In 1940, Lönnberg described the subspecies Cebuella pygmaea niveiventris from Lago Ipixuna, south bank of the Rio Solimões, based on its sharply contrasting whitish chest, belly, and inner surface of arms and legs. The ventral surface of C. p. pygmaea is ochraceous. Cruz Lima (1945) and Napier (1976) also recognized and described the two subspecies. Hershkovitz (1977) argued that the colour of the underparts is individually and locally variable and not justifying the subspecific status of niveiventris. However, Van Roosmalen and Van Roosmalen (1997) presented evidence for the validity of the two subspecies based on field observations and captive specimens of C. p. niveiventris, and confirmed its presence in the interfluvium of the Rios Purus and Madeira. A phylogenetic study by Boubli et al. (2018), which included the mtDNA cytochrome b gene and a reduced representation genome sequencing approach (ddRADseq) for geographically representative samples from the Brazil, showed that the forms pygmaea Spix (from the north of the Solimões-Amazonas) and niveiventris Lönnberg (from the south of the Solimões-Amazonas) were distinct species. Porter et al. (2020) confirmed the conclusions of Garbino et al. (2019) and Boubli et al. (2021) for Ecuador and Peru.

Cebuella niveiventris is assessed as Vulnerable A2cd, following a suspected population decline of >30% which took place over a three-generation period (18 years, as per the previous IUCN Red List assessment) from 2006 to 2024. This population decline was suspected due to a decline in area, extent and quality of habitat from deforestation, mining, oil palm cultivation, settlements and other anthropogenic threats, as well as from hunting. It is suspected that this population decline continues, due mainly to habitat loss. Few, short-term, population studies have been carried out with this species.

Following Van Roosmalen and Van Roosmalen’s (1997) and Porter et al. (2021), the Eastern Pygmy Marmoset (Cebuella niveiventris) occurs south of the Rio Napo - Solimões-Amazonas-Marañon in Ecuador and Peru, and east of the Río Ucayali in Peru. Aquino and Encarnación (1994a) indicated a larger range in Peru, south to the upper Río Purus and the basins of the Río Madre de Dios, and Río de las Piedras and the Río Tambopata. From there it extends east into northern Bolivia to the region of Cobija (Freese et al. 1982; Buchanan-Smith et al. 2000). In Bolivia, Izawa (1979) and Izawa and Bejarano (1981) confined it to the north and west of the Ríos Orthon and Manuripi, northern tributaries of the Río Madre de Dios. However, Brown and Rumiz (1986) doubt that it occurs as far south as the Río Manuripi, limiting its distribution to the north of the Río Tahuamanu. Buchanan-Smith et al. (2000) confirmed their presence south of the Río Tahuamanu along the Rio Muyumanu. The easternmost record they obtained was at Santa Rosa on the Río Abunã. Its presence in northern Bolivia indicates that it should occur in parts of eastern Acre, including the Ríos Acre and uppermost Abunã, not indicated by Hershkovitz (1977). This was confirmed by Bicca-Marques and Calegaro-Marques (1995). Van Roosmalen and Van Roosmalen (1997) observed Pygmy Marmosets between the lower Rios Purus and Madeira, and indicated a range extending south at least to the Rio Ipixuna (right bank tributary of the Rio Purus). The Río Abunã is a left bank tributary of the Rio Madeira so it is reasonable to believe that Pygmy Marmosets occur throughout the interfluvium of the Rios Purus and Madeira south to the Rio Abunã.

There is a suspected continuing decline in area, extent and quality of habitat from deforestation, mining, oil palm cultivation, settlements and other anthropogenic threats.

In Ecuador, densities range from 1–3 individuals/km of river (de la Torre et al. 2009).

Juruá River: 2.3 ind/km² in Altamira, Juruá River; 2.2 ind/km² in Barro Vermelho, Juruá River; 4.7 ind/km² in Fortuna, Juruá River; and 4.3 ind/km² in Riozinho, Riozinho River (Peres 1997); 0.02 groups/10 km of survey in RESEX do Cazumbá Iracema, Acre (Oliveira 2012).

