Capitina Watson, 1934

Herbert, D. G. & Moussalli, A., 2010, Revision of the larger cannibal snails (Natalina s. l.) of southern Africa - Natalina s. s., Afrorhytida and Capitina (Mollusca: Gastropoda: Rhytididae), African Invertebrates 51 (1), pp. 1-1 : 108-113

Genus Capitina Watson, 1934

Capitina: Watson 1934: 153 . Type species: Helix schärfiae [= schaerfiae ] Pfeiffer, 1861, by original designation.

Diagnosis: Shell of moderate size (adult diameter up to 34 mm), discoidal to globose-lenticular, usually with distinct spiral colour pattern; sculptured by anastomosing axial riblets producing a somewhat pitted or wrinkled sculpture; outer lip slightly thickened and without periostracal fringe; peristome interrupted in parietal region; umbilicus open, width moderate; protoconch of 1.25–1.5 whorls, with close-set axial riblets ( Fig. 4C ) and often with traces of spiral sculpture, diameter 4.0–7.0 mm. Radula possessing rachidian tooth; no clear distinction between lateral and marginal series and no one tooth noticeably larger than the others. Mantle lobe to left of pneumostome undivided. Penis very long, situated to left of retractor muscle of right optic tentacle; epiphallus short (<25 % of penis length); epiphallus and lower vas deferens connected to penis by connective tissue web; vagina very long; oviduct caecum absent. Distal part of suprapedal gland sinuous but not convoluted, lacking a swollen terminal vesicle.

External anatomy ( Fig. 76 ): Left body lobe of mantle undivided, forming a continuous skirt over neck region ( Fig. 6B ); skin texture finely to moderately granular; labial palps present but not large; optic and inferior tentacles with a ventrally distended apical bulb; tail region of foot relatively short; genital pore ventral and just posterior to right optic tentacle; lung venation strongly delineated by black pigmentation.

Radula ( Fig. 73 ): Formula 1+(20–32); length up to 15.5 mm, with up to 84 V-shaped transverse rows of teeth, 5.0–6.6 rows/mm in adult; no clear distinction between lateral and marginal series. Rachidian present, with a relatively short, broad cusp, one quarter to one third length of base-plate; remaining teeth (laterals and marginals), elongate and slender, progressively (slowly) increasing in size, those in middle of lateromarginal series largest, then decreasing in size somewhat more rapidly toward edge of radula, the outermost tooth being minute; inner teeth claw-like, with a relatively short, weakly curved, broadly acuminate cusp; larger teeth in middle of lateromarginal series with a flatter, more elongate cusp, but lacking an enlarged quadrate base-plate; those peripheral to this becoming spathulate, with a rounded tip and anteriorly acuminate base-plate.

Distal genitalia ( Figs 9C , 74 , 75 ): Penis very long and slender, often sinuously folded in situ; its wall muscular, particularly towards base; internal lumen lined by papillate epithelium ( Fig. 75A ), papillae close-set and relatively coarse, somewhat larger toward penis base. Apex of penis with small, rounded penis papilla, through which epiphallus lumen connects with penis lumen ( Fig. 75A ); penis papilla itself covered with micro-papillae similar to those lining the penis lumen. Epiphallus short, <25 % of penis length; joins penis at U-shaped bend where penial retractor muscle inserts; interior with longitudinal ridges lining outer wall, lying opposite a broad, rugose, tongue-shaped pilaster on inner wall (adjacent to penis) ( Fig. 75B ). Vas deferens runs alongside penis, vagina and free oviduct, broader and thrown into a series of bends in the latter region, before it fuses with spermoviduct.A web of connective tissue joins lower vas deferens and epiphallus to penis.

Vagina very long and slender with muscular wall; attached laterally to body wall by a well-developed series of muscle fibres; merges with free oviduct at origin of bursa copulatrix duct; interior wall of vagina with weakly crenulate, longitudinal ridges. Free oviduct expanded and thick-walled (site of spermatophore receipt), lined with smoother longitudinal ridges ( Fig. 75C ). Oviduct caecum absent. Bursa copulatrix duct long and slender, but not as slender as that of Natalina , running beside spermoviduct rather than within its coils; bursa copulatrix thin-walled, more or less ovate, situated posterior to pericardium. Spermoviduct relatively short, the lower half convoluted; hermaphrodite duct highly convoluted; ovotestis comprising a loose assemblage of slender acini, embedded in apical whorl of digestive gland.

