18 



cartilage chevrons, unique among lower teleosts, are associated with 

 the lateral tips of epicentral intermuscular bones in many clupeoids 

 and the derivation of parapelvic bones from these structures should 

 also be considered. 



Vertebral column 



Vertebrae of Sundasalanx are lightly ossified, with neural arches 

 present on all vertebrae preceding the compound caudal vertebra. 

 Caudal vertebrae appear to ossify first. All neural arches preform in 

 cartilage and the anterior few may not ossify. The first neural arch 

 has a broader base than the others and neural spines do not appear to 

 form on the first 4 or 5 arches. No supraneurals are present. Haemal 

 arches also preform in cartilage. Cartilaginous basiventrals are 

 present on all preural centra, including the first. No ribs are present. 



Intermusculars 



No intermuscular bones or ligaments (Patterson & Johnson, 1995) 

 are present. 



Dorsal- and anal-fin supports. 



Middle radials do not develop in dorsal- and anal-fin pterygiophores. 

 Distal radials are clearly present. Proximal elements (=proximal + 

 middle radials) of the last few dorsal pterygiophores appear to fuse. 



Jaws 



Toothed premaxillary and maxillary bones make up the upper jaw. 

 No supramaxillary bones were detected. Dentary, anguloarticular, 

 and retroarticular bones were identified in the lower jaw. 



Gill arches 



The primitive complement of structures that make up the median 

 series of hyoid- and gill arch elements of teleosts, not all of which 

 may be present in adult forms, develops from three copulae (copula 

 1-3; Nelson, 1969). Derivatives of all three copulae are present in 

 Sundasalanx. The series includes (Fig. 8): the basihyal (derived 

 from copula 1 ); basibranchial 1 -2 and basibranchial 3 (derivatives of 

 copula 2); and basibranchial 4-5 (derived from copula 3). Gill arches 

 1 and 2 articulate with basibranchial 1-2, gill arch 3 articulates with 

 basibranchial 3, and gill arches 4 and 5 articulate with basibranchial 

 4-5. Hypobranchials are not evident in the first three arches. Roberts 

 (1981) suggested they were fused to the median elements but such 

 fusion of lateral endoskeletal elements to median endoskeletal ele- 

 ments is rare (Nelson, 1969). A more likely explanation is that 

 hypobranchials 1-3 never condense from the hypo/ceratobranchial 

 precursors and thus never develop at all. Hypobranchial 4 is present 

 in all species examined, and a curious cartilage nodule, located in the 

 ligament between ceratobranchial 4 and 5, was seen in some speci- 

 mens of S. praecox, S. malleti, S. mesops, and S. megalops, but not 

 in S. microps or S. platyrkynchus, both from the Kapuas River. Five 

 conventional ceratobranchials are present. Four epibranchials and 

 three pharyngobranchials are present (Fig. 9). Epibranchials 2-A are 

 short. Epibranchial 1 is large, occupying the space of pharyngo- 

 branchial 1 in addition to its own. Epibranchial 4 curves 

 anteromesially to articulate with the lateral posterodorsal corner of 

 pharyngobranchial 4, dorsal to the tooth plate associated with the 

 posteroventral side of pharyngobranchial 4. The efferent arterial 

 canal of epibranchial 4 is completely closed, with no sign of any line 

 of fusion of interbranchial 4. A small levator process projects 

 dorsally from the top of the ring of cartilage that forms this canal. 

 The levator exturnus IV, which has its origin on the posterodorsal 

 corner of the skull, inserts on this process. Epibranchial 3 is short, 

 and articulates with the posterolateral end of a large pharyngo- 

 branchial 3. The mesioposterior end of pharyngobranchial 



Fig. 8 Lower branchial arches of Sundasalanx malleti (anterior to left); A 

 = ceratobranchial 1-5, B = hypobranchial 4, C = basibranchial 1-2, D = 

 basibranchial 3, E = anterior and posterior ceratohyals. F = hypohyal, G 

 = basihyal, scale bar = 1 mm. 



Fig. 9 Dorsal view of left side upper gill arch elements of Sundasalanx 

 malleti (anterior to left); A = epibranchial 1 . B = epibranchial 4. C = 

 tooth plates (circles indicate tooth positions diagramatically). D = 

 pharyngobranchial 2-4, scale bar = 0.25 mm. 



3 articulates broadly with the anterior end of pharyngobranchial 4. A 

 large tooth plate is associated with the ventral surface of the poste- 

 rior half of pharyngobranchial 3. The uncinate process of epibranchial 

 3 is modified to form a canal for efferent artery 3. The artery is 

 completely ringed inS. praecox, so that the lateral end of epibranchial 

 3 looks similar to the lateral end of epibranchial 4. It is almost 

 completely ringed inS. platyrhynchus, but only partially encircled in 

 5. malleti, S. mesops, and 5. megalops. Epibranchial 2 is also short, 

 but with a long uncinate process that articulates with the lateral edge 

 of pharyngobranchial 3, the point of articulation on pharyngo- 

 branchial 3 drawn out to form an 'uncinate' process in S. malleti. 

 Pharyngobranchial 2 is much longer than wide, extending from the 

 medial edge of epibranchial 2 in an anteromedial direction to the tip 

 of pharyngobranchial 3. No tooth plate was found to be associated 

 with pharyngobranchial 2. Epibranchial 1 is narrow near the articu- 

 lation with ceratobranchial 1, broadly spatulate at its medial edge. It 

 possesses a long uncinate process that articulates with the uncinate 

 process of pharyngobranchial 2. A separate pharyngobranchial 1 

 was not observed. Enlargement of epibranchial 1 may be the result 

 of fusion between it and pharyngobranchial 1, or of failure of 

 condensation of pharyngobranchial 1 from the epi-pharyngobranchial 

 anlagen in a shortened developmental programme. 



Very thin perichondral ossification of ceratobranchial 5 was the 

 only ossification detected for endoskeletal gill arch elements. If 

 other elements are ossified their ossification is beyond the limit of 



