Microlinices, Simone, 2014

Simone, Luiz Ricardo L., 2014, Taxonomic study on the molluscs collected during the Marion-Dufresne expedition (MD 55) off SE Brazil: the Naticidae (Mollusca: Caenogastropoda), Zoosystema 36 (3), pp. 563-593 : 566-576

Genus Microlinices n. gen.

DIAGNOSIS. — Small size, c. 5 mm. Protoconch wide, of c. 1.5 whorl, smooth, simple.Surface simple, smooth, glossy, only with growth lines; sometimes with narrow shoulder. Colorless or with pale-brown pigmentation, no spots, mostly translucent.Callus narrow, restricted to upper half of inner lip; only partially covering upper region of umbilicus. Umbilicus open, varying from narrow to wide, central fold absent.Head-foot lacking eyes and pedal gland.Operculum horny, translucent, paucispiral.Opercular attachment with opercular scar simple, uniform.Osphradium with few, but well-developed filaments; somewhat peduncular, with base much narrower than middle filamentary region. Proboscis broad and short.Odontophore possessing only basic muscles. Esophageal gland very large, occupying c. 80% or more of haemocoel. Penis simple, lacking appendices, not retractile. Pleural and cerebral ganglia fused with each other. Living in bathyal deep-waters (c. 400-1500 m).

TYPE SPECIES. — Microlinices latiusculus n. sp.

LIST OF INCLUDED TAXA. — Type species ; Microlinices ibitingus n. gen., n. sp.; M. benthovus n. gen., n. sp.; M. ombratus n. gen., n. sp.; M. apiculus n. gen., n. sp.; M. gaiophanis n. gen., n. sp.

GENDER. — Masculine.

ETYMOLOGY. — The generic name is a contraction of the Greek word mikros, meaning small, little, with one of the most diverse genus of the family, Polinices Montfort, 1810 , normally used to accommodate the horny-operculated species.

TAXONOMIC DISCUSSION The small size, i.e. the adult specimens mostly with less than 5 mm, is one of the most distinctive characters of Microlinices n. gen., as normally the naticids are relatively medium to large snails, easily reaching 30-40 mm and more of shell length.However, some specimens of Microlinices benthovus n. gen., n. sp. may reach about 10 mm. Besides, the characteristic shell of Microlinices n. gen. is relatively simple, lacking sculpture, spots, etc. which are common in other naticid genera.The umbilicus is poorly covered by the callus, and it completely lacks a middle fold, which are found in most genera except the more basal ones, like Amauropsis Mörch, 1857 , and Lunatia Gray, 1847 ( Simone 2011) . Microlinices n. gen. differs from both genera by the already mentioned much smaller size, in lacking a well-developed periostracum, by its relatively thick shell walls, and in having a paucispiral protoconch. Microlinices n. gen. still differs from other simple-shelled genera, such as Pseudopolinices Golikov & Sirenko, 1983 , and Bulbus Brown, 1839 in being much smaller (species of those genera are over 15 mm), with thinner callus and by the lack of the umbilical central fold. No other naticid genera can be confused with Microlinices n. gen., as the juvenile specimens of other genera with equivalent size of Microlinices n. gen. usually have fewer shell whorls, up to three.

Despite the relatively poor anatomical knowledge on the naticids, most genera have been anatomically studied elsewhere ( Simone 2011), therefore, it is possible to infer that the set of anatomical characters reported in the Diagnosis is exclusive of Microlinices n. gen., warranting the generic separation.The considered most important feature is the peduncle-like and few-filamentary osphradium. This is an apomorphic feature never found in any naticid, and demonstrates that the genus is a monophyletic assemblage, instead of an artificial arrangement of minute, simple shelled, deep-water species.On the other hand, most anatomical features, mainly the short pleurembolic proboscis possessing an accessory boring organ, points to the naticid nature of the genus. Other inferences are given in phylogenetic analysis below.

The odontophore is relatively simplified, as only the so called basic muscles (sensu Simone 2011) are discernible. Some muscles that are found in other naticids, such as m7, m14, are absent in the species of Microlinices n. gen. so far studied; despite a pair of m7 that is found in M. benthovus n. gen., n. sp. ( Fig. 7G ).

