Clathrodrillia Dall 1918
Creators: name: Fallon, Phillip J.
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Neogastropoda
Drilliidae
Clathrodrillia

description: Genus Clathrodrillia Dall, 1918
Type species by original designation: Murex gibbosus Born, 1778 (Recent, type locality unknown).
Diagnosis. The original description of the genus was very brief: "for the generally brown or brownish clathrate species a few of which are found in nearly every fauna, and of which Pleurotoma gibbosa Reeve may be specified as a typical example…" (Dall, 1918: 317). Not long afterwards, in his seminal work on the gastropods of the Bowden Formation of Jamaica (Miocene), Woodring based his diagnosis of Clathrodrillia on an illustration of Clathrodrillia gibbosa (Born, 1778) in Kiener (1840: pl. 16, fig. 2), and so was naturally limited by having only a single example of the genus, which he stated “seems to be a valid genus” (Woodring, 1928: 152). His description included two characteristics, a short, wide aperture and toothed outer lip that are true of C. gibbosa but not of all species included in the genus today. Subsequent workers emphasized one or more characteristics of the genus but did not specify all those that set Clathrodrillia apart from other genera in Drilliidae, e.g.: "The hump-backed variced body whorl is considered diagnostic of this genus." (Powell, 1966: 73). Some species in the genera Fenimorea, Splendrillia, Neodrillia, and Calliclava also possess this type of varix. Or: "Its wider, shorter aperture than in Crassispira and particularly the definite stromboid notch and shallow spiral furrow of some width leading to the notch set it apart" (Fargo, 1953: 368), who seemed to have followed Woodring’s description, but a clear mischaracterization of Clathrodrillia, which has a longer narrower aperture than Crassispira. Neither the form of the varix nor of the aperture alone is sufficient to separate Clathrodrillia from other genera in Drilliidae. Olsson (1964: 95–96) gave a broader diagnosis of Drillinae [sic], based on the model of C. gibbosa, and included such disparate genera as Hindsiclava and Compsodrillia. This accommodation required the diagnosis to include a “ridge-like spiral cord at the suture”, a feature not present in the family as it is known today.
The following diagnosis is a more complete diagnosis of the genus. Shell small to large (13–60 mm), slender with a high, acutely pointed spire composed of flat to convex whorls having a concave anal sulcus below the suture. Aperture narrowly oval, only slightly wider at its widest than the anal sinus and canal at opposite ends. Anterior canal well demarcated and of short to moderate length, and a weak to strong anterior fasciole with or without a weak false umbilicus, or chink. Protoconch of 2–3 smooth whorls. Sculpture of numerous ridged axial ribs (crests narrow, not round) that extend from suture-to-suture but are greatly reduced and recurved in the sulcus giving the shell a shouldered or turreted outline in most species; ribs either straight or slightly opisthocline. Varix hump-like in most, positioned ¼- to ⅓-turn from the outer lip. Strong spiral sculpture of incised grooves that create the appearance of bands, cords or threads that override or cut the axials. Outer lip thin, flattened from varix to lip edge, strengthened by irregular axial folds, with a stromboid notch anteriorly, and anal sinus posteriorly; edge of lip may be scalloped or “toothed” by spirals, or not. Inner lip margined, recumbent or erect, usually relatively wide; with a callus on the parietal wall at the anal sinus. Anal sinus deep, U-shaped, adjacent to the suture, offset from shell axis by parietal lobe and projected laterally so that it appears spout-like.
Key characteristics. The presence of the following characteristics is diagnostic of Clathrodrillia and separates the genus from all others in Drilliidae:
1. Strong spiral sculpture of grooves or cords; grooves may create the appearance of cords when close together, or broader bands when further apart;
2. Axial ribs that extend from suture-to-suture, and to the anterior fasciole on the last whorl; reduced in the sulcus;
3. Aperture narrow, only slightly wider than anal sinus and anterior canal; and
4. Varix hump-like (low and broad, shallow water species), or narrow and high (deep water species), positioned about ¼- to ⅓-turn from the edge of the outer lip, usually with a dark color patch.
Nomenclatural notes. Clathrodrillia is treated as a subgenus of Drillia Gray, 1838 by some workers (Abbott, 1974, Tippett, 1995, Tippett, 2006); others have dropped Dall’s name altogether (Harasewych & Moretzsohn, 2010: 573, as Drillia gibbosa). With recent general acceptance of the elevation of Drilliidae to family level, it is no longer necessary to tie TWA Clathrodrillia to the West African and Indo-Pacific genus Drillia at the subgeneric level, given their morphological differences, but perhaps instead at the subfamily level if supported by molecular or other data in the future. While some TWA Clathrodrillia appear to be similar to W African and Indo-Pacific Drillia, there are important differences that merit their separation on morphological grounds at the level of genus. The type of Drillia (Drillia umbilicata Gray, 1838) has broad swollen ribs, relatively few in number, while the type species of Clathrodrillia has numerous narrow ribs. The anal sulcus is on the shoulder slope of Drillia and only slightly impacts the ribs, but the sulcus forms a broader furrow, usually concave, just below the suture of Clathrodrillia where there is a marked reduction in the ribs. Drillia has an anterior fasciole that is usually strong, with a false umbilicus; the fasciole of Clathrodrillia is generally weak, and the false umbilicus only weakly developed at most. The spiral ornamentation consists of fine threads in Drillia, but in Clathrodrillia the spiral sculpture consists of grooves that produce the appearance of cords, or wider bands. These differences merit separation at the generic level.
Similar genera. Agladrillia Woodring, 1928 and Calliclava McLean, 1971 both have strong spiral elements in addition to numerous ribs and narrow apertures so may be confused with Clathrodrillia. Agladrillia differs in possessing a varix located ½-turn from the edge of the outer lip, and lacks ribs on the dorsal surface of the last whorl. Calliclava differs in possessing a carinate protoconch.
Fenimorea Bartsch, 1934 is similar in possessing hump-like varices (in shallow water species, and high and narrow ones in deep water species), axial cords that run from suture-to-suture that are heavily modified in the sulcus, and, in some, heavy spiral grooves that resemble those of Clathrodrillia. Clathrodrillia differs in usually possessing turreted whorls, stronger spiral sculpture, and all lack the surface microsculpture of Fenimorea.
Neodrillia Bartsch, 1943 is similar but is readily distinguished by the raised coarse spiral threads on the shell surface and shells that are not turreted.
Distribution. Clathrodrillia is widely distributed in the TWA, though most species are found in the southern Caribbean, in both shallow and deep water (> 50 m). Three species are found in the subtropical region of the Gulf of Mexico, Florida, and the Bahama Is., but appear to be restricted to deeper water. Approximate localities of all species are illustrated in Plate 50.
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 88-89, DOI: 10.11646/zootaxa.4090.1.1, http://zenodo.org/record/263299