Yoldiella haimaensis, Gao & Tang & Zhang, 2024

Gao, Qi, Tang, Yan & Zhang, Junlong, 2024, A new species of the genus Yoldiella (Bivalvia, Protobranchia, Yoldiidae) from Haima Cold Seep, South China Sea, China, ZooKeys 1204, pp. 223-240 : 223-240

Yoldiella haimaensis sp. nov.

Figs 2 , 3 , 4

Malletia sp.: Dong et al. 2021: 4, fig. 5 b; Ke et al. 2022: 4, fig. 2 h.

Yoldiella sp.: He et al. 2023: 6, fig. 2 Q.

Type specimens.

Holotype: MBM 229041 : length 7.5 mm, width 3.2, height 5.1 mm . Paratypes: MBM 229042 : length 7.4 mm, width 3.3 mm, height 5.0 mm ; MBM 229043 : length 6.5 mm, width 2.6 mm, height 4.4 mm ; MBM 229044 : length 6.3 mm, width 2.5 mm, height 4.1 mm ; MBM 229045 : length 7.6 mm, width 3.0 mm, height 4.9 mm .

Type locality.

Haima Cold Seep (depth 1390 m, 16 ° 43.00 ' N, 110 ° 28.00 ' E), off southern Hainan Island, South China Sea.

Diagnosis.

Yoldiella haimaensis sp. nov. differs morphologically from other known species within the genus in shell shape, degree of inflation, beaks, and number of hinge teeth. Diagnostic characteristics: shell small, ovate, inflated medially. Posterior end slight produced. Resilifer triangular, projecting. Beak rather lower than other species, suborthogyrate, and easily worn. Hinge plate narrow; posterior hinge plate smaller than anterior one, with taxodont teeth in two series; 17–19 anterior and 15–16 posterior teeth on hinge plate.

Description.

Shell small, elongate, ovate in outline, moderately inflated, opaque, fragile, 2.2–8.2 mm long, W / L about 0.40; H / L about 0.66, usually subequivalve, inequilateral. Shell surface smooth, with numerous very fine, regular, and nearly isometric growth lines, without radial stria. Periostracum light brown and flaky. Umbo slightly posterior to middle, low, large, obscure, opisthogyrate, and easily worn. Antero-dorsal margin convex; anterior end broadly rounded, merging smoothly to ventral margin. Ventral margin slightly convex, with very shallow sinus at postero-ventral corner. Postero-dorsal margin oblique and then convex, descending to blunt posterior margin. Posterior end slight produced. Escutcheon and lunule obscure. ligament amphidetic, thin, short.

Internal surface porcelaneous white. Hinge plate moderately broad, narrow below umbo, moderately long, and rather strong, with two chevron-shaped columns and moderately sized taxodont lateral teeth, about 17–19 anterior teeth, about 15–16 posterior teeth, interrupted by a triangular, projecting resilifer, and not extend beyond the inner limit of adductor muscles. Angle of about 140 ° between anterior and posterior hinge plates. Posterior hinge plate usually smaller than anterior. Resilium oblique and often obscure in dry preserved specimens. Adductor scar obscure to evident; triangular anterior adductor scar larger than droplet-shaped posterior adductor scar. Pallial sinus obsolete; pallial line usually entire.

Mantle large, thin, and opaque; anterior adductor crescent-shaped, twice or three times size of posterior. Ctenidium structure simple and lamellar, at posterior side parallel to the postero-dorsal shell margin. Labial palp size moderate, consisting of flat, paired lamellae on each side, with appendages of elongated palp proboscis. Foot muscular and large, with a regular series of nearly rectangular protrusions at margins, partially covered by labial palp. Siphons combined posteriorly.

Etymology.

The species epithet “ haimaensis ” is Latin and means “ from Haima ”, which refers to the name of the cold seep where the specimens were collected.

Distribution.

Currently known only from the Haima Cold Seep on the northwestern slope of the South China Sea.

Remarks.

Yoldiella haimaensis sp. nov. differs morphologically from other known species of Yoldiella in its shell shape, degree of inflation, beak characteristics, and number of hinge teeth. Its beaks are lower than those of other species, suborthogyrate, and prone to wearing easily. This new species resembles the type species of Yoldiella , Y. lucida . However, Y. haimaensis sp. nov. differs from Y. lucida in having lower, suborthogyrate beaks that wear easily and a slightly rounded posterior end. Yoldiella haimaensis sp. nov. has more teeth (17–19 anterior teeth, 15–16 posterior teeth) than Y. lucida (8 teeth on each end), with more anterior teeth than posterior teeth. Another species closely resembling Y. haimaensis sp. nov. in outline is Yoldiella sagamiana T. Okutani & K. Fujikura, 2022 from Sagami Bay, but Y. sagamiana has a larger W / L ratio and fewer teeth (15 anterior teeth, 10 posterior teeth) than the new species, and Y. sagamiana also has more pointed beaks and finer commarginal cords and lines. The outline of the new species is similar to Yoldiella biguttata Allen, H. L. Sanders & F. Hannah, 1995 from the Guyana Basin, but Y. biguttata has the more prominent umbo and the anterior and posterior series are either equal or with the anterior series having one additional tooth (5–6 in the largest specimen).

Figures

Figure 2. Yoldiella haimaensis sp. nov. A – D holotype, MBM 229041. Scale bar: 2 mm (all at the same scale).

Figure 3. Yoldiella haimaensis sp. nov. A – D paratype 1, MBM 229042 E – H paratype 2, MBM 229043 I paratype 3, MBM 229044 J paratype 4 MBM 229045. Scale bar: 2 mm (all at the same scale).

Figure 4. Anatomy features of Yoldiella haimaensis sp. nov. aa, anterior adductor; c, ctenidium; f, foot; lp, labial palp; m, mantle; pa, posterior adductor; pp, Palp proboscis; dg, digestive gland. Scale bar: 2 mm.