05 Rissoa parva

Surface appears smooth, but microscopic striae sometimes detectable (only very slight indications of spiral striae found on any shells examined by author).

 

1: strongest pair of striae may combine to form spiral groove (cord) a short distance below periphery near where costae terminate.

2: additional spiral cord.

3: medial dividing line on sole allows longitudinal folding to grasp strands of filamentous algae, and allows independent movement on either side of foot when in motion.

4: when magnified, narrow translucent slit may be detected in single white line in cephalic tentacle.

5: foot constriction enables transverse folding of narrow foot.

6: black osphradium that tests quality of inhalent water before it reaches ctenidium (gill).

7: brown lines absent from spaces between white costae on this specimen, but some brownish and green debris /growths in spaces.

8: encrustation of stony alga Titanoderma (syn. Lithophyllum)

Shell height 3.9 mm. Weymouth. Early April 2012.

 

Full SPECIES DESCRIPTION: flic.kr/p/uxy617

Key id. features: flic.kr/p/uxFKZK

Sets of OTHER SPECIES:

www.flickr.com/photos/56388191@N08/collections/

 

Done