Patelloidea, Rafinesque, 1815

Simone, Luiz Ricardo L., 2024, New species, misidentifications and problematic taxonomy of some Atlantic South American marine mollusks: a review, Papéis Avulsos de Zoologia 64, pp. 1-104 : 3-6

Superfamily Patelloidea Family Nacellidae

Genus Nacella Schumacher, 1817

Nacella mirim new species ( Figs. 2 A-O, 3D) https://zoobank.org/ 40815F89-F6F6-467D-AE98-0EB62AE4712E

Types: Holotype MZSP 165666 . Paratypes:MZSP 100736, 5 spm,MZSP 100903,13 spm,MZSP 100916,5 spm,MZSP 100718, 10 spm, all from type locality. BRAZIL. Espírito

Santo; Guarapari, Praia do Morro , 20°39′42″S 40°29′41″W, MZSP 165667 , 3 shells [Simone col., 15.i.1982] .

Type locality: BRAZIL. Bahia ; Cairu, Praia de Garapuá ( Morro de São Paulo), 13°29′32″S 38°54′21″W [Petronio Alves Coelho-Filho col., Petrobras, 2011] .

Diagnosis: E Brazilian species with up to ~ 5 mm, generally pigmented with a slight large white X-spot; edge with intercalated white and brown bands. Aped dislocat- ed anteriorly. Presence of eyes.

Description: Shell up to 5 mm, elliptic (~1.3 times longer than wide), conic (4-2.5 times longer than tall); anterior and posterior edges similar-sized ( Fig. 2A, D, K, L ). Walls thin, slightly translucent. Color beige to light brown, in base, with large white X-image more ( Fig. 2K, L ) or less ( Fig. 2A, D ) nitid in different specimens, plus intercalated brown and white bands near edges ( Fig. 2B, H, L ). Apex rounded, central slightly dislocated anteriorly ( Fig. 2C, J ). Protoconch not seen (eroded). Profile with angle 100-110°, anterior and posterior surfaces varying from planar to weakly convex. Outer surface only possessing growth lines and very weak concentric undulations, no other additional sculpture. Shell edges slightly concave laterally ( Fig. 2C, J ). Internal surface glossy ( Fig. 2D, L ), muscle scars not visible.

Snout large ( Fig. 1E, M : sn), with ~ ⅓ of head-foot size. Foot (ft) plane, sole concave, edges simple, 2-3 times wider than snout. Pair of cephalic tentacles located in lateral side of snout ( Fig. 2B, E, G, H, I , M-O: te), possessing small dark eye in outer base (ey), lacking ommatophore. Mantle edge (mb) thick, colorless; possessing ~20 small papillae (mp), equidistantly distributed along its ventral surface,their base located in inner region, tapering externally. Shell muscle (sm) horseshoe-shaped,narrow,sightly broader anteriorly. Pallial cavity (py) shallow, restricted only to head region; lacking gill or any other structure. Visceral mass fulfilled by yellowish gonad and digestive gland, and several intestinal, narrow loops, with final region fulfilled by white matter ( Fig. 2F, N : in). Radular sac ( Fig. 2N ) relatively rigid, with docoglossan radula.

Etymology: The specific epithet is a Latinization from native Tupi-Guarani language word mirim , meaning little, an allusion to the small size of the species.

Distribution: Coasts of Alagoas to Espírito Santo.

Habitat: From intertidal up to ~ 10 m, usually found sorting sediment.

Measurements (L, W, H in mm): Holotype MZSP 165666 ( Fig. 1 A-D): 2.2 by 1.7 by 0.9. Paratype: MZSP 100718, 2.1 by 1.5 by 0.5.

