Fusinus mauiensis: Type locality. Off Maalaea Bay, Maui, 55 m.
Distribution. Although chiefly known in collections from Maalaea Bay, F. mauiensis is distributed more widely, ranging northwards at least to Kauai and westwards at least to the Johnston Atoll (HURL dive 206, 21 October 1983, BPBM).

Fusinus mauiensis: The egg capsules of F. mauiensis have a distinctive incurved shape and rose-pink coloration. They were first illustrated by Kay (1979: fig. 82c) as those of a species of Fasciolaria, a genus that is not present in the Pacific, but the same figure was reproduced by Kay and Schoenberg-Dole (1991: 23, fig. 26) as representing F. undatus. The identification as F. mauiensis is here confirmed by the direct observation of an adult animal depositing capsules. Severe damage to the rostrum is common, and is apparently due to predation by the large Hawaiian Stingray Dasyatis lata (Garman, 1880).
While adult specimens are rarely confused, juvenile shells of F. mauiensis can resemble those of F. sandvichensis. However, the former always have broader, more inflated axial ribs on the first few whorls that are never vertically or even diagonally aligned with those above and below them but instead are interfingered. Juvenile F. sandvichensis can also have a thick, tapering rostrum and brown early whorls, both inviting confusion with F. mauiensis. The last is traditionally distinguished by having only three (or rarely four) knobs visible in dorsal view, as is the case here, while the latter has four and often five. Nevertheless, this specimen completely lacks the strong recurvature of the rostrum that characterizes F. mauiensis and has the anteriorly quadrate aperture typical of F. sandvichensis. The axial sculpture on the early whorls is somewhat coarser than is usual in F. sandvichensis, but the authors cannot confidently place this shell in either species. See Discussion below. Fusinus mauiensis is morphologically very similar to F. undatus (Fig. 20) which ranges from Indonesia to central Japan and northern Australia. Whether the latter occurs in the Hawaiian islands is an open question. Callomon and Snyder (2006: 181) asserted that it does, citing several photographs in literature that resembled F. undatus as much as F. mauiensis and a single specimen with the vague data "Hawaii" in the Snyder Collection. However, despite seeing many more examples of F. mauiensis since, we have yet to see a specimen with specific locality data from Hawaii that undoubtedly represents F. undatus. The principal distinction between the two, apart from the heavier shell, more prominent and inflated knobs and shorter, broader rostrum in F. mauiensis, is the profile of the early spire, which tends to be longer and more lanceolate in F. undatus. Juvenile F. undatus also often have short, dark brown spiral dashes between the shoulder knobs, while the first few whorls in F. mauiensis are often uniform dark brown.
The radula is typically fusinine with a trident rachidian and a pair of lateral teeth bearing eleven cusps. The innermost cusp is reduced to a small hook and can be absent on one side and the outermost two or three are bent inwards and progressively reduced towards the outer edge. The rachidian (Fig.is notably asymmetrical, with three major and one minor cusp on a relatively broad base. As is common in fusinine species its morphology changes ontologically with the fourth (leftmost) cusp becoming reduced.