Microlinices latiusculus n. gen., n. sp. ( Figs 1 A-K; 2A-H; 3A-E; 11D, E)

HOLOTYPE. — MNHN 27126 , 1 ♀.

PARATYPES. — MNHN 27127 , 14 shells, 2 ♂♂, 3 ♀♀ ; MZSP 105134 , 4 shells from type locality .

TYPE LOCALITY. — Brazil. Rio de Janeiro: off Arraial do Cabo, MD 55 sta. CB 104, 23°41’S, 42°06’W, 430-450 m, 01. VI.1987 (coll. Bouchet, Leal & Métivier).

DIAGNOSIS. — Shell c. 4 mm, c. 92% taller than wide. Umbilicus widely open, ¼ of upper area covered by callus, inner middle fold absent. Sculpture lacking, surface glossy, translucent white. Protoconch low, dome-shaped, of 1.5 whorls. Spire angle c. 120°.

DESCRIPTION

Shell ( Fig. 1 A-F)

Diameter of c. 4 mm; height c. 92% of width; general form globose-somewhat discoid. Color translucent white; thin periostracum pale brown in peri-umbilical area ( Fig. 1A , D-F). Protoconch simple, dome-shaped, of 1.5 flattened whorls ( Fig. 1C ); surface smooth, glossy; diameter c. 0.8 mm, occupying c. 18% of upper shell surface. Teleoconch of c. 2.0 whorls; suture well-marked by angle c. 135° ( Fig. 1B, E ); spire angle c. 120°. Sculpture absent except for growth lines and axial weak undulations; undulations slightly stronger in subsutural region ( Fig. 1D, E ). Aperture semicircular, narrow, occupying c. 70% of shell height and c. 43% of shell width; outer lip thick, prosocline weak ( Fig. 6D ), simple; inner lip slightly concave to almost straight ( Fig. 1A, D, E ), upper half covered by thick callus, lower half as thick edge ( Fig. 1A, D ). Umbilicus very widely open, lacking middle fold; c. ¼ covered by callus with straight-oblique, concave edge; its aperture occupying c. 21% of lower surface, possessing strong axial irregular undulations ( Fig. 1D ).

Head-foot ( Figs 2 A-C, F; 3D)

Head slightly protruded, pair of tentacles uniformly tapering up to pointed tip; eyes absent; tentacles separated from each other by distance c. 3 × tentacles width. Head as short flap uniting both tentacles ( Figs 2F ; 8D ). Rhinchostome in middle region of head ventral side; thick edged, accessory boring organ normally exposed inside. Foot broad, of c. 1/2 whorl ( Fig. 2A ); propodium from foot anterior edge up to flap covering head ventrally; mesopodium with thick edges, sole ( Fig. 2C ) simple, small notch preceding anterior edge. Opercular pad ( Fig. 2A, B [oa]) with thick edges, extending beyond mesopodium. Columellar muscle ( Fig. 2B [cm]) wide, of c. ¼ whorl. Haemocoel relatively small, occupying c. 20% of head-foot volume, mostly filled with foregut ( Fig. 2F ). Diaphragmatic septum thin, compressed by esophageal gland.

Operculum ( Fig. 1G, H )

Semi-circular, thin, corneous, flexible, occupying entire aperture. Nucleus in middle of inner to lower quadrant; spiral sculpture with 2 whorls, low, weakly visible; low undulations parallel to inner edge. Inner surface smooth, glossy; scar elliptical (twice wider than long), closer to inner edge, occupying c. 40% of inner surface ( Fig. 1H ).

Mantle organs ( Fig. 2D )

Pallial cavity triangular, of c. 1/3 whorl. Osphradium occupying c. ¼ of pallial hoof area; 14-16 filaments on right side, 10-12 on left side; anterior third slightly curved to left. Each osphradium filament relatively thick, its base narrower than middle portion, pro- jected outside, covering neighbor structures such as ctenidial vein. Gill slightly larger than osphradium; blunt anterior end, wider region between middle and posterior regions; each filament triangular, about as tall as wide, apex central. Ctenidial vein simple, narrow.Hypobranchial gland relatively thick, white, occupying area between gill and rectum. Rectum and genital structures running in left-ventral region, relatively narrow (possibly immature); anus simple, located between middle and anterior thirds of cavity.

