This species appearance is rare in the aquarium hobby with the majority of images both online and in the published literature instead depicting H. confuzona or H. parclitella.
H. orthogoniata can be told apart from all congeners by the following unique combination of characters: dorsal surface of body always with 3 large, saddle-shaped markings, the first posterior to the head, second covering the base of the dorsal-fin, and third between the dorsal-fin and caudal-fin (usually continuous laterally to origin of anal-fin); base of caudal-fin dark brown; 5-6 simple and 12-13 branched pectoral-fin rays; 61-70 lateral line scales.
H. confuzona, H. orthogoniata and H. parclitella appear similar at first glance but can be told apart by a few characters, the most useful of which to aquarists are the dark markings extending from the snout over the dorsal surface. These form a series of saddle-shaped blotches in most group members but there exist some marked differences.
For example in H. parclitella and H. orthogoniata the 'saddles' are noticeably broader, more regularly-shaped and well-defined than in H. confuzona and often extend into the lower half of the body.
H. parclitella always has two saddles and H. orthogoniata three, whereas in H. confuzona there may be up to four irregularly shaped markings which are normally restricted to the upper half of the body. One shared feature is an additional dark bar at the caudal peduncle.
Another feature shared by members of the genus is keeled scales; for example in H. bilineata each scale has a single, wide keel orientated posteriorly. In H. confuzona the keels are rounded and in H. ogilviei elongate; in both cases they're positioned at the posterior edge of the scale.
In H. orthogoniata, H. ocellata and H. parclitella a central, broad keel is flanked by two smaller ones. Other defining characters for H. orthogoniata include 5 branched anal-fin rays, 8-9 branched, 2 simple pelvic-fin rays, 12-13 branched, 5-6 simple pectoral-fin rays and 9-11 scale rows above the pelvic-fin origin.
The genus Homaloptera van Hasselt, 1823 has long been considered a polyphyletic assemblage (Kottelat, 1998)[3], and following Randall & Page (2015) the majority of members have been moved into other genera as recognized therein:
Homalopteroides Fowler, 1905 with 11 species (Homalopteroides wassinkii, H. modestus, H. rupicola, H. smithi, H. stephensoni, H. weberi, H. tweediei, H. indochinensis, H. nebulosus, H. yuwonoi, and H. avii), is the most diverse and widely distributed genus of species formerly in Homaloptera. It is known from northeast India, Myanmar, Thailand, Laos, Cambodia, Vietnam (? see Kottelat 2012:51), Peninsular Malaysia, Sumatra, Java, and Borneo.
Homalopterula Fowler, 1940 is only known to occur in Sumatra and consists of six species, five described from Aceh Province (H. heterolepis, H. ripleyi, H. modiglianii, H. amphisquamata, and H. vanderbilti) and H. gymnogaster from Sumatera Barat province.
Balitoropsis Smith, 1945 contains two species, B. zollingeri and B. ophiolepis. The original type species B. bartschi (Smith, 1945) is now considered synonymous with B. zollingeri.
Pseudohomaloptera Silas, 1953, which has not been valid since 1953, now contains six species (P. tatereganii, P. sexmaculata, P. leonardi, P. yunnanensis, P. vulgaris, and P. batek) and is known to occur in southern China, Thailand, Laos, Cambodia, Peninsular Malaysia, and Borneo.
Ghatsa Randall & Page, 2015, contains the type species G. montana Herre, 1945, and four tentatively assigned species (G. pillaii, G. menoni, G. santhamparaiensis, and G. silasi).
Homaloptera van Hasselt, 1823, consists of six species (H. ocellata [type species], H. bilineata, H. orthogoniata, H. ogilviei, H. confuzona, and H. parclitella) found in Myanmar, Thailand, Cambodia, Peninsular Malaysia, Sumatra, Java, and Borneo.
Homaloptera is distinguished by the following combination of characters: reddish tints on fins in life; dorsal-fin origin anterior to pelvic-fin origin; 7–8½, 8½ (M) branched dorsal-fin rays; 7 branched pelvic-fin rays; forked caudal fin; keeled scales; 20–27 predorsal scales; 59–73 total lateral-line scales; no adipose keel on caudal peduncle; anus closer to anal-fin origin than to pelvic-fin insertion; large rostral cap; 2 thick rostral barbels in close proximity to each other; thick triangular upper lip; fleshy pad between lateral portions of lower lip; absence of central furrow at isthmus.
All Homaloptera spp. make fascinating aquarium inhabitants and are often referred to as 'lizard' loaches due to their behaviour and appearance. Like all balitorids they have morphology specialised for life in fast-flowing water, i.e., the paired fins are orientated and extended horizontally, head and body flattened, belly depressed.
These features form a powerful sucking cup which allows the fish to cling tightly to solid surfaces. The ability to swim in open water is greatly reduced and they instead appear to crawl and hop their way over rocks and other surfaces.
The family Balitoridae as recognised by Kottelat (2012) is widely-distributed across much of the Indian subcontinent, Southeast Asia and China.
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