Proverruca ornata, Gale & Jagt, 2025

Proverruca ornata sp. nov.

urn:lsid:zoobank.org:act:43007378-D8CA-4C85-9E4A-EA62B83AEC3F

Fig. 2A, B, F–V View FIGURE 2

Diagnosis. Large Proverruca which bears a striate to complex cancellate sculpture on the fixed scutum, and in which the adductor muscle scar on the interior of this valve is very large and deeply impressed.

Type material. The large fixed scutum ( Fig. 2A, B View FIGURE 2 ; NHMM JJ 6503 View Materials ) is the holotype, the other figured valves ( Fig. 2F–V View FIGURE 2 ) are paratypes ( NHMM JJ 5886 View Materials , JJ 9619 View Materials a–f and JJ 13426) .

Derivatio nominis. In reference to the complex sculpture of the valves.

Type locality and horizon. Zeven Wegen Member (Gulpen Formation) from the former CPL quarry at Haccourt, Liège, Belgium .

Additional material. A total of 16 valves, including 7 fixed scuta, 4 carinae, 1 moveable scutum, 1 moveable tergum, all from the same locality and stratigraphical intervals as the types.

Description. The fixed scuta ( Fig. 2A–C, E, F, I–K, O–S View FIGURE 2 ) are triangular to subrectangular in outline and display considerable variation in sculpture and shape with ontogeny. The Smallest specimens, approximately 2.5 mm in length ( Fig. 2C, E, F View FIGURE 2 ), are nearly equilaterally triangular and is inclined dorsally. The external sculpture comprises interrupted apicobasal ridges, and the internal scutal adductor scar is large.

The moveable scutum ( Fig. 2L, M View FIGURE 2 ) is triangular in outline, slightly inclined dorsally, and the height (tip broken off) is greater than the breadth. The external surface carries 6 coarse apicobasal ribs, interrupted by regular growth increments. On the interior, an oval scutal adductor is present adjacent to the occludent margin. The moveable tergum ( Fig. 2N View FIGURE 2 ) is asymmetrically kite-shaped and bears a low, sinuous apicobasal ridge which separates the carinal and scutal surfaces. The carinal and occludent margins are long and straight, and angled at 120 o and the scutal margin is weakly convex. The tergal margin (contacting the fixed tergum) is short and convex. The apical part of the occludent/carinal surface carries weak apicobasal ridges, and the scutal surface bears tubercles aligned with the scutal margin. The carina ( Fig. 2D, G, H, T, U View FIGURE 2 ) is robust, hemiconical and inclined ventrally, and the external surfaces carries weak, interrupted apicobasal ridges. The margin contacting the fixed tergum is broad and serrate, bearing transverse ridges and intervening grooves ( Fig. 2D, H, U View FIGURE 2 ). The rostrum and fixed tergum are unknown.

As the fixed scuta grew during ontogeny, the adductor scar enlarged to occupy most of the internal surface ( Fig. 2J, Q, S View FIGURE 2 ) and the ventral margin of the valve elongated. The occludent surface became inturned ( Fig. 2K, S View FIGURE 2 ) and the basal part of this region articulates with the rostrum (see Fig. 1A, B View FIGURE 1 ). In very large specimens of a length of 10 mm ( Fig. 2A, B View FIGURE 2 ) the occludent surface is sharply inflexed, and the rostral margin is angled to the basal margin. The external sculpture changes with growth, and the apicobasal ridges became more numerous and finer ( Fig. 2J, K, Q, S View FIGURE 2 ). These are weaker and interrupted by growth increments in some specimens ( Fig. 2O View FIGURE 2 ). In the largest specimen ( Fig. 2A, B View FIGURE 2 ), the apicobasal ridges on the lateral (tergal) surface are replaced by transverse rows of closely spaced, irregularly shaped nodes, and a cancellate sculpture comprising weak apicobasal ridges and transverse ridges is present on the occludent surface ( Fig. 2A View FIGURE 2 ).

Remarks. Proverruca ornata sp. nov. differs from P. anglica Gale, 2020 ( Fig. 3K–M View FIGURE 3 ) in its larger scutal adductor scar on the fixed tergum and its finer apicobasal ribbing. It is differentiated from P. cancellata ( Withers, 1935; Fig. 3A–E, I, J, O–R View FIGURE 3 ) in its possession of apicobasal ribbing, and in the presence of tubercles on the scutal surface of the moveable tergum. In P. dentifer Gale, 2015 ( Fig. 3X, Y View FIGURE 3 ), the moveable scutum carries regular, apicobasal rows of thorns on the scutal surface; these are absent in P. ornata sp. nov. in which the few tubercles are arranged in margin-parallel rows. Additionally, the scutal adductor scar on P. dentifer is smaller and positioned close to the basal margin ( Fig. 3S View FIGURE 3 ). Proverruca ornata sp. nov. is distinguished from P. vinculum Withers, 1914 ( Fig. 3G, H View FIGURE 3 ), P. nodosa Withers, 1935 ( Fig. 3Z, A View FIGURE 3 1 View FIGURE 1 ) and P. laurae Withers, 1923 ( Fig. 3A View FIGURE 3 2 View FIGURE 2 ) in both the shape and sculpture of the valves.

Proverruca ornata sp. nov. is the only species of Proverruca of which a growth series is known and the ontogenetic variation in sculpture and valve shape displayed by the suite of fixed terga of P. ornata sp. nov. is remarkable. Although the diagnoses of other described species of Proverruca appear to hold true, care should be taken in describing new taxa of the genus on the basis of limited material.