Siphonaria undans, B. W. Jenkins & Köhler, 2024

Jenkins, Bruce & Köhler, Frank, 2024, Hidden in plain sight: Systematic review of Indo-West Pacific Siphonariidae uncovers extensive cryptic diversity based on comparative morphology and mitochondrial phylogenetics (Mollusca, Gastropoda), Megataxa 13 (1), pp. 1-217 : 191-192

Siphonaria undans sp. nov.

( Figs 76F–I, N–O , 77E–F )

Material examined. Type material. Holotype, from Waikoloa Beach , 19°55.456’N, 155°53.491’W, Big Island, Hawaii; coll. B.W. Jenkins, HA04-2, 25 June 2018 ( AM C.584901 [M294, SK213], Fig. 76F ) . Paratypes same data as holotype ( AM C.585587 4p, C.584903 p [SK257], Fig. 76G, C.584904 [SK258], Fig. 76H, C.585913 p [SK388], Fig. 76I ) .

Other, non-type material. Hawaii, Big Island: Waikoloa Beach , 19°55.026’N, 155°53.282’W, HA04-1 ( AM C.585375 10p, 19°55.456’N, 155°53.491’W, HA04- 2 ( AM C.584905 p [SK205]).

External morphology ( Fig. 76P ). Foot edge, foot wall, cephalic folds and pneumostomal lobe all evenly yellowish/green, foot sole cream; irregular black pigmentation markings around foot wall, concentrated over central cephalic lobes; mantle translucent narrow thickened edge strongly lobed/folded, mould/extend to cover area of shell lip and align with undulations of primary shell ribs; genital pore indistinct, located on foot wall to right anterior of right cephalic fold; small black epithelial eye spot centralised on each of centrally touching cephalic folds; pneumostome narrow, positioned between right adductor muscles and within mantle.

Shell ( Fig. 76I–L, N ; Table S9). Small sized (max sl mean = 13.2 mm SD = 0.8 mm, n = 3); height medium; circular ovate, exterior uneven with discontinuities in growth; apex offset posterior and left; apex slightly hooked, curled to posterior; apical sides weakly convex, weakly concave at posterior; protoconch direction weakly homostrophic (n = 2, Fig. 76N ), shell whorl dextral; growth lines indistinct, rib growth uneven; radial banding prominent; shell lip uneven, anterior slightly protruded; primary and secondary ribs similar, white, width narrow, very crooked, slightly raised, ridges rounded, not extending greatly beyond scalloped/corrugated shell lip, rib count (mean = 45, SD = 3.3, n = 4); siphonal ridge not prominent, formed by dual primary ribs; often only one small or no secondary rib between primary ribs, rib interstices narrow, brown/black; interior shell lip and margin white under primary ribs, dark chocolate brown rays aligning under rib interstices extend from shell lip to evenly dark chocolate brown spatula; siphonal groove prominent, often with calcification; CMS straight, ADM scar distinct, paler than spatula and shell margin, golden colour; thickening of inner shell lip not apparent in larger specimens.

Reproductive system ( Fig. 77E; n = 1). Positioned within right side of coelom, against foot wall on foot muscle, under the respiratory cavity; epiphallic parts ( GA, EG and ED) positioned between BM and RAM, GA medium, with singular GP through foot wall; AO medium, bluntly rounded, joined at base to upper GA, rests against MG; ED long broad twisted centrally bent, joins to side of GA and base EG; GA, AO, ED all white muscular fibrous tissue; EG small, soft folded whitish tissue; single long narrow flagellum (F1) centrally bent and looped, appears as an extension of much wider ED; BD and CD connect closely into GA between ED-join and GP, both ducts tightly aligned, broad whitish curved smooth featureless, pass closely together through outside of RAM ( BD over CD) into soft white folded tissues of MG / AG complex; CD short and curves to connect with AG duct, BD with distal loop and flat MA to inner foot wall, embeds in folds of AG; BC medium bulbous thin whitish translucent test, 2 SPM in BC (n = 1); HD broad short coiled whitish, links ducts in soft white folded tissues of AG to granulated yellowish small HG; AG much larger than HG.

