Notocrater christofferseni Lima, 2014, n. sp.

Notocrater christofferseni n. sp.

(Figs 1–3; Table 1)

Type material. Holotype—MNRJ 26704: Brazil: northeastearn Brazil: off the state of Alagoas, 10°06'35''S, 35°46'41''W, 720 m, 16.xii.2001, ‘Natureza’ collector.

Type locality. Off the state of Alagoas (northeastearn Brazil: 10°06'35''S, 35°46'41''W), 720 m depth.

Geographic distribution. Known only from the type locality.

Diagnosis. Shell highly arched (SH/SL = 0.51). Summit flattened, posterior of center (SP/SL = 0.50). Protoconch well below apex, vertically near posterior extremity. Anterior region occupying about 95% of shell length. Posterior slope very steep, weakly concave. Teleoconch at first sculptured with concentric riblets, following shell length of about 2.2 to 2.4 mm, riblets become irregular, then interrupted into roughly oval to elliptical pustules aligned to form about 50 concentrically arranged (regularly curved) rows from anterior margin to center of shell. Striae very fine between pustules.

Description. Shell small (SL: 2.81 mm; SP: 1.42 mm; SW: 2.01 mm; SH: 1.45 mm); opaque white, rather thin. Outline in dorsal and ventral view broadly elliptical (Figs 2 B, 3C), highly arched (SH/SL = 0.51), anterior region occupying about 95% of shell length (AP: 2.66 mm) (Fig. 2 A–B). Summit flattened, posterior of center (SP/SL = 0.50) (Fig. 2 A–B). Protoconch (PL: 205 µm; PW: 92.67 µm) well below apex, well posterior to center (AP/SL = 0.95) vertically near posterior margin of teleoconch (Figs 1 A, 2A), showing a smooth surface; it is not clear whether tiny pits/holes and minute, sparse crystals on surface are in living shell or are post-mortem bioerosion or adhesions/artifacts (respectively); apical fold and suture not clearly discernible due to presence of concretions (apical fold apparently long, narrow); posterior margin embedded in posterior slope of teleoconch (Fig. 3 A–B). Teleoconch at first sculptured with fine, rather crisp and irregularly spaced concentric riblets (Fig. 2 C–D); following shell length of about 2.2 to 2.4 mm, riblets become irregular (slightly anastomosed) (Fig. 2 E), then interrupted into roughly oval to elliptical, strong, rather regularly spaced pustules (rarely quadrate or hemispherical) (Fig. 2 F), that align to form about 50 concentrically arranged (regularly curved) rows; pustules most prominent at shell periphery (Fig. 2 A–B, F); very fine striae grouped concentrically between pustules; sparse, tiny, irregularly scattered pits/holes on and between pustules (Fig. 2 F); it is not clear whether pits/holes are in living shell or are post-mortem bioerosion. Radial striae or threads not observed on shell. Anterior slope broad, weakly convex (Fig. 2 A–B). Anterior end broadly rounded (Fig. 2 B). Posterior slope very steep, weakly concave (Fig. 2 A). Posterior end rounded, narrower anterior end (Fig. 2 B). Lateral slopes nearly flattened, straight, parallel (Fig. 2 B). Aperture broadly elliptical in ventral view (Figs 1 B, 3C), not planar, shallowly concave in lateral view (Figs 1 A, 2A). Shell edge rather thin, crisp (Figs 1 A, 2A, 3C). Inner surface polished, except for barely distinguishable muscle scars (Fig. 3 C).

Etymology. The species described herein is named in homage to Prof. Dr. Martin Lindsey Christoffersen (Department of Systematics and Ecology, Federal University of Paraíba, Brazil) who has dedicated three decades to the teaching of zoology and the training of masters and doctors of biological science (taxonomists and systematists), with emphasis on the phylogenetic systematics of marine invertebrates.

Comparison. Notocrater christofferseni n. sp., N. houbricki and N. youngi are similar in having a shell with a broadly elliptical outline in the dorsal and ventral views, rounded anterior and posterior ends, a weakly convex anterior slope, nearly flattened lateral slopes with a thin edge and flattened summit which is situated posterior to the center. Furthermore, these species have protoconchs with the posterior margin embedded in the posterior slope of the teleoconch.

There are a number of conchological differences between Notocrater christofferseni n. sp. and N. youngi. The new species has a more elongated protoconch (205 µm), well below the apex and well posterior to the center (AP/ SL = 0.95), with a smooth surface, a highly arched shell (SH/SL = 0.51) with the anterior region occupying about 95% of shell length (AP: 2.66 mm), the surface sculptured with prominent pustules (no radial striae or threads) and a very steep and convex posterior slope. In contrast, McLean & Harasewych (1995: 26, figs. 66–69) and Ardila & Harasewych (2005: 359, fig. 12) characterized N. youngi as having a protoconch measuring 190 µm in length, barely below the apex and posterior to the center (AP/SL = 0.64) sculptured with clumped crystals, some forming anastomosing threads, a moderately arched shell (SH/SL = 0.32 to 0.42), an anterior region occupying about 60% of shell length, a surface sculptured with slight pustules and a very fine radial threads and moderately inclined, straight posterior slope.

