Small, head capsule length 200-300 mm. Dorsal head with frontoclypeal apotome with SIII lying at narrowed anterior margin, merging into single anterior sclerite bearing SI and SII, without distinct suture and perhaps best described as frontoclypeolabral apotome.
Antenna with five or six segments; sixth very fine when present; segment 3 half length of fourth; proportional lengths of segments species-specific. Antennal ratio about one. Ring organ large but faint, in basal quarter. Blade slightly shorter than flagellum, extending to apex of fourth segment. Lauterborn organs as long as antennal segment 3, very strong in A. kiwi; style subequal in length to antennal segment 3.
Labrum with simple SI with pointed tip, SII simple, pointed-tipped, SIII simple, short, weak, SIV minute. Labral lamella apparently absent, perhaps a weak fringe. Chaetae simple, short. Pecten epipharyngis consisting of three simple lobes. Chaetulae laterales and chaetulae basales apparently all simple. Premandible with one large apical tooth, with modest brush.
Mandible with apical tooth shorter than combined width of four inner teeth (innermost delimited, but not strongly separated from mola). Seta subdentalis obovate, apically hooked, extending to third inner tooth. Seta interna a weak brush of 6-7 fine serrate branches.
Mentum with two narrow median teeth (medially division weak or indeterminate with wear), with five pairs of lateral teeth decreasing on an even slope. Ventromental plate weakly delimited anteriorly, but shallow posterolateral 'tooth'-shaped bulge is evident, without beard. Setae submenti (SSm) strongly retracted; genal cephalic setae S9 and S10 widely separated; VP more dorso-lateral than usual, DP large opposite side of apotome from frontal seta S5.
Maxilla squat, without pecten galearis. Lacinial chaetae and appendix simple, tapering, undifferentiated.
Body setae quite long and perhaps numerous, up to one third segment width. Anterior parapods with all claws serrate apically. Posterior parapods simple, golden. Procercus twice as high as wide, somewhat darkened with strong upper lateral seta, fine lower seta, bearing 6-7 apical setae. Supra-anal setae strong and long. Anal tubules unseen.
Larval diagnosis is based on tentative larval association from New Zealand confirmed by similarity of CO, and by larval exuviae of reared specimens in Australia. In possessing a 5-6 segmented antenna with third segment much shorter than fourth segment and large Lauterborn organs, mandible with short apical tooth and four distinct inner teeth, and simple SI seta, larval Anzacladius most resemble Echinocladius. This Australian monotypic genus differs in the proportions of the antenna, having much larger Lauterborn organs, and notably in having a single domed median tooth to the mentum. Other larval taxa resembling Anzacladius either have a well-developed ventromental plate, beard, or bifid SI seta, or permutations of these: furthermore, none have the combination of posteriorly retracted setae submenti, widely separated genal cephalic setae S9 and S10, and 'ventral' pit in near dorsal location. The undescribed trans-Andean larva has five segmented antenna, large Lauterborn organs, SI seta simple, bifid median mental tooth and characteristic quite broad ventromental plates which curve medially to end just posterior to the conventionally placed seta submenti.
At several sites in Australia and New Zealand, species of Anzacladius are common enough to assume that they form an important component of the lotic chironomid fauna. Although frequent in running waters, exuviae have been collected on the leeward shore of acid, dystrophic Lake Boomanjin on Fraser Island, and the somewhat similar Lake Como in Cooloola National Park. Many of the streams in Australia that support Anzacladius are sandy-bedded, and nutrient-poor. Anzacladius kangaroo larvae (as 'SO3') were found in sites 1-4 in the Clyde River, southern New South Wales, just upstream of estuarine conditions but absent from the most downstream, saline station and with environmental ordination showing association with salinity, pH and conductivity (Dimitriadis and Cranston, 2007).
On Kangaroo Island, South Australia, larvae of Anzacladius were found in running waters quite close to the ocean. In Western Australia larva of A. numbat were collected from permanent rivers of the south-west, which in the case of the Shannon River might be influenced by anthropogenic (dryland) salinity. In Lake Boomanjin (Fraser Island, Queensland) and Redback Stream (Barren Grounds, New South Wales) two species were present as exuviae at the same time. Although such an observation is quite common with speciose northern hemisphere genera, such as Eukiefferiella and Cricotopus, it is unusual among Australian orthocladiines. In New Zealand exuviae have been found likewise in lotic and lentic situations. Exuviae of A. kiwi have been collected from the shores of Lake Rotoiti (Nelson Lakes, South Island), and from high quality lotic habitats including Waipapa River, North Island, several streams around Nelson Lakes N.P., and together with larvae, the Hope, a tributary of the Buller, South Island. A single exuviae of a putative new species of Anzacladius (see above) was found in a first to second order un-named stream in Pukete Forest, northern North Island.