Anterior margin of wide cervical incision of carapace forming posterior margin of anterolateral angle of carapace; carapace shows no lateral margin between anterolateral angle and cervical incision. Carapace has 7 to 9 (usually 8, seldom 11) posterolateral teeth. Dorsal surface of body with short, woolly pubescence. Merus of third maxilliped with ventral surface slightly concave, not swollen, and not coloured differently from other segments, inner margin not with deep incisions. Fourth segment of antenna slender, without lateral teeth, regularly narrowing from base to tip.
Type locality of I. alticrenatus: "Challenger" "Station 167, west of New Zealand... lat. 39°32'S., long. 171°48'E.; depth, 150 fathoms [= 274 m]; bottom, blue mud". Four syntypes in BM, no. 88.22, in alcohol, condition fair.
Type locality of I. a. septemdentatus: "About 28 miles east from Port Jackson Heads" near Sydney, N.S.W. Australia. "250-300 fathoms [= 457-549 m)". Two syntypes in AM, no. G. 5424.
Australia (New South Wales, Bass Straits, Tasman Sea, Victoria, South Australia); New Zealand (North Island, South Island, Chatham Islands).
Habitat and Biology:
Depth range from 20 to 455 m, on soft muddy bottoms. Digs into the substrate and covers with the mud and sand. Ovigerous females from May to October.
Carapace length 1.5 to 6.3 cm; maximum total length about 16 cm.
Interest to Fisheries:
According to Lesser (1974: 260) the species has no commercial value in New Zealand. But in New South Wales, Australia, "commercial quantities of Ibacus alticrenatus are still taken by trawlers working off the continental shelf by day and by night" (Coleman, 1977: 132), and the species is sold at the Sydney market.