251 NEACTAEONINA ARGENTINA, NEW SPECIES, AND FAMILY PLACEMENT OF THE GENUS NEACTAEONINA THIELE, 1912 (MOLLUSCA: GASTROPODA) Diego G. Zelaya1, 2*, Laura Schejter3 & Cristián Ituarte4 ABSTRACT Neactaeonina argentina, a new species from the outer Argentine shelf off Buenos Aires province, is described. The species is characterized by the elongate, low-spired shell, with shouldered, nearly straight whorls, deep suture, and sculpture composed of numerous, Neactaeonina cingulata Thiele, 1912, except in having a greater number of teeth. The present details of the radula anatomy of Neactaeonina, both unknown to date. The study of anatomical characters demonstrates that Neactaeonina has clear similarities with other Acteonidae, with a combination of features present in Acteon with well-developed operculum; mantle cavity opening anteriorly; nervous system with only the cerebropleural ganglia fused; a single allosperm sac associated with the female system; radula without cardinal tooth; and oral cuticle with rod-like processes); and some characters present in acteonid genera other than Acteon (e.g., the number and morphology of teeth, and processes of the oral cuticle). However, Neactaeonina shows some characters thus far not reported for any other genus currently placed into the Acteonidae: salivary glands with laminar structure, male genital system with an open portion, a single allosperm sac opening Keywords: Gastropoda, Acteonidae, Neactaeonina, Southern Ocean. INTRODUCTION Neactaeonina was proposed by Thiele (1912) to include three species from sub-Antarctic and Antarctic waters: Actaeonina cingulata Strebel, 1908 (type species) from South Georgia; Actaeon (sic) edentulus Watson, 1889 from Kerguelen Islands, and Neactaeonina fragilis Thiele, 1912, from the Davis Sea of eastern Ant- arctica. Subsequently, Dell (1956) described a fourth species, Neactaeonina inexpectata, from Chatham Rise, off New Zealand. The descriptions of sub-Antarctic and Ant- arctic Neactaeonina species were based on subtle morphological shell characters observed in few specimens, if not on a single specimen. Differential characters were never clearly described, resulting in a confusing taxonomy instance, Powell (1951) reported specimens from South Georgia and South Shetlands MALACOLOGIA, 2011, 53(2): 251 263 1División Zoología Invertebrados, Museo de La Plata, Paseo del Bosque s/n, 1900, La Plata, Argentina 2Departamento Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, UBA, Argentina 3Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP). Paseo Victoria Ocampo 1, BH7602 Mar del Plata, Argentina 4Museo Argentino de Ciencias Naturales, Ángel Gallardo 470, C1405DJR Ciudad de Buenos Aires, Argentina *Corresponding author: dzelaya@fcnym.unlp.edu.ar Islands as Neactaeonina edentula, but latter (Powell, 1960) considered that these records correspond either “to [N.] cingulata or to a new species”. The familial assignment of the genus has never been properly discussed. Odhner (1926), based on the radula morphology described by Thiele (1912), placed Neactaeonina in the Acteonidae. New information on anatomy and radular morphology of a new species of Neactaeonina from the Argentine continental shelf described here, allowed a revision of the systematic position of the genus. MATERIALS AND METHODS The specimens described here were collected by the BIP “Capitán Cánepa” (Instituto Nacional de Investigación y Desarrollo Pesquero, IN- IDEP) during routine cruises for stock assess- ZELAYA ET AL.252 ment of the Patagonian scallop Zygochlamys patagonica (King, 1832). Benthic samples were collected using a non-selective dredge (2.5 m in a 5% formalin solution, and preserved in 75% alcohol. Voucher specimens were deposited in the malacological collection at Museo de La Plata (MLP), La Plata and Museo Argentino de Cien- cias Naturales “Bernardino Rivadavia” (MACN), Buenos Aires. For comparative purposes, the types or photographs of the type specimens of other species of Neactaeonina were examined: Museum of New Zealand Te Papa Tongarewa (NMNZ), Wellington, New Zealand [N. inexpec- tata]; The Natural History Museum (BMNH), London, United Kingdom [N. edentula]; Swedish Museum of Natural History (SMNH), Stockholm, Sweden [N. cingulata]; and Zoologisches Mu- seum (ZMB), Berlin, Germany [N. fragilis]. Gross anatomy was studied by dissection under a stereoscopic microscope; the radula was dissected, cleaned by rising in a commer- FIG. 1. Location map. Type locality ( A NEW NEACTAEONINA SPECIES 253 FIGS. 2 12. Neactaeonina argentina, new species. FIGS. 2, 3: Holotype (MLP 13264). FIG. 2: Dorsal view; FIG. 3: Apertural view. FIGS. 4 8: Paratypes. FIG. 4: Detail of shell sculpture; FIGS. 5 8: Onto- genetic series; FIG. 9: Operculum. FIGS. 10 12: Specimen from 38° 09.88’ S, 55° 35.42’ W (MACN-In 38141). FIG. 10: Apertural view (SEM); FIG. 11: Apical view; FIG. 12: Detail of protoconch. Scale bars FIGS. 2, 3, 5 8 = 10 mm; FIGS. 4, 12 = 200 μm; FIG. 9 = 1 mm; FIGS. 10, 11 = 2 mm. ZELAYA ET AL.254 cial sodium hypochlorite solution, washed in distilled water, and prepared dried for Scanning Electron Microscopy (SEM). Histological serial sections of three specimens were obtained after embedding tissues in Paraplast® (7 μm thick) and Historesin® (3.5 μm thick), and stained with eosin-hematoxylin. SYSTEMATICS Neactaeonina argentina, new species Figs. 1–50 Type Locality: 42°14.12’S, 58°32.97’W, off Buenos Aires province, 95 m depth. FIGS. 13 18. Neactaeonina argentina, new species: gross anatomy. FIG. 13: Ventral view; FIG. 14: Dorsal view; FIG. 15: Lateral view; FIG. 16: Detail of the roof of the pallial cavity; FIG. 17: Anterior part of digestive system; FIG. 18: Nervous system. bm: buccal mass; co: copulatory organ; cpg: cere- bropleural ganglion; cr: ciliated ridge; cs: cephalic shield; dg: digestive gland; ft: foot; gd: gonad; hg: hypobranchial gland; ldp: laterodorsal protractor muscle; lp: lateral protractor muscle; lvp: lateroventral protractor muscle; mb: mantle border; mo: mantle opening; op: operculum; pag: pallial ganglion; peg: pedal ganglion; pl: plicatidium; rg: repugnatorial glands (?); sbg: subesophageal ganglion; sd: salivary duct; sg: salivary gland; spg: suprapharyngeal ganglion. A NEW NEACTAEONINA SPECIES 255 Type Material: Holotype (23.5 mm length) (MLP 13264) and 4 paratypes from 38°33.82’– 38°34.96’S, 55°44.63’–55°46.71’W, 84–91 m (2 paratypes, MLP 13265; 2 paratypes MACN-In 38140). Other Material Examined: Off Buenos Aires prov- ince at: 1 specimen, 38°09.88’S, 55°35.42’W, 94 m (MACN-In 38141); 5 specimens, 38°55.30’S, 55°59.86’W, 84 m (MLP 13266); 1 specimen, 39°19.86’S, 55°54.62’W, 105 m (MLP 13267); 1 specimen, 43°14.18’S, 59°37.27’W, 100 m (MLP 13268); 1 shell, 41°41.95’S, 58°05.70’W, 96 m (MLP 13269); 1 specimen, 38°15.13’S, 55°35.55’W, 97 m (MACN-In 38142). Etymology The species name refers to Argentina, the country from whose continental shelf the spe- cies was collected. Diagnosis Shell solid, spire low, somewhat acute, weakly shouldered and nearly straight-sided whorls, with deep suture. Sculpture of numer- wide. Radular formula: 27–0–27. Description Shell of medium size (maximum observed elongated, with apex exposed (Figs. 2, 3, 5–8). (Fig. 12). Teleoconch of up to 4¾ whorls. Spire acute, high, with almost straight and shouldered whorls; suture deep (Figs. 2, 3, 5–8, 10–12). in small specimens (Figs. 2, 3, 5–8, 10, 11). Aperture elongate, about 65–70% of shell high, wider anteriorly. Outer lip thin, evenly curved. Columella slightly arcuate, nearly straight at the base, smooth. Columellar callus narrow, white, stronger anteriorly. Shell sculptured with broad, - 14–17 in the second whorl, 18–23 in the third whorl, and 72–76 in the last adult whorl. Each cord bearing microscopic striations. Spiral cords sinuous. Interspaces narrower than cords, evi- dencing growth lines, particularly anteriorly (Fig. 4). Shell surface glossy, straw yellowish. Oper- culum elongate, paucispiral, with basal nucleus, widely curved at external margin, angulated at inner margin, yellowish (Fig. 9). Anatomy Animal able to completely retract into the shell. Head-Foot: Eyes absent. Foot relatively small, ovate; anterior end with projecting triangular lateral horns; posterior end widely rounded (Fig. 13). Parapodia absent. Anterior part of cephalic shield rounded; narrow, deep medial sinus, present. Posterior part projecting in two widely separated lobes