Conus symmetricus (Sowerby I, 1850)

Description

Shell turbinate, short and broad, spire short, spirally striate; body whorl sharply carinate at the shoulder, ornamented with granulose spiral threads alternating with one or two finer smooth spirals; the canal is slightly produced and a trifle reflexed.

Length of shell 29, greatest width 18 mm.

Locality. — (Exp'd '16) Zone E, Rio Gurabo at Los Quemados.

Conus symmetricus—which is a common species, especially in the Gurabo Fm.—has a very distinctive shell shape that is not easily confused with co-occurring species. Its relationship to extant species is not clear. Petuch stated that C. tristensis Petuch, 1987 “probably represents the last living member of the C. symmetricus-dominguensis species complex” ⁽⁴⁾.

Kohn considered C. tristensis a synonym, albeit somewhat tentatively, of C. cancellatus Hwass in Bruguière, 1792, which was assigned to the subgenus Dauciconus by Puillandre et al. While many specimens of C. symmetricus have an overall shell shape that is somewhat similar to that of the holotype of C. tristensis, specimens of C. symmetricus always have beaded ribs on the last whorl, which were not reported by Kohn in his recent description of C. cancellatus. Additionally, shells of C. symmetricus are widest below the shoulder, but specimens of C. cancellatus are usually widest at the shoulder ⁽⁴⁾.

Finally, coloration patterns similar to those described above for C. symmetricus are not present in any known specimens of C. cancellatus, which are often—though not always — unpigmented ⁽⁴⁾.

Conus symmetricus ⁽⁶⁾

Plate 7 - fig. 7

Conus symmetricus

NHM G83969

Conus symmetricus ⁽⁴⁾

Specimens are from locality stations:

TU 1422 (Cercado Fm.)

TU 1215 (Gurabo Fm.)

TU 1354 (GuraboFm.)

(A-B) PRI 67665, TU 1215, SL 27.3 mm;

(C) PRI 67190, TU 1422, SL 17.1 mm;

(D) PRI 67192, TU 1422, SL 19.5 mm;

(E) PRI 67191, TU 1422, SL 27.4 mm;

(F) PRI 67675, TU 1354, SL 26.2 mm;

(G) PRI 66155, TU 1422, SL 46.1 mm.

All are reversed images of specimens photographed under UV light.

Comparison of lecithotrophic and planktotrophic gastropod protoconchs (outlined) in two Pliocene fossils from the Dominican Republic; position of protoconch-teleoconch boundary indicated by arrow.

Left: Conus symmetricus has a protoconch with about 2 whorls and a diameter of about 0.7 mm, indicative of lecithotrophic development.

Right: Conus planiliratus has a protoconch with over three whorls and a diameter of about 0.7 mm, indicative of planktotrophic development (the earliest protoconch whorl(s) are missing in the specimen shown).

Specimens are from the collection of the Paleontological Research Institution. Image by Jonathan R. Hendricks for the Digital Atlas of Ancient Life project.

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Conus symmetricus domingensis (Sowerby I, 1850)

Gabb and Guppy united Sowerby's C. domingensis with C. symmetricus. A specimen of the former species loaned by Dr. Dall from the National Museum shows it to be a flat-topped, broader shouldered mutation of C. symmetricus. This elegantly sculptured Cone is very common in Santo Domingo and is found at Bowden and Gatun.

Localities. — (Exp'd '16) Zones A, B, C, D, E, F, Rio Gurabo at Los Ouemados; Bluff 1, Cercado de Mao.

Conus symmetricus domingensis ?? ^(2) Plate XIX - fig. 7	Conus symmetricus domingensis ^(6) Plate 4 - fig. 10

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Conus symmetricus semiobsoletus (Sowerby I, 1850)

Shell resembling C. symmetricus in form but larger and with the granular spirals obsolete on the upper half of the body whorl.

Length 39, greatest width 24 mm.

The specimens were collected by Professor Gabb in Santo Domingo.

Conus symmetricus semiobsoletus Plate 7 - fig. 8 mm. 39 x 24	Conus symmetricus semiobsoletus

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Bibliografia Consultata

· (1) - Sowerby (i), G. B. Sr., 1849. Description of new species of fossil shells found by J. S. Heniken, Esq.. The Quarterly Journal of the Geological Society of London, 6: 44 -53

· (2) - Pilsbry () “Revision of W.M. Gabb’s Tertiary Mollusca of Santo Domingo”

· (3) - Ricardo Ramírez (1955) “Paleontología Dominicana Descripción de los formaciones geológicas Baltoa. Cercado. Gurab o y Arcilla Mao. y lista de los moluscos y corales fósiles procedente* de ellas, que Integran la colección preparad a par a ser exhibida en la Feria”

· (4) - Hendricks (2015) “Glowing Seashells: Diversity of Fossilized Coloration Patterns on Coral Reef-Associated Cone Snail (Gastropoda: Conidae) Shells from the Neogene of the Dominican Republic”

· (5) - Hendricks (2017) “Diversity and preserved shell coloration patterns of Miocene Conidae (Neogastropoda) from an exposure of the Gatun Formation, Colón Province, Panama”

· (6) - Maury, C. J., 1917. Santo Domingo Type Sections and Fossils. Bulletins of American Paleontology, 5 (29 )