Visceral mass ( Fig. 2D ) Of c. three whorls posterior to pallial cavity. Kidney and pericardium as anterior structures, kidney encroaching right-posterior region of pallial cavity; occupying c. 1/6 of visceral volume. Pericardium with c. 1/2 of kidney volume, located on opposed side, slightly more posteriorly. Digestive gland pale beige, occupying most of visceral volume. Gonad also pale beige, located in right and columellar side of each whorl posterior to kidney. Stomach narrow, located longitudinally c. 1/2 whorl posterior to pallial cavity.

Circulatory and excretory systems ( Fig. 2D ) Pericardium just posterior to gill posterior end, with small portion dorsal to gill. Auricle small and short, connected both to ctenidial vein and kidney anterior-left side. Ventricle with c. 1/2 of pericardium volume, rounded and simple. Aortas in postero-left side of ventricle; anterior aorta c. 3× wider than posterior aorta. Kidney mostly solid, white, dorsal and right regions entirely filled by solid lobe, ventral-left region narrowly hollow. Nephridial gland narrow, located between kidney and pericardium. Nephrostome as slit in left side of membrane between kidney and pallial cavity.

Digestive system ( Figs 2 D-H; 3A-C)

Pleurembolic proboscis ( Figs 2E ; 3D [pb]) short, occupying c. 1/8 of haemocoel length in retracted condition. Accessory boring organ rounded, located in apical proboscis region, in ventral side of mouth. Pair of retractor muscles in ventro-lateral region of proboscis base, originating in lateral-anterior region of haemocoel floor, running converging to medial region, inserting along ventral wall of proboscis. Buccal mass spherical c. 3 × larger than proboscis, protruding posteriorly beyond it in retracted condition. Pair of jaw plates ( Fig. 2G [jw]) large, thick, occupying most of dorsal surface of oral cavity; antero-medial edge serrated. Pair of dorsal folds of buccal cavity wide, running close to each other. Pair of salivary gland clustering posteriorly to nerve ring ( Fig. 2E [sg]); ducts very narrow, running through nerve ring attached to anterior esophagus; opening in anterior region of dorsal folds. Odontophore spherical ( Fig. 2E, G [od]), occupying same volume as proboscis.

Odontophore muscles ( Fig. 3 A-C)

mj. Pair of peri-buccal and jaw muscles, thick, originating in lateral and anterior surface of odontophore cartilages, running anteriorly splaying in oral tube.

m 1l. Two pairs of lateral protractor jugal muscles ( Fig. 3A, B ), one parallel to each other, originating in latero-ventral surface of proboscis, running towards dorsal, flanking odontophore lateral side c. 1/2 odontophore width, inserting superficially in latero-dorsal region of odontophore.

m2. Pair of thick retractor muscles of odontophore, originating in middle level of haemocoel ventral surface, part (c. 1/3) passing through nerve ring and part (c. 2/3) running ventrally to it ( Fig. 2E ), running towards anterior close to median line and attached to each other, inserting in median region of odontophore posterior surface, surrounding radular sac ( Fig. 3A, B ), mostly on m4.

m4. Pair of thick dorsal tensor muscles of radula ( Fig.3C ), originating in outer surface of odontophore cartilages just posterior and medial to origin of mj, surrounding entire ventral edge of cartilages, tensioning subradular membrane, additionally inserting in tissue of radula preceding oral cavity ( Fig. 3C [ir]).

m5. Pair of narrow and short auxiliary dorsal tensor muscles of radula ( Fig. 3C ), originating in posterior end of odontophore cartilages, running towards anterior and medial, inserting on radula in its portion preceding oral cavity, length c. 3/5 of cartilage length.

m6. Horizontal muscle, connecting both ventromedial edges of odontophore cartilages along almost their entire length, width c. 3/4 of cartilages width.

m10. Pair of small and thin odontophore protractor muscles ( Fig.2E ),originating in lateral region of mouth, inside proboscis, running towards posterior covering lateral edges of oral tube along c. 1/3of proboscis length, inserting in latero-anterior surface of odontophore.

oc. Odontophore non-muscular structures, pair of odontophore cartilages, somewhat elliptical, anterior region slightly wider than posterior region, c. twice longer than wide, c. 3 × wider than thick.

to. Tissue on radula occluding radular sac in region preceding oral cavity ( Fig. 3A ).

sc. Subradular cartilage, transparent, thin but strong, running all along radula holding teeth, expanding in oral cavity forming cover to odontophore, protecting br.

br. Subradular membrane, covering internally subradular cartilage and building it.