reaching base of mantle cavity (Figs. 14, 15). Mantle Cavity: Opening anteriorly, slightly displaced to right (Figs. 13, 15). Mantle border bent dorsally, left side with small papillae on ventral surface (repugnatorial glands?) (Fig. 16). Temporary “siphon” formed by small, triangular, smooth expansion of right mantle border. Plicatidium-like gill comprising few edges of roof mantle cavity; right anterior part free for about half of its length; left anterior part free for about a sixth of its length. Ciliated ridge (“raphe”), running along roof of mantle cavity, of mantle cavity, present. Both raphes extend posteriorly beyond mantle cavity, running to end of spire, inside pallial caecum. Hypobranchial gland difused on roof of pallial cavity, between dorsal raphe and gill (Fig. 16). Kidney relatively large, running along left side of gill. Heart one half kidney size; auricle anterior to ventricle. Reproductive System: Gonad with hermaph- roditic acini; oocytes developing at blind end of acini. Short hermaphroditic duct connecting with seminal vesicle (also called “ampulla”), serving for autosperm storage prior to ejacu- lation and for passage of ova toward female glandular complex, present (Fig. 19). Seminal vesicle large, elongate, sigmoid sac, lined by simple epithelium of cubic or low columnar cells (about 12 μm height) (Figs. 19, 20). Interior wall of vesicle facing columella ciliated. Female System: Glandular complex large, elongate, composed of two externally discern- ible glandular areas (Figs. 19, 29, 30). Single (allosperm) duct opening distally and running parallel to left side of female gland complex (Fig. 19). Allosperm duct with uniform diam- sinuous, becoming straight before opening into small globular sac (“gametolytic gland”) (Fig. 21). Histologically, bulb wall composed ZELAYA ET AL.256 of low columnar cells (about 15 μm height), with vacuolated cytoplasm suggesting some involvement in reabsorption (Figs. 22, 23). Distinct muscular layer absent; lumen usu- ally containing unordered sperm and debris of degenerating gametes which appears as eosinophilic spherules (Figs. 22, 23). Epithe- lium of allosperm duct formed by single layer of cubic cells, supported by thin connective tissue, ensheathed by somewhat thick layer of circular muscle (Figs. 25–28). Straight portion of duct containing unoriented sperm, whereas in sinuous portion, sperm oriented with heads perpendicular to wall of duct (Figs. 24–27). At distal end, duct of allosperm bulb joining lumen of female duct, to open shortly thereafter close to female genital opening (Fig. 30). Male System: Vas deferens, arising from seminal vesicle, running anteriorly, parallel to female gland and ventral to allosperm duct (Fig. 19). Epithelium of vas deferens formed by high co- lumnar cells forming several ridges into lumen; duct ensheathed by somewhat thick muscular layer. Vas deferens entering distally into glan- dular female complex; just before entering duct FIGS. 19 30. Neactaeonina argentina, new species: proximal portion of male and female reproductive systems. FIG. 19: Diagram (numbers indicate the histological sections showed in FIGS. 20 30); FIG. 20: Seminal vesicle; FIG. 21: Allosperm duct just before opening into the bulb; FIG. 22: Bulb; FIG. 23: Detail of degenerating gametes within bulb; FIG. 24: Straight portion allosperm duct; FIG. 25: Detail of FIG. 24 showing the duct epithelium; FIG. 26: Sinuous portion of allosperm duct; FIG. 27: Detail of FIG. 26 showing sperm attached to the duct epithelium; FIG. 28: Allosperm duct and vas deferens immersed in the terminal portion of the glandular complex; FIG. 29: Opening of the vas deferens; FIG. 30: Distal opening of allosperm duct. Scale bars: FIGS. 20, 29 = 200 μm; FIGS. 21, 22, 28 = 100 μm; FIGS. 23 27 = 50 μm; FIG. 30 = 30 μm. ad: allosperm duct; ado: allosperm duct opening; bu: bulb; dg: degenerating gametes; due: duct epithelium; gc: glandular complex; lu: lumen; oo: oocyte traversing the seminal vesicle; sid: sinuous portion of the duct; sp: sperm; std: straight portion of the duct; sv: seminal vesicle; vd: vas deferent; due: duct epithelium; vdo: vas deferent opening. A NEW NEACTAEONINA SPECIES 257 epithelium lined by large cells