Siphonaria guamensis Quoy & Gaimard 1833
Creators: name: Jenkins, Bruce
name: Köhler, Frank
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Mollusca
Gastropoda
Siphonariida
Siphonariidae
Siphonaria
Siphonaria guamensis

description: Siphonaria guamensis Quoy & Gaimard, 1833
(Figs 26A–E, 27A–B)
Siphonaria guamensis Quoy & Gaimard 1833: 343, pl. 25, figs 15– 16 (type locality: ‘Port d’Humata’ [Umatac Bay, Guam]).— Lamarck 1836: 558; Catlow & Reeve 1845: 100; H. Adams & A. Adams 1855 (in 1853–58): 271; Hanley 1858b: 152; Paetel 1889: 428; White & Dayrat 2012: 63.
Siphonaria (Sacculosiphonaria) guamensis — Hubendick 1945: 72, fig. 33, 37; 1946: 41, pl.6, fig. 30–32; Marcus & Burch 1965: 256, figs 40–43.
Material examined. Type material. Lectotype of Siphonaria guamensis Quoy & Gaimard, 1833, present designation, from ‘Est tres-commune dans l’ile dont elle porte le nom, surtout au port d’Humata’ [is very common in the island of which it is named, especially at the port of Humata, Iles Mariannes [Umatac Bay, Guam] (MNHN IM 2000-35953, Fig. 26A). Ten paralectotypes, same data as lectotype (MNHN IM 2000-5054).
Other, non-type material. Guam: Umatac Bay Nth point, 13°17.917’N, 144°39.494’E GM01-1 (AM C.585553 10+p, C.584911 p [SK142], C.584929 p [SK378], C.584928 p [SK379], C.585031 p [SK426]); Umatac Bay, Sth point, 13°32.549’N, 144°48.443’E GM01-3 (AM C.585392 10p, C.584870 p [M344], C.584871 p [M345], C.584872 p [M346]).
Taxonomic remarks. The largest syntype with clearest external sculpture is herein designated as the lectotype of Siphonaria guamensis for the stabilisation of the name (Art. 74.1 of the Code). Labels associated with type specimens just give ‘Iles Mariannes’. Our delineation of this species is based on comparative analyses of the morpho-anatomy and mitochondrial genetics of freshly collected topotypes specimens (Figs 26B–C) and a series of additional specimens (Table S1). The topotypes studied here match characteristics mentioned in the original description, such as ‘raised and distinctive ribbing, prominent dark radial banding and the slightly hooked apex anteriorly [sic! posteriorly]’.
External morphology. Foot sole, foot wall, pneumostome, cephalic folds and mantle evenly cream/ light grey; genital pore inconspicuous, located on foot wall posterior to right cephalic fold; mantle narrower than foot wall, thin translucent, edge weakly lobed with light black bands aligning to rib interstices extends to shell edge, pneumostomal lobe thin and within mantle between the right ADMs, closes the pneumostomal and anal openings at the mantle edge; two small black epithelial eye spots centralised on two thick centrally touching cephalic folds; light black pigmentation over posterior foot wall and centre of cephalic folds.
Shell (Figs 26A–C, E; Table S9). Small sized (max sl mean = 10.96 mm, SD = 1.6 mm, n = 6), height medium; ovate; apex offset weakly to posterior and left; apical sides convex, posterior concave to straight; protoconch hooks to posterior, area black colouration, protoconch direction weakly homostrophic (n = 2; Fig. 26E), shell whorl dextral; growth striae weak; shell thickness thin; colouration uneven with some radial banding; rib count (mean = 38, SD = 4.9, n = 6); slightly raised, pale white, fairly straight, faintly protrude beyond shell lip; predominantly primary ribs, in parts interspersed with 0–2 finer secondary ribs, rib interstices darker; siphonal ridge indistinct. Interior evenly dark brown to black from margin to spatula, paler on shell lip aligning under rib ends, siphonal groove clear; ADM scar indistinct, CMS weakly convex; No evidence of growth variations in shell thickness or shell margin colouration.
