Daffymitra lindae Species
- Daffymitra lindae Harasewych & Kantor, 2005: 150-152; figs. 1-7.
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"Daffymitra lindae new species
Description: Shell (Figures 1-4) of moderate size (to 27.9 mm), thin, fragile, with matte surface, inflated, fusiform, tapering anteriorly, with conical spire. Protoconch (Figures 5-6) large, mammilate, 1970 µm in height, diameter increasing from 676 µm to 2570 µm in 2 5/8 convex whorls. Protoconch-teleoconch transition distinct (Figures 5, 6, arrow), marked by onset of weak closely spaced prosocline ribs. Teleoconch of 3 1/8 strongly convex, ovate whorls with rounded shoulder. Suture impressed. Axial sculpture of thin, sharply demarcated, weakly prosocline raised ribs, 42 on last whorl, 34 on penultimate whorl. Ribs closely spaced on first teleoconch whorl, becoming more widely spaced on later whorls, but again closely spaced along final 1/8th whorl. Spiral sculpture of very low, narrow cords, subequal in width, alternating in prominence, covering entire shell surface, about 50 on final whorl, 10 on penultimate whorl. Aperture large (0.74 shell length), broadly oval, smooth, deflected from shell axis by 15°. Outer lip very thin, weakly reflected, edge forming final axial rib, with shallow anal sinus at suture. Columella weakly sinuate, convex posteriorly, distinctly concave medially, and again anterior to 3 obliquely oriented, recessed folds (Figure 2). Central fold most pronounced, anteriormost fold even more obliquely oriented than central and posterior fold. Parietal callus, broad, very thin. Siphonal canal broad, long, well delimited from aperture. Shell color white. Periostracum thin, olive brown, covering entire shell. Operculum, radula and anatomy unknown.
Type Locality: Bellingshausen Abyssal Plain, 61°27' S, 94°58'-95°22' W, in 4419-4804 m [R/V ELTANIN cruise 23, sta. 1621, 10 Apr. 1966].
Type Material: Holotype, USNM 1080443, shell length 27.9 mm, final whorl length 23.4 mm, aperture length 21.5 mm, shell width, 13.5 mm.
Distribution: Known from the type locality only.
Etymology: This species is named for the senior author's wife, Linda Lee Harasewych.
Remarks: Despite the absence of anatomical and radular data, this new species can be unambiguously assigned to the family Volutomitridae on the basis of its distinctive shell shape, sculpture, presence of the diagnostic paucispiral mammilate protoconch, and weak columellar folds.
Seven genera are currently recognized within the family Volutomitridae (Cernohorsky, 1970; Bouchet and Kantor, 2004). The large size, long, broad aperture, and thin shell of this new species, as well as the presence of three obliquely oriented and deeply recessed columellar folds and a siphonal fold preclude its assignment to either the fossil genus Proximitra Finlay, 1927, or the Recent genera Conomitra Conrad, 1865; Microvoluta Angas, 1877; Peculator Iredale, 1924; or Magdalemitra Kilburn, 1974.
Conchologically, the new species is closer to the genera Volutomitra H. and A. Adams, 1853 and Paradmete Strebel, 1908, which are considered to be closely related (Powell, 1951: 165; Cernohorsky, 1970: 91). The 13 known species of Volutomitra are widely distributed in the World Ocean, ranging from South Africa, Southern Australia, New Zealand and to the Bering Sea in the Pacific, and from Colombia to the northern part of the Atlantic Ocean. Daffymitra lindae differs from all known species of Volutomitra in having a proportionally shorter spire and inflated rather than fusiform shell, coarse spiral sculpture and sharp, narrow, broadly spaced axial ribs, as well as columellar folds that are weak, recessed within the aperture and obliquely oriented rather than being strong, prominent, and nearly perpendicular to the columellar axis. The only species of Volutomitra with pronounced axial sculpture, V. erebus Bayer, 1971, from Colombia, has axial ribs that are thicker, more rounded, orthocline, and more densely spaced.
