85
Figure 2. Operculum of Iheyaspira bathycodon
The new species, designated Iheyaspira bathycodon, was evaluated from molecular phylogenetics (the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships [5]) and morphological differences in the radula and appendage structure of the head-foot compared to the most closely allied vent species. The operculum and radula were mounted uncoated onto an aluminium sample stub and micrographs were taken with the tabletop microscope. The radula, in particular, is conventionally considered as a sample which is highly susceptible to charging and is therefore considered difficult to image. Using the variable pressure tabletop SEM, however, data was acquired quickly and easily without any charging artifact appearing in the image.
Radula Tooth Structure
Micrographs of the radula produced by the tabletop microscope (Figures 3, 4 and 5) show bilateral symmetry with at least 60 transverse rows of teeth along the total length. The central tooth is different in form from the lateral teeth (Figure 3). It is smooth-sided, bell-shaped and wider proximally than distally, with a single incurved central cusp. The lateral teeth (Figures 3 and 5) are of similar size to the central tooth, increasing in size outwards; with a long, rounded single central cusp, and an outer apical margin with several flanking denticles; dentition attenuates towards the cusp and is strongest on the outermost lateral. Figures 3 and 4 show more than twenty marginal teeth on both sides. The cutting plate is concave, terminating in a single short cusp, The apical margins are oblique, each with about 10–14 denticles that are longer and finer than those on the lateral teeth. The outermost marginal teeth in a row are smaller, with weaker dentition and straighter shafts. The marginal rows overlap each other and no jaws are present. This radula pattern appears to be unique in both number of teeth and shape. The new species is similar in morphology to Iheyaspira lequios [6] and Fucaria mystax [7], both of which are known only from hydrothermal vents in the Pacific at water depths less than 1500 m. However, differences in the radula (as well as the appendage structure of the head- foot not discussed here) differentiate it from both these species. The central tooth on the radula of the new species is bell-shaped, not rhombic/arrow-shaped like Iheyaspira lequios and there are only nine (not twelve) pairs of lateral teeth. It is closest in morphology to I. lequios and so the generic name Iheyaspira has been given to the new species to indicate the similarity between the two species. Iheyaspira bathycodon sp. nov. is the second new species to be described from the Von Damm Vent Field, and the tenth turbinid gastropod to be described from a hydrothermal vent environment to date.
Figure 4. Iheyaspira bathycodon radula marginal teeth Additional Capabilities
This article has concentrated on the importance of morphological information in marine biological research, and the ease with which high quality images can be produced using the tabletop electron microscope. However there are two other important capabilities offered by the tabletop microscope; atomic number contrast and chemical element analysis. Images in the tabletop microscope are produced by collecting high energy electrons backscattered from the sample. Backscattered electrons contain information related to the average atomic number of the materials in the sample which can result in enhanced contrast in the image if materials of different atomic number are present. In addition to generating backscattered electrons to form the image, the electron beam interacts with the sample to generate X-rays, which are characteristic of the chemical elements present. The addition of an energy dispersive X-ray analysis system to the tabletop microscope allows these X-rays to be collected and analysed to give semi-quantitative or fully quantitative analysis of the elemental composition. These two features have been of particular interest to geologists at BAS elsewhere, and some of their applications will be discussed in a future article.
Figure 5. Iheyaspira bathycodon radula lateral teeth References
1.
http://en.wikipedia.org/wiki/Operculum_(gastropod) 2.
http://en.wikipedia.org/wiki/Radula 3.
http://en.wikipedia.org/wiki/Ctenidium_(mollusc)
4. Verity Nye, Jon Copley, Katrin Linse and Sophie Plouviez Iheyaspira bathycodon new species (Vetigastropoda: Trochoidea: Turbinidae: Skeneinae) from the Von Damm Vent Field, Mid Cayman Spreading Centre, Caribbean. Journal of the Marine Biological Association of the United Kingdom, Available on CJO 2012 doi:10.1017/S0025315412000823
5.
http://en.wikipedia.org/wiki/Molecular_phylogenetics
6. Okutani T., Sasaki T. and Tsuchida T. (2000) Two additional new species to gastropod fauna of chemosynthetic site on North Knoll of Iheya Ridge, Okinawa Trough. Venus 59, 267–275.
Figure 3. Iheyaspira bathycodon radula
7. Ware n A. and Bouchet P. (2001) Gastropoda and monoplacophora from hydrothermal vents and seeps: new taxa and records. Veliger 44, 116–231. 8.
http://www.hit-eu.com/cms/
19823.html
INTERNATIONAL LABMATE - JANUARY/FEBRUARY 2013
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96
