Adapedonta, Cossmann & Peyrot, 1909

Order Adapedonta View in CoL Superfamily Hiatelloidea

Family Hiatellidae Genus Hiatella Bosc, 1801

Hiatella marisqueira new species ( Figs. 60-61 View Figure 60 View Figure 61 ) https://zoobank.org/ 37E1F27B-9C6E-43A2-9698-020852D76AE9

Saxicava arctica : Morretes, 1949: 47 (non Linné, 1767). Saxicava solida : Morretes,1949:47 (non Sowerby I, 1834). Hiatella solida View in CoL : Rios, 1970: 210; Narchi, 1973: 332-337

(figs. 1-7) (non Sowerby I, 1834). Hiatella arctica View in CoL : Rios,1975:253 (pl. 80,fig. 1212),1985:272

(pl. 95, fig. 1339), 1994: 294 (pl. 100, fig. 1432),

2009: 589 (fig. 1627) (non Linné, 1767). Hiatella cf. solida : Passos et al., 2024: 46.

Types: Holotype MZSP 166300 View Materials . Paratypes: MZSP 28813 View Materials , 4 View Materials spm from type locality. BRAZIL. São Paulo ; Ilhabela, Praia do Gato , 23°50′37.36″S 45°16′50.3″W (vii.1936). Paraná GoogleMaps ; Paranaguá, Ilha do Mel, Praia do Farol , 25°32′19.15″S 48°17′30.41″W, MZSP 20120 View Materials , 16 View Materials shells (Morretes col., 15.iv.1933) GoogleMaps .

Type locality: BRAZIL. São Paulo ; São Vicente, Ilha Porchat , 23°58′47.96″S 46°22′21.8″W, intertidal [O. Domaneschi col., vi.1993] GoogleMaps .

Diagnosis: SE-S Brazilian species living usually associat- ed to other intertidal invertebrates. Shell of rather rectangular outline, up to ~ 15 mm; lacking posterior carina. Muscle shell scars, both adductor muscles and foot retractor muscles proportionally large. Palps wide. Stomach lacking muscular belt. Intestine intensely coiled. Pair of siphons mostly separated from each other, with single line of terminal papillae.

Description: Shell variable, rather moldable, usually twice longer than wide, twice longer than height; outline slightly rectangular. Color white, with light beige periostracum, usually eroded in umbonal region ( Figs. 60A, B View Figure 60 , 61G, H View Figure 61 ), exceeding shell borders, mainly in posterior edges ( Fig. 61J, K View Figure 61 : pe). Umbones broad, occupying ~¼ of dorsal surface, slightly prominent; from terminal ( Figs. 60 View Figure 60 J-N, 61A-E) to subterminal ( Fig. 60 View Figure 60 A-E). Valves symmetric ( Figs. 60L View Figure 60 , 61C View Figure 61 ) to slightly asymmetric ( Figs. 60C View Figure 60 , 61H, I View Figure 61 ). Surface matte; sculpture lacking, except for growth lines and strong concentric undulations ( Fig. 60 View Figure 60 A-B, J-K); in some few specimens with weak oblique carina present between ventral and posterior slope ( Fig. 61 View Figure 61 A-B). Anterior and posterior regions round- ed, similar-sized or with posterior region slightly larger; dorsal edge usually straight; ventral edge from convex ( Fig. 60 View Figure 60 D-E) up to slightly concave ( Fig. 61 View Figure 61 D-E). Inner surface glossy, pure white, weakly iridescent. Muscular scars shallow ( Fig. 61 View Figure 61 D-E); scar of anterior adductor muscle slightly rectangular, located in ventro-anterior corner, occupying ~¹/₁₅ of inner surface; scar of posterior adductor muscle rounded, slightly larger than anterior muscle, located between middle and posterior thirds of dorsal shell edge; scar of posterior foot retractor muscle located adjacent to posterior adductor, slightly anterior and dorsal to it, rather triangular, with ~75% of posterior adductor scar size; other scar, including pallial line, not detectable. Hinge only of cardinal teeth ( Fig. 60 View Figure 60 F-I, L, O); left valve with small anterior, flattened cardinal teeth, corresponding to anterior socket in right valve; right valve with broad, slightly bifid posterior teeth, posteriorly interlocking with anterior teeth, and fitting in socket of left valve. Ligament occupying about double length as hinge, located posterior to hinge, protruding outside posterior to umbo ( Figs. 60C, H, I View Figure 60 , 61H View Figure 61 ).

