Shell generally depressed turbiniform to sublenticular; whorls somewhat flattened and more sharply curved at the periphery; teleoconch of up to 5 whorls. Sculpture generally absent or of fine spiral lirae, few species corded; superficially smooth species usually with spiral lirae on early whorls; axial sculpture of fine growth lines, rarely pliculate. Umbilicus deep, open to apex, variable in width but always relatively wide, margin evenly rounded or distinctly angled. Aperture variable in shape, peristome incomplete; outer lip crenulate only in corded species; interior nacreous. Protoconch: Typically solarielline, diameter of known species ranging from 290-500 µm; comprising approximately l,25 whorls. Colour: Variable; some monochrome, some dark above and light below, others mottled or axially striped; colour pattern characteristic for some species, not for others; often very variable within species, some showing marked bathymetric variation in pattern. Occasionally iridescent. Dimensions: Small to minute, but some species relatively large for subfamily, exceeding 15 mm in diameter. Radula: Radula short and broad with ca 20 transverse rows of teeth, rows without a pronounced posterior dip in mid-line; formula (6 -10) + (3 - 4) +1 + (3 - 4) + (6 -10). Rachidian more or less equilaterally triangular, lateral margins denticulate and frequently curved, occasionally somewhat flattened proximally; inner laterals less elongate than those of Spectamen. Third lateral with reduced cusp, whole tooth may be missing in small species. Fourth lateral long, relatively broad and sickle-shaped, finely toothed distally on one or both sides. Rachidian and inner laterals close set with relatively well-developed interlocking bases. Latero-marginal plates lacking. Marginals few; usually less than 10, elongate, curved and frequently toothed distally.

Diagnosis. Following Herbert (1987) and using the additional Indo-Pacific species described in this work, the main conchological features of this genus are:
• shell width 5 mm to about 20 mm;
• shape of shell conical, sometimes slightly cyrtoconoidal or coeloconoidal, with a moderately elevated to strong¬ly depressed spire; periphery from rounded to subangulate;
• protoconch typically solariellid of about 1-1.25 whorl, diameter 200-500 um, often with several spiral lines;
• teleoconch of up to 5 more or less convex whorls; sculpture of a few spiral cords on first whorl, usually quickly vanishing on next whorls, making an almost smooth surface on last whorl;
• umbilicus wide, deep, open to apex, with a rounded or angulate margin, spiral cords and occasionally thin axial
threads inside; axial pleats around umbilicus present or absent, sometimes visible on some parts of umbilicus but absent from others;
• aperture with an incomplete peristome; outer and inner lip thin; inner lip usually with weak basal thickening against umbilical rim; interior nacreous;
• colour variable, often with flames, chevron-like patterns and spiral bands.
Remarks. The genus Ilanga was initially defined and used for species living in the south-western Indian Ocean (Herbert 1987). The present work, based on molecular and morphological study, shows that species assigned to Ilanga are in fact distributed throughout the tropical Indo-West Pacific. The genus does not occur in the Atlantic or in temperate regions. Its depth range is given from 16-1280 m by Herbert (1987), with 40-1280 m for living specimens; in this study we found living specimens from 50-616 m, which is shallower than the depth range of some other solariellid genera (e.g. Bathymophila 326-1570 m, Archiminolia 91-1385 m, Zetela 139-2421 m; Marshall 1999). There are no apparent biogeographic radiations in the Ilanga taxa included in molecular analyses (Williams et al. 2013, Sumner-Rooney et al. 2016, Fig. 2). For instance, Indian Ocean species are found scattered throughout the phylogenetic tree of Ilanga and do not form a clade. Most species have been sampled from only one locality (which suggests low sampling intensity) and only I. oxeia n. sp., I. corrineae and I. fulgens are more widespread. There are two instances of species pairs, where one species found in the North West Pacific is sister to a species found in the South West Pacific (I. harrytaylori & I. eurystoma; I. comes & I. navakaensis). Similar patterns have also been noted in other solariellid taxa (Williams et al. 2013). However, sampling to date is limited and needs to be expanded before meaningful biogeographic studies can be undertaken,
Herbert (1987) figured living specimens of Ilanga and provided details about their feeding habits. He observed animals using a ring of digitate palps around the mouth to sort and process sediment. He also observed some specimens swimming short distances to avoid predators. All species examined to date appear to have functional eyes with open apertures and pigment (Williams et al. 2013, Sumner-Rooney et al. 2016, this study). Shells are typically flattened and wider than high. Most species have shells with some colour (usually brown or pinkish-brown, occasionally yellow) and pattern, although a few species lack any colour.