Endosymbiotic bacteria in Nudibranchs

Dear Joseph,
I guess you have looked at the Bacteria page. That discovery of bacteria in Dendrodoris nigra by Annette Klussmann-Kolb and Gilianne Brodie is apparently the first record of symbiotic bacteria in any gastropod. Have a look at their publicatiion and if you have further questions you will find their email addresses on that page.

My understanding is that they were not actually searching for bacteria but came across these odd structures during an histological examination of the species. Like many scientific discoveries it resulted from the ability of the researchers to realise that what they saw was worth following up.

If you definitely need to find bacteria another species of Dendrodoris would be more likely than the unrelated Dendronotus but a much more likely group would be the protobranch bivalves of the family Solemyidae. They either have no stomach or a very reduced stomach and live in anaerobic mud. They depend partially or wholly on sulphur-oxidising symbiotic bacteria which live in their gills. I can't tell you where to find them in New Hampshire but there is a species, Solemya borealis in the northwestern Atlantic and species I am familiar with live in shallow water, on muddy, sheltered shores. If you can find a copy of Volume 1 of Mollusca. The Southern Synthesis there is a couple of pages on Solemya and references.
Best wishes,
Bill Rudman.