Key to all Laonice species from South America

1 Prostomium fused or partially fused to peristomium.......................................................... 2

- Prostomium free from peristomium....................................................................... 6

2 Prostomium clearly fused with peristomium along the anterior margin........................................... 3

- Prostomium partially fused with peristomium, generally only by an inconspicuous membrane......................... 5

3 Branchiae with appendages on frontal basal region........................ L. branchiata Nonato, Bolivar & Lana, 1986

- Branchiae without appendages (smooth)................................................................... 4

4 Ventrolateral pouches present from chaetigers 3–17, or absent; dorsal transverse ridges absent; hooded hooks complete; main fang of hooded hooks is accompanied at the base by apical teeth........................ L. brevicornis (Kinberg, 1866)

- Ventrolateral pouches present from chaetigers 35–48; dorsal transverse ridges present; hooded hooks with distal opening; main fang of hooded hooks is not accompanied at the base by apical teeth............................ L. ayseniensis sp. nov.

5 Caruncle and nuchal organs reach chaetigers 15–21; branchiae present until chaetigers 32–59; ventrolateral pouches present from chaetigers 9–24; dorsal transverse ridges present; hooded hooks from chaetigers 17–24; sabre chaetae from chaetigers 11–15.............................................................. L. praecirrata Hartmann-Schröder, 1965

- Caruncle and nuchal organs reach chaetigers 12–13; branchiae present until chaetiger 32; Ventrolateral pouches present from chaetigers 3–4; dorsal transverse ridges absent; hooded hooks from chaetigers 34–38; sabre chaetae from chaetigers 16–22.............................................................................. L. antarcticae Hartman, 1953

6 Prostomium with short frontolateral horns; sabre chaetae from chaetigers 27–29......................................................................................... L. parvabranchiata Radashevsky & Da Cunha Lana, 2009

- Prostomium without short fronto-lateral horns; sabre chaetae from chaetigers 5–17................................. 7

7 Caruncle and nuchal organs reach chaetigers 21–28; branchiae present until chaetiger 42; dorsal transverse membranes absent; hooded hooks from chaetiger 31; sabre chaetae from chaetigers 16–17............ L. postcirrata Hartmann-Schröder, 1965

- Caruncle and nuchal organs reach chaetiger 20; branchiae present until chaetiger 50; dorsal transverse membranes present; hooded hooks from chaetigers 16–25; sabre chaetae from chaetiger 5....................... L. weddellia Hartman, 1978