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Atlanta echinogyra Richter 1972

Roger R. Seapy
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Containing group: Atlanta

Introduction

Atlanta echinogyra is a small species (to 2.5 mm shell diameter). The shell is colorless, although the tissues underlying the shell spire give it a red-violet to red-brown color. The spire is low conical and consists of 3-3/4 whorls. The spire whorls have incised sutures and bear low spiral ridges on the second through most of the fourth whorls. The outer edge of the third and fourth whorls have a raised ridge (seen best in the larval shell). The keel is moderately elevated with a slightly truncate leading edge. The keel does not insert between the last two shell whorls. The keel base is either clear or brown. Eyes type a. Operculum type c, with a gyre that bears a raised spiral row of strong, distally-tapering spines (hence the specific epithet, "echinogyra"). Radula type I, with unlimited numbers of tooth rows and lacking sexual dimorphism. Geographic distribution Indo-Pacific. Vertical distribution limited to the upper 100 m in Hawaiian waters.

Diagnosis

Characteristics

  1. Shell
    1. Shell small, with a maximal diameter of 2.5 mm
    2. Shell colorless, except for the keel base (in the Indian Ocean; see below)
    3. Shell spire consists of 3-3/4 whorls
    4. Spire low conical and can be slightly to moderately inclined relative to the plane of the whorls comprising the teleoconch (see tilted views of SEM images below)
    5. Spire region is red-violet to red-brown due to color of underlying tissues, which contrasts with the clear tissues of the remaining adult tissues (see title illustration)
    6. Sutures of spire whorls deep, enabling easy distinction of the whorls (see second and fourth SEM images below)
    7. Low spiral ridges present on second (two ridges) and third through most of the fourth (three ridges) spire whorls (see second SEM image below)
    8. Keel moderately elevated, with slightly truncate leading edge (clearly illustrated in the photograph of the holotype shell with a nearly-intact keel in Richter 1972, fig. 5)
    9. Keel base is either clear (in North Pacific, Hawaiian specimens; Seapy, 1990a; see title illustration) or dark brown to yellow-brown (in Indian Ocean specimens; Richter, 1974)
    10. Keel does not insert between penultimate and last shell whorls
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      Figure. Scanning electron micrographs of Atlanta echinoygra shell (left) and shell spire (right) viewed from the right side. Scale bars = 0.5 mm (left) and 100 µm (right). © Roger R. Seapy

      Figure. Scanning electron micrographs of Atlanta echinoygra shell (left) and shell spire (right) viewed from the right side at about a 60° tilt. Scale bars = 0.5 mm (left) and 100 µm (right). © Roger R. Seapy


      Figure. Scanning electron micrographs of Atlanta echinoygra shell (left) and shell spire (right) viewed from the right side. Scale bars = 0.5 mm (left) and 100 µm (right). © Roger R. Seapy


      Figure. Scanning electron micrographs of Atlanta echinoygra shell (left) and shell spire (right) viewed from the right side at about a 60° tilt. Scale bars = 0.5 mm (left) and 100 µm (right). ©

    11. Internal walls of spire whorls intact; not decalcified as in the Atlanta inflata species group
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      Figure. Transmitted light photograph of a Atlanta echinogyra juvenile shell (1.0 mm diameter). The inner walls of the spire are clearly seen in the photograph. Scale bar (= 0.5 mm) added to image from Richter (1987, fig. 36). © 1987 G. Richter

    12. Larval shell with spiral ridges and raised ridge on the outer margin of the whorls. Complex pattern of primary spiral and secondarily diagonal ridges on lateral sides of the exposed whorls (see second SEM image below)
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      Figure. Larval shell of Atlanta echinogyra viewed from the right side (left) and right side, tilted about 60° (right). Scale bars = 100 µm. ©

  2. Eyes type a, without a transverse slit in the distal pigmented tissue
  3. Operculum type c (monogyre)
    1. Shape of operculum broad, oval
    2. Opercular gyre with an elevated spiral row of strong spines that taper distally to a rounded point. When mounted on a microscope slide with a cover slip added, the pressure of the cover slip causes the thinner tips of the spines to bend (see second image below). Additional photographs of the opercular gyre were included in three papers by Richter (1972, fig. 3; 1974, fig. 5; and, 1987, fig. 42). Drawings of 10 opercula of A. echinogyra (misidentified as A. inflata) were included in a study of atlantids by Tokioka (1961, figs. 11, 12); four are included below from animals of different sizes (shell diameters = 0.6-1.5 mm)
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      Figure. Operculum from a 1.0 mm Atlanta echinogyra (left) and close-up of gyre region with spiral row of raised, broad spines (right). Scale bars = 100 µm. © Roger R. Seapy


