Atlanta echinogyra
| Atlanta echinogyra | |
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| Apical view of the shell of Atlanta cf. echinogyra from the Pliocene of Philippines. Notice the flange-like keel. | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| Subclass: | Caenogastropoda |
| Order: | Littorinimorpha |
| Family: | Atlantidae |
| Genus: | Atlanta |
| Species: | A. echinogyra
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| Binomial name | |
| Atlanta echinogyra Richter, 1972[2]
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Atlanta echinogyra is a species of sea snail, a holoplanktonic marine gastropod mollusk in the family Atlantidae.[3]
Description
[edit]Atlanta echinogyra was described in 1972 by Dr. Gotthard Richter (from Senckenberg Museum, Frankfurt am Main, Germany) based on specimens collected during the Meteor Expedition to the northern Indian Ocean.[4] Richter named the species after the unique structure of the opercular gyre, with its raised spiral row of spines.[4]
Atlanta echinogyra is a small species (to 2.5 mm shell diameter).[4] The shell is colorless, although the tissues underlying the shell spire give it a red-violet to red-brown color.[4] The spire is low conical and consists of 3-3.25 whorls.[1][4] The spire whorls have incised sutures and bear low spiral ridges on the second through most of the fourth whorls.[4] The outer edge of the third and fourth whorls have a raised ridge (seen best in the larval shell).[4] The fourth whorl (first teleoconch whorl) increases rapidly in width and bears a flange-like keel.[1] The keel is moderately elevated with a slightly truncate leading edge.[4] The keel does not insert between the last two shell whorls.[4] The keel base is either clear or brown.[4] The early whorls are covered with a distinct and relatively coarse ornament consisting of four spirals.[1] This ornament is also visible on the base of the shell, where it is present in the umbilicus, on the last part of the protoconch.[1]
Eyes are type a.[4] Operculum is type c, with a gyre that bears a raised spiral row of strong, distally-tapering spines (hence the specific epithet, "echinogyra").[4] Radula is type I, with unlimited numbers of tooth rows and lacking sexual dimorphism.[4]
Description overview:
- Shell small, with a maximal diameter of 2.5 mm elevated spiral row of outwardly-directed spines that taper distally[4]
- Shell colorless[4]
- Spire region of shell red-violet to red-brown due to underlying tissues[4]
- Spire of 3-3/4 whorls, with low conical shape and deep sutures[4]
- Low spiral ridges present on the second through most of the fourth spire whorls[4]
- Outer edge of third and fourth whorls with a raised ridge[4]
- Keel moderately elevated, with a slightly truncate leading edge[4]
- Keel does not insert between last two whorls[4]
- Keel base clear (North Pacific Ocean) or dark to yellow-brown (northern Indian Ocean)[4]
- Eyes type a[4]
- Operculum type c; gyre bears a raised spiral row of distally-tapering spines[4]
- Radula type I[4]
Distribution
[edit]Geographic distribution of Atlanta echinogyra is Indo-Pacific.[4]
In the plankton samples from the Meteor Expedition studied by Richter (1974), Atlanta echinogyra was the fourth most abundant species of heteropod (accounting for 9.1% of the total).[4] By contrast, the species was uncommon off northeastern Australia (ranking ninth, accounting for 1.5% of the total number of heteropods collected) in a study by Seapy et al. (2003).[4] In Hawaiian waters Atlanta echinogyra was variable in its presence and numbers among different collections, ranking eleventh out of thirteen species of atlantids (Seapy, 1990a); from five different sampling periods between 1984 and 1986, it was not collected twice, was represented by a single individual once, and by 27 and 19 individuals in two collections.[4] In eastern Australian waters, Newman (1990) recorded Atlanta echinogyra as rare in northern and central Great Barrier Reef waters.[4] Thus, it would appear that in the Pacific and Indian Oceans, Atlanta echinogyra is only abundant in the northern Indian Ocean.[4]
Fossil distribution
[edit]Atlanta cf. echinogyra is known from the Pliocene of Anda, Pangasinan, Luzon, Philippines.[1]
Ecology
[edit]Vertical distribution limited to the upper 100 m in Hawaiian waters.[4]
References
[edit]This article incorporates CC-BY-3.0 text from references.[1][4]
- ^ a b c d e f g Janssen A. W. (2007). "Holoplanktonic Mollusca (Gastropoda: Pterotracheoidea, Janthinoidea, Thecosomata and Gymnosomata) from the Pliocene of Pangasinan (Luzon, Philippines)". Scripta Geologica. 135. Archived from the original on 24 July 2011. Retrieved 19 August 2010.
- ^ (in German) Richter G. (1972). "Zur Kenntnis der Gattung Atlanta (Heteropoda: Atlantidae)". Archiv für Molluskenkunde 102: 85–91.
- ^ Atlanta echinogyra Richter, 1972. WoRMS (2009). Atlanta echinogyra Richter, 1972. Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=430420 on 14 August 2010 .
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag Seapy R. R. (2010). Atlanta echinogyra Richter 1972. Version 28 March 2010 (under construction). http://tolweb.org/Atlanta_echinogyra/28756/2010.03.28 in The Tree of Life Web Project.