16 



D.J. SIEBERT 



region. The second section, consisting of the intestine, is separated 

 from the oesophagus-stomach by an obvious sphincter, and meas- 

 ures approximately 73% of total gut length. The anterior third of the 

 intestine is marked by irregular folds, which are more vertically 

 oriented and regular in the region of the air bladder and parapelvic 

 bones. Posterior to the air bladder the folds are regular, nearly 

 vertical, and wavy. They appear to encircle the gut so that the 

 posterior half of the intestine looks very much like the external 

 appearance of an earthworm. The end of the intestine is conical and 

 projects slightly into the third section. The third section of the gut is 

 short, less than 10% of total gut length and is slightly greater in 

 diameter than the intestine. It also is characterised by wavy, vertical 

 folds, but these are more numerous (distinctly closer together) and 

 more wavy than those of the intestine. 



Gonads 



The gonads lie dorsal to the gut and when mature occupy nearly the 

 entire length of the body cavity, as described forS. praecox (Roberts, 

 1981). Testes exhibit the vertical striations characteristic of at least 

 some other clupeomorphs (Roberts, 1981; Whitehead & Teugels, 

 1985). Judging from enlargement of posterior sections of testes in 

 some individuals, maturation of testes proceeds from posterior to 

 anterior. Ovaries contain eggs of distinct size classes, egg size 

 presumably being an indication of degree of egg maturation. One 

 female contained 1 8 very large eggs, nine in each ovary arranged in 

 a single file. These eggs were slightly wider than the width of two 

 myotomes (nearly 1 mm in diameter) and occupied nearly the entire 

 length of the ovaries. Smaller eggs of two distinct size classes were 

 interspersed among the larger eggs (Fig. 4). Among clupeomorphs 

 the presence of distinct size classes of eggs in ovaries is considered 

 indicative of repeat spawning within a single breeding season. 

 Sundasalanx may thus have considerable fecundity even though 

 relatively few mature ova are present (can fit) within an ovary. 

 Roberts (1981) reported egg size in 5. praecox of only 0.20-0.25 

 mm in diameter. Sundasalanx praecox may have smaller ova than 

 other Sundasalanx species, but among clupeiforms that are repeat 

 spawners final enlargement of the egg does not occur until shortly 

 before spawning (Blaxter & Hunter, 1982). Thus the difference in 

 egg size between Barito River species of Sundasalanx observed here 

 and S. praecox may be due to the stage of egg development at which 

 materials were preserved. 



Fig. 4 Outline drawing of the left ovary of Sundasalanx mesops (anterior 

 to left); A = large ovum, B = smaller size classes of ova, C = duct to 

 genital opening, scale bar = 2 mm. 



Gas Bladder and Associated Structures 



The gas bladder is located above the gut in the region of the pelvic 

 fins, and is somewhat constricted by the parapelvic bones (Fig. 3). 

 The pneumatic duct appears to enter the anterior end of the gas 

 bladder, an entry position unusual among clupeomorphs (White- 

 head and Blaxter, 1989). The gas bladder was deflated in most 

 specimens but in a few the anterior portion was partially filled with 

 gas. Nocturnal, facultative filling of the gas bladder by swallowing 

 air is well known among larval clupeomorphs. Thus no special 

 significance is attached to the observation that in some Sundasalanx 

 specimens the gas bladder is partially filled with air whereas in most 



Fig. 5 Photograph of the head of a skeletal preparation of Sundasalanx 

 malleti (BMNH 1996.7.18.15) showing the relative position, size, and 

 shape of the prootic bulla (A). 



it is deflated. A duct leading from the gas bladder to the region of the 

 anus, usually present in clupeomorphs, was not observed. 



A very large, vertically oriented, spindle-shaped bulla is present 

 in the prootic (Fig. 5). It is approximately 40% of head depth in 

 height, protrudes ventrally into the branchial chamber, and extends 

 dorsally nearly to the dorsal surface of the head. It is capped with 

 melanophores and is among the few structures other than the eyes 

 that can be seen on living Sundasalanx. A canal for the precoelomic 

 gas duct is apparent but the duct itself was not detected. Ossification 

 of the prootic bulla is not apparent in counter stained preparation, 

 only in preparations stained solely with alizarin. 



Lateral to the prootic bulla lies a cavity, identified as a recessus 

 lateralis, on which the supraorbital, temporal, and infraorbital 

 laterosensory canals converge (Fig. 6). A small, circular fenestra on 

 the dorsolateral side of the prootic bulla communicates with the 



Fig. 6 Schematic representation of the recessus lateralis and cephalic 

 laterosensory canals of Sundasalanx malleti (anterior to left); A = 

 temporal canal, B = infraorbital canal, C = supraorbital canal, D = 

 infraorbital bone, E = recessus lateralis chamber, F = fenestra on the 

 medial wall of the recessus lateralis, G = prootic bulla. 