The forests where C. niveiventris occurs are affected by human activities (e.g., mining Asner et al. 2013, deforestation Killeen et al. 2007). There is an ongoing population size reduction suspected to be >30% over a three-generation period (18 years) due to a continuing decline in area, extent and quality of habitat from deforestation, mining, oil palm cultivation, settlements and other anthropogenic threats, and from hunting.

As per the previous IUCN Red List assessment (de la Torre et al. 2021), which was completed in 2015 and published in 2020, the species was suspected of undergoing a population decline of at least 30% over a three-generation period (of 18 years); i.e., between 2006 and 2024 for this assessment. Continued population decline is suspected.

This species is largely restricted to river-edge forest (Soini 1988) and its abundance in a given locality is dependent on the availability of suitable habitat. Some authors have indicated its occurrence in secondary forest (Canizo and Calouro 2011, Canizo 2012, Moynihan 1976, Hernández-Camacho and Cooper 1976).

Cebuella is a gum-feeding specialist, with behavioural and dental adaptations to gnaw holes in the bark of certain species of trees and vines to stimulate gum production (Soini 1988, Yepez et al. 2005).

Group sizes range from 2–9, with 1–2 adult males and 1–2 adult females. As in other callitrichids, the single breeding female in the group produces twins twice a year, and the adult males and other group members help her to carry them (Soini 1988). Successful reproduction in couples may take several years (six in a couple that was studied at the Tiputini Biodiversity Station in Ecuador (de la Torre pers. obs.). Home ranges are typically small from 0.1 to 1.5 ha, centred on one or two trees which supply the gum they need. The entire group will move to a new home range when the gum sources become inadequate (de la Torre 2009, Soini 1988).

Habitat loss is taking place in several areas of its range. The forests where Cebuella niveiventris occurs, are affected by human activities (e.g., mining—Asner et al. 2013; deforestation—Killeen et al. 2007). The population was suspected to have reduced by >30% over a three-generation period (18 years) from 2006 to 2024 due to a continuing decline in area, extent and quality of habitat from deforestation, mining, oil palm cultivation, settlements and other anthropogenic threats, and from hunting. It is suspected that population decline is ongoing.

The principal reason for the species' inclusion on the CITES Appendix I in 1977-1979 (now relegated to Appendix II; see Mack and Mittermeier 1984) was the international trade, particularly from the area of Iquitos, Colombia.

This species is hunted for food and collected as pets by humans.

The following protected areas are within its known range:

Ecuador

• Yasuní National Park (Porter et al. 2021)

Bolivia

• Manuripi Health Nature Reserve (1,884,375 ha)

Brazil - Acre

• Serra do Divisor National Park (605,000 ha) (Rylands et al. 1993, Calouro 1999)
• Rio Acre Ecological Station (72,000 ha) (Rylands and Bernardes 1989, Rylands et al. 1993, Calouro 2007)
• Cazumbá-Iracema Extractive Reserve (750,794 ha) (Oliveira 2012)
• Antimary State Forest (57,629 ha) (Calouro 2005)
• TI Campinas/Katukina (187,400 ha) (Calouro 2006)
• PE do Chandless State Park (693,970 ha) (Calouro 2008, Borges 2014)
• Chico Mendes Environmental Park (57 ha) (Carmo et al. 2009)
• Parque Zoobotânico (144 ha) (Bicca-Marques and Calegaro-Marques 1995, Canizo and Calouro 2011, Canizo 2012)

Brazil - Amazonas

• Abufarí Biological Reserve (288,000 ha) (left bank of Rio Purus) Rylands and Bernardes 1989, Rylands et al. 1993)
• Jutaí-Solimões Ecological Station (289,511 ha) Rylands and Bernardes 1989, Rylands et al. 1993)

Brazil - Rondônia

• Serra Três Irmãos Ecological Station (87,412 ha) (Ferrari et al. 1996).