Atlanta vanderspoeli Wall-Palmer, Hegmann & Peijnenburg

Wall-Palmer, Deborah, Hegmann, Mona, Goetze, Erica & Peijnenburg, Katja T. C. A., 2019, Resolving species boundaries in the Atlanta brunnea species group (Gastropoda, Pterotracheoidea), ZooKeys 899, pp. 59-84 : 59

Atlanta vanderspoeli Wall-Palmer, Hegmann & Peijnenburg sp. nov. Figures 7 , 8

Atlanta turriculata forma B - van der Spoel 1972: 550

Atlanta turriculata forma B - van der Spoel 1976: 146-147

Atlanta brunnea - Quesquén Liza 2017: 265

Atlanta brunnea form B - Wall-Palmer et al. 2018b: 10, Fig. 3

Type locality.

DANA expedition (1928-1930) station 3558VII, South Pacific 0.30S, 99.12W. Specimen collected on the 18h September 1928 at 19:00 from 200-300 m water depth.

Holotype. Figure 7 D–E , NHMD-232132, Housed at the Natural History Museum of Denmark, Copenhagen.

Paratypes. NHMD-232153. DANA_3613V, South Pacific 22.72S, 166.10E. Specimen collected on 28 April 1928 at 03:15 from 100-200 m water depth. Housed at the Natural History Museum of Denmark, Copenhagen. RMNH.MOL.342212. Type material of A. turriculata forma B ( Figure 10 ) was deposited by van der Spoel in the collections of the Zoological Museum of Amsterdam (now housed at the Naturalis Biodiversity Center, Leiden, RMNH). We designate these specimens as paratypes of A. vanderspoeli . They were collected during the “Siboga” Expedition at station 136 in the equatorial Pacific 0.80N, 127.28E.

Diagnosis.

Atlanta species with a larval shell of 3 ¼ to 4 whorls. The larval shell is much higher than wide, conical with an apical angle of 35-46°. The larval shell has a prominent carina slightly above mid-whorl height. The whorls of the larval shell are further covered in a micro-ornamentation of interrupted spiral lines and small projections roughly arranged in spiral lines (approximately five lines in total) above this carina, and zig-zagged ornamentation below it ( Figs 7 D–F , 8 ).

Description.

The shell is small and fresh specimens vary in colour from brown to pink-purple. The adult shell is on average 1000 μm in diameter without the keel (Suppl. material 2: Table S1). The shell begins to inflate on the boundary of teleoconch and protoconch at 3¼ to 4 whorls and has a total of 4¾ to 5 whorls in adults. The keel begins after 3¾ to 4 whorls and inserts between the final whorl and the preceding in larger specimens (filling the space between the whorls). The keel is tall (~400 μm), thin and transparent, and gradually truncates towards the aperture (after ca. ¾ of a whorl). The soft tissues of the foot/fin and sucker can be mottled black (see Suppl. material 3: video clip). The last whorl of the larval shell is ca. 262 to 372 μm in diameter (Suppl. material 2: Table S1). The larval shell is high and conical, with heavy ornamentation covering the surface. A prominent carina is situated slightly above mid-whorl height and is visible with light microscopy. The spiral lines and zig-zag ornamentation is more clearly visible using SEM. The operculum is type a (macro-oligogyre) and the eyes are of type a, with no transverse slit ( Seapy et al. 2003).

Discussion.

The shape of the larval shell, shell size, colouration, operculum and eye type demonstrate that A. vanderspoeli belongs within the A. brunnea species group. This is supported by the molecular analysis presented within this study and by Wall-Palmer et al. (2018b). Molecular data finds A. vanderspoeli to be most closely related to A. brunnea , followed by A. turriculata . These are also morphologically the most similar species. Atlanta vanderspoeli can be distinguished from these two species using the apical angle, which is more narrow than in A. brunnea , but wider than in A. turriculata . Van der Spoel (1972) noted that the operculum of ( A. turriculata forma B) A. vanderspoeli generally does not have tubercles/spines, or that these are less developed ( van der Spoel 1976) compared to the operculum of A. turriculata . Due to a lack of adult specimens, we were unable to extract an operculum to confirm this.

Distribution.

All specimens were found in the equatorial and south Pacific Ocean from 0.80N to 29.95S, and from 127.28E to 100.00W ( Figure 3 ). Specimens were collected from the upper 600 m using oblique and vertical plankton tows. During this study we only found specimens of A. vanderspoeli in the south Pacific Ocean. However, specimens identified as A. turriculata forma B by van der Spoel (1976) were collected at 'Ternate Anchorage’ in the Indomalayan Archipelago ( “Siboga” Expedition station 136, equatorial Pacific 0.80N, 127.28E. Figure 10 ).

Etymology.

Named after Professor emeritus Siebrecht van der Spoel, who first noticed A. vanderspoeli , but described it only as A. turriculata forma B due to a lack of specimens ( van der Spoel 1976). Professor van der Spoel spent many years working on holoplanktonic gastropods and made important contributions to our understanding of their taxonomy and distributions.

Figures

Figure 3. A Distribution maps showing the collection locations for each clade identified in B. The collection location of specimens of A. turriculata forma B identified by van der Spoel (1976) from offshore of Ternate Island is marked with a white triangle B maximum likelihood phylogeny based on the mitochondrial cytochrome c oxidase subunit 1 gene, with strong bootstrap support for four clades within the A. brunnea group. Atlanta vanderspoeli is supported as a valid species, and A. brunnea is formed of two geographically isolated clades. Bootstrap support (%) for nodes is displayed and branch lengths are proportional to the amount of inferred change, as indicated by the scale bar (mean number of nucleotide substitutions per site).

Figure 7. Scanning Electron Microscopy (SEM) and stacked light microscopy images of representative specimens of A. brunnea: A, B DANA _ 3929 VIII C SN 105 _ 08, A. vanderspoeli: D-E DANA _ 3558 VII (Holotype, NHMD- 232132) F KH 1110 _ 15 and A. turriculata: G, H DANA _ 3929 VIII I SN 105 _ 19. Apical angle is the most useful morphological feature for distinguishing between the species (B-C, E-F, H-I). The shell of A. brunnea is always brown (C); however, the colour of A. vanderspoeli and A. turriculata shell and soft tissues (F, I) can vary and these are not reliable features for identification.

Figure 8. SEM images of the A. vanderspoeli holotype from station DANA _ 3558 VII (NHMD- 232132) A apical view of the entire shell showing the rapid inflation of the shell B magnified view of the micro-ornamentation C magnified apical view showing the extent of the carina.

Figure 10. Five specimens of Atlanta turriculata forma B identified by van der Spoel and held in the collection at the Naturalis Biodiversity Center. These specimens are now designated as paratypes of Atlanta vanderspoeli RMNH. MOL. 342212.