New morphological data on Solariella obscura ( Trochoidea : Solariellidae ) from New Jersey , USA

Anatomical data on Solariellaobscura (Couthouy, 1838) are presented and analyzed. The main features of this species, when compared with other known trochoids, are: ctenidium with thick lamellae; enlarged ureter (that may indicate sexual dimorphism) instead of a modified urogenital papilla; odontophore very different from other trochoids such as Calliostoma, Agathistoma, Monodonta, and Gaza, with short m6, large mj and m4 pairs and absent m8 pair and posterior cartilages; esophageal valve surrounding the odontophore ventrally; anterior and mid-esophagus composed of several thin folds and a very wide cerebral ganglion. Solariellaobscura differs from Solariellavaricosa (Mighels & Adams, 1842) by having lower spire, spiral cords weaker on the base and axial rib oblique. There are no differences between S.obscura and S.varicosa in the external morphology and radula. These internal anatomical data are described for the first time for a solariellid and might improve our understanding of the relationships within this taxon.


MATERIAL AND METHODS
Specimens preserved in 70% ethanol were extracted from their shells and subsequently dissected and photographed under the stereomicroscope.The terminology of the odontophore muscles follow DORNELLAS & SIMONE (2013).All drawings were made with the aid of a camera lucida.Samples examined with the SEM (radulae and protoconchs) were mounted on stubs and coated with gold-palladium alloy.The specimens were analyzed and photographed under a stereomicroscope.
Foot thick, occupying half of total head-foot length; whitish, non papillated; anterior end truncated and drawn out laterally into two long processes (horns).Epipodium (Fig. 25: ep) surrounding latero-dorsal region of mesopodium, equidistant from sole and base of ommatophores.Right neck lobe with two tentacles, anterior tentacle postoptic (Fig. 25: pt); left neck lobe with one tentacle.Three pairs of epipodial tentacles (Figs. 24, 25) symmetrical on both sides; epipodial sense organs at base of epipodial tentacles.Opercular pad (Figs. 25,34: oa) rounded, located in median dorsal region, with free edge in posterior area; posterior end with several chevron furrows, apex pointed posteriorly and two pairs of longitudinal furrows on median line.Furrow of pedal glands along entire anterior edge.
Mantle organs (Figs. 13,(26)(27)(28).Pallial cavity of 3/4 whorl.Mantle border (Fig. 26: mb) thick, white; anterior end papillated, occupying 1/3 of mantle border.Gill located on left side of pallial cavity; less than half of width and height of pallial cavity; projecting anteriorly, sustained by gill rod, lacking suspensory membrane (Fig. 26: sk).Anterior end of gill narrow, with acuminate tip.Ventral lamella larger than dorsal lamella (Figs.27).Afferent gill vessel ~3/4 of gill's length, originating in transverse pallial vessel, running along distal region of central axis of gill.Transverse pallial vessel ~1/5 of afferent vessel length, originating in left nephrostome and discharging in afferent gill vessel.Ctenidial vein (efferent gill vessel) length more than twice afferent vessel length, running along basal region of central axis of gill; posterior end of vein (half) free from gill filaments, lying parallel to afferent vessel up to pericardium.Osphradium rounded, whitish, located at base of gill rod.Hypobranchial glands (Figs.26: hg) on both sides of rectum; more developed on left side.Rectum occupying 1/4 of pallial cavity ZOOLOGIA 32 (2): 162-170, April 2015 width, sigmoid; posterior region under kidneys.Anus siphoned, preceded by pleated and short free end, located on posterior right side of pallial cavity.Kidneys length more than half of rectum length, located on posterior region of pallial cavity.
Visceral mass (Fig. 34).Pericardium and posterior portion of right kidney exposed on pallial cavity roof.Stomach and spiral caecum (sc) located 1/3 whorl posterior to pallial cavity.Digestive gland (dg) located on left side and gonad (go) on right side, both posterior to right kidney.
Circulatory and excretory systems (Figs. 26,28).Pericardium located between pallial cavity and visceral mass (Fig. 26: pc), close to median line and immediately posterior to kidneys.Left side of pericardium receiving ctenidial vein and right side receiving right pallial vein.Ventricle volume 1/3 of pericardium volume; surrounding rectum and flanked anteriorly by left auricle and posteriorly by right auricle; left auricle ventral, triangular, occupying about half of pericardium volume; right auricle weak, smaller than left one (Fig. 28).Papillary sac (or left kidney) base oval, wide, gradually narrowing towards anterior portion, ending at left nephrostome; inner wall covered by numerous thin, long papillae.Right kidney (Fig. 28: ur, rk) divided into two regions; anterior region as hollow tube (ureter), right nephrostome located in anterior region; ureter might be as large as papillary sac (probably males) (Fig. 26) or twice papillary sac width (probably females) (Fig. 28); no mucus observed in females ureter.Posterior region spreading around visceral mass immediately beneath mantle, encircling inner surface of columellar muscle.Kidney expanding ventrally, covering half of right surface of adjacent visceral hump.
Radular sac short (Fig. 31: ra), as long as odontophore.Radular nucleus (Fig. 32) located on ventral side of odontophore.Central complex (rachidian and laterals) well-developed, with interlocking process and correspondent sockets (Fig. 18); shafts expanding laterally, hood-shaped.Rachidian large (Fig. 19), triangular, cutting edge with projection turned posteriorly (almost 90°) and covering posterior end of preceding tooth; tip narrowly tapered, serrated; base and cusp with within-column interaction.Four lateral teeth (Figs. 20,21); cusps oriented toward midline of radula, most strongly serrate along their outer margins; three inner lateral teeth similar to rachidian in shape; outermost lateral teeth broad, large, length twice of inner teeth length.Lateromarginal plate not observed.Marginal teeth (Fig. 18) as long as outermost lateral teeth, slender, serrate, ~10-12 teeth pairs.Anterior esophagus with esophageal Central nervous system (Figs. 16,30).Nerve ring surrounding anterior half of buccal mass.Cerebral ganglia rounded, located in lateral region of buccal mass (Fig. 30: cg), size ~1/3 of odontophore size; commissure thick, long, dorso-ventrally flattened; cerebropleural and cerebropedal (Fig. 30: cp, cd) connectives long, thin, originating in anterior region of cerebral ganglia and running ventrally and back to pedal and pleural ganglia.Labial ganglia (Figs.30: lg) 1/6 of cerebral ganglia, located in ventro-lateral region of buccal mass, anteriorly to cerebral ganglia; connected to cerebral ganglia by short cerebrolabial connective.Buccal ganglia posterior to cerebral ganglia; connected to cerebral ganglia by a buccolabial connective.Pleural and pedal ganglia (Fig. 16: pl, pe) close to each other, located inside pedal musculature immediately below ventral surface of haemocoel; both of about half size of cerebral ganglion.Pedal commissure thick, very short.Pedal nerve running forward from each pedal ganglion, surrounding medial pedal blood sinus.Supra-esophageal connective emerging from right pleural ganglia.Subesophageal connective (Fig. 30) emerging from left pleural ganglia.Statocysts (Fig. 16: st) rounded, bright, located very close to posterior side of pedal ganglia.