The genus Paradmete, contains six species, all confined to Antarctic and sub-Antarctic waters. Daffymitra lindae may easily be distinguished from Paradmete fragillima (Watson, 1882), the type species, as well as from P. briedensis Numanami, 1996, and P. arnaudi Numanami, 1996, by its larger size, shorter spire, inflated rather than narrowly fusiform shell, and distinctive narrow, prosocline axial ribs, as well as by its well demarcated siphonal canal. The Magellanic Paradmete crymochara (Rochebrune and Mabille, 1885) approaches Daffymitra lindae in size, but differs in its elongate, fusiform shape, absence of a distinct siphonal canal, and presence of four columellar folds. The distinctive Paradmete percarinata Powell, 1951, can be recognized by its prominent peripheral carina, sharply shouldered shell and pronounced columellar folds that are nearly perpendicular to the columellar axis. Most similar to Daffymitra lindae is Paradmete curta (Strebel, 1908), which reaches a similar size, has a low spire, and has axial ribs, which, however, are opisthochne rather than prosocline. Daffymitra differs in lacking a strong shoulder and in having an inflated shell shape with an attenuated anterior and distinctive siphonal canal.
The shell of Daffymitra lindae bears a surprising resemblance to some members of the Mesozoic genus Volutomorpha, particularly V. mutabilis Wade, 1926 (see Wade, 1926: pl. 37, fig. 10, pls. 40, figs. 6, 9; Sohl, 1964: pl. 39, figs. 1, 2, 6). Volutomorpha was restricted to the Upper Cretaceous faunas of the Gulf and Atlantic coastal plains (for a review, see Sohl, 1964: 252-254), and was "the giant of Cretaceous gastropods" (Wade, 1926: 20) with shell lengths extrapolated to exceed 45 cm. Pilsbry and Olsson (1954: 19) included Volutomorpha in the Cretaceous subfamily Volutodermatinae, which they placed in the family Volutidae together with Volutomitrinae. More recently, Dzhalilov (1977: 93) proposed a new subfamily Volutomorphinae, also within Volutidae, while Bouchet et al. (2005: 255) considered Volutomorphinae a synonym of Volutodermatinae, which they transferred from Volutidae to the extinct family Pholidotomidae.
While Daffymitra is easily distinguished from Volutomorpha by its far smaller size, thinner shell, absence of thick axial ribs, and lack of a pronounced shoulder, this conchological similarity raises the intriguing possibility that Daffymitra is a "living fossil," a surviving descendent from a group presumed to have become extinct at the end of the Cretaceous. Further research is clearly required to reevaluate the relationships between the various Cretaceous genera assigned to Volutoderminae and the earliest Volutomitridae.
The family Volutomitridae has a broad geographic range, but has previously been known only from continental shelf and continental slope faunas, while the genus Paradmete has been reported only from shelf and upper slope depths (Figure 7). The greatest diversities for both the family and the genus occur at upper continental slope depths.
Although Daffymitra lindae is represented by a single empty shell, the fragility of the shell, the presence of periostracum, and the fact that it was collected below the aragonite compensation depth indicate that the specimen could not have been dead for long, and that the species inhabits the area in which this specimen was collected. Thus, this taxon represents the first record of Volutomitridae from abyssal depths. In a survey of Antarctic and Magellanic Buccinoidea, Harasewych and Kantor (2004) found that the abyssal buccinoidean fauna of the region has no genera in common with the sublittoral or bathyal faunas, but that credible sister taxa and likely origins for at least some of the abyssal genera occur on the adjacent continental slope. Based on shell morphologies, the genera Volutomitra, Paradmete, and Daffymitra appear to represent a lineage within Volutomitridae distinct from the predominantly austral genera Proximitra, Conomitra, Microvoluta, Peculator, and Magdalemitra. The genus Paradmete, a member of the upper slope fauna of Antarctica, is likely the sister taxon of the abyssal genus Daffymitra.
This research was supported by a grant from the NSF – USAP United States Antarctic Program [Contract Number OPP-9509761]. We are grateful to Bruce Marshall for bringing to our attention the similarity of Daffymitra and Volutomorpha.”
(Harasewych & Kantor: 2005, 150-152)
Known from the type locality only.
|Type Status||Catalog No.||Date Collected||Location||Coordinates||Depth (m)||Vessel|
|Holotype||1080443||4/10/1966||Antarctic Ocean||61.5° S, 94.7° W||4419 – 4804||Eltanin R/V|
|870720||1/30/1966||Scotia Sea||54.1° S, 52.2° W||419 – 483||Eltanin R/V|