Paracaudina Heding, 1932

O'Loughlin, P. Mark, Barmos, Shari & VandenSpiegel, Didier, 2011, The paracaudinid sea cucumbers of Australia and New Zealand (Echinodermata: Holothuroidea: Molpadida: Caudinidae), Memoirs of Museum Victoria 68, pp. 37-65 : 38

Key to the Australian and New Zealand species of Paracaudina Heding

1. Ossicles in body wall small irregular rods only Paracaudina bacillis O’Loughlin and Barmos sp. nov. (southern Australia)

— Ossicles in body wall include small buttons or perforated plates or thick cups 2

2. Ossicles in mid-body predominantly small rods and loops, and in caudal end predominantly spinous perforated plates Paracaudina ambigua O’Loughlin and Barmos sp. nov. (central Western Australia)

— Ossicles similar in mid-body and caudally 3

3. Ossicles in body wall predominantly octagonal plates with central perforation over which there is a bridging box on the basal side and cross on the outer side 4

— Ossicles in body wall rarely octagonal plates with box and cross bridges, or such ossicles completely absent 6

4. Octagonal plates predominantly with marginal bluntly pointed projections and knobs; perforations not significantly smaller in collective area than the surface area of the plate; body with long thin tail Paracaudina chilensis ( Müller, 1850) (circum-Pacific, north-western Australia)

— Octagonal plates predominantly with rounded margin, margin lacking bluntly pointed projections and knobs 5

5. Ossicles predominantly thick and button-like, perforations significantly smaller in collective area than the plate surface area; body with long thin tail Paracaudina coriacea ( Hutton, 1872) ( New Zealand)

— Ossicles predominantly thin-walled and open mesh-like, perforations not significantly smaller in collective area than the plate surface area; body with short thin tail Paracaudina keablei O’Loughlin and Barmos sp. nov. (north-eastern Australia)

6. Ossicles in body wall predominantly thick-walled with 4 perforations 7

— Ossicles in body wall include irregular plates and buttons with irregular perforations, with marginal and surface knobs and pointed projections variably present; plates with up to 12 perforations 8

7. Ossicles in body wall predominantly thick, shallow concave crossed cups Paracaudina luticola Hickman, 1962 (southern Australia)

— Ossicles in body wall predominantly thick, knobbed and irregularly oval flat plates Paracaudina tetrapora (H. L. Clark, 1914) (southern Australia)

8. Ossicles in body wall predominantly buttons with smooth rounded lateral margin, short thick blunt surface spines, frequently with central perforation bridged by a tripod of rods Paracaudina tripoda O’Loughlin and Barmos , sp. nov. (north-eastern Australia)

— Ossicles in body wall plates, most with lateral and surface rounded marginal spines and knobs 9

9. Deeper mid-body wall with irregular rods, less than 50 µm long; colour never yellowish-red (rusty) Paracaudina australis ( Semper, 1868) (north-eastern Australia)

— Deeper mid-body wall lacking irregular rods; larger specimens increasingly yellowish-red (rusty) in colour Paracaudina cuprea O’Loughlin and Barmos sp. nov. (southern Australia)

Remarks. The remaining subspecies and species of Paracaudina Heding, 1932 that are not included in this key are: Paracaudina chilensis obesacauda (H. L. Clark, 1908) , a central American east Pacific and west Atlantic subspecies, retained with subspecific status solely on geographical grounds by Pawson et al. 2001; Paracaudina delicata Pawson and Liao, 1992 , from the Gulf of Tonkin, has thin-walled chilensis -like ossicles, with box and cross bridging a central perforation, and fine digitiform projections around the ossicle margin.