Cocculina delphinicula, Zhang & Zhang, 2018

Zhang, Shuqian & Zhang, Suping, 2018, Cocculina delphinicula sp. nov., a new cocculinid species from whale bone in the East China Sea (Gastropoda: Cocculiniformia), Zootaxa 4455 (1), pp. 189-195 : 191-193

Cocculina delphinicula sp. nov.

( Figs 2–4 )

Type material. Holotype: MBM 285103 (length 4.9 mm, width 3.8 mm), East China Sea, November 2017; Paratypes: MBM 285104, six specimens, collected with the holotype at the type locality, November 2017.

Six additional immature specimens were also observed.

Type locality. East China Sea, approximately 28°N 127°E, at depth of 300–400 m.

Etymology. The species is named after dolphin family Delphinidae because it was found living on a dolphin skull.

Diagnosis. Shell medium-sized, depressed, shell width 77%–81% of shell length, height 31%–36% of length. Shell surface sparsely pitted. Protoconch slightly posterior to center, with reticulate sculpture. Teleoconch sculptured with regularly spaced concentric growth lines and even finer radial threads. Aperture oval, longer than wider. Radula has a formula of (ca. 20)+5+1+5+(ca. 20), rachidian vestigial. Lateral 1 weak but well defined. Laterals 2 and 3 similar, overhanging tip with 3–4 cusps. Lateral 4 smaller and slender with a large primary cusp and an outer secondary cusp.

Description. Shell ( Fig. 2 ; Tab. 1) medium-sized for genus (maximum length 5.9 mm), thin, fragile, white, semi-transparent, periostracum not observed. Shell depressed, height of holotype 0.33 times length. Apex slightly posterior to center, situated at 56–62% of shell length from anterior end. Protoconch offset to left, deflected from longitudinal axis of adult teleoconch by up to 20°. Aperture oval, longer than wide (width/length ratio 0.77–0.81), anterior end slightly narrower than posterior end. Apertural margin not planar, shallowly concave from side to side. Anterior and posterior slopes faintly convex, lateral slopes at first slightly convex, then weakly concave.

Protoconch ( Figs 2E–H ) about 260 µm long and 145 µm wide, located slightly below the highest point of the shell. Tip of protoconch partly immersed in the posterior slope of the teleoconch. Protoconch surface sculptured with a reticulate pattern of flattened, broad ridges ( Figs 2E–F ). Surface between ridges of protoconch finely pitted ( Figs 2G–H ).

Teleoconch sculpture at first with regularly spaced concentric growth lines, then becoming coarser and stronger toward the aperture, crossed by even finer radial threads. The lines and threads producing waved nodules at intersections (see Figs 2C–D ). Shell surface sparsely pitted (see Fig 2F ).

Soft parts ( Fig. 3 ). Copulatory organ bifurcated, at tip of right oral lappet. Foot with rounded pedal sole. Posterior end of foot with a pair of epipodial tentacles. Detailed morphology of head area and dorsal side of animal (visceral mass) could not be observed due to poor preservation.

Radula ( Fig. 4 ) has a formula of (ca. 20)+5+1+5+(ca. 20). Rachidian vestigial, represented by a longitudinal ridge. Lateral teeth numbering 1–5 in each half row, lateral 1 weak but well defined, having an outline that frequently terminates in a small beaklike cusp. Laterals 2 and 3 similar to each other, with long, parallel-sided shafts, tip overhanging, with 3–4 cusps. Lateral 4 smaller and slender, with a large primary cusp and an outer secondary cusp. Lateral 5 transformed to a broad claw-like tooth, equipped with a large primary cusp and a smaller secondary cusp on either side, finely longitudinally striated on its posterior surface. Marginal teeth with long, laterally compressed shafts, tips overhanging, cutting edges weakly serrated at inner margins and strongly serrated at outer margins.

Remarks. Cocculina delphinicula sp. nov. is superficially similar to Cocculina alveolata Schepman, 1908 from Indonesia in shell size and sculpture. From that species, however, the new species differs in having a larger width/length ratio (0.77–0.81 vs. 0.72), a less convex anterior slope and a concave rather than elevated apertural margin. Moreover, Cocculina delphinicula sp. nov. can be separated from Cocculina alveolata Schepman, 1908 by having an outer secondary cusp on the first and fourth lateral teeth.

Five species from Japan, Cocculina japonica Dall, 1907 , Cocculina pacifica Kuroda & Habe, 1949 , Cocculina surugaensis Hasegawa, 1997 , Cocculina tenuitesta Hasegawa, 1997 and Cocculina tosaensis Kuroda & Habe, 1994 as well as two species from Taiwan, Cocculina japonica Dall, 1907 and Cocculina subcompressa Schepman, 1908 ( Wu & Lee 2005; Chen 2005), may represent the geographically closest congeners to Cocculina delphinicula sp. nov. Of those, Cocculina tenuitesta Hasegawa, 1997 resembles the new species in shell size. However, Cocculina delphinicula sp. nov. differs from this species in having a depressed shell with regularly spaced, concentric growth lines and finer radial threads, a sparsely pitted shell surface and a protoconch that has wavy ridges and numerous microscopic pits.

Figures

FIGURE 2. Shells of Cocculina delphinicula sp. nov. A. Dorsal, and B. lateral view of holotype, 4.9 mm, MBM285103, scale bar=10 mm; C, D. Microsculpture of shell near margin; E. Dorsal, and F. lateral view of protoconch; G, H. Microsculpture of protoconch.

FIGURE 3. Ventral view of soft part of Cocculina delphinicula sp. nov., holotype MBM285103. Abbreviations. (co) copulatory organ; (ept) epipodial tentacle; (flw) lateral wall of foot; (mm) mantle margin; (o) oral; (ol) oral lappet; (ps) pedal sole.

FIGURE 4. Radular of holotype of Cocculina delphinicula sp. nov., MBM285103. A. Dorsal view of intact radular segment; B. Enlargement of central region; C. Marginal portion, showing marginal teeth, scale bar=100 µm; D. Inner marginal teeth, scale bar=50 µm; E. Outer marginal teeth, scale bar=10 µm.