with vesiculous cytoplasm (Fig. 28). Shortly after junction of vas deferens and lumen of female glandular complex, vas deferens opening into exterior slightly ante- rior to female genital opening (Fig. 29). From this point to the base of copulatory organ, male way open, forming ciliated groove (Fig. 32). At base of copulatory organ, closed U-shaped ejaculatory duct opening, after several convolutions, at tip of the copulatory organ (Fig. 31). Just after entering base of copulatory organ, ejaculatory duct en- larges for short length, to continue with U-shaped branch. First half of U-shaped duct lined by high columnar glandular epithelium (Figs. 33, 34, 36), with sperm embedded in epithelium (Fig. 36). Duct of second half of U and distal convoluted portion lined by columnar, non-glandular epithe- toward lumen (Figs. 33, 34, 36, 37). Ejaculatory duct ciliated along its entire length, surrounded by muscular sheath (Fig. 38). Prostatic tissue associated with ejaculatory duct not observed. Copulatory organ triangular, non-retractile, un- armed (Fig. 39). A ventral fold (like a prepuce) at base of copulatory organ expanding into lateral, FIGS. 31 39. Neactaeonina argentina, new species: distal portion of male reproductive system. FIG. 31: Schematic drawing (not in scale) of the ejaculatory duct (lines and numbers indicate the histological sections showed in FIGS. 32–34, 37, 38); FIG. 32: External seminal groove; FIGS. 33, 34: Transverse ejaculatory duct; FIG. 38: Distal part of ejaculatory duct, close to the tip of the copulatory organ; FIG. 39: Copulatory organ. Scale bars: FIGS. 32, 37, 38 = 100 μm; FIG. 33 = 200 μm; FIG. 34 = 50 μm; lumen; eds: second part of ejaculatory duct; edw: ejaculatory duct wall; esg: external seminal groove; ZELAYA ET AL.258 Digestive System: Oral tube short. Buccal mass bulbous, strongly muscular, with three pairs of lateral protractor muscles (laterodor- sal, lateral, and lateroventral) (Fig. 17). Pair of large salivary glands, ventrolaterally embrac- ing esophagus (Fig. 17). Salivary glands open at posterodorsal end of buccal mass, above radular ribon. Left salivary duct relatively long; highly branched. Posterior portion of esopha- gus enlarged, forming crop. Stomach saculate, surrounded by female glandular complex. Digestive gland externally visible only at last whorl of visceral mass (Figs. 13–15). Intestine opening at anterior part of stomach, close to esophagus opening. Intestine relatively short, right side of female glandular complex to open at base of temporal “siphon”. Radula: Composed of approximately 30 rows of 27 teeth each. Rachidian tooth absent. Lat- eral teeth long, prominently hooked, sharply pointed, smooth, similar in size and shape, except for two outermost rows, where teeth are smaller and less solid, each bearing one or two tubercles close their bases (Figs. 40–42); base numerous rows of somewhat irregular, sharply pointed rod-like processes (Fig. 43). Nervous System: Streptoneurous. Nerve ring prepharyngeal, composed of four large gan- glia: one dorsal pair, originating from fusion of cerebral and pleural ganglia, and ventral pair, the pedal ganglia. Right and left cerebropleural ganglia connected by long, thick commissure; pedal ganglia connected by very short com- missure; connectives between cerebropleural FIGS. 40 43. Neactaeonina argentina, new species. FIGS. 40 42: Radula. FIG. 40: General morphol- ogy; FIGS. 41, 42: Detail of lateral teeth. FIG. 43: Oral cuticle. Scale bars: FIG. 40 = 100 μm; FIGS. 41 43 = 20 μm. A NEW NEACTAEONINA SPECIES 259 and pedal ganglia double, short (Fig. 18). Pal- lial ganglia small, located at sides of buccal mass, clearly separated from cerebropleural and esophageal ganglia by long connectives. Right esophageal ganglion smaller than left, which is represented by only slight enlargement of connective; left connective running below esophagus, joining well-developed subesopha- geal ganglion (Fig. 18); right connective running over esophagus, where it joins supraesopha- geal ganglion. From subesophageal and su- praesophageal ganglia, two connectives run posteriorly, passing below alimentary canal, to join visceral ganglion. FIGS. 44 50. Other Neactaeonina species. FIGS. 44 