New species, misidentifications and problematic taxonomy of some Atlantic South American marine mollusks: a review Author Simone, Luiz Ricardo L. text Papéis Avulsos de Zoologia 2024 2024-08-09 64 1 104 https://doi.org/10.11606/1807-0205/2024.64.031 journal article 10.11606/1807-0205/2024.64.031 1807-0205 14705562 Order Mytilida Superfamily Mytiloidea Family Mytilidae Genus Brachidontes Swainson, 1840 Brachidontes ynous new species ( Figs. 49-50 ) https://zoobank.org/ AE6AA3AF-E95F-4664-B185-10EF4FC6BC4B Types: Holotype MZSP 165671 . Paratypes : MZSP 105355 , 40 spm from type locality. BRAZIL . Espírito Santo ; Trindade Island (ProTrindade Project),Farrilhões, 20°31′22.4″S 28°19′52″W , MZSP 109572 , 25 spm ( 02.vi.2012 ), Tartarugas , 20°31′01.3″S 29°17′56.9″W , MZSP 115081 , 7 spm ( Abbate col., 2013), Enseada da Cachoeira , 20°30′57.1″S 29°20′15.2″W , MZSP 108114 , 3 spm ( J. MendonÇa col., 2012), Ponta do TÚnel, 20°31′36.8″S 29°18′14.3″W , MZSP 109914 , 3 spm ( J. MendonÇa col., 2012) . Type locality: BRAZIL . Espírito Santo ; Trindade Island , Enseada do Lixo , 20°31′43.5′S 29°19′28.1″W [ 17.ii.2012 ] . Diagnosis: Endemic species from Trindade Oceanic Island, living subtidal, isolated. Shell smaller than 10 mm . Color mostly light. Sculptured by relatively uniform, delicate, numerous radial cords. Hinge with 4 teeth anterior to ligament, 12-15 taxodont-like teeth posterior to ligament. Description: Shell up to 10 mm , outline rather trapezoid-mytiliform. Anterior region 2-3 times smaller than posterior region; ~1.5 times longer than heigh; ~2 ( Fig. 49F ) to ~1.3 ( Fig. 50E, K ) times longer than wide. Color beige to light brown ( Figs. 49B, G, F , 50A, B, F ), with some few reddish ( Fig. 50L, M ) and brownish specimens ( Fig. 50D, E ). Umbones weakly protruded, subterminal, anterior.Sculpture relatively uniform,narrow,numerous, radial cords; located close from each other (interspaces smooth, ~ ⅓ of cords width); from umbo up to posteri- or, ventral and anterior edges, forming weak crenulate borders ( Figs. 49A, H , 50G, H ); cords slightly wide in some specimens, ~40 per valve ( Fig. 49B, G ), up to very narrow, ~60 per valve ( Fig. 50F ); cords rarely dichotomic, except for those located in strip between umbo and corner of ventral-posterior edges ( Figs. 49B , 50B, D, L ). Anterior edge narrowly rounded, sometimes as beak anterior to umbo ( Fig. 50 F-H, J), sometimes as soft- er slope ( Figs. 49A, B, G, H , 50A, B, D, L ); dorsal edge straight; posterior edge amply rounded; ventral edge straight ( Figs. 49A, B, G, H , 50A, B, D ) to weakly convex ( Fig. 50F, G, H, L ). Inner surface glossy, translucent. Hinge with ligament occupying ~ ⅓ of its length, from umbo beak towards posterior ( Fig. 49A, D, H, J, G, H ); set of 4 teeth located anterior to ligament, weakly oblique, slightly uniform, except for more posterior tooth, being larger in right valve ( Figs. 49C , 50J ), and very oblique in left valve ( Figs. 49I , 50I ); set of 12-15 aligned, taxodont-like teeth posterior to ligament, being anterior teeth slightly smaller than posterior teeth ( Figs. 49D, J , 50G, H ). Scars of adductor muscles very weak; scar of anterior adductor muscle antero-posteriorly elongated, located in ventral region of anterior edge ( Figs. 49A, H, J , 50G, H, I ), with ~¹/₃₀ of inner valve area; scar of posterior adductor muscle united to that of pair of posterior retractor muscles of foot, located from posterior region of umbonal cavity up to posterior region of hinge, both occupying ~¹/₁₀ of