Radula ( Figs 1J, K ; 11D, E )

Rachidian. About as long as wide, occupying c. 1/5 of radular width, triangular, strongly bent in middle level, forming anterior shallow concavity, 3 terminal pointed cusps being median cusp c. twice larger than lateral cusps and about as long as basal length, pair of basal cusp in edges of base; pair of rachidian expansions, triangular, wing-like, wider distally ending in small cusp same sized as basal rachidian cusps, expansions widening rachidian c. 50%.

Lateral tooth. Similar to rachidian, but strongly turned medially, c. twice rachidian width, 3 terminal cusps, being middle cusp c. twice larger than remaining cusps.

Inner marginal tooth. Similar to lateral tooth in form and length, but slightly narrower and with only 2 terminal cusps, outer cusps about twice inner cusp’s size.

Outer marginal tooth. Hook-like, same length as inner marginal, terminal cusp single, sharply pointed, base wide, with small blunt projection on base of distal concavity. Radular sac relatively narrow, almost twice odontophore length. Anterior esophagus originating just posterior to odontophore ( Fig. 2E [es]), c. twice odontophore length, c. 1/8 odontophore width; inner surface simple, smooth. Middle esophagus as base of esophageal gland, with c. 1/2 anterior esophagus length. Esophageal gland as wide ventral expansion of mid esophagus ( Fig. 2E [eg]), c. half expanded anteriorly as blunt beak; size c. 3/4 of haemocoel volume ( Fig. 2F ); internally filled by transverse glandular septa, except for narrow dorsal canal. Posterior esophagus as long and wide as anterior esophagus ( Fig. 2D [es]). Stomach as simple curve and expansion, c. 5 × wider than adjacent esophagus, dorso-ventrally flattened; wider (posterior) region with c. ¼ adjacent width of visceral mass; inner surface smooth, simple. Stomach gradually narrowing anteriorly, with no clear separation from intestine. Intestine ( Fig. 2D [in]) slightly broader than esophagus; with perpendicular curve in left side, just posterior to pericardium; crossing from left to right sides in visceral mass portion preceding kidney; in kidney cavity crossing through kidney lobe. Rectum and anus described above.

Genital system

Male ( Figs 2A, D ; 3D ). Testis lying in right and columellar side of visceral coils, cream in color; anterior end just posterior to kidney.Seminal vesicle simple zigzags located subterminally in left-ventral side of testis ( Fig. 2D [sv]), restricted to short distance (c. 1/8 whorl). Vas deferens running in perpendicular curve flanking postero-ventral border of pallial cavity ( Fig. 2D [vd]), narrow; becoming slightly broader in pallial cavity right edge as prostate gland ( Fig. 2D [pt]). Vas deferens running somewhat sinuously in right edge of pallial cavity floor ( Fig. 2A [vd]) up to right side of penis base. Penis originated in ventro-right side of head, near side of rhinchostome ( Fig. 3D [pe]); size c. 1/8 that of head-foot ( Fig. 2A [pe]); base wide and slightly flattened, gradually tapering up to sharply pointed tip; terminal papilla pointed, with c. 1/5 remaining penis length and width ( Fig. 3D [pp]). Penis duct simple, non-sinuous, running along middle region of penis; opening at penis tip.

Female. Visceral structures similar to those analogous in the males. Pallial oviduct occupying c. ¼ of pallial cavity. Albumen and capsule glands mixed with each other in coiled pattern. Female aperture simple, close to anus.