46: N. edentula. FIG. 44: Original illustration George Island, South Shetland (BMNH 1961619). FIGS. 47, 48: N. cingulata. FIG. 47: Original illustration the holotype of N. fragilis (ZMB 62978); FIG. 50. Holotype of N. inexpectata (NMNZ M.009793). Scale bars: FIGS. 44 46 = 30 mm; FIG. 47 = 5 mm; FIGS. 49, 50 = 2 mm. ZELAYA ET AL.260 Known Distribution 38°09.88’–43°14.18’S, 55°35.42’–59°37.27’W, off Buenos Aires Province; 84–126 m (Fig. 1). Habitat Neactaeonina argentina, n. sp., was found in soft-bottoms, being part of the benthic assemblage of the Patagonian scallop Zy- gochlamys patagonica. DISCUSSION Comparison of Neactaeonina argentina, n. sp., with other Neactaeonina Species Neactaeonina argentina, n. sp., is most simi- lar to N. edentula (Figs. 44–46), from which it dif- fers in having a more acute spire with shouldered whorls and deeply channeled suture. According to Watson (1886) sutures in N. edentula are “axi- ally impressed rather than channeled”. Neactaeonina argentina, n. sp., differs from N. cingulata (Figs. 47, 48) in having a lower spire, and a different number of lateral teeth. Thiele (1912) described the radula of N. cingula- ta as having one central tooth and 7 to 8 laterals at each side – interpreted as 8.0.8 by Hoffmann (1932–1940) – whereas N. argentina, n. sp., has 27 laterals in each row. The morphology of the lateral teeth, however, shows no differences in N. argentina, n. sp., and N. cingulata. Compared with Neactaeonina inexpectata (Fig. 50), N. argentina, n. sp. has a more solid shell, sculptured with a greater number of spiral cords and a wider columellar callus. Furthermore, in N. inexpectata the spire whorls are rounded, whereas in N. argentina, n. sp., whorls are nearly straight. Neactaeonina argen- tina, n. sp., and N. fragilis - tablish. The original description of N. fragilis is poor, lacking in detail and illustration. The type material consists of fragments of a single shell (Fig. 49), which show a shell thinner than in N. argentina, n. sp., with more delicate sculpture. After the original description, the only subse- quent references to this species are those by Hedley (1916) and Hain (1990), who tentatively assigned to N. fragilis specimens from Adelia Land and Weddell Sea, respectively. Hedley specimen which differs from N. argentina, n. sp., in having a depressed spire. Dell (1990) pointed out that “[Neactaeonina] fragilis may ultimately prove to be indistinguishable from [N.] edentula”. The overall similarities in shell morphology, radula, and oral cuticle of Neactaeonina argen- tina, n. sp., and N. cingulata, the type species of the genus, clearly support the generic status of the new species. Information on the soft part anatomy of the other Neactaeonina species is unknown. Suprageneric Placement of Neactaeonina Although the text by Thiele (1912) containing the description of Neactaeonina is printed im- mediately following the text corresponding to Acteon antarcticus, the familial placement of this genus was not formally proposed until 14 years later, when Odhner (1926) placed it into the Ac- teonidae. This was followed by all subsequent authors (Thiele, 1931 [as Actaeonidae]; Powell, 1951, 1960; Carcelles, 1953; Dell, 1990; Hain, 1990 [as Acetonidae, by misspelling]); however, the generic placement of Neactaeonina was only pointed out some differences between Neactaeonina and Acteon Montfort, 1810 (the type genus of Acteonidae), not discussing on the similarities that allowed him to unite the two genera in the same family. The Acteonoidea were traditionally regarded as comprising three families: Acteonidae, Aplustridae, and Bullinidae (Rudman, 1972a; Burn & Thompson, 1998; Bouchet & Rocroi, 2005). Göbbeler & Klussmann-Kolb (2010), these families, concluding that only two of these clades appear well-supported: Acteonidae (without Rictaxis) and Aplustridae (including Bullina and Rictaxis). The characters previously described for Neactaeonina may be therefore now traced in Göbbeler & Klussmann-Kolb’s (2010) phylogeny. Is Neactaeonina Actually an Acteonid? Neactaeonina has an elongate, strongly a small and unlobed foot; a short oral tube; absence of central radular tooth; mantle cavity opening anteriorly; and