Diaphana lactea ( Jeffreys, 1877 )

Ohnheiser, Lena Tina & Malaquias, Manuel António E., 2014, The family Diaphanidae (Gastropoda: Heterobranchia: Cephalaspidea) in Europe, with a redescription of the enigmatic species C olobocephalus costellatus M. Sars, 1870, Zootaxa 3774 (6), pp. 501-522 : 507-509

Diaphana lactea ( Jeffreys, 1877)

( Figs 5 A–D, 6 A–D)

Utriculus lacteus Jeffreys 1877: 334 .

Retusa lactea — Sykes 1905: 31, pl. 3, fig. 4

Diaphana lactea — Bouchet & Warén 1979: 229 –231, 237. Høisaeter 1986: 100. Schiøtte 1998: 122, figs 22 A, 24 A–C. Sneli et al. 2005: 96.

Diaphana jonica Geronimo 1974: 151 , 152, pl. 2 fig. 2 (based on Schiøtte 1998).

Diagnosis. Shell external, white to transparent, elongate cylindrical, smooth. Body white. Foot posteriorly bifurcated, cephalic shield with tentacular lobes. Rachidian tooth denticulate, asymmetrical, lateral teeth with minute denticulation, teeth on left side smaller than on the right.

Type locality. Station 12, Valorous expedition.

Material examined. Norwegian Sea, off Trondheim (64°16'54’’ N, 00°11'42’’ W), 3 spcs (dissected), ZMBN 85923, H = 3.7, 3.8 mm. SE of Jan Mayen (70°26'12’’ N, 06°31'48’’ W), 1 spc (dissected), ZMBN 85934, H = 5.8 mm. Norwegian Sea, Trondheim area (63°58'12’’ N, 00°23'42’’ W), 1 spc (dissected), ZMBN 85932, H = 3.9 mm. North of Faroe Islands (63°45'12’’ N, 00°07'60’’ W), 1 spc (dissected), ZMBN 85933, H = 3.9 mm. Between Iceland and Jan Mayen (68°46'57" N, 012°31'39.6" W), 3 sh, ZMBN 90574, H = 2.14–2.26 mm.

Shell ( Fig. 5 A–D): Maximum H = 5.8 mm. External, thick; white to whitish transparent; elongate cylindrical in shape, middle part of shell straight, narrowing anteriorly and posteriorly, other side uniformly rounded, aperture wide with thin parietal callus, columellar lip straight, apex sunken, mammillate, but protoconch not protruding top of last whorl, umbilicated; shell surface smooth.

Animal: Body white. Foot posteriorly bifurcated. Cephalic shield with tentacular lobes posteriorly.

Radula ( Fig. 6 A–C): Radular formula 11 x 1.1.1. Rachidian tooth with two flat denticulate lobes separated by gap with a pointed small cusp, lobes asymmetrical, right lobe larger. Lateral teeth long, inner edge denticulate. Radula asymmetrical with left inner laterals much smaller than the right laterals, one large denticle on tip of left laterals only.

Male reproductive system ( Fig. 6 D): Prostate emerging as undivided lump from penial sheath in a right angle, external seminal groove continuing as open groove through penial sheath.

Ecology. Specimen examined by Schiøtte (1998) were found on mud, sand, silty sand, shell sand, clay, foraminifera, gravel and silt from 559–4268 m depth.

Distribution. Reported from the Norwegian Sea, the Faroe Islands, the Denmark Strait, North Atlantic and the Mediterranean Sea ( Schiøtte 1998; Høisaeter 2009; Sneli et al. 2005; present study).

Remarks. This species was redescribed by Schiøtte (1998). Lemche (1948) did not include Diaphana lactea in his review of northern Atlantic species. During the present study denticulation of the rachidian tooth was found to be variable from almost absent to coarsely denticulate (fig. 6 F, G). The seminal groove continued as open channel in the penial sheath, which was not the case in the other Diaphana species studied here. It is most abundant below 2000 m depth and therefore considered a species of abyssal affinities ( Høisaeter 2010).

Figures

FIGURE 5. Diaphana lactea. A. dorsal view of shell (SEM). B. ventral view of complete animal (automontage picture). C. apex of shell (automontage picture). D. dorsal surface of shell (SEM). Scale bars: A = 200 µm; B = 1 mm; C = 250 µm; D = 20 Μm.

FIGURE 6. Diaphana lactea. A. radula (SEM). B. detail of lateral teeth (SEM). C. rachidian teeth (SEM). D. male reproductive system (drawing). Abbreviations: ga, genital aperture, pr, prostate; ps, penial sheath; sgr, seminal groove. Scale bars: A = 30 Μm; B, C = 10 Μm; D = 200 µm.