as Figures 1V, X View FIGURE 1 ) are more elongate (perhaps male), with a conspicuously extended, tapering caudal process, a broad anteroventral edging on the RV, and only eroded stubs of posteroventral spines on the LV.

Ba. fimbriata shows some resemblance to Ba. sima in general outline, carapace inflation, and densely punctate surface. Ideally, Ba. fimbriata is easily distinguished by the spinose posteroventral extension of the LV, whereas Ba. sima is characterized by the subtly flaring sima and the exaggerated anteroventral and posteroventral vela of the RV. Isolated RV of Ba. fimbriata and LV of Ba. sima are less remarkable and not as easy to assign, however. The RV of Ba. fimbriata lacks the exaggerated anterior and posteroventral overreach of Ba. sima , which is visible in dorsal, ventral, and right-lateral views. Although the LV of Ba. sima may have a narrow posteroventral velum, it lacks any indication of the blunt spines of Ba. fimbriata .

In Ba. fimbriata the LV is abruptly inflated centrally, and many specimens have a rather compressed marginal brim; whereas the RV appears to be less convex. In both valves of Ba. sima the lateral curvature merges more gradually into the compressed marginal zone, and the posteroventral margin is weakly reflexed (up-curved) to form a shallow channel, or sima.

LV of Ba. fimbriata tend to be higher in proportion to length than is the case for Ba. sima , whereas no clear distinction is apparent in the H:L proportions of RV for the two species (Graphs 2, 6). The LV cluster for Ba. fimbriata is remarkably compact, and it is not offset (to the right, relative to the RV cluster), as much as is usual for bairdiids. The RV cluster is longer (because of variability in width of the anterior velum), and it extends beyond the LV cluster at either end. Within each cluster, it is likely that the longer, higher specimens are females, and shorter, lower specimens are males, as usual in bairdiids, but there is no distinct separation. Specimens from Belize and Roatan show no difference in size (completely overlapping clusters). This is to be expected, because of their geographic proximity.