Central nervous system ( Fig. 3E )

Located at base of proboscis ( Fig. 2E, F ). Cerebral and pleural ganglia fused with each other, each cerebro-pleural ganglia with approximately same size as adjacent esophagus section, form spherical. Cerebral commissure c. ¼ narrower than ganglia, with c. 1/2 length of each ganglion. Sub- and supra-esophageal ganglion located close to cerebral ganglia. Pedal ganglia c. 1/2 larger than cerebro-pleural ganglia, spherical, closed placed to each other. Each one with pair of anterior nerves. Statocyst ventral to pedal ganglia, with large statolith each ( Fig. 1I ). Pair of buccal ganglia ( Fig. 2E, G [bg]) located in region between odontophore and esophagus; buccal commissure very narrow, as long as each ganglion.

Measurements (width and height in mm)

Holotype ( Fig. 1 A-D): 4.1 × 4.3.

Paratype: MNHN, 1 ♀ (sta. 104; Fig. 1E ): 4.3 × 4.1 ; 2 ♂♂ ( Fig. 1F ): 3.7 × 3.3.

Habitat

430-450 m depth, muddy bottoms. Etymology

The specific epithet is a diminutive of the Latin word latus, meaning broad, wide, an allusion to the wide shape of the shell.

Microlinices ibitingus n. gen., n. sp. ( Figs 4 A-G; 5A-F; 11F, G)

HOLOTYPE. — MNHN 27128 .

PARATYPES. — MNHN 27129 , 3 shells ; MZSP 105250 , 3 shells from type locality. Brazil ( MD55 ; coll. Bouchet, Leal & Métivier). Espírito Santo: off Itaúnas, slope of Abrolhos (27. V.1987) ; 18°58’S, 37°48’W, 1200 m, MNHN 27130 , 4 shells (sta. CB78 ), 18°58’S, 37°48’W, 682 m, MNHN 27131 , 1 shell (sta. SY74) ; 18°58’S, 37°49’W, 367 m, MNHN 27132 , 16 shells ; MZSP 105252 , 6 shells (sta. CB76 ) ; 18°59’S, 37°48’W, 607-620 m, MNHN 27133 , 7 shells ; MZSP 105251 , 3 shells (sta. DC73 ) ; 19°00’S, 37°48’W, 950-1050 m, MNHN 27134 , 2 shells (sta. DC72 ) ; 19°01’S, 37°47’W, 1500-1575 m, MNHN 27135 , 3 shells (sta. CB79 ) ; off Regência , off mouth of Rio Doce, 19°36’S, 38°53’W, 640 m, MNHN 27136 , 1 ♀, 4 shells (sta. CB93 , 30. V.1987). Rio de Janeiro: off Cape of São Tomé, 21°34’S, 40°05’W, 750 m, MNHN 27137 , 1 shell (sta. DS08, 10. V.1987) .

TYPE LOCALITY. — Brazil, Espírito Santo: off Regência , 19°40’S, 37°48’W, 790-940 m ( MD55 sta. CB77 ; coll. Bouchet, Leal & Métivier, 27.V.1987) .

DIAGNOSIS. — Shell c. 10 mm, c. 105-120% taller than wide. Umbilicus open, upper part covered by thick callus, inner middle fold absent; low peri-umbilical carina. Sculpture lacking, surface glossy, translucent white with pure white subsutural band. Protoconch wide, dome-shaped, of 1.5 whorls. Spire angle c. 110°.

DISTINCTIVE DESCRIPTION

Shell ( Fig. 4 A-F)

Diameter of c. 10 mm; height c. 105-120% of width; general form globose. Color translucent white; broad subsutural pure white band, lower border unclear, occupying c. 15% of body-whorl area ( Fig. 4B, C, E ). Protoconch dome-shaped, of 1.5 flattened whorls ( Fig. 4E, F ); surface smooth, glossy; diameter c. 1.5 mm, occupying c. 15% of upper shell surface. Teleoconch of c. 2.5 whorls; suture well-marked by angle c. 150° ( Fig. 4 A-C); spire angle c. 110°. Sculpture absent except for growth lines and axial weak undulations; undulations stronger in subsutural region ( Fig. 4E, F ). Aperture semicircular, wide, occupying c. 70% of shell height and c. 48% of shell width; outer lip thick, weakly prosocline ( Fig. 4B ), simple; inner lip slightly concave to almost straight ( Fig. 4A, D ), upper half covered by thick callus, lower half as thick edge ( Fig. 4A ). Umbilicus lacking middle fold, wide, open; c. 3/4 covered by callus with straight-oblique edge; its aperture occupying c. 15% of lower surface; umbilicus protected by peripheral, low carina ( Fig. 3D ).

