Boulengerula niedeni is a caecilian with a slightly dorsoventrally compressed sub- to cylindrical body. The total length of eight known adults is between 196 – 275 mm. In width, the body is mainly uniform, expect for the where the body narrows toward the head and vent. Dorsally they have a parabolic head that tapers from the first nucal groove toward the nares. There is a slight bulging near the tentacles. Laterally, the top of the head is almost straight and goes in slightly toward the tip of the lower jaw, where it dramatically goes inward toward the tip of the snout. Anterior to the nares, the snout tip is narrow and rounded. Laterally, the snout has a blunt round shape and comes to a point on the horizontal line that is halfway between the naris and the tentacle. The short, globular sensory tentacles are located ventrolaterally on head lying straight between jaw angle and nostril. They are in an almost perfect circular shape and are raised, creating an elevated rim around the tentacular opening. Ventrally, the tentacular apertures are easier to see than dorsally. Above the margin of the upper lip the rostrum slightly concaves. Ventrally, the tip of the lower jaw is rounder than the tip of the snout. Their nares, sitting at the anterior rim of an oval shallow depression, 0.26 mm in length, are small kidney shaped, and less than 0.1 mm in diameter. Laterally, the nares are in between the upper side, underside, and apex of the rostrum. The distance between the nares and apex is the smallest while the distance between the nares and underside is the longest. The choana have an oval shape with no visible choanal valves. Laterally, the rim of the choana is slightly raised and formed by the vomeropalatine shelf. However, the medial rim is not raised. The eyes are hidden and no dent or rise has been found in the area where eyes should be (Müller et al 2005).
The position of the mouth is subterminal, the teeth begin posterior of the snout. There are about 21 - 26 premaxillary-maxillary (PMM). They are wide and have an anterior arc across the middle extends posteriorly towards the jaw angle. Vomeropalatine teeth range from about 17 - 22 in number. The vomerine teeth have a short arc and are anteriorly wider than the premaxillary-maxillary teeth. The palatine teeth are divided from vomerine teeth via diastemata. The right side of the palatine series has eight teeth. There are no teeth on left side excluding the most posterior tooth. There are 17 - 21 dentary teeth that have a continuous arc that extends posteriorly towards jaw angle. There are 1 - 2 small splenial teeth. Lastly, there is one pair of anterior teeth, hidden in gums (Müller et al 2005).
The species has two nuchal collars that are slightly broader than the surrounding areas. Laterally, the second nuchal is around 2.2 mm while the first is 1.9 mm. The nuchal collars are distinguished by three nuchal grooves, the first of which is incomplete dorsally. While the second is compete and has a small forward pointing bend on the dorsal side. Ventrally, the third nuchal groove is interrupted and has a gap that is slightly shifted to the left side. The first and second nuchal groves are straight ventrally, however, the third groove’s open ends are bent slightly backwards. There is a faint short transverse groove on the dorsal side of the first nuchal collar. There is a clear narrow crease on the ventral side of the first nuchal collar. The second nuchal collar as a broader transverse groove. There are no lateral transverse grooves on either collar. Boulengerula niedeni has no true tail. There are 138 - 144 primary annuli present. Secondary and tertiary annuli are not present (Müller et al. 2005).
Two juvenile specimens had total length of 92 and 121 mm with head lengths of 3.4 to 3.6 mm. The juveniles measured 10 mm in circumference at the midbody, and at the vent, juvenile bodies are between 2.0 and 2.2 mm wide (Muller et al. 2005).
Boulengerula niedeni can be most easily identified from other Boulengerula species by its coloration, which is brown with a pinkish tint in life. It is also one of the larger species in the genus Boulengerula and, on average, has more vertebrae. Boulengerula niedeni differs morphologically from all other species in the genus (excluding B. taitanus) in that its annular grooves have whitish marks. Unlike B. taitanus, in B. niedeni the sphenethmoid is exposed, the average number of annuli and vertebrae is higher, the general coloration is brownish (B. taitanus is blueish-black), and the phallus has large ornamented tuberosities and no dorsolateral longitudinal ridges (Müller et al. 2005).
Juvenile B. niedeni are most similar to B. taitanus, whose young also have a thin dark dorsal stripe (Muller et al. 2005).
In life, B. niedeni adults dorsally brown with a pinkish tint. Ventrally, they are is pink to light brown and looks slightly translucent. There is a gradation between the dorsal and ventral colors on the lateral sides. The annuli have white marks that are fainter on the anterior side and more obvious in the posterior region. The head is pinkish, and contrasts faintly with the body (Müller et al. 2005).
In preservative, the dorsal coloration of adults fades to gray and ventral coloration fades to light gray. The flanks are more pale giving the appearance of wide ventrolateral stripes without distinct ventral borders (Müller et al. 2005).
Juveniles lack pigmentation along the ventral and lateral sides, but are dark brown along the dorsal side. From the top, the juveniles appear to be dark brown, but from the sides appear to be light brown (Wojnowski and Malonza 2009). They have a thin dark dorsal stripe. The pigmentation from this band radiates to the rest of the body as the young mature, so this may be how B. neideni young grow to be darker adults as well (Muller et al. 2005).
Adult specimens do not vary in coloration, however juveniles in preservative vary distinctly. Three juvenile specimens have no coloration on their ventral or lateral surfaces. Dorsally, they have a dark narrow band (Müller et al. 2005)
The species authority is: Müller, H., Measey, G.J., Loader, S.P., Malonza, P.K. (2005). “A new species of Boulengerula Tornier (Amphibia: Gymnophiona: Caeciliidae) from an isolated mountain block of the Taita Hills, Kenya.” Zootaxa 1004: 37-50.Maximum likelihood analysis of 12S, 16S and cytb mitochondrial gene sequences from 32 samples from Kenya and Tanzania showed that B. taitanus, and B. niedeni a sister species. The clade formed by the two species is sister to a clade formed by B. changamwensis and B. uluguruensis, however B. uluguruensis may be split into more species. The analysis also revealed a positive correlation between genetic difference and geographic distance both among and between the clades described (Loader et al. 2011).
Boulengerula niedeni is named after German herpetologist Fritz Nieden from the Zoologisches Museum Berlin, who greatly contributed to African herptile taxonomy (Müller et al. 2005).
Taita Taveta Wildlife Forum and the Kenyan Forest Service have been replacing some eucalyptus with native trees in the hopes that the caecilian population will increase with the return of part of their natural habitat (IUCN 2013).