Spermatophore ( Figs 10A , 76 ): A single allospermatophore was found in a specimen of Capitina calcicola sp. n. collected in early October. It was in good condition, suggesting recent copulation and thus that mating occurs in spring, at least. Spermatophore tadpole-shaped (straightened length 8.2 mm) and situated in swollen, thick-walled, lower portion of free oviduct. Head of spermatophore foremost, lying close to origin of free oviduct from spermoviduct, tail curving downward into opening of bursa duct. Spermatophore head pale orange-pink and hard, with numerous irregular, sometimes sinuous, longitudinal ridges; underside of the head concave, corresponding to tongue-like pilaster in epiphallus; internal contents of spermatophore head whitish; tail considerably thinner and without pink coloration or internal contents. No obvious vent evident, but central portion of concave underside of head thin-walled and possibly representing rupture site.

Notes: The phylogenetic analysis of morphological characters and DNA sequence data published by Moussalli et al. (2009) has shown that Capitina represents a highly distinctive lineage within Natalina s. l. As a result, we have proposed that the taxon be ranked as a genus in its own right. In terms of shell features, Capitina is characterised by the brown spiral lines on the adapical surface, wrinkled sculpture and thickened apertural lip of the adult. In addition, Capitina exhibits a number of distinct anatomical character states associated with the mantle edge, radula and distal genitalia which clearly distinguish it from Natalina and Afrorhytida .

The distribution of the genus is confined to the southern part of the south-western Cape and appears not to overlap with that of either Natalina 2 or Afrorhytida . It is the only genus of relatively large rhytidids known from the south-western Cape, west of 20°E. This, combined with the basal split between Capitina and ( Natalina + Afrorhytida ) ( Moussalli et al. 2009) suggests that Capitina stems from an early divergence event which divided the ancestral Natalina s. l. stock into western and eastern lineages. Using a conservative mutation rate of 5 % pairwise, mtDNA sequence data places this basal split in the mid-Miocene ( Moussalli et al. 2009). However, Spencer et al. (2006) suggested an even slower rate for COI evolution within the New Zealand rhytidid radiation, and there is thus a possibility that the initial split within Natalina s.l. may date from as far back as the early Miocene ( Moussalli et al. 2009). It is interesting to note here in terms of an ancestral reconstruction, that the radula of Capitina is closer to that of the Australian Strangesta Iredale, 1933 (Smith 1979) and New Zealand Schizoglossa Hedley, 1892 ( Powell 1930) than it is to either Natalina or Afrorhytida . However, such similarities may be diet-related homoplasies and need to be interpreted with caution.

When proposing Capitina as a new taxon, Watson (1934) included in it only ‘ Natalina ’ schaerfiae , but noted the existence of light coloured specimens which Layard (in Benson 1864) had suggested were simply pale varieties or bleached specimens of the same species.Watson, however, observed additional differences in sculpture, shell proportions and protoconch size, and speculated that these specimens may ultimately prove to belong to a second and unnamed taxon.With considerably more material available and accurate locality data we are able to confirm Watson’s observations and here describe this paler lineage as a new species.

The Agulhas Plain, to which this new species is limited, has experienced repeated Neogene marine transgressions of up to 200 m, with sea levels retreating to present levels only as recently as 2 Mya ( Siesser & Dingle 1981; Linder 2003). Such transgressions may have constituted an effective isolating mechanism, restricting ancestral Capitina populations to refugial foci in the Riviersonderendberge and at higher elevations

2 Juvenile specimens of Trigonephrus species occurring in the Agulhas area can deceptively resemble juvenile specimens of Natalina .

on the Agulhas Plain, facilitating divergence within the ancestral stock. This is consistent with a Late Pliocene estimate for the divergence of the two lineages based on COI sequence data (unpubl. data).