Spermatophore ( Fig. 77F ). Thread-like, test thin, translucent, comprises a translucent cylindrical body section containing a white gelatinous thread-like core, tapers rapidly into a filamentous transparent flagellum (head length = 17.33 mm, n = 1), flagellum incomplete, head section much thicker than flagellum (head width = 222 μm, flagellum width = 74.1 μm, n = 1); head tip narrow bluntly rounded; both sections smooth, featureless; 2 SPM tightly coiled, embedded in dark-brown gelatinous mass [M294].

Comparative remarks. Siphonaria undans sp. nov. ( plicata group, unit 61) is a well differentiated lineage in the mitochondrial tree ( Figs 1 , 3 ). It differs from its sister species S. mauiensis sp. nov. (unit 60) by COI distances of ≥ 29.6% (Table S7). We found S. undans sp. nov. in sympatry with S. waikoloaensis on Big Island, Hawaii. Both species are similar, but S. waikoloaensis differs by having a less scalloped shell edge, darker shell lip with paler interior, a slightly larger BC, and shorter SPM.

Distribution and habitat. Recorded from Big Island, Hawaii only ( Fig. 78 ). In this study, found in sheltered positions (mainly rock crevices) on moderately exposed fine-algal covered volcanic-rock shores, at upper littoral level.

Etymology. Derived from Latin adjective ‘undans’ meaning ‘wavy’, referring to the prominent waviness and unevenness of the primary ribs in the shell of this species.

Figures

FIGURE 1. Maximum Likelihood phylogram based on analyses of a concatenated sequence data set of 16S and COI. Branches are collapsed at the species level. Branch labels give unit numbers and accepted species names. Numbers on branches indicate branch support employing 10,000 ultrafast bootstraps.Available genus-group names are shown next to their type species. Scale bar indicating modelled sequence divergence.

FIGURE 3. Maximum Likelihood phylogram (partial, species not collapsed). Clades J–L (laciniosa and plicata groups) of the tree shown in Fig. 1. Branch labels give specimen identifiers for new sequences or Genbank accession numbers for imported sequences from other studies and geographic regions (see Tables S1–S2 for details). Identical haplotypes are merged into single tips. Numbers on branches indicate branch support by employing 10,000 ultrafast bootstraps. Clade names give unit numbers and accepted species names. Scale bar indicating modelled sequence divergence.

FIGURE 76. Shells of S. poindimiensis sp. nov., S. umbra sp. nov. and S. undans sp. nov. A–C, J–K. S. poindimiensis sp. nov. A. Holotype AM C.584999 [M352], NC, Poindimie. B. Paratype AM C.585837 [SK129]. C. Paratype AM C.585002 [SK261], NC, Tiari. J. Protoconch, AM C.585010 [SK262]. K. In situ. D–E, L–M. S. umbra sp. nov., CI, Ethel Beach. D. Holotype AM C.584672 [M409, SK084]. E. Paratype WAM S74051 [M306]. L. Protoconch, AM C.585320 [SK022]. M. In situ. F–I, O–N. S. undans sp. nov.. Hawaii, Big Island. F. Holotype AM C.584901 [M294, SK213]. G. Paratype AM C.584903 [SK257]. H. AM C.584904 [SK258]. I. Paratype AM C.585913 [SK388]. N. Protoconch, AM C.584905 [SK205]. O. In situ. P. Animal. Scale bars 10 mm.

FIGURE 77. Reproductive morphology of S.poindimiensis sp. nov., S.umbra sp. nov. and S. undans sp. nov. A–B. S. poindimiensis sp. nov., NC, Poindimie. A. Holotype AM C.584999 [M352, SK128]. B. Paratype AM C.585837 [SK129]. C–D. Holotype of S. umbra sp. nov. AM C.584672 [M409, SK084], CI, Ethel Beach. E–F. Holotype of S. undans sp. nov., AM C.584901 [M294, SK213], Hawaii, Big Island. Scale bars = 1 mm.

FIGURE 78. Known occurrences of S. tenebrae sp. nov., S. poindimiensis sp. nov., S. umbra sp. nov., S. undans sp. nov., S. vudaensis sp. nov., S. waikoloaensis sp. nov. and S. yagasaensis sp. nov.