Abstract
Halisarca harmelini sp. nov. is described from the northwestem Mediterranean Sea at depths between 15-65 m from cor-alligenous rocks. The new species occurs as thin sheets only on the bryozoan Smittina cervicornis. Morphologically, it is characterizedby its thin layer architecture, skin-like, lusterless and smooth surface, a soft, very delicate and easily torn texture, and pale-yellow colour. At the cytological level H. harmelini is characterized by a complex of cells with inclusions: sphemlous, vacuolar, granular, microgranular and rhabdiferous cells. The new species is clearly different in cell and endobiotic bacteria content and in extemal morphology from all previously described species of Halisarca. In addition to the description of the new species, we have conducted a thorough ultrastmctural investigation and re-described the type species Halisarca dujardini Johnston, 1842 using specimens from different region of the North Atlantic, Arctic and North Pacific. To investigate the relationshipsbetween H. harmelini and H dujardini on the molecular level, we determined the complete mitochondrial DNA (mtDNA) sequences of the new species of Halisarca and compared it with that of H. dujardini. The two mitochondrial genomes are identical in gene content and gene arrangement but differ in size by -1,300 bp (6.8%). The overall genetic distance between coding sequences is 0.1, much greater than what has been previously reported for individual species of non-bilaterian animals. The latter observation supports the new species status ofH. harmelini.
NSTL