      Figure. Sketches of four opercula from Atlanta echinogyra. Shell diameters of specimens from which opercula were removed = 0.6 mm (A), 1.0 (B), 1.2 mm (C) and 1.5 mm (D). Drawings scanned from Tokioka (1961, fig. 11). © 1961 T. Tokioka

  4. Radula type I
    1. Number of tooth rows unlimited
    2. No sexual dimorphism in radular or tooth size or shape
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      Figure. Radula of Atlanta echinogyra; section of radula (left) and close up of two central teeth. Images from Richter (1987, figs. 47 and 57), modified by addition of scale bars. Scale bars = 50 µm (left) and 10 µm (right). © 1987 G. Richter

Comments

Atlanta echinogyra was described in 1972 by G. Richter based on specimens collected during the Meteor Expedition to the northern Indian Ocean. Richter named the species after the unique structure of the opercular gyre, with its raised spiral row of spines (see second SEM image of the operculum above).

In the plankton samples from the Meteor Expedition studied by Ricther (1974), Atlanta echinogyra was the fourth most abundant species of heteropod (accounting for 9.1% of the total). By contrast, the species was uncommon off northeastern Australia (ranking nineth, accounting for 1.5% of the total number of heteropods collected) in a study by Seapy et al. (2003). In Hawaiian waters A. 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. In eastern Australian waters, Newman (1990) recorded A. echinogyra as rare in northern and central Great Barrier Reef waters. Thus, it would appear that in the Pacific and Indian Oceans, A. echinogyra is only abundant in the northern Indian Ocean.

References

Newman, L. J. 1990. Holoplanktonic mollusks (Gastropoda: Thecosomata and Heteropoda) from the waters of Australia and Papua New Guinea: their taxonomy, distribution and biology. Ph.D. thesis. University of Queensland, Brisbane Australia.

Richter, G. 1972. Zur Kenntnis der Gattung Atlanta (Heteropoda: Atlantidae). Archiv fur Mollusken-Kunde 102: 85-91.

Richter, G. 1974. Die Heteropoden der "Meteor" Expedition in den Indischen Ozean 1964/65. "Meteor" Forschungs-Ergibnisse Ser. D, No. 17, pp. 55-78.

Richter, G. 1987. Zur Kenntnis der Gattung Atlanta (III), Atlanta inflata, A. helicinoides, A. echinogyra und A. plana (Prosobranchia: Heteropoda). Archiv fur Mollusken-Kunde 117: 177-201.

Seapy, R. R. 1990a. The pelagic family Atlantidae (Gastropoda: Heteropoda) from Hawaiian waters: a taxonomic survey. Malacologia 32: 107-130.

Seapy, R. R. 1990b. Patterns of vertical distribution in epipelagic heteropod molluscs off Hawaii. Marine Ecology Progress Series 60: 235-246.

Seapy, R. R. 2008. Offshore-inshore and vertical distributional patterns of heteropod mollusks off leeward Oahu, Hawaii. Marine Biology 154: 985-995.

Seapy, R. R., C. M. Lalli and F. E. Wells. 2003. Heteropoda from Western Australian waters, pp. 513-546. In: F. E. Wells, D. I. Walker and D. S. Jones (eds), The marine flora and fauna of Dampier, Western Australia. Western Australian Museum: Perth.

Title Illustrations
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Scientific Name Atlanta echinogyra
Location Hawaiian waters
Specimen Condition Live Specimen
Sex Female
Life Cycle Stage adult
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About This Page


California State University, Fullerton, California, USA

Correspondence regarding this page should be directed to Roger R. Seapy at

Page: Tree of Life Atlanta echinogyra Richter 1972. Authored by Roger R. Seapy. The TEXT of this page is licensed under the Creative Commons Attribution License - Version 3.0. Note that images and other media featured on this page are each governed by their own license, and they may or may not be available for reuse. Click on an image or a media link to access the media data window, which provides the relevant licensing information. For the general terms and conditions of ToL material reuse and redistribution, please see the Tree of Life Copyright Policies.

Citing this page:

Seapy, Roger 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, http://tolweb.org/

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