Species of the genus Lioconcha Mörch, 1853 are among the more difficult of the Veneridae to identify because of their sometimes wide variation in colour pattern and the vestigial nature of the pallial sinus, the latter structures widely used as a valuable species diagnostic elsewhere within the Veneridae. Species of Lioconcha are usually characterised by bright, sometimes intricate shell colour patterns and a smooth shell. Species are known from tropical and subtropical regions of the Indo-West Pacific, but have yet to be reported from the eastern Pacific or the Atlantic. They are infaunal, occurring in clean, muddy or coral sand, typically in sheltered shallow water habitats and, sometimes, in moderately deep water (>100 m; Lamprell and Stanisic 1996). Lioconcha shells are commonly collected either as beached specimens or in the vicinity of octopus dens, but living material can usually only be gathered by dredging or digging into the sediment. Although Lioconcha from New Caledonia (Lamprell and Stanisic 1996) and South Africa, Mozambique and the Mascarene and Andaman Islands (Lamprell and Kilburn 1999a,b) have been previously discussed, the genus as a whole has not been reviewed in the modern literature.

Diagnosis Equivalve; resembling Pitar but with pallial sinus vestigial; valves rounded to elongate-trigonal, moderately to well inflated with strongly developed veneroid hinge dentition (prominent cardinal and lateral teeth); lunule flat to raised, heart or tear-drop shaped with margin strongly to weakly incised; periostracum usually thin, but sometimes thick peripherally in large adults; externally smooth to glossy with only sculpture consisting| of concentric growth lines or striae, often supplemented by variously developed concentric ridges (especially at ventral and /or anterior and posterior margins); exterior coloration typically with zigzag or triangular patterning, sometimes supplemented or replaced by one or more rays originating umbonally; internal colouration within genus variable, but usually species specific (usually white, but often with yellow, brown or purple patches).

DETERMINATION TABEL SPECIES UNTIL 2002

Although most species of Lioconcha are relatively constant in colour pattern, some of the larger-sized (30-55 mm) species may exhibit significant variation, even at a single collection site. Certain structural features also alter with age, such as the position of umbones in relation to the anterior and posterior extremities and the size of hinge teeth. External colour pattern and internal colour also often vary to some extent between size classes in some species. The following key is intended to be used in conjunction with the plates and text. It should be expected that occasional specimens may prove difficult or impossible to determine accurately, especially in the case of extremely juvenile or worn and bleached material. The key is largely intended for the identification of late juvenile to mature specimens (the size ranges given for each species are indicative of adult specimens). In general, we have emphasised the most accessible and constant shell features, but have also attempted to accommodate any variation in features based on the material available for study.
1. External colouration of shell with a single, broad orange ray posteriorly 2
External colouration of shell lacking a single, broad orange ray 3
2. Shell smooth; tented-reticulate background colour; lunule white or pink; dorsal margin
speckled L. berthaulti (20-30 mm)
Shell with raised, concentric ridges; white background colour; orange lunule and dorsal
margin L. melharteae (10-15 mm)
3. Raised ridges present over all or most of valve surface 4
Raised ridges absent or evident only on marginal regions of valves 9
4. Lunule or perilunular area (and usually dorsal margin) purple-brown in colour 5
Lunule and perilunular area white, patterned or brown/black; dorsal margin white or
patterned 7
5. Shell smooth but not glossy; fine raised ridges externally; internally usually with
brown blotch associated with each adductor scar L. trimaculata (20 mm)
Shell glossy; coarse raised ridges externally; internally, colour patches not
associated with one or either adductor scars 6
6. Shell externally chestnut brown, with two to five darker brown rays and sometimes faint
zigzags; dorsal margin brown or purple-brown; internally white with light brown
blotch under umbones
L. philippinarum (20-30 mm)
Shell externally white overlain with zigzag reticulations; dorsal margin white or with
some line patterning; internally white with brown/purple blotch mid-valve
L. gordoni (10-15 mm)
Shell externally white overlain with broad bands or brown and zigzag reticulations;
dorsal margin purple-brown; internally white with purple patch mid-valve and brown on
posterior adductor scar
L. dautzenbergi (10-15 mm)
7. Shell minute; rounded; thin and fragile; fine, concentric raised ridges developed as
fine ribs; white tented reticulate pattern on tan externally
L. richerdeforgesi (5-8 mm)
Shell small, robust, well developed, concentric raised ridges developed as ribs;
externally white with small, scattered, faint tent markings L. caledonensis (10-20 mm)
Shell moderately to very large (20-55 mm), robust to moderately thin; concentric raised
ridges clearly marked or subdued; externally tan to brown, pattern of fine, diffuse
zigzags 8
8. Posterior-ventral margin showing sinuation; umbones slightly to moderately prosogyrate; lunule weakly delineated by incised line; internally white to yellow, usually with mauve-purple staining posteriorly L. schioellei (30-40 mm)
Posterior-ventral margin evenly convex; umbones slightly to moderately prosogyrate; lunulc weakly delineated by incised line; internally white with extensive postero-ventral brown staining L. sowerbyi (25-35 mm)
Posterior-ventral margin evenly convex; umbones strongly prosogyrate; lunule well delineated by
incised line; internally white, often with some median brown staining L.polita (30-40 mm)
9. Lunule raised, well delineated by deeply incised line 10
Lunule flat, poorly delineated by incised line 12
10. Shell with abruptly truncate posterior margin; heart-shaped lunule; valves externally white overlain with sparse, irregular tents or blotches, most of which appear smudged and diffuse L. macaulayi (40-50 mm)
Shell with rounded posterior margin; heart-shaped to lanceolate lunule; valves externally white to grey-white with well-defined markings 11
11. Shell circular to ovate; umbones slightly progyrate; externally valves with variable pattern of tents, zigzags or rods (or a mixture of these) L. castrensis (30-55 mm)
Shell ovate-trigonal; umbones markedly prosogyrate; externally valves with rod or angular markings L. hieroglyphica (40-50 mm)
12. Ridges clearly marked on ventral third of valve 13
Shell lacking or essentially lacking ridge sculpture (i.e. growth striae only) 14
13. Colour pattern composed of many, open brown tents of varying sizes (pointing away from the umbones), often diffuse (and with patches of grey); umbones not markedly raised above hinge line L. annettae (30-40 mm)
Colour pattern composed of solid tents (pointing towards the umbones) of reddish-brown on a white background, the tents often amalgamating ventrally into coarse, angled rays; umbones markedly raised above hinge line L. tigrina (30-40 mm)
14. Colour pattern externally of heavy, open black-brown tents often interconnected; rays of colour never present externally; lunule with black-brown blotch umbonally; shell internally white often flesh
coloured umbonally L.fastigiata (20-40 mm)
Colour pattern externally of solid black-brown tents sometimes connected; rays ot colour never present externally; lunule with black-brown blotch umbonally; shell internally white, often flesh coloured umbonally, always with broad, diffuse purple-brown ray or blotch medially L. pseudofastigiata (25-34 mm)
Colour pattern externally of small to minute open tents of brown, very commonly intersected by rays of brown or white; lunule lacking black-brown blotch umbonally; shell internally white to orange L. ornata (25-45 mm)