Danilia textilis, Herbert, 2012
Herbert, D. G., 2012, A revision of the Chilodontidae (Gastropoda: Vetigastropoda: Seguenzioidea) of southern Africa and the south-western Indian Ocean, African Invertebrates 53 (2), pp. 381-381 : 415-420
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Etymology: From Latin textilis (woven); in reference to the regular, net-like sculpture.
Shell: Trochoid-turbiniform, moderately elevated (L/D=1.10–1.30); teleoconch of 5–6 whorls; whorls rounded, but peripheral spiral cord frequently slightly stronger than others, giving the appearance of a weak peripheral angulation; apical angle approx. 75°; protoconch sunken and apex thus appearing truncated; suture indented, but somewhat adpressed, narrowly channelled, inserted at level of subperipheral cord, but descending below this just prior to outer lip; outer lip with well-developed subterminal varix. First teleoconch whorl sculptured with 15–18 axial pliculae; 4 spiral cords develop during second whorl, others arising by intercalation with growth; penultimate and last adult whorls with ±8 primary spiral cords between suture and periphery (inclusive); cords well defined, narrower than their intervals; an intermediary cord often developing between primary cords in latter half of last adult whorl. Axial sculpture of prosocline pliculae persists throughout growth; pliculae generally slightly weaker than cords, these together producing a regular, oblique cancellation with equilaterally rhomboidal interstices; cords roundly beaded where crossed by pliculae; beads stronger and more angular on subsutural cord and still larger and scale-like or spine-like on peripheral cord. Base with ±7 primary spiral cords, their intervals usually with a weaker intermediary in final half whorl; axial pliculae continue onto base but their number appears to double in latter third of last adult whorl, rendering spiral cords more finely and closely beaded; umbilicus lacking in all except small juveniles (<4 whorls), but often obscured by reflected columella even in these. Peristome markedly oblique, more or less in one tangential plane; aperture roundly D-shaped, flattened parietally; columella lip a thickened pillar with 2 well developed teeth separated by a shallow concavity; lower tooth stronger and frequently squarish with a raised ridge along its lower margin, upper tooth weaker and clearly representing the end of a subparietal spiral pleat; pleat separated from paries by a U-shaped notch; umbilical region median to thickened columella pillar sunken, forming an elongate, more or less rectangular pit; pit bordered basally by a medial extension of ridge of lower columella tooth; umbilical/parietal region covered by inductural callus; callus translucent, smooth and glossy, raised somewhat basally and confluent with flaring margin of outer lip; interior of outer lip with a subterminal thickening corresponding in position with the external labral varix; thickening set with numerous elongate denticles and rounded tubercles, these not running into deeper portions of aperture; 2–3 denticles closest to junction of basal and columella lips larger, forming a two- to three-humped bulge, which together with the lower columella tooth delineates a pronounced U-shaped notch; margin of outer lip flaring; interior of aperture nacreous, somewhat angled beneath spiral cords of shell exterior, but not spirally lirate.
Microsculpture ( Fig. 16B, C View Fig ): First teleoconch whorl with vermiform spiral threads, replaced on subsequent whorls by prosocline, scratch-like microsculpture, filled with intritacalx deposit.
Protoconch ( Fig. 16A, C View Fig ): Translucent white; diameter ca 360 µm; level with or slightly sunken below first teleoconch whorl and somewhat down-tilted; degree of tilting variable between individuals; surface mostly worn, but with traces of irregular granulation; terminal lip weakly sinuous.
Colour: Spire apex uniform white, later whorls (3 rd onwards) with pale fawn ground patterned with darker, brownish markings; markings initially in the form of axial bands or blotches, but penultimate and last adult whorls rather more randomly mottled; subterminal varix and flaring edge of outer lip with brownish spiral bands in cord intervals; precise shade and density of colour pattern variable between individuals, some specimens very sparsely marked, but outer lip varix evidently patterned in all; cord intervals with pink/green iridescence; living and fresh specimens with a buffish intritacalx deposit. Shell exterior of live-taken specimens often with some encrustation by other marine organisms, but not (in the material available) entirely covered with sponge.
Dimensions: Holotype (largest specimen), length 11.4 mm, diameter 8.8 mm.
Operculum ( Fig. 4E View Fig ): Initially tightly multispiral, but whorls broadening with growth and becoming more openly multispiral.
Radula ( Fig. 17 View Fig ): Formula ∞+4+1+4+∞, with ca 60 transverse rows of teeth. Lateral flanges of rachidian well developed creating a distinct hood, base of cusp with well-developed transverse ridge, cutting edge coarsely dentate with elongate-lanceolate central denticle with narrowly acuminate tip, and up to 5 lateral denticles on each side, last of which forms a rounded boss at shoulder of tooth. Laterals with overlapping shafts and trigonal, distinctly asymmetrical cusps, decreasing in size from first to fourth; inner cutting edge curved and finely serrate almost from tip, outer cutting edge nearly straight and set with coarse, close-set, more elongate denticles, starting some distance back from tip; first lateral strongly hunched at outer base of cusp. Marginals very long and slender, the cusp elongate, sides frequently in-rolled, and with a fringe of fine denticles on outer margin and at tip; outer shaft base of inner 1 or 2 marginals expanded and jaggedly serrate; serrations continue sparsely up shaft.
