White awl snail
| White awl snail | ||||||||||||
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Casing of Melanella alba |
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| Scientific name | ||||||||||||
| Melanella alba | ||||||||||||
| ( da Costa , 1778) |
The White Pfriemschnecke ( Melanella alba ) is a worm - type from the family of eulimidae (genus Melanella ), as Ectoparasite of sea cucumbers lives.
features
Melanella alba has a tall, narrow, cone-shaped, strongly shiny snail shell with a slightly convex outline, which in adult snails reaches a length of around 20 mm and a width of around 6 mm. The protoconch is often eroded, leaving 12 to 14 slightly convex whorls. The thread has about 5 to 13 almost flat, hardly curved, smooth, opaque whorls with an inconspicuous seam and is sometimes slightly curved. The pear-shaped housing mouth has an outer lip with a bulge that is clearly visible in a side view and an inner lip that is slightly bent over at the base. The housing is milky white, with the body color visible through the shell.
The head forms a flat protrusion with two narrow antennae at the front and a trunk that can be turned in and out on the underside. There is a black eye behind each of the two antennae that are brought closer together . The coat does not form a feeler. Behind the right antennae, the male has a curved penis with a dorsal open sperm channel. The foot is quite small and carries an operculum . The snail is white, the anterior portion and the sides of the foot, the opercular lobes and the antennae orange or with orange markings.
Distribution and way of life
Melanella alba is distributed in the north-eastern Atlantic Ocean from the Mediterranean to Norway .
It lives on muddy sand and gravel at depths of 16 to 135 m.
Development cycle
Melanella alba is segregated. The animals mate in the summer months, with the smaller male inserting his long, slender penis into the sexual opening of the larger female. The female attaches its thick-walled, egg-shaped, opaque, 3 mm long, 2.5 mm wide and 1.75 mm high egg capsules to the substrate. There are several hundred pink eggs in each capsule. Three weeks after egg-laying, free-swimming, plankton- eating Veliger larvae hatch from the capsules , which after a longer phase sink down as zooplankton and metamorphose into crawling snails .
Way of life
Melanella alba sucks on sea cucumbers , the daily rhythm of which it orients itself in its activity. She seeks the landlord to eat and lives free in between. Since the coelom liquid of the sea cucumber sucked in via the ejectable trunk is not very nutritious, a snail usually sucks for several hours to get full.
In the Atlantic , it sucks the humors of Neopentadactyla mixta , which in some places can infect practically all individuals. In the Mediterranean , it was as a parasite on Pseudothyone raphanus observed. Also on sea cucumbers of the genus Ocnus numerous white awl snails were often observed sucking. In Plymouth , Melanella alba has often been seen on the sea urchin Spatangus purpureus , but it has not yet been observed that it introduces its proboscis into the sea urchin.
The proboscis ( proboscis ), which is everted hydraulically as well as by muscle movement, has a strongly glandular epithelium on the section inserted into the host , the secretion of which apparently dissolves the connective tissue under the skin of the sea cucumber so that it can be sucked in.
literature
- Alastair Graham : Molluscs: Prosobranch and Pyramidellid Gastropods. Keys and Notes for the Identification of the Species . Linnean Society, London 1988. Eulimidae, Genus Melanella, Melanella alba (da Costa, 1778) , p. 526.
- Anders Warén (1983): A Generic Revision of the Family Eulimidae (Gastropoda, Prosobranchia). Journal of Molluscan Studies 49 (Supplement 13), pp. 1-96, here pp. 76-80. doi: 10.1093 / mollus / 49.Supplement_13.1
Web links
- Yves Müller, Frédéric André: Melanella alba (da Costa, 1778). Données d'Observations pour la Reconnaissance et l'Identification de la faune et la flore Subaquatiques (DORIS), December 13, 2018.
- MJ de Kluijver, SS Ingalsuo, RH de Bruyne: Melanella alba (da Costa, 1778). Marine Species Identification Portal
- Fischhaus Zepkow: Family Eulimidae
Individual evidence
- ↑ Timothy B. Smith (1984): Ultrastructure and function Of the proboscis in Melanella alba (Gastropoda: Eulimidae). Journal of the Marine Biological Association of the UK 64 (3), pp. 503-512. doi: 10.1017 / S0025315400030198