Diaphana minuta Brown, 1827

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 : 509-510

Diaphana minuta Brown, 1827

( Fig. 7 A–F)

Bulla debilis Gould 1840: 196 ; 1841: 164–165, fig. 95.

Diaphana debilis — Pilsbry 1893: 281, pl. 59 fig. 27.

Bulla hyalina Turton 1834: 353 .

Utriculus hyalinus — Jeffreys 1867: 427 –429.

Diaphana hyalina — Thorson 1946: 251, fig. 147. G. O. Sars 1878: 289, pl. 18 fig. 1, pl. XI fig. 10.

Diaphana candida Brown 1827 : pl. 38 figs 13, 14.

Utriculus candidus — Brown 1844: 59, pl. 19 figs 13, 14.

Amphisphyra expansa Jeffreys 1865: 330 –332.

Utriculus expansus — Jeffreys 1867: 426.

Diaphana expansa — G. O. Sars 1878: 289, pl. 18 fig. 2. Pilsbry 1893: 284, pl. 26 fig. 69.

Diaphana minuta Brown 1827 : pl. 38 figs 7, 8. Odhner 1939: 8. Høisaeter 1986: 100. Burn & Thompson 1998: 947. Schiøtte 1998: 96, figs 13, 18 F–H. Høisaeter et al. 2001: 250. Sneli et al. 2005: 96. Kantor & Sysoev 2006: 250, pl. 124 fig. I. Templado 2011: 403.

Utriculus minutus — Brown 1844: 58, pl. 19 figs 7, 8.

Diaphana pellucida Brown 1827 : pl. 38 figs 10, 11.

Utriculus pellucidus — Brown 1844: 59, pl. 19 figs 10, 11.

Diagnosis. Shell external, white to transparent, smooth. Body white. Foot posteriorly bifurcated, cephalic shield with tentacular lobes. Rachidian tooth denticulate, lateral teeth with minute denticulation, teeth on left side slightly smaller than on the right. Gizzard with no plates. Short elongate penial sheath dividing into prostate with two coiled branches, thick branch with blunt ending, thin branch with bulky lump at the end.

Type locality. Loch Torridon, Scotland.

Material examined. Gullmarn, Sweden, 5 spcs (dissected), ZMUC unnumbered, H = 2–3.3 mm. 60°19'45.0120" N, 005°15'01.8" E, Bergen, Knappen, Norway, 1 spc (dissected), ZMBN 90597, H = 2.6 mm.

Shell ( Fig. 7 A–D): Maximum H = 5.8 mm ( Schiøtte 1998). External, thin; white to transparent; globoseelongate in shape, tapering in straight line posteriorly from widest point in middle of shell, anterior part rounded, aperture wide with parietal callus, apex truncate, protoconch protruding, umbilicate; shell surface smooth, faint growth lines.

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

Radula ( Fig. 7 E): Radular formula 12 x 1.1.1. Rachidian tooth with two coarsely denticulate lobes. Lateral teeth long, inner edge denticulate. Radula slightly asymmetrical with left laterals smaller than the right laterals, no large denticle on tip of left laterals.

Male reproductive system ( Fig. 7 F): Short elongate penial sheath dividing into prostate with two coiled branches, thick branch with blunt ending, thin branch with bulky lump at the end.

Ecology. This species can be found from the intertidal down to 350 m ( Thompson 1988; Poppe & Goto 1991). Specimens examined by Schiøtte (1998) were found in tide pools, on mire, pebbles, mud, sand, clay, shell gravel, algae and stones with Corallina .

Distribution. Circumpolar from New England, the Canadian Archipelago, over Greenland, Iceland, the Barents Sea, White Sea, Kara Sea, Laptev Sea to the east Siberian Seas, down to Japan, British Columbia ( Schiøtte 1998; Kantor & Sysoev 2006). In Norway along the entire coastline; British Isles southwards to the Mediterranean Sea and the Canary Islands ( Thompson 1988; Poppe & Goto 1991; Schiøtte 1998; Høisaeter et al. 2001; Sneli et al. 2005).

Remarks. Diaphana minuta was re-described recently and its taxonomic status discussed thoroughly ( Schiøtte 1998). Before the latter revisionary work the species was surrounded by much taxonomic uncertainty. G. O. Sars (1878) recognized four species of Diaphana but mixed them up as he illustrated D. minuta (as D. hyalina and D. expansa ) having an asymmetrical radula. Lemche (1948) synonymised most northern European species of Diaphana ( D. globosa , D. hiemalis , D. glacialis , D. minuta ) under the name D. minuta . However, these species show considerable differences in shells, radulae and male reproductive system as well as in ecological preferences and distributions ( Schiøtte 1998). Thompson (1988) included three species, but only one ( D. minuta ) is identified correctly.

Figures

FIGURE 7. Diaphana minuta. A. dorsal view of shell (automontage picture). B. ventral view of shell (SEM). C. apex of shell (SEM). D. dorsal surface of shell (SEM). E. detail of radula (SEM). F. male reproductive system (drawing). Abbreviations: ga, genital aperture; pr, prostate; ps, penial sheath. Scale bars: A = 0.5 mm; B = 200 Μm; C, D, E = 100 Μm; F = 250 Μm.