Microcaecilia iwokramae (Wake & Donnelly 2010)

Microcaecilia iwokramae is the smallest described caecilian of the New World (112 mm total length). The original description was based on one female individual, but 13 additional specimens (11 preserved) have since been collected. The head is longer than wide with an underslung jaw. The internal nares (choanae) are small and difficult to see, but feature small valves like other terrestrial caecilians. Microcaecilia iwokramae has eyes, but the orbit is covered by bone and a thick layer of skin. The tentacles can be seen as small spherical bulges near the covered eyes. The tongue is highly vascularized, possibly serving a respiratory function. The holotype is 3.5 mm wide over most of the body posterior to the head and flattens toward the posterior end. Specimens have between 102 - 113 primary annuli and fewer secondary annuli than other Microcaecilia. The holotype has 102 primary annuli, with six complete secondary annuli and three incomplete annuli ventrally. Microcaecilia iwokramae has a small keel in its terminal annulus. The small vent is longitudinal and located in the slightly ridged basin of an annulus. The vent is anteriorly surrounded by lobe-like denticles and posteriorly by two large denticles on either side. A total of 107 vertebrae are present, with no ribs present on the three posterior vertebrae and lacking a true tail. The epidermis is thin with a keratinized outermost layer. The dermis is deeper and has capillaries near to its surface as well as mucous and granular glands. There are some scattered scales present (Wake and Donnelly 2009; Wilkinson et al. 2014).Microcaecilia iwokrama can be distinguished from most other Microcaecilia by having fewer secondary annuli. From M. taylori, M. iwokrama can be distinguished based on having a range of fewer primary annuli (>114 vs. 113 – 130) and the absence of a dorsal transverse groove on the first nuchal collar. From M. dermatophaga, M. iwokrama can be distinguished by its paired nasopremaxillary bones with shorter tooth rows and fewer total teeth. Microcaecilia iwokrama was not placed in the genus, Caecilia, based on the dorsally unexposed mesethmoid, the lack of inner mandibular teeth, the lack of narial plugs, the location of the tentacle, and the presence of the keel. Microcaecilia iwokramae is not a member of Oscaecilia based on several traits above and the placement of the vomeropalatine tooth rows. The specimen can be distinguished from Parvicaecilia due to the presence of the terminal keel and long premaxillopalatine tooth rows, and from Brasilotyphlus due to the lack of a diastema between the palatine and vomerine dentition. Wake and Donnelly (2009) distinguish M. iwokramae from Luetkenotyphlus, Siphonops, Mimosiphonops, Gymnopis, and Dermophis based on combinations of the features listed above. The specimen can also be distinguished from Old World members of the family, Caeciliidae, based on combinations of these features (Wake and Donnelly 2009).In preservative, M. iwokramae is light yellow-brown on the ventral and dorsal aspects with mottled dark pigmentation around light skin glands. The throat is cream colored. The annuli become darker posteriorly (Wake and Donnelly 2009).Species authority is: Wake, M. H. and Donnelly, M. A. (2009). ''A new lungless caecilian (Amphibia: Gymnophiona) from Guyana.'' Proceedings of the Royal Society B, published online 18 November 2009, doi: 10.1098/rspb.2009.1662. The species epithet refers to the forest in which Microcaecilia iwokramae was found (Wake and Donnelly 2009).Microcaecilia iwokramae was originally place in a new genus, Caecilita, based on skeletal and soft tissue features (i.e. the absence of lungs, closed external nares, and open orbits) by the species authority. However, further inspection by Wilkinson et al. (2014) contradicted these findings and the species was placed consequently into the genus Microcaecilia.The type specimen (CSBD HA 1500, Center for Biological Diversity, Univ. of Guyana) is an adult female discovered opportunistically during a survey of the vertebrate fauna in Iwokrama Forest in central Guyana (Wake and Donnelly 2009). Microcaecilia iwokramae has a single right lung that was identified based on the well-developed pulmonary artery. The left lung and left pulmonary artery are completely missing (Wilkinson et al. 2014).

Microcaecilia iwokramae can be found in Guyana. It is known only from the Iwokrama Forest between 100 and 1,000 m asl (Wake and Donnelly 2009; Wilkinson et al. 2014). Iwokrama Forest is lowland tropical forest, with a warm tropical climate. The habitat at the type locality consists of low, mixed scrub forest (Donnelly et al. 2005).

Microcaecilia iwokramae is terrestrial and likely insectivorous, judging by the unidentified insect remains found in the stomach of the holotype (Wake and Donnelly 2009). It is one of only two caecilian species that are miniaturized, the other being Idiocranium russell (Maddin 2011). The ovaries of the holotype were approximately 10 mm long. The left ovary contained four large well-developed ova (1.2 mm diameter) and the right contained three. Several developing ova were also found in both ovaries (Wake and Donnelly 2009).

Wilkinson et al. (2014) found 13 individuals during approximately 56 person hours of digging, which suggests that the species is common in the type locality.

Microcaecilia iwokramae is a species of caecilian in the family Siphonopidae. It is endemic to Guyana and only known from its type locality in the Iwokrama Forest. It was first described as Caecilita iwokramae in the monotypic genus Caecilita, before being recognised as belonging to Microcaecilia.