Eoacmaeide Nakano and Ozawa, 2007

Nakano, Tomoyuki, Sasaki, Takenori, Kosuge, Takeharu & Chan, Benny K. K., 2021, Martesia fragilis Verrill and Bush 1898, Zoological Studies 60 (68), pp. 1-12 : 4-9

Family Eoacmaeide Nakano and Ozawa, 2007 Genus Eoacmaea Nakano and Ozawa, 2007 Type species Patella profunda Deshayes, 1863

Diagnosis: Light-colored shell medium and high in profile. Lateral teeth of radula typically equal size and shape. Habitats limited to limestome in high intertidal to splash zone.

0.05 substitutions/site

Fig. 2. Phylogenetic tree of Bayesian analysis based on the mitochondrial COI gene (658 bp). The numbers above each branch are Bayesian posterior probabilities/ NJ bootstrap/ MP bootstrap.

Eoacmaea nivea n. sp. ( Figs. 3–5 ) urn:lsid:zoobank.org:act:4F15A48A-538A-43D5-935B-F4DF30407758

Cellana mauritiana in part, not Pilsbry, 1892: Oyama and Takemura, 1959, Fig. Cellana (2). 1, 2.

Acmaeidae sp.: Takenouchi, 1993, Fig. 2C.

Patelloida sp. : Kosuge and Sasaki, 2002, Figs. 3A–I .

Eoacmaea sp. : Nakano, 2017, Fig. 9, Pl. 16

Material examined: Holotype, UMUT-RM28074 (Length 20.4 mm, width 16.5 mm, height 8.2 mm), Umahana-saki , Yonaguni Island, Japan . Paratype 1, UMUT-RM28705, Sanninu-dai, Yonaguni Island, Japan. Paratype 2, UMUT-RM28706, Umahana-saki, Yonaguni Island, Japan. Paratype 3, ASIZM0001712, Jialershui, Taiwan. Paratype 4, SMBL-V0595, Green Island, Taiwan. Paratype 5, SMBL-V0596, Green Island, Taiwan. Paratype 6, SMBL-V0597, Green Island, Taiwan.

Shell morphology

Shell ( Fig. 3 ) conical. thickened and oval in outline (width/length = 0.78–0.81). Apex located at the anterior 47–53% of shell length, and dorsally pointed as the highest point of shell. Exterior is sculptured by thin radial ribs, which are variable in thickness from evenly to differentially ribbed conditions. Ribs granulate at intersections with growth lines and fine commarginal sculpture. Shell exterior color is almost white except corroded apex in part of examined specimens (UMUT-RM28074). Margin of shell is roughened with minutely projected ends of radial ribs.

From lateral view, anterior and posterior slopes almost straight. Ventral margin apparently concaved, not planar.

From ventral view, shell interior smooth and lustrous. Shell muscle scar deeply impressed. Interior color white in the marginal area, and yellow to orange in inner area; depth and size of colored area variable among specimens; brown markings may be formed in apical area.

Anatomy

Mantle margin (mm: Fig. 4 A – C ) thick, circumpallial tentacles completely invisible in fixed specimens (may be retracted or tiny length). Foot muscular, well developed and stiffened. Pallial cavity (pc: Fig. 4A–C ) possesses a large ctenidium (ctn: Fig. 4D ) extending from posterior left to anterior right. A pair of small elongate osphradia attached on floor of pallial cavity. Attachment area of shell muscle (sm) U-shaped, and divided into bundles, more finely in posterior than in anterior.

Mouth (m: Fig. 5A ) surrounded by thick outer lip (oli) and laterally extended oral lappets (ola). Eyes (e: Fig. 5B ) exist at bases of cephalic tentacles (ct).

Head contains muscular buccal mass (bm). Radular sac (rds: Fig. 5B ) forms two loops; first loop (L1) on left posterior, second loop (L2) on right anterior. End of radular sac (ers) enlarged and bulbous behind the buccal mass.

Part of stomach (st: Fig. 4A, C ) and intestine (i) visible as pale lines on darker background color of digestive glands (dg) which on dorsal surface of the animal.

Pericardium (pd: Fig. 4A, C ) located on the left anterior side of limpet and with a single auricle (au: Fig. 4D ) and ventricle (vn). Right kidney (rk) discernible on the right side of the animal.

