As suggested by previous messages, it depends on what criteria you use for defining phyla.  If you do not allow one phylum to give rise to another, you will have fewer, for example.  Various extinct forms are considered to possibly represent additional phyla.  Mollusks have interactions with quite a few of the extant animal phyla (even not considering the high probability that many phyla may eat planktonic mollusk larvae or mollusks eating their larvae), and even with protists, bacteria, or plants.

If you believe the latest molecular analyses and insist that no phylum can produce another phylum, here is a list, with molluscan focus:
Porifera-sponges.  Many mollusks are commensals; pleurotomariids eat sponges.
Cnidaria: corals, jellyfish, etc.  Coral reefs provide molluscan habitat, and many gastropods feed on cnidarians, notably epitoniids and many opisthobranchs.
Ctenophora: comb jellies.
Placozoa: obscure little bunches of cells
Chaetognatha: arrow worms
Ectoprocta: bryozoans, often grow on mollusk shells
Echinodermata: sea urchins, starfish, etc.  Many starfish eat mollusks, and many mollusks feed on echinoderms (e.g., cassids), as well as commensal or parasitic forms.
Hemichordata: acorn worms, pterobranchs, graptolites
Chordata: tunicates, vertebrates.  Mollusks provide fascinating years of study to the most advanced vertebrates, in addition to many vertebrates that feed on mollusks, various parasites that inhabit both at points in the life cycle, etc.
Platyhelminthes: flatworms.  Some poorly studied forms may represent additional phyla.  Free-living flatworms are significant predators on oysters; some parasites infest mollusks.
Gastrotrichia: Tiny, ciliated; probably eaten by small gastropods.
Gnathostomulida: Tinier, in anoxic sediments
Cycliophora: lives on lobster lips
Syndermata: rotifers(wheel animals), acanthocephalan worms (parasites-not on mollusks)
Mesozoa: mostly parasitic in mollusks, especially cephalopods.
Priapulida: deep-sea worms, fossil ones ate hyolithids that might have been mollusks
Kinorhynchia: tiny marine worms
Loricifera: tiny marine
Nematomorpha: horsehair worms
Nematoda: roundworms, many parasitic, including on mollusks
Onychophora: velvet worms
Tardigrada: water bears
Arthropoda (includes Pentastomida): many prey on mollusks, hermit crabs use their shells

The following phyla appear relatively closely related to Mollusca:
Phoronida: phoronid worms
Brachiopoda: brachiopods, often mistaken for bivalves
Ectoprocta: bryozoan-like, may live on mollusk shells
Nemertea: ribbon worms
Sipuncula: peanut worms, some live in empty gastropod shells
Mollusca: many interactions with other mollusks
Pogonophora: beardworms, hot vent worms.  Deep-sea Acesta have been found growing on the worm tubes.
Echiurans: spoonworms
Annelida: segmented worms, popular food for many gastropods.

That's 33 if I counted correctly.


    Dr. David Campbell
    "Old Seashells"
    Biology Department
    Saint Mary's College of Maryland
    18952 E. Fisher Road
    St. Mary's City, MD  20686-3001 USA
    [log in to unmask], 301 862-0372 Fax: 301 862-0996
"Mollusks murmured 'Morning!'.  And salmon chanted 'Evening!'."-Frank Muir, Oh My Word!