Taxonomy & naming
Corydoras thanatos was described in 2022 by Luiz F. C. Tencatt, Willian M. Ohara, Leandro M. Sousa and Marcelo R. Britto in a paper in Neotropical Ichthyology that named two superficially similar spotted corys from the rio Tapajós basin together: C. thanatos and C. hypnos. The two were given the names of the Greek twin brothers — Thanatos, the personification of death, and Hypnos, the personification of sleep — to underline that although the two fish share a broadly spotted colour pattern they differ markedly in other morphological features and are not as alike as they first appear.
The species was placed in Corydoras Lacépède, 1803, the vast genus of South American armoured catfishes in the family Callichthyidae. That genus had become unwieldy and demonstrably non-monophyletic, and in 2024 Dias, Tencatt and colleagues published a large revision (DOI 10.1093/zoolinnean/zlae053) that split it into several genera. Under that scheme C. thanatos belongs to the resurrected genus Hoplisoma, so the current valid combination is Hoplisoma thanatos. The aquarium trade still overwhelmingly uses 'Corydoras,' and had circulated the fish as the code CW146 before its formal description, so we keep that heading while noting the new combination. The Catalog of Fishes treats the name as valid.
Morphology
This is a small, short-snouted cory of the classic deep-bodied, flat-bellied build, with the holotype measured at around 1.5 in standard length; it reaches a little over 1.5 in SL. Like all members of the subfamily it is armoured rather than scaled: two rows of overlapping bony plates run down each flank and meet in a ridge along the back, the head is a hard helmet, and short sensory barbels fringe the downturned mouth.
The ground colour is pale, overlaid with a dense scatter of small dark spots across the head and body that give the fish its busy, peppered look — the feature it shares with its 'twin' Hoplisoma hypnos. The two species are separated by details of the dark markings and of the underlying bony anatomy rather than by any single obvious mark. The dorsal, pectoral and adipose fins each carry a stiff leading spine, the usual defensive armament of the group.
Habitat
Corydoras thanatos is known from clear-water streams in the rio Tapajós basin of the southern Brazilian Amazon, the Tapajós being one of the great clear-water tributaries of the lower Amazon. Fish of this kind live over sand and leaf litter in the shallow, well-oxygenated margins and runs of small forest streams, among submerged wood and root tangles.
No published temperature or pH figures are tied specifically to this species, so the water values given here are conservative estimates drawn from the warm, soft, slightly acidic clear waters of the Tapajós drainage rather than from measurements at the type locality — they should be read as indicative, not exact. Like other corys it is a facultative air-breather, darting to the surface to gulp air and absorb oxygen through a vascularised hindgut, which lets it cope with warm, low-oxygen shallows.
Feeding
Like its relatives, Corydoras thanatos is a benthic omnivore and detritivore. It works the bottom continuously, burying its snout and barbels in sand to taste out small invertebrates, insect larvae, worms, micro-crustaceans and the organic film of detritus, expelling cleaned sand through the gill openings. No diet study specific to this newly described species has been published, but its mouth and feeding anatomy are those of the typical sand-sifting cory, and there is no reason to think it differs from the omnivorous, opportunistic pattern of the group.
Mating
No spawning of Corydoras thanatos has been documented; the account here is the well-established pattern for short-snouted Hoplisoma-group corys and is offered as the expected behaviour rather than as observed fact for this species. Corydoradine catfishes are egg-laying shoalers with no pair bond and a distinctive courtship: a ready female cleans a site, a male takes up the classic 'T-position' at right angles to her head, and she clasps a few eggs in a basket formed by her pelvic fins before pressing them onto the cleaned surface. The sequence repeats a few eggs at a time until a clutch of sticky eggs is distributed across leaves, stones or wood.
Breeding
There are no published breeding reports for Corydoras thanatos, which remains an uncommon fish in the trade. By analogy with related spotted corys, spawning would be expected to follow the familiar pattern — adhesive eggs scattered in small batches across firm surfaces, no parental care (the adults will eat the eggs), and a cool, large water change mimicking the rainy season as the likely trigger. Eggs of related species hatch in three to five days, and the fry take microworm, baby brine shrimp and powdered foods once the yolk is absorbed. Until someone breeds it and reports the details, all of this should be treated as informed expectation, not established husbandry.
In the aquarium
Corydoras thanatos is a rarely seen cory, traded under the code CW146 and usually wild-caught, but its care follows the standard recipe for the group. It is a shoaling species and should be kept in a group of six or more over a soft sand substrate; sharp or coarse gravel erodes and infects the barbels, one of the commonest signs of poor cory husbandry. Provide warm, soft, slightly acidic water that reflects its clear-water Tapajós origins, gentle current, good oxygenation and regular water changes. It is peaceful and suits a quiet community of small, calm fish. As with all corys, the fin spines can catch in nets, and a distressed fish can release a skin toxin that, in the confined volume of a bag, can kill the whole group — so transport with care.
Conservation
Corydoras thanatos has been described too recently to carry its own IUCN Red List assessment, so its conservation status is formally Not Evaluated. It is known only from the rio Tapajós basin, and a narrow-ranged Amazonian stream fish is inherently more vulnerable to localised pressures — deforestation, run-off, mining and the damming proposed and built across the Tapajós system — than a widespread generalist. Without survey data its true range and population are unknown, and an honest account simply records that it is unassessed and that its restricted known distribution warrants attention.