31 Pusillina inconspicua COMPARISON Pusillina sarsii.

CAUTION: the text below is an interpretation of this image. Others may differ, but it matches well the P. sarsii shells illustrated and described from the brackish Isefjord by Rasmussen (1973). (Roskilde Fjord joins Isefjord). The type locality for this form of P. sarsii is Bohuslän on the Swedish side of the Kattegat facing the area of Denmark containing Isefjord and Roskilde Fjord. Several sources point out that the majority of specimens of all three species in some populations lack costae and may have inconspicuous or absent body-markings. The distinctiveness of the shell suggests P. sarsii is a species distinct from P. inconspicua, but the similarity of the soft parts suggests they could be forms of one species. DNA sequencing is planned to attempt to decide the issue.

Shell
Squat with swollen whorls. (Rissoa parva and Pusillina inconspicua have more slender shells).
1: no tiny apical purple spot (P. inconspicua usually has purple spot 08 Pusillina inconspicua ).
2: body whorl swollen with 6 widely spaced strong costal ribs visible in apertural view (Rissoa parva 5-6 ribs 14 Rissoa parva ; Pusillina inconspicua 9-15 fine, closely spaced ribs 30 Pusillina inconspicua
Body
3: tip of long, translucent, pallial tentacle protruding beyond shell (in common with P. inconspicua 18 Pusillina inconspicua , but short on R. parva 06 Rissoa parva ).
4: posterior of opercular lobe unpigmented apart from small black mark (Rissoa parva all black 17 Rissoa parva ; Pusillina inconspicua unpigmented 10 Pusillina inconspicua).
5: anterior of opercular lobe black (in common with Rissoa parva 17 Rissoa parva. and Pusillina inconspicua 10 Pusillina inconspicua ).
6: broad transverse band on dorsal surface of foot extends onto edge of sole (in common with R. parva and P. inconspicua).
7: dorsal surface of head dark (in common with many P. inconspicua 14 Pusillina inconspicua ; but R. parva usually pale or with narrow medial dark mark 16 Rissoa parva.)
8: cephalic tentacles blurred by motion in image, but rows of dots similar to those on P. inconspicua 23 Pusillina inconspicua were observed by photographer.
9: black peripheral line on foot extends well beyond proximity of broad, dorsal, transverse band (in common with P. inconspicua 18 Pusillina inconspicua but not R. parva 17 Rissoa parva ) .
10: opening of posterior pedal gland dark on this specimen (usually pale on R. parva 17 Rissoa parva and P. inconspicua 18 Pusillina inconspicua
11: Opaque white posterior pedal gland stops well-short of edge of sole (similar to P. inconspicua but different from R. parva 28 Pusillina inconspicua ).