Figures

Fig. 4. Protoconchs of Natalina, Afrorhytida, Capitina and Nata (all NMSA): (A) Natalina cafra cafra (W4225), scale bar = 5.0 mm; (B) Afrorhytida trimeni (V7904), scale bar = 2.5 mm; (C) Capitina schaerfiae (W5672), scale bar = 2.5 mm; (D) Nata sp. n. (W6029), scale bar = 0.5 mm; arrows mark protoconch/teleoconch junction.

Fig. 76. Capitina calcicola sp. n., spermatophore, straightened length 8.2 mm (paratype, NMSA W5670/ T2265): (A) spermatophore in situ in dissected lower part of free oviduct; (B) two views of extracted spermatophore, scale bar = 3.0 mm.Abbreviations: bd – bursa copulatrix duct, fo – free oviduct wall with longitudinal folds, o – oviduct, obd – opening of bursa copulatrix duct, sh – spermatophore head, st – spermatophore tail, v – vagina, vd – vas deferens.

Fig. 6. Mantle edge anatomy of Afrorhytida, Capitina and Natalina, showing variation in left body lobe structure (all NMSA): (A) Afrorhytida knysnaensis (W5211); (B) Capitina calcicola sp. n. (W3201); (C) Natalina (Natalina) cafra natalensis subsp. n. (V8415); (D) Natalina (Tongalina) wesseliana (V7668).Abbreviations: lbl – left body lobe of mantle, pn – pneumostome, rbl – right body lobe of mantle.

Fig. 73. Capitina species, radula: (A, B) Capitina schaerfiae (Pfeiffer, 1861), Oubos (NMSA W5672), scale bars = 300 µm and 100 µm; (C, D) Capitina calcicola sp. n., Cape Agulhas (paratype, NMSA W3360/T2270), scale bars = 200 µm and 100 µm.

Fig. 9. Distal genitalia of Natalina, Afrorhytida and Capitina (all NMSA): (A) N. cafra natalensis subsp. n. (E7682), (B) A. knysnaensis (W4643), (C) C. schaerfiae (W5672). Abbreviations: bd – bursa copulatrix duct, ep – epiphallus, ga – genital atrium, oc – oviduct caecum, p – penis, pr – penial retractor muscle, sod – spermoviduct, v – vagina, vd – vas deferens.

Fig. 74. Capitina calcicola sp. n., reproductive tract (paratype, NMSA W5670/T2265), scale bar = 5.0 mm. Abbreviations: ag – albumen gland, bc – bursa copulatrix, bd – bursa copulatrix duct, ep – epiphallus, fod – free oviduct, gp – genital pore, hd – hermaphrodite duct, oc – oviduct caecum, ot – ovotestis, p – penis, pr – penial retractor muscle, sod – spermoviduct, v – vagina, vd – vas deferens.

Fig. 75. Distal genitalia of Capitina schaerfiae, Oubos, Riviersonderendberge (NMSA W5672): (A) epiphallus–penis junction with penis dissected to show penis papilla and micropapillate lumen wall (in situ the epiphallus lies beside the penis and is joined to it by a connective tissue web – not shown); (B) epiphallus cut open longitudinally to shown internal pilaster and ridges; (C) female tract with upper part of vagina and swollen free oviduct cut open to show internal structure.Abbreviations: bd – bursa copulatrix duct, ep – epiphallus, epp – epiphallus pilaster, epr – internal epiphallus ridge, fod – free oviduct, obd – opening of bursa copulatrix duct, p – penis, pl – penis lumen with micropapillate lining, pp – penis papilla, pr – penial retractor muscle, v – vagina, vd – vas deferens.

Fig. 10. Spermatophores of Capitina, Afrorhytida and Natalina (all NMSA):(A) C. calcicola sp. n. (paratype, W5670/T2265), length 8.2 mm; (B) A. burseyae sp. n. (paratype, W5231/T2260), length 10.5 mm; (C) A. kraussi kraussi (W5803), length 20 mm; (D) N. cafra natalensis subsp. n. (paratype, E7682/T2375), length 16.3 mm; (E) N. quekettiana lucaris subsp. n. (paratype, W3305/T2559), length 26.5 mm; (F) N. wesseliana (V7668), length 32 mm. The head of the spermatophore is uppermost in all cases and the lengths given are for the spermatophore as if straightened out.