External anatomy ( Fig. 6C View Fig ): Body whitish with some brownish pigmentation on sides of foot, lateral regions of snout and around base of cephalic tentacles. Cephalic lappets distinct, their free margin smooth or at most shallowly lobate (rather than digitate), its edge minutely papillate; lateral expansions of snout broad; right post-ocular peduncle present in both sexes, a longitudinal groove on its upper surface; right subocular tentacle not evident; right neck lobe with approx. 4 moderately large, first-order tentacles anteriorly; left neck lobe with a group of 8–10 slightly smaller first-order tentacles anteriorly, with even smaller intermediaries; left neck lobe with approx. 5 epipodial sense organs on under surface, right lobe with approx. 3; posterior part of both lobes smooth; epipodial fold with 7–9 tentacles of various sizes, but without very small intermediary tentacles; larger tentacles each with a distinct epipodial sense organ at the base.
Holotype ( Fig. 15A–C View Fig ): SOUTH AFRICA: Eastern Cape: off Rame Head (31.8450°S 29.4750°E), living, - 150–160 m, sponges, dredged NMDP, RV Meiring Naude, st’n K10, 20.vii.1982 ( NMSA E7756 View Materials /T2595) GoogleMaps . Paratypes: SOUTH AFRICA: KwaZulu-Natal: SE of Neill Peak [ Cunge Hill ] (28.7400°S 32.5367°E), - 320–340 m, sandy mud, dredged NMDP, RV Meiring Naude, st’n ZP5, 12.vi.1988 ( MNHN 24817 View Materials , 1 specimen) GoogleMaps ; SE of Port Durnford (29.0150°S 32.2017°E), - 215 m, glutinous sandy mud, dredged NMDP, RV Meiring Naude, st’n ZQ8, 13.vi.1988 ( NMSA E3119 View Materials /T2597, 4 specimens) GoogleMaps ; SE of Port Durnford (29.0967°S 32.1567°E), - 165 m, mud with sand, dredged NMDP, RV Meiring Naude, st’n ZQ15, 17.vi.1989 ( NHMUK 20110382 View Materials , 1 specimen) GoogleMaps ; off Matigulu River mouth (29.3567°S 31.9417°E), - 145 m, mud, shell-rubble, dredged NMDP, RV Meiring Naude, st’n ZR7, 16.vi.1989 ( NMSA E8790 View Materials /T2599, 1 specimen) GoogleMaps . Eastern Cape: same data as holotype ( NMSA S9912 View Materials /T2594, 1 specimen) GoogleMaps ; off Qora River (32.3967°S 28.8117°E), living, - 196 m, sponge, dredged NMDP, RV Meiring Naude, st’n U9, 14.vi.1983 ( NMSA C5153 View Materials /T2593, 1 specimen) GoogleMaps ; off Nqabara Point (32.4533°S 28.9317°E), living, - 250 m, live sponges, some corals, dredged NMDP, RV Meiring Naude, st’n S10, 12.vii.1984 ( NMSA W7501 View Materials /T2592, 1 specimen) GoogleMaps ; off Nqabara Point (32.4550°S 28.9267°E), living, - 210 m, live sponges, dredged NMDP, RV Meiring Naude, st’n S9, 11.vii.1984 ( NMSA W7502 View Materials /T2671, 1 specimen) GoogleMaps ; off Qolora River (32.7633°S 28.6067°E), - 240–250 m, live sponges, dredged NMDP, RV Meiring Naude, st’n Y9, 14.vii.1984 ( NMSA C7026 View Materials /T2598, 1 specimen) GoogleMaps .