Head-foot ( Fig. 5C )

General organization as those described for Microlinices latiusculus n. gen., n. sp., with main differences as follows: Tentacles separated from each other distance c. 2 × their width. Haemocoel occupying c. 30% of head-foot volume.

Operculum ( Fig. 4G )

Characters similar to those of preceding species, except in being weakly more rounded and with clearer spiral sculpture in region surrounding nucleus.

Mantle organs ( Fig. 5A, B )

Most characters similar to those of Microlinices latiusculus n. gen., n. sp., with main differences as follows: Osphradium larger, occupying c. 1/3 of pallial hoof area; c. 30 filaments in right side, c. 25 in left side; anterior third curved to left. Each osphradium filament also with its base narrower than middle portion. Gill slightly more elongated; each filament triangular, about as tall as wide, apex central. Hypobranchial gland thick, white.

Visceral mass ( Fig. 2D )

As described for preceding species.

Circulatory and excretory systems

Same characters as Microlinices latiusculus n. gen., n.sp.

Digestive system ( Fig. 5C, E, F )

General organization as those of Microlinices latiusculus n. gen., n. sp., with main distinctions as follows: Pleurembolic proboscis occupying c. ¼ of haemocoel length in retracted condition. Odontophore muscles similar, except for slightly longer pair of m5. Radula ( Fig.11F, G ) similar to that of M. latiusculus n. gen., n. sp., except for: rachidian with short bent tricuspid portion (c. 1/2-3/4 of base), lateral expansions c. 50% narrower, basal cusps turned perpendicularly to base (instead of distally); lateral tooth with terminal cusps slightly smaller, turned medially (instead of distally); inner marginal tooth forming small cusp in middle level of outer edge; outer marginal tooth slightly more curved in apex. Anterior esophagus with same width but c. 50% longer. Esophageal gland similarly-shaped, but with transverse septa strongly-marked, forming transverse folds in ventral and lateral surfaces. Midgut not seen.

Genital system

Male: not seen (only female available). Female: not seen in details (pallial oviduct not fully mature).

Central nervous system ( Fig. 5D )

Arrangement and localization ( Fig. 5C ) similar to those of preceding species.Single detected difference: pair of pedal ganglia with single main anterior nerve, preceded by shallow constriction.

Measurements (width and height in mm)

Holotype ( Fig. 4 A-F): 10.1 by 12.3.

Paratype: MZSP 105252: 10.3 × 10.5.

Habitat

640-1575 m depth, muddy bottoms.

Etymology

The specific epithet is derived from the native Tupy language, ibitinga, meaning white earth, an allusion to the white subsutural band characteristic of the shell.

Microlinices benthovus n. gen., n. sp. ( Figs 6 A-J; 7A-H; 11A-C)

HOLOTYPE. — MNHN 27138 .

PARATYPES. — MNHN 27139 , 37 shells, 1 ♂, MZSP 105250 , 3 shells from type locality. Brazil ( MD55 ; coll. Bouchet, Leal & Métivier), Espírito Santo: off Itaúnas, slope of Abrolhos, sta. CB78 , 18°58’S, 37°48’W, 1200 m, 27.V.1987, MNHN 27140 , 1 shell, sta. SY74, 18°58’S, 37°48’W, 682 m, MNHN 27141 , 22 shells, sta. DC73, 18°59’S, 37°48’W, 607-620 m, MNHN 27142 , 22 shells, MZSP 105269 , 5 shells, sta. DC70, 18°59’S, 37°47’W, 1540-1550 m, MNHN 27143 , 4 shells, sta. DC72, 19°00’S, 37°48’W, 950-1050 m, MNHN 27144 , 15 shells, MZSP 105270 , 5 shells, sta. CB79 , 19°01’S, 37°47’W, 1500-1575 m, MNHN 27145 , 7 shells, MZSP 105272 , 2 shells ; off Regência, off mouth of Rio Doce , sta. CB93 , 19°36’S, 38°53’W, 640 m, MNHN 27146 , 10 shells, 2 ♀♀, sta. CB77 , 19°40’S, 37°48’W, 790-940 m, 27.V.1987, MNHN 27147 , 16 shells, MZSP 105271 , 8 shells ; Rio de Janeiro: off Saquarema , sta. CB105 , 23°46’S, 42°10’W, 610 m, 02.VI.1987, MNHN 27148 , 1 shell .

