Siphonaria thersites Carpenter, 1864

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 : 109-111

Siphonaria thersites Carpenter, 1864

( Figs 40O–Q, T , 41D–G )

Siphonaria thersites Carpenter 1864b: 561 , 627, 647, 676, 684 (type locality: Neeah Bay [Washington, USA]).—Carpenter 1864c: 425; Paetel 1883: 178; 1889: 429; Yonge 1960: 111; Abbott 1974: 335, 4113; Galindo 1977: 416; Nagy 1984: 1, figs 1–9; White & Dayrat 2012: 68.

Siphonaria (Liriola) thersites — Dall 1870: 33, pl. 4, 8a–b, 1926: 26; Oldroyd 1927: 57; Thiele 1931: 427; Hubendick 1945: 64, fig. 1; 1946: 19, fig. 3, pl. 5, figs 35–38; Palmer 1958: 258; Morrison 1963: 7.

Liriola thersites — Dall 1921: 66; Trew 1983.

Material examined. Type material. Holotype of S. thersites from ‘ Neeah Bay, Washington, West Coast, North America’; coll. Swan, J. G. ( USNM 11852 ; Fig. 40O ).

Paratype, same data as holotype ( MCZ 275190 ) .

Other, non-type material. USA, Alaska: Cook Inlet, Camel Rock Camel Rock , 59°26.68’N, 151°43.02’W ( CBG 11 BIOAK-0589 p [SK554], 11BIOAK-0592 p [SK553], 11BIOAK-0593 p) . Canada, British Columbia: Houston Stewart Channel, Kunghit Island , 53°0’N - 132°0’W ( RBCM 80283 d) .

Taxonomic remarks. Carpenter (1864b:423) donated the types to the Smithsonian Institution (i.e., USNM). Palmer’s (1958: 258) statements regarding missing type and potential lectotype specimens are incorrect and explicitly not based on examination of the holotype. Siphonaria thersites is the type species of Liriola Dall, 1870 , by original designation.

External morphology. Animal not fully enclosed by shell, foot sole pale grey, foot wall, foot edge, mantle and cephalic folds all darker grey, paler at foot edge; foot wall pustulose, without darker markings; mantle narrow with dark grey edge band, half as wide as foot wall; two small indistinct black epithelial eye spots centralised on two centrally touching cephalic folds, pneumostomal lobe thick, under mantle behind right cephalic fold; closes the pneumostomal and anal openings at the mantle edge.

Shell ( Figs 40O–Q ; Table S9). small sized (max sl mean = 10.6 mm, SD = 1.7 mm, n = 9), elongate ovate, apex offset strongly posterior and left, apical sides strongly convex, height low, protoconch below apex, close to posterior edge; protoconch direction homostrophic (n = 2), shell whorl dextral; exterior uneven, radially ribbed, reddish brown, growth striae prominent in shaded radial bands, shell thin, lip even fragile, periostracum freely extending; rib count (mean = 36, SD = 3.2, n = 9), ribs weak to indistinct, primary ribs flatly rounded, not protruding beyond shell lip; often interspersed finer secondary ribs, rib interstices darker; siphonal ridge clear, bulged, extends beyond shell edge, formed by paired primary ribs. Interior glossy, shell margin dark brown to tan, lip paler with white markings aligned under ribs, siphonal groove distinct, shallow, same colour as margin; spatula mottled tan, uneven darker markings; ADM scar distinct, CMS convex; thickening of shell lip not observed.