inner valve area. Pallial line simple. Mantle lobes (ml) translucent, except for middle and dorsal regions, fulfilled by whitish gonad ( Fig. 49L : go). Mantle edges (mb) relatively thick, unpigmented; fusion between both lobes only between incurrent (ih) and excurrent (ex) canals ( Fig. 49M : un); both canals lacking siphons or papillae, only simple edges ( Fig. 49M ). Gill (gi) very large, almost as large as pallial cavity; inner (id) and outer (od) demibranchs of equal length and width ( Fig. 49K, L ). Foot very small, peduncle-like ( Fig. 49K : ft). Anterior adductor muscle from flattened to elliptic in section ( Fig. 49K, L : aa), located in antero-ventral region. Posterior adductor muscle large, located as posterior end of visceral mass ( Fig. 49 K-M: ap). Pair of anterior retractor muscles of foot ( Fig. 49K : ar) narrow, long, ~ ⅓ of visceral mass length, running from foot base up to umbonal cavity, flanking ventral surface of local visceral mass. Pair of posterior retractor muscle ( Fig. 49K : rr) with insertion as large as anterior adductor muscle, just anterior to it. Strong cruciform-like pallial muscle ( Fig. 49M : pm) in region between incurrent and excurrent muscle. Figure 49. Brachidontes ynous Holotype MZSP 168671, shell and anatomy. (A) left valve, inner view (L 8.4 mm); (B) same, outer view; (C) same, detail of hinge; (D) same, detail of dorsal edge; (E) whole anterior view (W 4.8 mm); (F) whole dorsal view; (G) right valve, outer view; (H) same, inner view; (I) same, detail of hinge;(J)same,detail of dorsal edge;(K) holotype extracted specimen,right view,right mantle lobe,gill,and posterior region of mantle removed;(L-M) soft parts of paratype 109572#1,just removed from shell,left and posterior views.Scales:=0.5 mm.Lettering:ap,posterior adductor muscle;ar,anteriror foot retractor muscle; ex, excurrent aperture; ft, foot;id, inner demibranch;ih, incurrent aperture;gi, gill; go,gonad (in mantle lobe);ml, mantle lobe; od, outer demibranch;pm, pallial muscles;rr,posterior retractor muscle of foot;un,mantle fusion separating apertures;vm,visceral mass. Etymology: The specific epithet is a Latinization of the native Guarani word yno′õ, meaning island, or insular, an allusion to the endemism of the species to the Trindade oceanic island. Distribution: Endemic from Trindade Island. Habitat: Under rocks, from intertidal up to ~ 16 m . Shell usually covered by incrustations, rare specimens with valves exposed. Measurements (respectively L, H in mm): Holotype ( Fig. 49 A-J): 8.4 by 5.5. Paratypes : MZSP 105355#1 ( Fig. 50 A-C): 8.3 by 5.5; MZSP 105355#2 ( Fig. 50 D-E): 6.3 by 4.4; MZSP 109572#1 ( Fig. 50 F-K): 7.6 by 6.2; MZSP 109572#2 ( Fig. 50 L-M): 7.6 by 5.6. Additional material examined: BRAZIL . Espírito Santo ; Trindade Island ( ProTrindade Project ), Andradas , 20°30′50″S 29°18′20″W , MZSP 101235 , 3 spm ( J. MendonÇa col., 24.vii.2011 ) ; Farrilhões , 20°31′28.9″S 29°19′34.8″W , MZSP 104352 , 2 spm ( Abbate col., 16.ii.2012 ), MZSP 104445 , 1 spm ( Abbate col., 31.i.2012 ), MZSP 104419 , 3 spm ( Abbate col., 21.ii.2012 ), Enseada do Lixo ,20°31′43.5′S 29°19′28.1″W , MZSP 105356 , 6 spm ( 17. ii.2012 ), MZSP 105376 , 25 spm ( 21.ii.2012 ), MZSP 108238 , 1 spm, Ilha da Racha , 20°30′26.5″S 29°20′48″W , MZSP 108108 , 5 spm, Calheta , 20°30′26.1″S 29°18′44.2″W , MZSP 108122 , 12 spm, 20°30′37.6″S , 29°18′28.1″W , MZSP 109617 , 3 spm ( 12.vi.2012 ), 20°30′18.72″S 29°18′31.67″W , 16.7 m , MZSP 162509 , 1 spm ( 24.v.2022 ), MZSP 121639 , 7 spm ( 26.x.2014 ), Ponta do