Radular morphology

The radular sac contains 75 rows of radular segments in paratype UMUT-RM28075 ( Fig. 6A–C ). Rows 1–66 have thickly mineralized orange-brown teeth, rows 67–70 are weakly mineralized, and rows 71–75 are organic and translucent. Each radula row consists of three pairs of lateral teeth and two pairs of marginal teeth. The first teeth are thickest among three pairs; cusps (L1c: Fig. 6D ) are almost in contact between the right and left teeth; posterior margins of their cusps blunt and roundly curved; shafts (L1s: Fig. 6D ) stout and short; bases concaved on inner side and broadly fused with second and third teeth on outer posterior side. Second lateral teeth (L2: Fig. 6D, E ) almost 50% of first teeth in width and about 55% in length; inner margins of bases are curved towards the midline of the radula. Third lateral teeth (L3) slightly wider than second teeth; bases are mostly hidden in the dorsal view, anterior sides are thinly extended along the first teeth. Posterior margins of cusps of second and third teeth blunt, rounded, and more strongly curved than those of first teeth; boundaries of cusps of second and third teeth discernible as distinct lines. Marginal teeth (M1, M2: Fig. 6F ) tightly overlapped; cusps curved backwards; shafts elongate; bases concealed by anterolateral corners of basal plates of the next row of the radula; inner marginal teeth slightly wider than outer teeth. Basal plates (bp: Fig. 6D ) tightly fused between right and left, considerably thickened, and wider than long (height/width = ca. 0.67); anterior margins weakly convex; anterolateral corners obliquely truncated and broadly extended laterally; posterolateral corners straight; posterior margins overlaid by next basal plates.

Distribution: The species is restricted to calcareous substrates in Yonaguni Island, Japan and eastern and southern Taiwan (note rock substrate in northern Taiwan is not calcareous).

Habitat: The species lives in crevices and hollows on vertical limestone faces on exposed shores in the high intertidal to supratidal zone. Although it does not occur in dense communities in Yonaguni Island, Japan and Jialershui, Taiwan, the species is abundant on Green Island and Orchid Island, southeastern Taiwan.

Etymology: The species name nivea is given for the white color of the shell.

Figures

Fig. 3. Shell morphology of Eoacmaea nivea n. sp. A–C, Holotype, UMUT-RM28704, Umahana-saki, Yonaguni Island, Japan; 20.4 × 16.5 × 8.2 mm. D–F, Paratype 1, UMUT-RM28705, Sanninu-dai, Yonaguni Island, Japan; 17.9 × 13.9 × 7.6 mm. G–I, Paratype 3, Jialershui, Taiwan; 11.8 mm × 10.1 mm × 4.9 mm.

Fig. 4. External view of animal. UMUT-RM28074.A, Dorsal view. B, Ventral view. C, Left lateral view. D, Enlarged view of ctenidium and adjacent organs, with mantle removed. Abbreviations: a, anus; acs, afferent ctenidial sinus; au, auricle; cpt, cephalic tentacle; ctn, ctenidium; dg, digestive gland; ecs, efferent ctenidial sinus; epc, end of pallial cavity; ft, foot; h, head; i, intestine; mm, mantle margin; pc, pallial cavity; pd, pericardium; ps, pedal sole; rk, right kidney; sm, shell muscle; st, stomach; vn, ventricle. Animal size: length = 15 mm, width = 12 mm.

Fig. 5. Ventral and internal view of animal. UMUT-RM28075. A, Ventral view of mouth region. B, Dorsal view of buccal mass and radular sac, with pallial and visceral organs removed. Abbreviations: bm, buccal mass; cpt, cephalic tentacle; e, eye; ers, end of radular sac; I, intestine; L1, first loop; L2, second loop; m, mouth; ola, oral lappet; oli, outer lip of mouth; rds, radular sac; sm, shell muscle. Size of buccal mass: length = 3.6 mm, width = 2.9 mm.

Fig. 6. Radula. A–C, Radular sac cut into three portions. The numbers 1 to 75 represent the first to 75th rows from the anterior. D–F, Scanning electron micrographs of radular teeth. D, Enlarged view of single radular segment. E, Second and third cusps of lateral teeth. F, Marginal teeth. Abbreviations: bm, basal membrane; bp, basal plate; L1c, cusp of first lateral tooth; L1s, shaft of first lateral tooth; L2, second lateral tooth; L3, third lateral tooth; M1, first marginal tooth; M2, second marginal tooth.