Amiet (2004) believes that this is probably a complex of at least three species. Herrmann (2005) documented various morphs of a possible new species. Color morph 1 differs from P. sandersoni by a white stripe which extends from the tip of the snot, over the upper lip, ending above the arm. Color morph 2 has dark-brown to black dorsal coloration with two dorso-lateral white-grey stripes; this morph was reported by Amiet (1975) for the western flank of Mt. Nlanako at 950-1000 m. Color morph 3 has dark-brown to black dorsal coloration with two light, broad, irregular shaped spots of greenish or reddish coloration; this morph was reported by Amiet (1975) for Ekomtolo. Color morph 4 has a broad, light red, longitudinal stripe on the dorsum.
Phrynobatrachus sandersoni is a medium sized species (SVL < 26 mm) of puddle frog known from Cameroon and Equatorial. Members of this genus are identified by the presence of a midtarsal tubercle, elongate inner metatarsal tubercle, and outer metatarsal tubercle. This species is characterized by a distinct tympanum, tips of fingers and toes dilated into large T-shaped discs, and moderate pedal webbing. Breeding males exhibit nuptial pads on finger I, lateral vocal folds, femoral glands and enlarged pseudo-teeth in the lower jaw.
The IUCN Red List (2010) categorizes this species as Least Concern in view of its relatively wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category (Amiet, 2004).
It occurs within Korup National Park of Cameroon and Monte Alen National Park of Equatorial Guinea (Amiet, 2004).
It is presumably threatened by the loss of forest habitat for agriculture, logging and human settlements (Amiet, 2004).
Populations are decreasing (Amiet, 2004).
This species is characterized by a distinct tympanum, tips of fingers and toes dilated into large T-shaped discs, and moderate pedal webbing. Breeding males exhibit nuptial pads on finger I, lateral vocal folds, femoral glands and enlarged pseudo-teeth in the lower jaw.
Amiet (1981) asserted that the expansions of the digital discs facilitate climbing and the maintenance of this species on its perches on low plants where it breeds and females lay and guard clutches.
Placement of Phrynobatrachus sandersoni differed between the mitochodrial sequence data (12S rRNA, valine-tRNA, and 16S rRNA fragment mtDNA) and both the RAG-1 and combined topologies in analyses by Zimkus et al (2010). RAG-1 results supported the placement of P. sandersoni within clade A, which contains P. acutirostris, P. krefftii, and P. petropedetoides, whereas mtDNA supports a sister group relationship between this species and the other two major clades identified in the study (B and C) as this species falls outside clade A.
Endotrophic or non-feeding larvae with a small mouth (when compared to P. alticola) that lacks jaw sheaths and keratodonts (Rödel and Ernst, 2002). The tadpole does not have a fully developed alimentary canal, it only develops and is functional at the time that the tadpole develops into a frog (Amiet, 1981). A description of the tadpole can be found in Amiet (1981).
The presence of enlarged “teeth” the lower jaw makes males of this species easily identifiable. The only other species of Phrynobatrachus that exhibits mandibular pseudo-teeth is Phrynobatrachus africanus, which exhibits only small digital discs.
The tongue is deeply notched with a median papilla. There are maxillary teeth but no vomerine teeth present. The head is naroow, much longer than broad. The snout is pointed, prominent, and obliquely truncate in profile, slightly longer than the eye. The canthus rostralis is anguular, and the loreal region is vertical and slightly concave. The nostril is equidistant from the eye and the tip of the snout. The tympanum is half the diameter of the eye. The first finger is shorter than the second, which is shorter than the fourth. Manual webbing is absent. Digital discs are well developed, trapezoid or T-shaped. The disc of the third finger is approximately 2/3 the diameter of the tympanum. Toes are 1/3 webbed; Zimkus (unpublished) examined specimens with 3 phalanges free of webbing on toe iV. Toe V is shorter than the toe III. Digital discs of the toes are slightly smaller than those of the fingers. Subarticular tubercles are flat. A flat, elongate inner metatarsal tubercle and a small, prominent outer metatarsal tubercle are present. An indistinct, short, curved fold is present from the inner metatarsal tubercle to the tarsus. Drewes and Perret (2000) found Phrynobatrachus (Phrynodon) sandersoni to lack a tarsal tubercle, while Zimkus and Blackburn (2008) found this tubercle present, albeit rather reduced in size. The tibio-tarsal articulation reaches the nostril. The dorsum has a few, small, scattered tubercles, while the venter is smooth. A curved supra-tympanic fold is present. Males exhibit nuptial pads on finger I, long mandibular pseudo-teeth, termed odontoids, and femoral glands that are as long as the snout on the posterior thigh (Parker, 1935). The pair of peudo-teeth that are half the diameter of the tympanum. Lateral vocal folds are present when the vocal sad is deflated. According to Böhme (1994), the femoral glands are closer to the knee than to the vent, and they are present in both sexes.
Dorsum is brown with a darker cross-bar between the eyes and a chevron-shaped marking from the occiput to the scapular region. Tympanic region, as well as the anterior part of the flanks, is dark brown with white flecks. The limbs exhibit distinct cross-bars. A diagonal white stripe is present on each side of the vent. The ventral surface is white, and the chin and throat are dusted with brown.
Adults measure 21-26 mm (Perret, 1966). The holotype measures 22 mm (Parker, 1935).
This species occurs from southwestern Cameroon south to Monte Alen and in mainland Equatorial Guinea at Rio Muni (Amiet, 2004).
It is a lowland species that probably occurs up to over 1,000m asl., living in the vicinity of streams in forest. It only survives in secondary habitats at higher elevations (Amiet, 2004).
It is common (Amiet, 2004).
Eggs are incubated by the female on the leaves of bushes at night (Amiet, 1981). In the evening the female climbs onto a low plant or a small shrub and waits on the perch for the males. A clutch normally includes 12 to 17 eggs of 2.5 millimeters in diameter. During the period of development, which is at least twelve days, the female returns each evening to the clutch and guards them. When the female feels that the clutch is threatened, she may place her body over it. After leaving, she rests in the vicinity, on the leaf being used as support. Amiet (2004) believes that is unlikely that this parental care actually protects the clutch against the predators or parasites. The eggs are not protected during the day when very effective predators, such as sparrows and ants, are active.
After hatching, the non-feeding tadpole, which is dependent on its yolk, falls to the ground and develops on land, never entering water. This process is referred to as semi-direct development. (Amiet, 2004).