Notocrater christofferseni n. sp. most closely resembles N. houbricki in the curvature of the shell, distribution pattern and strength of the pustules arranged concentrically on the teleoconch. However, the new species differs from N. houbricki in having a protoconch with a larger PL vertically near the posterior margin of the teleoconch (AP/SL = 0.95), in having the highest point of the shell at about 1.42 mm from the anterior margin (SP/SL = 0.51), an anterior region occupying about 95% of shell length with double pustule rows (about 50) arranged concentrically from the anterior margin to the center of the shell. The surface is also ornamented with very fine concentric striae between pustules (no radial striae or threads). The apex is situated posterior to the center at about 95% of shell length (AP/SL = 0.95), it has concentric riblets distributed at a shell length between 2.2 to 2.4 mm, then becoming slightly anastomosed and interrupted into pustules. The aperture is shallowly concave in lateral view. Notocrater houbricki has a protoconch measuring 170 to 172 µm in length, densely sculptured only with fine crystals. The highest point of the shell is situated at about 1.03 mm from the anterior margin (SP/SL about 0.57). The anterior region occupies about 75 to 83% of shell length and is sculptured with fewer of rows of pustule (about 25) arranged concentrically from the anterior margin to the center of the shell. The surface of the shell is also ornamented with a number of radial threads. Furthermore, this species has an apex posterior to the center at about 75 to 83% of shell length (AP/SL about 0.83), concentric ribs/bands distributed at shell length 1.10 to 1.35 mm, then becoming slightly anastomosed and interrupted into pustules and a planar aperture (McLean & Harasewych 1995: 24–25, figs. 58–60; Ardila & Harasewych 2005: 358, fig. 11).

Table 1 displays the comparative data for Notocrater christofferseni n. sp., N. houbricki and N. youngi based on the present paper and information taken from the texts and figures found in McLean & Harasewych (1995) and Ardila & Harasewych (2005).

The superfamily Lepetelloidea is represented by eight families (Bouchet & Rocroi 2005; Bouchet & Gofas 2014), four of which (Addisoniidae Dall, 1882, Bathyphytophilidae Moskalev, 1978, Lepetellidae Dall, 1882 and Pseudococculinidae Hickman, 1983) are reported from the Western Atlantic (Rosenberg 2009), where about 20% of the known species richness of Lepetelloidea occurs (Rosenberg 2009; Bouchet & Gofas 2014). Pseudococculinidae is the most diverse family (Leal & Harasewych 1999; Rosenberg 2009; Bouchet & Gofas 2014) and Notocrater is one of the most diverse genera in Lepetelloidea (Marshall 1986; McLean & Harasewych 1995; Ardila & Harasewych 2005).

The present study extends knowledge of the latitudinal and bathymetric distribution of Notocrater from the Bahamas (26°N; 518 m) (McLean & Harasewych 1995) to the Southeastern Atlantic (northeastern Brazil: 10°S; 720 m). However, the actual biodiversity as well as geographic and bathymetric ranges of Notocrater and other genera of Lepetelloidea along the Western Atlantic is little known (McLean & Harasewych 1995; Leal & Harasewych 1999) due to insufficient sampling. As part of a review of the family Pseudococculinidae from New Zealand and New South Wales, Marshall (1986) ascertained that few species have a widespread geographic distribution, but the author also recognized insufficient sampling in that region.

Notocrater christofferseni n. sp. and N. houbricki closely resemble the Indo-Pacific N. gracilis and N. ponderi (except for the sculpture on the protoconch) and no other described congeners exhibit a similar shell morphology (Marshall 1986; McLean & Harasewych 1995; Ardila & Harasewych 2005). However, it is remarkable that the Notocrater fauna from the Atlantic and Indo-Pacific differs in terms of anatomy (Marshall 1986; McLean & Harasewych 1995).

The holotype of Notocrater houbricki (from the Bahamas: 412 m) has a larger size (SL: 2.6 mm; SW: 1.5 mm; SH: 0.8 mm), a narrowly elliptical (elongate-oval) outline in dorsal view, an anterior end which is slightly narrower than the posterior end, a narrowly convex anterior slope, a moderately inclined, rather straight posterior slope, narrowly flattened lateral slopes, more narrowly spaced and less projected pustules on the teleoconch, a more anteriorly located apex at 3/4 (1.95 mm) shell length from the anterior margin (AP/SL = 0.75) and a summit position at about 1.40 mm (SP/SL about 0.54) (McLean & Harasewych 1995: 20, fig. 58). In contrast, the specimen identified by Ardila & Harasewych (2005: 359, fig. 11A) from the Caribbean coast of Colombia (270 m) has a smaller size (SL: 1.8 mm; SW: 1.3 mm; SH: 0.8 mm), a widely elliptical outline. The posterior termination is slightly narrower than the anterior end. It has a widely convex anterior slope, a very steep, weakly concave posterior slope, widely flattened lateral slopes, more widely spaced and projected pustules on the teleoconch, a more posteriorly located apex at about 83% (about 1.50 mm) of shell length from the anterior margin (AP/SL = 0.83) and a summit position at about 1.03 mm (SP/SL about 0.57). Although both specimens have approximately the same number of pustule rows arranged concentrically from the anterior margin to the center of the shell (McLean & Harasewych 1995; Ardila & Harasewych 2005), the conchological variations presented herein should be further investigated based on anatomy and molecular analysis to ascertain if the specimens are actually conspecific.

Some pseudococculinid genera are widely distributed in the oceans (Marshall 1986; McLean & Harasewych 1995; Leal & Harasewych 1999), while pseudococculinid species can be considered a priori restricted geographically and bathymetrically to certain ecoregions (McLean 1988, 1991; Leal & Harasewych 1999; Leal & Simone 2000) until more collections (mainly from the deep waters) and studies are conducted. The mode of lecithotrophic development inferred from the protoconch morphology (Marshall 1986; Lesicki 1998) and the association with biogenic substrates commonly reported in the literature (Marshall 1986; McLean 1988, 1991; Haszprunar 1988; McLean & Harasewych 1995; Lesicki 1998; Leal & Harasewych 1999; Leal & Simone 2000; Ardila & Harasewych 2005) suggest a slow or limited dispersal capacity among pseudococculinids, especially on deep sea plains.