Additional material examined (all NMSA): MOZAMBIQUE: off Beira , - 110–145 m, ex pisce, v.2005 (J. Rosado coll’n) . SOUTH AFRICA: KwaZulu-Natal: SE of Neill Peak [ Cunge Hill ] (28.7400°S 32.5367°E), - 320–340 m, sandy mud, dredged NMDP, RV Meiring Naude, st’n ZP5, 12.vi.1988 (E3977, E3978, E6958) GoogleMaps ; SE of Port Durnford (29.0250°S 32.1967°E), - 310–320 m, glutinous sandy mud, dredged NMDP, RV Meiring Naude, st’n ZQ9, 13.vi.1988 (E3168) GoogleMaps ; ditto (29.0967°S 32.1567°E), - 165 m, mud with sand, dredged NMDP, RV Meiring Naude, st’n ZQ15, 17.vi.1989 (E8697) GoogleMaps ; off Glenton Reef (29.2450°S 32.0367°E), - 200–210 m, sandy mud, dredged NMDP, RV Meiring Naude, st’n ZRR9, 18.vi.1989 (S481) GoogleMaps ; off Matigulu River mouth (29.3650°S 31.9367°E), - 200–220 m, mud and coarse sand with Dendrophyllia , dredged NMDP, RV Meiring Naude, st’n ZR9, 16.vi.1989 (E8989) GoogleMaps . Eastern Cape: off Rame Head (31.8583°S 29.4683°E), - 170–200 m, sandstone, yellow hydroids, dredged NMDP, RV Meiring Naude, st’n K11, 20.vii.1982 (S9944) GoogleMaps ; off Mbashe River (32.3033°S 29.0683°E), - 200–220 m, sponge rubble, dredged NMDP, RV Meiring Naude, st’n Q1, 18.vii.1982 (V495) GoogleMaps ; off Shixini Point (32.5267°S 28.8833°E), - 500 m, muddy sand, coral rubble, dredged NMDP, RV Meiring Naude, st’n T17, 13.vii.1984 GoogleMaps (C7060).
Distribution and habitat ( Fig. 13 View Fig ): Known primarily from Zululand to south-western Transkei (Neill Peak [Cunge Hill] to Qolora River), with one additional record from central Mozambique; - 110–500 m (living specimens - 150–250 m). Evidently a rather rare species, dead shells have been dredged in relatively deep water on rather lifeless muddy substrata (e.g. the Tugela Bank), but the five living specimens available were all collected in sponge communities on hard substrata near the continental shelf break. The absence of records from off central KwaZulu-Natal probably reflects less extensive dredging on the outer continental shelf and upper slope in this area.
Remarks: Danilia textilis closely resembles D. discordata Vilvens & Héros, 2005 from Vanuatu, particularly in terms of the number and relative strength of the spiral cords. In both species there are eight spiral cords above (and including) the periphery (the ninth cord mentioned by Vilvens and Héros (2005) is subperipheral), of which the peripheral cord is somewhat larger and distinctly more spiniform than those above it. Both species also have a strong, squarish lower columella tooth and a colour pattern of brown, frequently axial, markings on a pale fawn ground. However, in D. discordata the six spiral cords between the subsutural and peripheral cords are wider and conspicuously flattened, as are the beads where the cords are crossed by the axial pliculae. In D. textilis the spiral cords are rounded and narrower than their intervals and retain raised rounded beads. The sculpture throughout is of a regular, open, oblique, net-like reticulation. In this regard it resembles D. insperata Beu & Climo, 1974 from New Zealand, but that species has more evenly rounded whorls with fewer spiral cords (six above and including periphery) and a less robust lower columella tooth. D. weberi Schepman, 1908 from Indonesia and the western Pacific has more numerous spiral cords due to intercalation of intermediaries, has beads that are angular rather than rounded and has a broader, more robust basal columella tooth. The recently described D. stratmanni Poppe, Tagaro & Dekker, 2006 from shallower water (- 50–150 m) in the Philippines has much finer sculpture, more numerous spiral cords and lacks spiniform beads on the peripheral spiral cord. D. boucheti , the only other species of Danilia recorded from the south-western Indian Ocean, is considerably smaller and has an almost biangular whorl profile.
The precise form of the apertural dentition varies considerably between individuals and is presumably related to maturity. There is evidently further thickening of the columella lip and its teeth, even after the subterminal varix and flared outer lip margin have formed.
Genus Ascetostoma gen. n.
Etymology: From Greek asketos (curiously wrought or ornamented) and stoma (a mouth); in reference to the complex apertural features. Gender neuter.
Type species: Euchelus providentiae Melvill, 1909 .
Diagnosis: Whorls rounded, suture indented and somewhat channelled; sculpture of finely beaded spiral cords; umbilicus present, lined and apically plugged with callus; columella pillar with a well developed, squarish, basal tooth and a smaller, more rounded, upper one; parietal region with spreading, glossy, translucent callus deposit bearing short oblique ridges; callus deposit extending around umbilical margin and joining basal lip; umbilical margin with several small denticles and one larger one in parietal region; interior of outer lip subterminally thickened and bearing ridge-like denticles arranged more or less in 2 rows; base of columella with pronounced U-shaped notch between basal columella tooth and first outer lip denticle; exterior of outer lip also with a low, broad, subterminal thickening; suture descending at aperture when mature.
Remarks: Similar to the Herpetopoma group of species, but characterised by the callus lined umbilical depression, spirally ridged parietal callus and denticulate umbilical margin. Danilia also has a callus lined depression in the umbilical region, but in members of that genus it is shallower and trough-like; they also possess a strong, well-defined, rib-like external varix behind the outer lip. Clypeostoma has at most a faint umbilical depression and a much more extensive inductural callus deposit. In Ascetostoma the sculpture is also more finely and closely beaded than in Clypeostoma .
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