Shell medium-sized to large for genus (to 222.4 mm SL; average adult size 173.8 mm SL, n = 11), thick, robust, of approximately ten whorls. Whorl profile evenly rounded with no peripheral keel or angulation. Protoconch missing in all material examined. Primary (post-nuclear) whorls bear four strong, evenly spaced spiral cords, with a weaker fifth immediately below suture; fifth cord strengthens from third whorl and other minor cords emerge; fourth whorl with four major cords and at least one minor one on either side of central four. By seventh whorl, seven major spiral cords present, with interspersed minor cords in troughs; penultimate whorl at terminus of suture bears 12 major cords and numerous minor cords. Approximately 50 spiral cords of even strength distributed over body whorl, angle of cords to axis steepening towards end of neck; cords slightly crowded near suture, evenly distributed otherwise.
Axial sculpture of characteristic broad, closely spaced ribs spanning whorl from suture to suture; ribs present from first whorl through entire teleoconch, but often becoming reduced or absent on final half of body whorl. Spiral cords cross ribs, thickening slightly at apex of ribs on later whorls but not forming lobes. Interspaces of spiral cords with very numerous, fine axial growth lines that can be slightly lamellate; growth lines do not cross cords.
Aperture almond-shaped, smooth and porcellaneous within. Labral wall bears spiral cords that terminate in tapered points shortly before lip and correspond in position to troughs between spiral cords on shell exterior; lip thus corrugate, with slight indentations and thickened, glazed margin in adults, but no developed dentition. Parietal wall of aperture smooth, thickened; margin clearly pronounced and detached in very large specimens, but not recurved. Neck tapered, slightly to strongly recurved in distal half. Canal open, of even width over whole length, even in specimens with heavily twisted neck; parietal margin of canal pronounced but not detached except in largest specimens.
Shell dull white overall, with occasional pale brown staining of earliest whorls. Periostracum thin, pale brown, of axial lamellar construction, lamellae bearing finely pointed thorns with broad, triangular bases. Periostracum occasionally reduced or absent on anterior quarter of spire whorls and entire anterior part of body whorl. Operculum typical for genus, thick, chitinous and almond-shaped, with nucleus at pointed tip; dark brown. Animal and radula unknown.

Fusinus marisinicus is a distinctive species characterized by its broad, rounded axial ribs that span all the spire whorls from suture to suture and that normally persist, though often in diminished form, onto the body whorl. Very large specimens can have somewhat reduced axial sculpture, but it is rarely altogether absent on the body whorl. The parietal margin of the aperture and columellar margin of the canal are usually defined, but are only detached in the very largest specimens.
The nearest congener to F marisinicus morphologically is F. crassiplicatus from central Japan, but that species is far smaller (to 84.2 mm SL; average adult size 70.1 mm SL, n = 6) than F. marisinicus (to 222.4 mm SL; average adult size 173.8 mm SL, n = 11), with a more slender profile and fewer, more pronounced axial ribs on the early whorls. In addition, the aperture in F. crassiplicatus becomes somewhat ventricose in adult specimens.
Another sympatric species of similar size is F salisburyi, from which F marisinicus may be distinguished by its generally thinner shell with broad, rounded axial ribs, its much finer, less numerous spiral cords, and the absence both of a detached, recurved parietal shield and of a pronounced whorl periphery. In addition, the early whorls of F salisburyi have much deeper sutures and sharply defined spiral cords with deep interstices. From certain large specimens of F perplexus from Japan and the East China Sea off Kyushu,F. marisinicus can be distinguished by its longer, more slender neck, the absence of a peripheral cord or knobs and its smoothly curved outer lip, in contrast to the often ventricose or quadrate aperture of E perplexus of comparable size. F undatus is a sympatric species with axial ribs that can span the entire whorl, but it has a thicker, smoother shell with a broader neck, pronounced shoulder knobs that form axial buttresses, and reduced or absent spiral cords.
Since its description, the number of specimens of F marisinicus offered for sale at any given time by Chinese dealers has grown into the hundreds. It might thus prove to be the most common large Fusinus species in the East China Sea, rivaled only by F. diandraensis.

Currently known only from East and possibly South China Seas on outer continental shelf off southern and eastern China, from 150 to 350 meters on sand and mud bottoms.