nervous system with long conective between the supraesophageal ganglion and the right cerebro-pedal ganglia. It is thus evident that Neactaeonina exhibits the characters reported as diagnostic for the Acteonidae. A NEW NEACTAEONINA SPECIES 261 Comparison of Neactaeonina with other Acteonids The radula of Neactaeonina clearly differs from that of Acteon both in the number and morphology of teeth. Acteon species have nu- merous, minute, denticulate, and identical teeth – radular formula: 100+.0.100+ (Mikkelsen, 1996); 50–150.0.50–150 (Gosliner, 1996). In contrast, Neactaeonina species have a minor number of teeth, with the two outermost rows smaller; the teeth in Neactaeonina species are larger and almost smooth (except for one or two tubercles close to the bases of the outermost laterals). The radulae of Neactaeonina species closely resemble that of Crenilabrum exilis (Jeffreys, 1870), Japonacteon pusillus (Forbes, 1843), and Maxacteon cratericulatus (Hedley, 1906), respectively described by Bouchet - pointed laterals. However, in Neactaeonina, such as in Japonacteon and Maxacteon, the rachidian tooth is absent, whereas in C. exilis (according to Bouchet, 1975), this tooth is pres- ent, although reduced at the base. Japonacteon has differentiated marginal and lateral teeth, and Maxacteon has bicuspid laterals. The oral cuticle in Neactaeonina is composed of rod-like processes resembling lateral teeth, whereas in Acteon species these processes are multicusped (Marcus, 1972; Gosliner, 1994, 1996: fig. 2.3B). The oral cuticle of Neactaeonina is similar to that described by Crenilabrum exilis, but unlike those of Pupa species (described by Rudman, 1972a), which are similar to those of Acteon species. The opening of the single allosperm sac (composed of a seminal receptacle in tandem with the gametolytic gland) in Neactaeonina argentina, n. sp., is distally with respect to the gonad (i.e., near the genital opening), whereas in Acteon species the opening is proximal (i.e., near the gonad), at the level of the seminal vesicle (Johannson, 1954; Fretter & Graham, 1954; Ghiselin, 1966; Gosliner, 1981). Accord- ing to Gosliner (1994), the presence of only one sperm storage “organ” is a derived condition for the acteonids; the primitive condition for the Actaeonoidea is the presence of two allosperm sacs: the proximal, functioning as seminal re- ceptacle, and the distal serving as gametolytic gland, as for example in Pupa and Maxacteon species (Rudman, 1972b; Gosliner, 1981). The male system in Neactaeonina argentina, n. sp., is peculiar, resulting from the combina- tion of a closed spermatic duct running along- side the female glandular complex (the vas deferens) and an external groove, carrying the sperm from the end of the vas deferens to the base of the copulatory organ; from this point, another closed portion (the ejaculatory duct) carry sperm to the tip of the copulatory of the ejaculatory duct seems to be involved in the temporary sperm storage before ejacula- tion. In Acteon species, the male genital duct is closed, and the vas deferens is continuous with the ejaculatory duct (Fretter & Graham, 1954; Johansson, 1954). The latter condition was also reported for Pupa and Maxacteon species (Rudman, 1972b), and was previously regarded as characteristic of the Acteonoidea (Gosliner, 1994). Associated with the vas deferens, a glandular portion forming a prostate (the so-called “pallial prostate”) was described for some acteonids (Johannson, 1954; Fretter & Graham, 1954; Gosliner, 1994; Mikkelsen, 1996). In Neac- taeonina argentina, n. sp., no prostatic tissue associated with any portion of the vas deferens, was observed. The copulatory organ in Acteon species is a straight, tubular structure (Marcus, 1972, 1974), whereas in Neactaeonina argentina, n. sp., the copulatory organ is a triangular Graham (1954) reported in Acteon tornatilis the presence of a shallow basal fold, like a prepuce; a similar structure is also present in N. argentina, n. sp. (this study). In Neactaeonina species the salivary glands structures embracing part of the esophagus. In Acteon species, as in Pupa, Maxacteon, and Crenilabrum species, the salivary glands are tubular, elongate, and