Common names:

* proposed name

Synonyms:

Etymology:
'Periophthalmus' is a compound name from the Greek 'peri' (around), and 'ophthalmôn' (eye), which refers to the wide visual field of these species

the specific name is in commemoration of the tenth anniversary of the foundation of the Walailak University, Thailand (Darumas & Tantichodok, 2002)

Maximum recorded length:
127 mm SL (Darumas & Tantichodok, 2002)

Live colouration (Darumas & Tantichodok, 2002; pers. obs.: Peninsular Malaysia):
background colouration dorsally and laterally brownish, with numerous, irregular white to pale yellow speckles on flanks, cheeks and throat, as large as the exposed field of the underlying scale. 4-7 diagonal, saddle like, dorsal and irregular dark bars; irregular black blotches on cheeks; short, irregular black stripe frequently visible posteriorly to the orbit. Venter white. D1 proximally dark brown and black for the distal third; margin white. D2 with transparent background, medial dark brown stripe and reddish margin in some individuals; 2-3 horizontal series of dark speckles on rays in some specimens; caudal and pectoral fins background greyish, with series of dark brown speckles along rays; anal fin white; pelvic fins ventrally white, dorsally darker

Colouration on preservation ( Darumas & Tantichodok, 2002; pers. obs.):
ground colour pale to dark brown dorsally and laterally, ventrally yellowish to greyish; irregular saddle bars and darker or paler speckles and blotches may disappear after some time; D1 background completely dark brown, inframarginally darker and a transparent margin; D2 background translucid with a dark brown medial stripe, and 2-3 horizontal series of dark brown speckles on rays; caudal and pectoral fins background greyish, with series of dark brown spots along rays, often disappearing on pectoral fins, but much more persistent on the caudal fin; anal and pelvic fins hyaline

Diagnosis (Darumas & Tantichodok, 2002: Thailand; Jafaar et al., 2006: Singapore - ranges include both datasets; Polgar & Khaironizam, in press):
D1 VI-IX; total elements of D2 10-12; total elements of anal fin 9-12; longitudinal scale count 53-69; TRDB 10-15; head length 23.8-30.3%SL; head depth 14.3-21.2%SL; head width 12.1-23.3%SL; pelvic fin length 10.3-15.8%SL; length of anal fin base 17.6-27.1%SL; length of D2 base 19.1-28.7%SL. D1 with neither stripes, nor spots: completely dark brown with a white margin, which is transparent on preservation; rays of caudal and pectoral fins with series of dark brown speckles; pelvic fins with prominent frenum and completely fused into a round disk.
The genus is yet undefined by synapomorphies

Diet:
carnivorous, opportunistic (crustaceans, insects, etc.: Khaironizam & Norma-Rashid, 2002; pers. obs.)

Reproduction:
it digs burrows 9-13 cm wide and 100-120 cm deep in the high mangrove forest ( Darumas & Tantichodok, 2002, pers. obs.); the details of its reproductive cycle have not been described in literature: it probably follows the general model proposed for all the congeneric species (see also Reproductive behaviour)

Ecological notes (pers. obs.: Peninsular Malaysia):
not common in mangrove ecosystems, from the low forest to the high forest zone; more common in Singapore (Jaafar, Z., pers. comm.); larger individuals live also in the high supratidal zone; its disruptive colouration allows for efficient camouflage on the forest floor; there are descriptive accounts on a nocturnal behaviour in Thailand (Darumas & Tantichodok, 2002); these observations have not been confirmed by other authors in Peninsular Malaysia and Singapore ( Jaafar et al., 2006; Polgar & Khaironizam, in press); on the other hand, nocturnal behaviours had been described in other congeneric species (e.g. P. argentilineatus e/o P. kalolo: Colombini et. al., 1996)

left: Sementa, Malaysia: pioneer shore; few specimens of P. walailakae were found here (photo: G. Polgar, 2007)

right: Kuala Selangor, Malaysia: high forest, nearby the reclamation bund; a reproductive male was found here inside its burrow (photo: G. Polgar, 1996)

Distribution:
Straits of Malacca; type locality: Andaman Sea, Southern Thailand ( Darumas & Tantichodok, 2002)

Remarks:
This species had been long misidentified as Periophthalmodon schlosseri, probably for the relatively large size, the black stripes behind the orbits, and the dorsal fins' colouration (Jaafar et al., 2006).
In the field, it can be discriminated from Periophthalmodon schlosseri by examination of the colouration of cheecks and opercula: P. walailakae lacks the white-bluish, iridescent speckles present in the other species (Khaironizam M.Z., pers. comm.; pers. obs.)

Photographs of Periophthalmus walailakae:

A: P. walailakae, a reproductive male into its burrow, in the high forest (photo: G. Polgar; Kuala Selangor, Peninsular Malaysia, 1996); B: a close-up (photo: anonimous; Chek Jawa, Pulau Ubin, Singapore); C: P. walailakae perching on a trunk of Sonneratia alba at low tide (photo: M.Z. Khaironizam, 1999); D: a specimen inside a plastic bag (photo: G. Polgar; Kukup Is., Peninsular Malaysia, 2007); E: the same specimen in D, ventral view (photo: G. Polgar; Kukup Is., Peninsular Malaysia, 2007) - * with permission

Drawings of Periophthalmus walailakae:

cephalic sensory and nasal pores of Periophthalmus spp.: an= anterior nostril; pn= posterior nostril (modified from Murdy, 1989)* - * with permission