Additional material examined: BRAZIL. Alagoas; Japaratinga (F. Hartmann col.), off Bitingui, 09°07′05.53″S

35°15′45.82″W, 5 m, MZSP 166753 , 2 shells, off Praia do Salgado , 09°05′53.63″S 35°13′48.08″W, 10 m, MZSP 166754 , 30 shells. Bahia ; Cairu, Praia de Garapuá ( Morro de São Paulo), 13°29′32″S 38°54′21″W, MZSP 100717 , 2 spm, MZSP 100719 , 1 spm, MZSP 100732 , 1 spm, MZSP 100734 , 1 spm, MZSP 100775 , 1 spm, MZSP 100815 , 2 spm, MZSP 100833 , 2 spm, MZSP 100849 , 2 spm, MZSP 100901 , 2 spm, MZSP 100904 , 1 spm, MZSP 100908 , 1 spm, MZSP 100933 , 8 spm, MZSP 101290 , 3 spm, MZSP 101292 , 1 spm ; MZSP 101303 , 3 spm [Petronio Alves Coelho-Filho col., Petrobras, 2011] ; Abrolhos, Recife de Sebastião Gomes , 17°58′03″S 38°42′13″W, 3-8 m (Ex coleÇão Vanin, IOUSP col., vii.2007.

Remarks: N. mirim is another species usually found identified as N. mytilina in collections, as well as Lottia leucopleura ( Gmelin,1791) , a species from the Caribbean. The minuteness of N. mirim , i.e., up to 5 mm, easily distinguishes it from both species,which possibly do not occur in Brazilian coast.A set of anatomical features,such as absence of gill in pallial cavity ( Fig. 2B, E, F, H, M, N ), the absence of secondary gill surrounding the foot ( Fig. 2G, O ), the papillae in the mantle edge ( Fig. 2E, M : mp), and the docoglossate radula ( Fig. 2N : ra), indicate the generic attribution of the species. The presence of eyes is an extraordinary discover. The presence of cephalic eyes is something practically absent in patellogastropods ( Simone, 2011, 2023), its presence in N. mirim , associat- ed to the small size, are indicative of a neotenic origin of this species. The disparity of size and shell features of N. mirim with other species can be detected in Fig. 3D . It differs from N. mytilina ( Fig. 3 A-B) by the size, in having a non-subterminal apex,and in not being monochromatic. It differs from L. leucopleura ( Fig. 3E ) also by the size, in having a lighter, thin walled, less colorful shell, and by the apex dislocated anteriorly ( Fig. 2C, J ), instead of posteriorly.

Figures

Figure 1.Tecturaiguypisshells of typespecimens:(A-D)Holotype 165600(L 2.6mm);(A)right-slightly ventral view;(B)dorsal view;(C) ventral view;(D)rightview; (E-F) Paratype MZSP 165664 (L 3.1 mm),dorsal and left views.

Figure 2. Nacella mirim shells and anatomy of type specimens:(A-G) Holotype 165666 (L 2.2 mm); (A) dorsal view; (B) whole ventral view;(C) left-slightly ventral view;(D) shell,ventral view;(E) extracted specimen,ventral view; (F) same, dorsal view;(G) same,right view;(H-O) paratype MZSP 100718(L 2.1 mm);(H) whole ventral view; (I) right-ventral view; (J) right view; (K) dorsal view; (L) shell, ventral-inner view; (M) extracted specimen, ventral specimen; (N) same, dorsal view, first layer of glandsand intestinal loopsremoved toexpose radularsac;(O) same,right view,pallial cavity removed.Scales:= 0.5mm.Lettering:an,anus;ey,eye;ft, foot sole;in, intestinal loop; mb:mantle border;mo,mouth;mp,mantle papillae;py,pallial cavity;ra, radurar sac;sm,shell muscle;sn snout;te, cephalic tentacle.

Figure 3. Confrontation among shells of Tectura iguypis, Nacella mirim, N. mytilina, and Lottia leucopleura in a same scale:(A) N. mytilina, MZSP 8587 from Santa Cruz,Argentina;(B)same,MZSP 155805Tierradel Fuego,Argentina;(C) T.iguypis, holotype;(D)N.mirim,holotype;(E) L.leucopleura, MZSP162468fromW Jeremie, Haiti.Scale:= 10 mm.