running parallel to the esophagus (Rudman, 1972a, b; Bouchet, 1975; Gosliner, 1994). Neactaeonina argentina, n. sp., lacks eyes, whereas Acteon has well-developed eyes. In shell morphology, species of Neactaeonina clearly differ from those of Acteon in having a smooth columella (without columellar folds) and the shell surface sculptured with spiral cords (punctated spiral grooves are present in Acteon species). of Present Knowledge of the Geographic Dis- tribution of the Genus The new species here described represents the northernmost record for Neactaeonina, a ZELAYA ET AL.262 genus thus far known only from Antarctica, New Zealand, and the Scotia Arc islands. However, the extension of the distribution of the genus to a different biogeographic realm: in fact, the localities where the new species was collected correspond to an area affected by the so-called - nas oceanic current, which is a branch of the West Wind Drift extending northwards, along the outer margin of the Argentine shelf, up to 23°S (off Brazil) (Boltovskoy et al., 1999). In fact, the benthic assemblages occurring at the sites where Neactaeonina argentina, n. sp., was collected include several well known sub-Antarctic taxa: the bivalves Zygochlamys patagonica (King, 1832), Limatula pygmaea (Philippi, 1845), Hiatella meridionalis d’Orbigny, 1846; the gastropods Calyptraea pileolus d’Orbigny, 1841, Fusitriton magellanicus (Röding, 1798), Odontocymbiola magellanica (Gmelin, 1791), Adelomelon ancilla ([Lightfoot], 1786); the sponges Tedania massa Ridley & Dendy, 1886, Tedania mucosa Thiele, 1905, Hy- medesmia antarctica Hentschel, 1914, Iophon proximum (Ridley, 1881), Phorbas leptochela (Hentschel, 1914), Tedania charcoti Thiele, 1905, Isodictya verrucosa (Topsent, 1913), Haliclona kerguelensis (Hentschel, 1914); the echinoderms genera Labidiaster Lütken, 1871, Odontaster Verrill, 1880, Acodontaster Verrill, 1899, Porania Gray, 1840, Ophiacanta Müller & Troschel, 1842, Gorgonocephalus Leach, 1815, Sterechinus Koehler, 1901; and the cnidarian genera Alcyonium Linnaeus, 1758, Thouarella Gray, 1870, and Actinostola Verrill, 1883 (Bertolino et al., 2007; Roux et al., 2005; Schejter et al., 2006; Schejter unpubl. data). Neactae- onina is a genus clearly associated with the sub-Antarctic and Antarctic waters. Species Erroneously Reported under Neac- taeonina Marcus (1974) reported under Neactaeonina, Acteon (Actaeonina) chariis Watson, 1881, a living species from the Azores. The only argument for this generic placement was that “The genus Acteonina d’Orbigny, 1850, was erected for a fossil species”. Thiele (1912: 220) and Zilch (1959–60: 14) retained the use of Acteonina for fossil shells. The radula and soft part anatomy of Acteon (Actaeonina) chariis are unknown; however, several shell characters, such as the presence of a rela- tively high spire, the sinuous (“hair-like”) growth lines, and the protoconch “extremely blunt”, strikingly different from the condition present in the sub-Antarctic and Antactic species of Neactaeonina. Mikkelsen (1995), Malaquias (2001), and Cervera et al. (2004) retained this species under Actaeonina. ACKNOWLEDGEMENTS We would like to express our gratitude to K. Sindemark, A. MacLellan, B. Marshall, and M. Glaubrecht, for sending the types or photographs of the types of the Neactaeonina species housed at their Museums; the crew of the RV “Capitán Cánepa”, technicians and biologists, participating during the cruises for helping during sample collection; the INIDEP librarians for helping with bibliography; and D. Waloszek and O. Heilmayer for helping us with the translations of some German original descriptions. P. Mikkelsen and an anonymous reviewer provided valuable criticisms that im- proved the manuscript. The authors are members of the Consejo - nicas (CONICET), Argentina. This study was partially founded by PICT 38015. This is IN- IDEP Contribution Nº 1623. LITERATURE CITED BERTOLINO, M., L. SCHEJTER, B. CALCINAI, C. CERRANO & C. BREMEC, 2007, Sponges from a submarine canyon. Pp. 189–201, in: M. R. CUSTÓDIO, E. HAJDÚ, G. LOBO HAJDÚ & G. MURICY, eds., Porifera research: biodiversity, innovation and sustainability. 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