TYPE LOCALITY. — Brazil. Espírito Santo: off Conceição da Barra, MD 55 sta. CB 76, 18°58’S, 37°49’W, 637 m, 27. V.1987 (coll. Bouchet, Leal & Métivier).

DIAGNOSIS. — Shell c. 5 mm, c. 105-140% taller than wide. Umbilicus open but narrow, 3/4 upper area covered by thick callus, inner middle fold absent. Sculpture lacking, surface glossy, translucent white with pure white subsutural band barely visible. Protoconch mammillate, dome-shaped, of 1.5 whorls. Spire angle c. 80°.

DISTINCTIVE DESCRIPTION

Shell ( Fig. 6 A-F, I, J)

Diameter of c. 4 mm; height c. 105-140% of width; general form globose-elongate. Color translucent white; broad subsutural pure white band barely visible, lower border unclear, occupying c. 15% of body-whorl area ( Fig.6E, J ). Protoconch mammilate, of 1.5 flattened whorls ( Fig. 6E, F ); surface smooth, glossy; diameter c. 0.9 mm, occupying c. 25% of upper shell surface. Teleoconch of c. 2.0 whorls; suture well-marked by angle c. 160° ( Fig. 6B, C ); spire angle c. 80°. Sculpture absent except for growth lines and weak axial undulations; undulations slightly stronger in subsutural region ( Fig. 6E ). Aperture semicircular, narrow, occupying c. 61% of shell height and c. 39% of shell width; outer lip thick, weakly prosocline ( Fig. 6B ), simple; inner lip slightly concave to almost straight ( Fig. 6A, D, I, J ), upper half covered by thick callus, lower half as thick edge ( Fig. 6A, D ). Umbilicus lacking middle fold, narrow, open; c. 3/4 covered by callus with straight-oblique, concave edge; its aperture occupying c. 8% of lower surface, possessing strong axial irregular undulations ( Fig. 6D ).

Head-foot ( Fig. 7A, B )

Characters similar to those of Microlinices latiusculus n. gen., n. sp., except for proportionally wider head.

Operculum ( Fig. 6G,H )

Semi-circular, thin, corneous, flexible, occupying entire aperture. Nucleus in middle of inner to lower quadrant; spiral sculpture with 2 whorls, slightly scale-like; low undulations parallel to inner edge ( Fig. 6G, I ). Inner surface smooth, glossy; scar elliptical (twice wider than long), closer to inner edge, occupying c. 40% of inner surface ( Fig. 4H ).

Mantle organs ( Fig. 7C, E )

Most characters similar to those of Microlinices latiusculus n. gen., n. sp., remarks and distinctions as follows: Osphradium proportionally shorter, with fewer filaments (c. 11 at right, c. 7 at left); each filament narrow, flattened, separated from each other. Gill with more rounded anterior region; filaments with elongated, slightly rounded tip.

Visceral mass ( Fig. 7E )

Organization similar to that of Microlinices latiusculus n. gen., n. sp.; length c. 2 whorls posterior to stomach.

Circulatory and excretory systems ( Fig. 7E )

Same characters as Microlinices latiusculus n. gen., n. sp.

Digestive system ( Fig. 7F, G )

Most features similar to those of Microlinices latiusculus n. gen., n. sp., remarks and distinctions as follows: Proboscis with narrow extra pair of ventral retractor muscles passing through nerve ring. Buccal mass c. 30 % smaller. Pair of jaw plates slightly ticker.

Odontophore muscles ( Fig. 7G )

m2. With single insertion, in border between m4 and m5.

Figures

FIG. 7. — Microlinices benthovus n. gen.,n. sp.,anatomy:A, B, head-foot,frontal view:A, female;B, male;C, pallial cavity hoof,female, transverse section in middle level of osphradium; D, penis,ventral view,some adjacent structures also shown; E, pallial cavity roof and visceral mass, ventral view,digestive gland portion ventral to stomach and ventral region of pericardium removed;F, foregut,left view; G, odontophore, dorsal view, superficial layer of muscles and membranes removed, both odontophore cartilages deflected, radular sac only partially shown; H, nerve ring, ventral view. Abbreviations: see Material and methods. Scale bars: 0.5 mm.

