Agladrillia rhodochroa (Dautzenberg, 1900)

Fallon, Phillip J., 2016, Taxonomic review of tropical western Atlantic shallow water Drilliidae (Mollusca: Gastropoda: Conoidea) including descriptions of 100 new species, Zootaxa 4090 (1), pp. 1-363: 19-21

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Agladrillia rhodochroa (Dautzenberg, 1900)


Agladrillia rhodochroa (Dautzenberg, 1900) 

( Plate 2View PLATE 2)

Drillia rhodochroa Dautzenberg, 1900: 165  , pl. 9, fig. 3.

Agladrillia rhodochroa (Dautzenberg, 1900)  : Díaz (1994: 40); Díaz & Puyana (1994: 224, fig. 885); Williams (2009: 1503 [left photo only]); Massemin et al. (2009: 203, text photo).

Agladrillia scissurata  auct. non (Dall, 1890) are misidentifications by Williams (2009: 1502 [right photo only]) and Daccarett & Bossio (2011: 129, fig. 778) that may be this species. Syntomodrillia scissurata (Dall, 1890)  is a fossil of the St. Petersburg, Caloosahatchie Formation [Florida Pliocene-Pleistocene].

Agladrillia lassula  auct non Jung, 1969: Daccarett & Bossio (2011: 128–129) erroneously place A. rhodochroa  in synonymy with A. lassula  .

Not this species or unconfirmed fossil and extralimital reports.

Agladrillia  (?) lassula Jung, 1969  [fossil]: is placed in synonymy with A. rhodochroa  by Diaz & Puyana (1994: 224). Agladrillia rhodochroa  (auct. non Dautzenberg, 1900): Williams (2009: 1503, right photo only [= Syntomodrillia  sp.]).

Type material. The illustrated type (note on label accompanying specimen), 11 x 4 mm, is in RBINS/MT/ 524919. It was not examined; instead, high quality photographs were provided by the museum that are reproduced in Pl. 2, Fig. 1View Fig. 1. Inasmuch as this specimen is the illustrated type, it is here declared the lectotype. The existence of paralectotypes is surmised from Dautzenberg’s list of stations at which the species was reportedly taken. Dautzenberg’s original illustration is reproduced in Pl. 2, Fig. 4 and differs principally in the number of ribs, probably a liberty taken by the artist.

Type locality. Rio Hacha [Guajira Dept.] Chazalie Station 52, Colombia, at 6 m depth (locality of the lectotype). Other specimens from the type series were collected at Chazalie Stations 41, 42, 44, Santa Marta [Magdalena Dept.], Colombia, at 15, 40, and 23 m depths, respectively.

Material examined. An total of 8 specimens were examined: 2 spec., 10.2 x 4.1 & 10.3 x 4.0 mm, from in soft sand at 18 m, Tayrona Park, Santa Marta, Magdalena Dept., Colombia (author’s coll.); 2 spec., 13.6 x 4.5 & 12.7 x 4.8 mm, in 2–6 mm, Punta de Betin, Santa Marta, Magdalena Dept., Colombia (P. Stahlschmidt coll.); 3 spec., 12.6 x 4.6, 10.9 x 3.9 & 10.3 x 3.9 mm, in 20–30 m, Bahia Concha, Magdalena Dept., Colombia (P. Stahlschmidt coll.); 1 spec., 11.8 x 4.6 mm, in 37 m, Cartagena, Bolivar Dept., Colombia (USNM 900073).

Range and habitat. Colombia (Bolivar, Magdalena & Guajira Depts.), at depths between 2 and 60 m. If the specimen illustrated by Massemin et al. is this species, then its southern range would extend to French Guiana.

Description. Shell small (to 13.6 mm in total length), glossy, fusiform, up to about 10 ¼ slightly convex whorls, the last approximately 53 % of total length, flattened dorso-ventrally and rapidly tapering, “pinched” when viewed ventrally, to a narrow anterior canal. Spire whorls appear compressed—proportionally shorter than wide. Shell sculpture of ribs with deep intercostal spiral grooves. Protoconch of approximately 1 ½– 1 ¾ smooth translucent whorls, the first not immersed in the second. Axial sculpture of narrow opisthocline ribs that run from suture-to-suture on spire whorls, evanesce at anterior fasciole of last whorl and are absent on dorsum of last; intercostal spaces greater than rib width. Ribs recurved in sulcus, sigmoid on ventrum of last whorl, number 12–14 on penultimate, 7–9 on last whorl to varix. Spiral sculpture of evenly spaced deep grooves in intercostal spaces (rib crests are smooth) more closely spaced in sulcus. Grooves present across the dorsum of the last whorl. Grooves give the appearance of closely packed spiral cords, number about 8 on penultimate and 12 on shell base, and 7 on anterior fasciole. Sulcus with recurved ribs that are lower than the ribs on the whorl face, ribs overridden by spiral grooves giving sulcus the appearance of having 3–4 spiral cords. Varix hump-like, positioned ½-turn from edge of outer lip; its position causing the body whorl to appear compressed dorso-laterally. Outer lip thin, but strengthened by up to 4 axial folds clustered on about the last ¼-turn, the one closest to the edge the strongest; edge forms a low almost flat arch from anal sinus to stromboid notch where it is bent slightly inward. Stromboid notch deep. The dorsum of the last whorl thin, translucent, and except for their presence in the sulcus, ribs obsolete. Anal sinus deep, U-shaped, entrance constricted by parietal lobe and projection of outer lip, somewhat tubular and projecting laterally. Inner lip edge free, erect anteriorly, recumbent on parietal wall, and formed into a parietal lobe posteriorly, arching over the rear of the aperture. Anterior canal moderately long, open and narrow, turned slightly to the right and dorsally; deeply notched. Color pink, rib crests lighter, varix white, apex violet, and dorsum of last whorl brown.

Remarks. Taxonomy. Agladrillia rhodochroa  has the distinguishing characteristics of the genus: a varix ½- turn from the edge of the outer lip, a strongly constricted anterior canal, and a smooth dorsum on last whorl. Dautzenberg described his specimens, which were from Colombia, as having a pink base, ribs a purplish rose, and the back of the last whorl a wide brown spot. The specimens depicted in Plate 2View PLATE 2, all from Colombia, closely match his description and drawing. Variability. The average length of 9 measured specimens is 11.37 mm (9.9–13.6 mm) and average W/ L ratio  is 0.376. Some difference in color and form is seen between the Cartagena and Magdalena Departments’ specimens that is believed at this time to be geographic variation, not rising to the level of species. Identification. Agladrillia rhodochroa  is most similar to A. aureola  , new species. It differs in color, which is pink with a brown varical spot and not golden yellow with an orange brown varical spot, and in relative whorl height, which is higher in A. aureola  . Also, whorls are less convex and axial ribs more oblique than in A. aureola  . Agladrillia rhodochroa  differs from Calliclava tobagoensis  , new species, in possessing a smooth protoconch, a greater constriction of the anterior canal and a varix located ½-turn from the edge of the outer lip. The latter species has a carinate protoconch, a less-constricted anterior canal, and a varix located about ⅓-turn from the edge of the outer lip. Both species of Agladrillia  and of Calliclava  are show in the lineup in Plate 20View PLATE 20.