Anatomical details in Narchi (1973, as H. solida ). Complement ( Fig. 61 View Figure 61 J-K): foot (ft) small, strongly attached to byssus fibers (by) in its ventral furrow. Mantle edge (mb) mostly fused between both lobes (un), only small gap present (fg) for foot and byssus access. Pair of siphons more than 50% separated from each other; incurrent siphon (ih) slightly broader and longer than excurrent siphon (ex); tip rounded, simple, with row of papillae in edge. Outer region of siphons protected by periostracum (pe). Anterior adductor muscle (aa) dislocated ventrally, close to ventral-anterior edge. Posterior adductor muscle (ap) slightly larger than anterior muscle, located between middle and posterior thirds of dorsal region. Pair of posterior foot retractor muscles (rr) strong, originated anterior to posterior adductor muscle, running almost vertically towards ventral, inserting in foot base, near byssus main insertion. Pair of anterior foot retractor muscles (ar) very narrow, originated in middle of anterior region, running directly towards posterior, inserting in same region of posterior retractor muscles.

Etymology: The specific epithet is derived from the Brazilian term marisqueira , meaning women that collect mussels.This is allusive to the habitat of some of the collected specimens, among the byssus of intertidal mussels.

Distribution: Rio de Janeiro to Rio Grande do Sul, Brazil.

Habitat: Intertidal, attached by byssus among mussels, usually Brachidontes spp. , Perna perna ( Linné, 1758) , as well as to ascidian Polyandrocarpa zorritensis (Van Name, 1931) and among tubes of the polychaete Phragmatopoma caudata KrØyer in Mörch, 1863 (both Narchi, 1973).

Measurements (L, H in mm): Holotype MZSP 166300 ( Fig.60 View Figure 60 A-I):12.4 by7.1. Paratype:MZSP28813 ( Fig.60 View Figure 60 J-O): 11.2 by 7.0; MZSP 14160 ( Fig. 61 View Figure 61 A-E): 12.1 by 6.5; MZSP 20120 ( Fig. 61 View Figure 61 F-I): 14.6 by 5.1.

Additional material examined: 132 additional lots in MZSP collection from Rio de Janeiro up to Rio Grande do Sul.

Remarks: Hiatella marisqueira has been identified as both H. solida and H. arctica . Both species are part of a complex of ~60 taxa considered synonymous with H. arctica (MolluscaBase, 2023) , occurring worldwide, from glacial up to tropical environments, from deep up to intertidal waters. Due to the wide plasticity of its shell, hard is to challenge this taxonomic insanity – a species exhibiting remarkable habitat tolerance, unknown dispersion patterns, and a wide range of forms and sizes. Focusing on what was referred to as H. arctica in SE Brazil up to N Argentina , a study started with samples collect- ed in the latter region, in relative deep water (Simone & Penchaszadeh, 2008). In that study was concluded that the north Argentinian deep-water population could be secluded from the H.arctica complex, as it brings an own set of anatomical characters. A formerly synonym was revalidated – H. meridionalis d′Orbigny, 1846 . The present paper refers to the neighbor population, occurring in SE Brazilian coast, up to Rio Grande do Sul. It occupies a distinct niche – intertidal, associated with some local invertebrates. As no one of the H. arctica complex taxa have type locality in SE Brazil, a new taxon was necessary to be introduced. The closest type locality is Santa Helena, of H. solida Sowerby I (1834: 88) , collected at 33 m depth. Most remaining species are from Northern Atlantic region ( H.arctica itself has"Oceano Norvegico" as type locality – Linné, 1767: 1113), or from Indo-Pacific.

Hiatellamarisqueira differsfrom H.meridionalis (Simone & Penchaszadeh,2008) in being slightly larger (12-15 mm) (while the other species rarely reaches 10 mm); in mostly lacking carina in shell posterior slope (almost always present in H.meridionalis ), and by the muscle scars much larger, proportionally about double than those of H.meridionalis . Anatomically, the differences in muscle size, as referred above in the shell, are evident in both adductors and foot retractors; H. marisqueira still lack developed such quantity of papillae in the siphons, as that of H. meridionalis . The palps are also proportionally larger in H. marisqueira , as well as the stomach lacks a muscular belt, and the intestine is much more intensely coiled in H. marisqueira ( Narchi, 1973) if compared to H. meridionalis .

An important feature of H. marisqueira , that looks exclusive if compared to all known Hiatella , including H.meridionalis (Simone & Penchaszadeh,2008) ,and what is known about H. arctica ( Hunter, 1949) is the conformation of the siphons. It has both siphons mostly separated from each other ( Fig. 61J, K View Figure 61 : ex, ih). The other species they are fused almost up to their tip, being a single large tube in an external view, and both incurrent and excurrent apertures are only distinguishable at tip of this tube.