FIG. 1. — Microlinices latiusculus n. gen., n. sp.: A-D, holotype MNHN; A, apertural-slightly umbilical view; B, dorsal view; C, apical view; D, umbilical view; E, paratype MNHN (sta. 104), apertural view; F-H, another more globose specimen (sta. 104): F, apertural view; G, operculum, outer view; H, inner view; I, statocyst in SEM; J, K, radula in SEM extracted from dry specimen. Measurements: A-D, W 4.1 mm; E, W 4.3 mm; F, W 3.7 mm; G, H, W 2.5 mm; I, W 0.1 mm. Scale bars: J, 20 µm; K, 10 µm.

FIG. 6. — Microlinices benthovus n. gen., n. sp.: A-F, holotype: A, apertural view; B, right view; C, dorsal view; D, umbilical-slightly apertural view;E, apical view;F, detail of apex;G, H, operculum of paratype MNHN,1 ♀: G, outer view;H, inner view;I, paratype MNHN, 1 ♀, apertural view,specimen still inside;J, paratype MZSP 105270,apertural view.Measurements:A-F,W 3.8 mm;G, H, 3.2 × 2.2 mm; I, W 4.8 mm; J, W 3.4 mm.

FIG. 2. — Microlinices latiusculus n. gen.,n. sp.anatomy; A-C, head-foot,male:A, frontal view;B, dorso-posterior view;C, ventral view (foot sole); D, pallial cavity roof and last whorl of visceral mass, ventral view, digestive gland portion ventral to stomach and ventral region of pericardium removed; E, foregut, left view, transverse section of indicated region of esophageal gland shown; F, head and haemocoel, ventral view, foot removed; G, H, buccal mass, right view, odontophore partially deflected. Abbreviations: see Material and methods. Scale bars: 0.5 mm.

FIG. 8. — Shells of MD55 naticid species: A-B, Microlinices ombratus n. gen., n. sp. shell of holotype: A, frontal view; B, dorsal view; C-G, Microlinices apiculus n. gen., n. sp.: C-F, holotype: C, apertural view; D, dorsal view; E, right view; F, apical view; G, paratype MZSP 105146; H-K, Microlinices gaiophanis n. gen., n. sp., holotype MNHN: H, apertural view; I, dorsal view; J, right view; K, apical view. Measurements: A, B, W 3.2 mm; C-F, W 5.3 mm; G, W 4.4 mm; H-K, W 5.2 mm.

FIG. 3. — Microlinices latiusculus n. gen., n. sp. anatomy: A-C, odontophore: A, dorsal view, oral tube and some superficial muscles removed;B, ventral view;C, dorsal view,superficial layer of muscles and membranes removed,both odontophore cartilages deflected; D, head, male, ventral view, foot removed; E, nerve ring, ventral view. Abbreviations: see Material and methods. Scale bars: 0.5 mm.

FIG. 11. — Radulae in SEM: A, B, Microlinices benthovus n. gen., n. sp.; C, radula of other specimen; D, M. latiusculus n. gen., n. sp.; E, same of other specimen; F, G, Microlinices ibitingus n. gen., n. sp. Scale bars: A, C, D, F, G, 20 µm; B, 50 µm; E, 10 µm.

FIG. 4. — Microlinices ibitingus n. gen., n. sp., shell holotype: A, frontal view; B, right view; C, dorsal view; D, umbilical-slightly apertural view;E, apical view; F, detail of apex; G, operculum of specimen (sta. CB93), outer view. Measurements: A-F, W 10.1 mm; G, L 2.9 mm.

FIG. 5. — Microlinices ibitingus n. gen., n. sp., anatomy: A, pallial cavity roof, ventral view; B, same structure, transverse section on middle level of osphradium; C, head and haemocoel, ventral view, foot removed; D, nerve ring, ventral view; E, foregut as in situ, right-slightly ventral view, topology of nerve ring also shown; F, same structure, most structures uncoiled, right view. Abbreviations: see Material and methods. Scale bars: 0.5 mm.