Splendrillia Hedley 1922
Creators: name: Fallon, Phillip J.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neogastropoda
Drilliidae
Splendrillia

description: Genus Splendrillia Hedley, 1922
Type species: Drillia woodsi Beddome, 1883 by original designation (Recent, New South Wales, Australia).
Wells (1995: 529) adopted a broad view of the genus on account of the general lack of anatomical data for most species assigned to the genus (for the description of 13 species from New Caledonia), with the expectation that many will be reassigned since most are included solely on the basis of shell morphology. The TWA species are similarly classified on shell characters alone but are as a group more similar to each other than to species in other TWA genus groups. While TWA species differ from Hedley’s designated type of the genus in morphological features that may or may not be conserved at the level of genus, reassignment might best await analysis of anatomical or molecular data.
Hedley (1922: 250) did not provide a detailed description of Splendrillia, so a diagnosis has been drawn from the type species, Splendrillia woodsi (Beddome, 1883), but modified to include differences in western Atlantic species. Differences include the lack of a sub-tubular anal sinus, shorter anterior canal, the presence of fine spiral microsculpture, and occasionally heavy, not microscopic growth striae.
Diagnosis. Shell small (generally less than 20 mm in total length), glossy, fusiform, truncated anteriorly; whorls convex. Protoconch of about 1¾–2 smooth round whorls. Axial sculpture of oblique ribs and microscopic to strong growth striae, which may be closely packed rendering the shell opaque, not glossy. Rib length usually short and can be almost nodulose. Varix large and broad, usually hump-like, located approximately ⅓-turn from the edge of the outer lip. Spiral sculpture absent except on shell base with stronger ridges on the anterior fasciole; microsculpture of very fine spiral lines on spire whorls, which may be almost entirely obscured by growth striae. Sulcus narrow to broad and flat or slightly excavated, usually without ribs but if present greatly reduced. Anal sinus deep, adjoins suture behind parietal lobe; may be partially occluded by a parietal callus. Outer lip somewhat flattened from the varix to its edge, with a shallow stromboid notch anteriorly. Inner lip thin, not margined except anteriorly. Anterior canal very short, open, notched.
Key characteristics. The presence of all of the following characteristics is diagnostic of and separates the genus from other TWA Drilliidae:
1. Shell surface glossy-smooth, usually without spiral sculpture except for threads or ridges on anterior portion of shell base and on anterior fasciole; growth striae faint, or strong in some species, strongest on last whorl. Microsculpture of very fine spiral lines or none at all;
2. Sulcus appearing girdle-like (flat to concave) at the suture, without axial ribs or mostly so;
3. Anal sinus adjoins the suture behind the parietal lobe; and
4. Varix hump-like, about ⅓-turn from edge of outer lip, frequently with a dark-colored patch.
Similar genera. Fenimorea has been synonymized with Splendrillia (Petuch, 1987: 18, 19), but the two differ in a number of important morphological characteristics, which are covered in the introduction to the genus Fenimorea. Members of the two genera have different patterns of shell surface microsculpture. Under the dissecting microscope, Splendrillia has fine spiral lines that, under the SEM at 1,000x, resolve into rows of adjoining punctae creating the appearance of solid dark lines. Between these “lines”, for most Splendrillia examined so far, are widely spaced punctae that may be aligned in rows or somewhat more randomly placed (see Plates 140–141). While this pattern is consistent in Splendrillia examined so far, with the noted variation—possibly the density and arrangement of punctae between “lines” being species-specific, it is not known if the general pattern of widely spaced rows of adjoining punctae holds for all members of the genus. Under the dissecting microscope, Fenimorea has fine spiral grooves or ridges spaced greater than their width and intersected by more closely spaced axial growth striae forming “pits” or axially aligned depressions. SEM microscopy reveals punctae are more-or less aligned in rows overall but are overridden by the spiral ridges and growth striae that form “pits” (see Plate 65).
The following genera also have some resemblance to Splendrillia: Decoradrillia, new genus, Syntomodrillia, Leptadrillia, and Cerodrillia.
Decoradrillia lacks the flat subsutural band characteristic of Splendrillia and has a different shell surface microsculpture. As seen under the dissecting microscope, it has closely packed fine spiral threads between heavier ones. The threads are more distinct than those found on any of the Splendrillia genus. Differences in pattern exhibited by the two genera are much more dramatic when viewed with a SEM. Examples of SEM images of the pattern in some species of Splendrillia is shown in Plates 140–141 and for some species of Decoradrillia in Plate 51.
Syntomodrillia is small and glossy like Splendrillia but differs in possessing ribs that extend suture-to-suture, a longer anterior canal, a narrow varix that is not hump-like and fine spiral threads or spiral grooves between ribs.
Leptadrillia is similar in appearance to Splendrillia but differs in having a more spindle-shaped shell with a long anterior canal, ribs suture-to-suture, a narrow varix that is not hump-like, and a shell surface without microscopic spiral lines. Spiral threads or ridges are confined to the lower shell base and anterior fasciole.
Cerodrillia differs in having a stouter shell, and a cup-handle-like varix within about ¼-turn from the edge of the outer lip. Although ribs usually extend from suture-to-suture, they may be absent in the sulcus of later whorls of some species.
The bathyal species Drillia? centimata Dall, 1889, recently reassigned to Splendrillia by Figueira & Absalão (2010), appears to meet criteria of the genus. This species has been reported from the Gulf of Mexico, off North Carolina, and off southern Brazil at depths of 1,122 to 3,590 m, demonstrating a wide geographic and bathymetric range. Because it is a bathyal not shallow water species it is not addressed in this work.
Splendrillia coccinata complex. A group of morphologically similar species may represent a complex that includes Splendrillia coccinata (Reeve, 1845), the first in the group to be described. Each species is restricted to the shallow water of an island or group of adjacent islands primarily in the Antilles (Greater and Lesser) but including Bermuda. Confirmation of their relationship awaits future genetic analysis. Possible members of the complex are shown in Plate 162 at the end of the Splendrillia section.
Distribution. Splendrillia is distributed throughout the TWA region, from Bermuda to southern Brazil from the Lesser Antilles to the western Caribbean. Species of the genus appear to be allopatric; few localities have more than a single representative. So far though, it has not been reported the waters around Florida; most of the species appearing to favor the warmer tropical seas. The drilliids of Florida are most commonly members of the genus Cerodrillia.
description: Published as part of Fallon, Phillip J., 2016, Taxonomic review of tropical western Atlantic shallow water Drilliidae (Mollusca: Gastropoda: Conoidea) including descriptions of 100 new species, pp. 1-363 in Zootaxa 4090 (1) on pages 277-280, DOI: 10.11646/zootaxa.4090.1.1, http://zenodo.org/record/263299