Reproductive system (Fig. 27A; n = 2). Positioned withincoelomundertherespiratorycavity,hermaphroditic glands positioned to posterior against right foot wall and over foot sole, epiphallic parts positioned over and looped/folded in front of BM and to side of RAM; AO large, elongated, bluntly pointed (embeds into MG), centrally bent with MA, merges with indistinct GA; ED relatively short, slightly twisted, thick with side appendage; EG relatively large, folded, elongated and pointed; single short narrow bent flagellum F1 on EG; AO, GA and ED all muscular white tissue; BD and CD with opposing connections (bulbous at CD) into GA between ED, AO and GP; BD longer and narrower than CD with a prominent distal loop, top of loop attached via a long MA to inner foot wall in front of BM, both ducts smooth and pass together through RAM connecting into folds of MG (BD above CD), BC translucent test, midsized and bulbous; HD brownish long coiled links AG to a small elongated narrow brownish finely granulated HG; MG and AG small folded soft white tissue; dark SV embedded within AG, AG larger than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.
Spermatophore (Fig. 27B). Thread-like, test thin, smooth, featureless, translucent (length = 9.38 mm, n = 1), head bulbous, tip bluntly rounded, containing a white gelatinous mass; taper region into the filamentous transparent flagellum is extended; both sections smooth, featureless; head longer and much thicker than flagellum (head length = 7.00 mm, head ~75% of SPM length; head width = 80 μm; flagellum width = 13 μm); three SPM tightly coiled in a brown gelatinous mass found in one BC [SK241].
Radula. Dentition formula 26:1:26 (Hubendick 1946: 42).
Comparative remarks. Based on our molecular phylogeny (Figs 1, 3), S. guamensis (plicata group, unit 70) is the sister species of an unidentified Siphonaria species from Rarotonga (unit 17). The next most closely related species is S. nusalikensis sp. nov. (unit 89). The minimum distance between S. guamensis and these species is 9.6% (unit 17) and 11.1% (unit 89) in COI. The minimum distance to any other species is at least 25% (Table S7).
Three congeners occur in sympatry with S. guamensis in Guam: Siphonaria lirata is very similar, but has finer ribbing, paler interior colouration, a non-hooked protoconch, and a shorter, wider ED, and longer F1. Siphonaria normalis is extremely variable, but has less raised ribbing, a non-hooked apex, paler interior, a shorter, wider ED and F1, larger BC, and shorter SPM. Siphonaria tanguissonensis has more raised and prominent ribbing, an unhooked apex, paler golden-brown interior with more prominent dark rays on shell lip, a smaller AO, longer BD, F1 looped, and a longer SPM. None of these species are closely related to S. guamensis (Figs 1, 3).
RS figures of ‘ S. guamensis ’ in Hubendick (1945: 26, fig. 33, 37) correspond well with S. costellata sp. nov., but not S. guamensis. Correspondingly, specimens from ‘Billiton, Paudua, The Sunda Islands’ depicted as ‘ S. guamensis ’ by Hubendick (1946: 93, pl. 6, fig. 30– 32) are likely S. costellata sp. nov. for resembling shell characteristics of this species, but not of S. guamensis. ‘ Siphonaria guamensis ’ recorded from Singapore (Tan & Chou, 2000: 115, fig 115) is also likely S. costellata sp. nov. based on shell characteristics, such as interior colouration, protoconch shape, which differs in S. guamensis. Unfigured records of ‘ S. guamensis ’ from Hong Kong (Christiaens, 1980a: 81), Anambas and Natuna Islands (Tan & Kastoro, 2004: 50; Chim & Tan, 2009: 269) are mis-identified specimens of S. sipho. The identity of ‘ S. guamensis ’ reported from Visakhapatnam, India by Murty et al. (2013: 104, fig. 1) is erroneous and outside of the range of this species.
Distribution and habitat. Endemic to Guam (Fig. 28), found in crevices on rock platforms and boulders on exposed rocky shores at mid to upper littoral levels (Fig. 26D).
description: Published as part of 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), pp. 1-217 in Megataxa 13 (1) on pages 64-67, DOI: 10.11646/megataxa.13.1.1, http://zenodo.org/record/14984186