I recently asked about obscure Tekumel creatures, when I came upon a web blog that mentioned odd reptilian creatures beneath Tu'umnra, with four arms and armed with blowpipes. The author of the blog said the creature was considered canon. Is this information published anywhere?

I'm pretty familiar with the creatures in published material, and I'm confident the subterranean multi-legged creatures described in that blog post
(here: http://theshenblog.blogspot.com/2010/07 ... kumel.html )
never appeared in a publication.

His second paragraph, referring to odd humans around Purdimal who are hybridized with Nyagga, and also "lost" is, I think confusing two different peoples and ignoring published information.

The odd people around Purdimal are described in the first novel, Man of Gold, and some secrets are revealed. There is no indication of a connection to another species. They are strange, some strange sub-group of humanity, gray-skinned, short, and "lumpy", but no mention is made of hybrids. They are called "the Old Ones" and "Heheganu."

The people who may be somehow tainted with an aquatic strain live far outside the Empire, in towns around Lake Parunal, far north east of Tsolyanu. The lake is inhabited by the aquatic and alien Nyagga, and the people of the towns of Prajnu and especially Ngaku are mentioned has having strangely aquatic features, including gill slits. This is mentioned briefly in the Sourcebook and in Adventures on Tekumel 2:2, also there is gurek of soldiers from Prajnu noted in the Armies of Tekumel book on Yan Kor.

There are thousands and thousands of pages of material created by Dr. Barker that have never been published, so probably many many undocumented creatures.