Reproductive system ( Figs 41D, F, G; n = 3). Positioned within coelom under the respiratory cavity, hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned to anterior between BM and elongated RAM; AO indistinct, appears as a bulge under medium sized GA, ED short wide, joins to side of GA, singular prominent GP; EG large bulbous soft, flagellum (F1) indistinct to absent; BD indistinct, very narrow, enclosed in ventral tissue of wider whitish CD from BC to GA ( Fig. 41F–G ); both ducts are of similar length, emerge from folds of MA, together pass between foot wall and outside of RAM, and join into side of GA; GA, ED and BD all muscular white tissue; BC small deflated flattened whitish or expanded (5 SPM in a single BC), positioned under MG / AG; MG and AG small, heavily folded, soft white tissue; yellowish SV embedded on left side of AG, AG larger than HG; HD short, thickened, uncoiled and unlobed, links AG to a small, elongated, brownish/yellow, finely granulated HG.

Spermatophore ( Fig. 41E ). Body cylindrical, thread-like (length = 14.6 mm, n = 1, 118% of AL), test thin, translucent; head section long even, bluntly rounded, tapers to a thin flagellum and tip; both sections smooth, featureless; head longer, thicker than flagellum (head length = 11.8 mm; 81% of SPM length; flagellum length = 2.8 mm; head width = 150 μm; flagellum width = 14 μm).

Radula.Dentitionformula22:1:22or7.3.3.9:1:9.3.3.7 ( Dall, 1870: 33), 24:1:24 ( Hubendick 1946: 20).

Comparative remarks. Siphonaria thersites (unit 42) is the sister species of all other Siphonaria species included herein ( Fig. 1 ). It differs from other species by COI distances of ≥ 15.6%. It is not known to occur in sympatry with any other congener. As the only species found in Alaska, it has not been mistaken with other species in previous taxonomic literature. Contrary to Hubendick (1945: 15, fig. 1; 1946: 8, figs 1, 3), a BC is present and the genital pore ( GP) is monoaulic ( Fig. 41D, F ). Hence, the general layout of the reproductive anatomy of S. thersites corresponds well with that of other Siphonaria species.

Distribution and habitat. Endemic to northern hemisphere temperate zone from Kurile Islands, Russia, to west coast of Alaska, USA, British Columbia, Canada and Washington USA ( Fig. 45 ). Found on sheltered rocky shores at lower littoral level often on Fucus rockweed ( Fig. 40T ).

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 40. Shells of S. belcheri, S. nuttallii and S. thersites. A–J, R. S. belcheri. A. Lectotype NHMUK 1900.3.19.29. B–G. Paralectotypes NHMUK 1900.3.19.30-34. G. NHMUK 1900.3.19.28. H. Pakistan, Karachi, AM C.585102 [M227]. I. Karachi, AM C.585500 [SK146]. J. Karachi, AM C.585101 [M238]. R. Karachi, in situ. K–N, S, U–V. S. nuttallii. K. Lectotype NHMUK 20120166/1. L. Hawaii, Maui, TS, AM C.584898 [SK211]. M. TS of S. chirura AM C.584895 [M471, SK273]. N. Paralectotypes NHMUK 20120166. S. Protoconch, AM C.584894 [M470]. U. Maui, in situ. O–Q, T. S. thersites, O. Holotype USNM 11852. P–Q. Alaska, Cook Inlet. P. CBG 11BIOAK-0592 [SK553]. Q. 11BIOAK-0589 [SK554]. T. Washington, Neeah Bay, TS, in situ. Unlabelled scale bars = 10 mm.

FIGURE 41. Reproductive morphology of S. incerta, S. thersites and S. tasmanica. A–C. S. incerta. A–B. Réunion, Saint Paul, neotype MNHN IM-2000-35954 [M263, SK276]. C. CI, AM C.584889 [SK081]. D–G. S. thersites, Alaska, Cook Inlet. D–E. BIOUG 11BIOAK-0592 [SK553]. F. Dorsal view.G. Ventral view. BIOUG 11BIOAK-0589 [SK554]. H–I. Tas, TS of S. tasmanica. H. AM C.585255 [SK020]. I. SPM, AM C.585512 [SK080]. Unlabelled scale bars = 1 mm.

FIGURE 45. Known occurrence records of S. thersites, S. acmaeoides, S. sirius, S. subatra and S. rucuana