Nordeste , 20°29′46.4″S 29°20′35.4″W , MZSP108136 , 4 spm,Parcel dasTartarugas, 20°31′01.3″S 29°17′56.9″W , MZSP 108398 , 13 spm ( 11. vii.2012 ), Enseada do Meio , 20°29′32.3″S 29°20′32.6″W , MZSP 108409 , 9 spm, Ponta do TÚnel, 20°31′36.9″S 29°18′14.3″W , MZSP 108533 , 2 spm ( 19.vi.2012 ), Ponta Norte, 20°29′18.7″S 29°20′18.3″W , MZSP 162608 , 5 spm, MZSP 162499 , 6 spm ( 26.v.2022 ), Praia do Noroeste , 20°29′46.4″S 29°20′35.4″W , MZSP 162607 , 7 spm, MZSP 162580 , 8 spm ( 28.xi.2017 ), MZSP 162595 , 2 spm (06. viii, 2018), 9 m , MZSP 162538 , 15 spm ( 30.vii.2018 ), Orelhas, 20°29′40.2″S 29°20′32.9″W , MZSP 162597 , 1 spm ( 07.viii.2018 ), MZSP 121604 , 5 spm ( 01.xi.2014 ), MZSP 162592 , 8 spm ( 06.xii.2017 ), 9 m , MZSP 162529 , 1 spm ( 08. viii.2018 ) ; Martin Vaz Island , 20°31′36.9″S 29°18′14.3″W , MZSP 108429 , 3 spm ( 30.vi.2012 ) . Figure 50. Brachidontes ynous paratypes shell.(A-C) MZSP 105355#1 (L 8.3 mm), left valve outer view,right valve outer view, and whole dorsal view;(D-E) MZSP 105355#2 (L 6.3 mm), right valve outer view and whole dorsal view; (F-K) MZSP 109572#1 (L 7.6 mm); (F) right valve, outer view; (G) same, inner view; (H) left valve,inner view;(I) right valve,detail of hinge;(J) same for left valve;(K) whole dorsal view;(L-M) MZSP 109572#2 (L 7.6 mm), left valve outer view,whole dorsal view.Scales:= 1 mm. Remarks: Despite the Brachidontes that occur in Brazilian coast are far in being taxonomically well-known, the morphology, conchology and lifestyle of B. ynous are sufficiently different to be convincing that it is a new species. It appears to be endemic of Trindade oceanic island, a very remote place, ~ 2,000 km off the coast of Espírito Santo . It is the only species that does not occur in aggregates, i.e., it does not make colonies covering rocks like other local species do. On contrary, it is usually found isolated, on the hidden surface of the rocks. Also, it differently occurs much deeper, up to ~ 15 m , while the other congener species are intertidal. Three species of Brachidontes are reported to Brazilian coast ( Rios, 2009 ), but mostly possibly they are all misidentifications (personal observation), two of Caribbean species [ B. exustus ( Linné, 1758 ) and B.solisianus (d′Orbigny, 1842) (presently in the genus Mytilaster Monterosato, 1884 )], and one of an Argentinian species [ B. rodriguezii (d′Orbigny, 1842) ]. Sometimes, the Argentinian B. darwinianus (d′Orbigny, 1842) is also reported to Brazil ( e.g., Rios, 1975 ). All these species have some synonyms, but only 2 have type locality in Brazil [ Mytilus exiguus Dunker, 1875 – Santa Catarina; and M. janeirensis Dunker, 1866 – Rio de Janeiro ], both considered synonym of M. solisianus . From these species, the only one that have the richness of teeth in the hinge is B. exustus (Simone et al., 2015: figs. 55-58), as well as the Caribbean B. modiolus ( Linné, 1767 ) , a very similar species. Brachidontes ynous differs from these two species in being much smaller (they easily reach 30 mm , while B. ynous rarely reach 10 mm ), by more rounded outline (they are much more elongated), in lacking yellow pigment, in having the radial sculpture much more dense (while the sculpture of those species have wid- er interspaces), and by the anterior set of teeth being curved, instead of forming a straight platform with 1-2 more teeth, projected beyond the umbonal level. The other species lack these teeth or have them much less developed; additionally, they are dark-brown pigment- ed, with coarser sculpture.