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

Siphonaria tanguissonensis View in CoL sp. nov.

( Figs 74G–J, N, Q–R View FIGURE 74 , 75E–H View FIGURE 75 )

Material examined. Type material. Holotype, from S end Tanguisson Beach , 13°32.549’N, 144°48.443’E, Guam; coll. B.W. Jenkins, GM02-1, 27 Dec 2018 ( AM C.584877 [M417, SK102 (RS, SPM)], Fig. 74G View FIGURE 74 ) GoogleMaps . Paratypes same data as holotype ( AM C.585897 7p, C.584878 p [M438, SK163], Fig.74I View FIGURE 74 ; C.584875 p [M342], Fig.74H View FIGURE 74 ; C.584881 p [SK253], Fig. 74J View FIGURE 74 ) GoogleMaps .

Other, non-type material. Guam: Tanguisson Beach, S end 13°32.549’N, 144°48.443’E GM02-1 ( AM C.585995 10p, C.584876 d[M349], C.584879 p [M341], C.584880 p [M350], C.584882 p [SK141 protoconch D10]) GoogleMaps .

External morphology ( Fig. 74R View FIGURE 74 ). Foot sole and foot wall evenly pale grey, paler at foot/wall edge; foot wall with patches of black pigmentation, mantle edge with vertical bands of black pigmentation aligned with shell rib interstices; mantle weakly lobed to unlobed, non-translucent, narrower than width of foot wall, covers exposed inner shell lip; genital pore noticeable, located on foot wall to right anterior of right cephalic fold; two small black epithelial eye spots centralised on two centrally touching black pigmented cephalic folds; pneumostomal lobe long, under the mantle, unpigmented, between the right ADMs.

Shell ( Figs 74G–J View FIGURE 74 ; Table S9): small sized (max sl mean = 12.9 mm, SD = 0.6 mm, n = 7), circular ovate; height low; apex offset central and to left; apical sides weakly convex, posteriorly weakly concave, protoconch direction homostrophic (n = 1, Fig. 74Q View FIGURE 74 ), shell whorl dextral; growth striae not prominent; radial colour bands, protoconch area dark, paler central band, edge band dark; in some individuals central band is eroded creating concave sides ( Fig. 74H View FIGURE 74 ); shell thick, pale grey; rib count (mean = 36.3, SD = 3.9, n = 7), primary ribs white, fairly straight, flattened, increasingly broaden (up to double width) and often raised to shell edge, weakly protrude beyond uneven shell lip to corrugate the edge; 1–2 secondary ribs between primary ribs, rib interstices narrow, black to dark brown; paired primary ribs (often fused) form siphonal ridge, end raised at shell edge. Interior shell margin and shell lip off-white under primary/secondary ribs, dark chocolate brown rays align under rib interstices; siphonal groove distinct, white to golden brown; spatula and distinct ADM scar dark brown to mottled tan, CMS convex; thickening of shell lip not noted.

Reproductive system ( Figs 75E, G; n View FIGURE 75 = 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 RAM. Join of AO and GA indistinct, AO elongated, bluntly pointed, centrally bent with no prominent MA, larger than GA, much thicker than ED; ED relatively long, coiled, twisted, thickened; EG white, folded, elongated; single flagellum F1 on EG, very long, reasonably straight, unlooped, positioned over BM, thin; AO, GA and ED all muscular white tissue; BD and CD with opposing bulbous connections to GA between ED, AO and GP; BD wrinkled, not twisted, much longer and thinner than short CD with prominent looping on anterior side, both ducts smooth and pass together through RAM connecting into MG ( BD above CD), BC translucent, white test, small sized and bulbous; HD short, coiled, links AG to a small elongated yellowish finely granulated HG; MG and AG relatively large, folded, soft white tissue; SV embedded on left side of AG, AG larger than HG, sides match curvature of inner foot wall at right posterior quarter of coelom.

Spermatophore ( Figs 75F, H View FIGURE 75 ). Relatively long (length 12.7 ± 4.4 mm, AL = 9 mm, n = 2), test thin, translucent, over half-length comprises a translucent cylindrical head section (~ 64% of SPM length), lip bluntly rounded, containing a white gelatinous thread-like core; tapers into a filamentous transparent flagellum; head section longer and much thicker than flagellum (head length = 7.9 ± 0.4 mm, head width = 78 ± 12 μm, flagellum width = 14 ± 4 μm, n = 2), both sections smooth, featureless; SPM tightly coiled, embedded in red-brown gelatinous mass [SK102, SK414].

Comparative remarks. In our mitochondrial phylogeny ( Figs 1 View FIGURE 1 , 3 View FIGURE 3 ), S. tanguissonensis sp. nov. ( plicata group, unit 59) is the sister species of S. lirata (unit 58) also from Guam. Both species differ by COI distances of ≥ 11.6% (Table S7).

We found S. tanguissonensis sp. nov. in sympatry with three congeners on Guam: For comparative remarks see under S. guamensis , S. lirata , and S. normalis , respectively.

The shell sculpture and ribbing in S. tanguissonensis sp. nov. is coarser and more raised than in the former species. The rayed colouration of the internal shell lip in S. tanguissonensis sp. nov. resembles that of S. normalis , S. guamensis (darker), and S. lirata (paler, finer).

Distribution and habitat. Recorded only from northern Guam ( Fig. 73 View FIGURE 73 ). In this study, found in sheltered positions on moderately exposed rocky shores, at upper littoral level ( Fig. 74N View FIGURE 74 ).

Etymology. For the type, of Tanguisson Beach, Guam.