DISCUSSION
The organs and systems of S. obscura are congruent with the features of solariellid mentioned by previous authors (HERBERT 1987, HICKMAN & MCLEAN 1990, WILLIAMS 2012), such as: small and nacreous shells; presence of a ring of digitate papillae around the snout; short radula with 20-30 transverse teeth rows; anterior end of foot bilobed, forming the horn; long and thick cephalic tentacles, and an eye-stalk much shorter than the cephalic tentacle.Some of these features are not exclusive to solariellids, however, especially when compared with other trochoids.The presence of digitate papillae around the snout can also be found in Gaza Watson, 1879(SIMONE & CUNHA 2006), and the Umboniinae also have a bilobed foot (HICKMAN & MCLEAN 1990, pers. obs.).The radula, on the other hand, is the main structure for characterizing this family and its genera (HERBERT 1987, MARSHALL 1999), being short (20-30 rows of teeth), with reduced number of marginal teeth (~10 per half row).
The Artic species Solariella varicosa (Mighels & Adams, 1842) is similar in shape to S. obscura, but differs by having a taller spire, strong oblique axial rounded ribs and stronger spiral cords on the base.The distributions of both species overlaps in the Artic, south of Labrador and northern Canada (WARÉN 1993).The neck lobe shows a variety of shapes among trochoids and might be used to diagnose subfamilies, genera and even species (HICKMAN & MCLEAN 1990, DORNELLAS & SIMONE 2013).They are usually digitate, fringed or smooth, as well as symmetrical or asymmetrical to each other according to the taxa.The neck lobes of solariellids show some inter-generic variation in shape (HERBERT 1987, MARSHALL 1999) and are characterized by the presence of one or two short tentacles, the right neck lobe bearing the postoptic tentacle located at its anterior edge (Fig. 25: pt).The neck lobe of S. obscura was reported as being virtually identical to that of S. varicosa (WARÉN 1993: 161, figs. 4a, b).
Usually, the anterior and mid-esophagus of vetigastropods is composed of four folds that compartmentalize it (FRETTER & GRAHAM 1962, FRETTER 1964, HASZPRUNAR 1988, SASAKI 1998, DORNELLAS & SIMONE 2013).In S. obscura, on the other hand, the anterior and mid-esophagus are composed of several thin folds (Fig. 15).The presence of papillate glands covering the inner wall of that region, which is also present in S. obscura, is a morphological synapomorphy of the clade Vetigastropoda (HASZPRUNAR 1988, SALVINI-PLAWEN 1988, SASAKI 1998).
The radula of S. obscura is a typical solariellid radula, comprising a straight and short radular ribbon (as long as the odontophore), triangular rachidian, with the outermost lateral tooth being larger than the innermost teeth, and reduced number of marginal teeth (~10 teeth along the same row).In Solariella, the radula is characterized by the presence of welldeveloped, elongate, cuspless lateromarginal plates (HERBERT 1987).Solariella obscura and S. varicosa lack lateromarginal plates (WARÉN 1993, FRETTER & GRAHAM 1977), whereas all southern Solariella bear lateromarginal plates (MARSHALL 1999).
Despite the gastric spiral caecum being a variable structure, a large spiral caecum is considered derived within Vetigastropoda.This structure opens ventrally in the posterior end of the stomach, more or less as continuous extensions of the typhlosoles (STRONG 2003).The 0.5 whorl long caecum observed in S. obscura (Fig. 31: sc) can also be found in Calliostoma depictum Dall, 1927, but the number of spiral caecum whorls seems to be an inter-specific feature rather than a generic one, because it may vary among congeners such as in Calliostoma and Lithopoma (MONTEIRO & COELHO 2002, DORNELLAS & SIMONE 2013).
Solariellidae has been recently recognized as a family (BOUCHET et al. 2005), with molecular studies supporting this rank (WILLIAMS et al. 2008, WILLIAMS 2012).As discussed above, several features seem to be exclusive of Solariellidae such as the above-mentioned radular pattern and external morphology.These features have also been further used to trace patterns between solariellid genera (HERBERT 1987).On the other hand, there is no described data about the internal anatomy for any solariellid, and the new data described herein for S. obscura might improve our understanding about the relationships within this taxon, at generic and even suprageneric levels.