Hemitriakis indroyonoi White & Compagno, 2009, sp. nov.
Creators: name: White, William T.
name: Compagno, Leonard J. V.
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Carcharhiniformes
Triakidae
Hemitriakis
Hemitriakis indroyonoi

description: Hemitriakis indroyonoi sp. nov.
Indonesian Houndshark
Figures 1–4, 5 c, Tables 1, 2
Hemitriakis sp. 1: White et al., 2006: pp. 188–189, fig; White, 2007.
Holotype. MZB 16672, immature male 696 mm TL, Kedonganan fish market, Bali, Indonesia, 0 8°45′ S, 115°10′ E, 0 7 July 2004.
Paratypes. 8 specimens: CSIRO H 5873–05, adult male 947 mm TL, Kedonganan fish market, Bali, Indonesia, 0 8°45′ S, 115°10′ E, 16 June 2002; CSIRO H 6817–01, female 656 mm TL, CSIRO H 6817–02, female 497 mm TL, CSIRO H 6817–03, female 554 mm TL, Kedonganan fish market, Bali, Indonesia, 0 8°45′ S, 115°10′ E, 27 April 2004; CSIRO H 6818–01 (3 late-term embryos), 1 female, 2 males, 254–260 mm TL, Tanjung Luar fish market, Lombok, Indonesia, 08°45' S, 116°35' E, 25 April 2004; CSIRO H 6819–01, male mid- to late-term embryo, 178 mm TL, Tanjung Luar fish market, Lombok, Indonesia, 08°45' S, 116°35' E, 10 September 2004.
Other material. 5 specimens: CSIRO H 5884–01, female late-term embryo 278 mm TL, MZB 15481, female 1130 mm TL, Tanjung Luar fish market, Lombok, Indonesia, 08°45' S, 116°35' E, 12 April 2001; MZB 15174, male 893 mm TL, MZB 15427, female 843 mm TL, MZB 15483, male late-term embryo 267 mm TL, MZB 15493, female 1130 mm TL, Tanjung Luar fish market, Lombok, Indonesia, 08°45' S, 116°35 'E, 25 April 2004.
Diagnosis. Hemitriakis with large, horizontally oval eyes (length 2.7–3.3% TL, 2.3–4.2 times eye height); snout narrow, acutely pointed, prenarial length 4.5–5.1% TL, preoral snout 1.8–2.0 times internarial width; posterior nasal flaps present, but small; pre-first dorsal length 2.3–2.9 times anal–caudal space; second dorsalfin height 6.5–7.1% TL; 69 rows of teeth in both jaws (based on one paratype); dorsal, pectoral and anal fins strongly falcate in adults; first dorsal origin anterior to pectoral free rear tips; total vertebral counts 143–160, precaudal counts 105–122, monospondylous precaudal counts 35–38; late-term embryos with a bold colour pattern of complicated saddles and rings over head, body and fins; small post-natal juveniles (<500 mm TL) with faint dark blotches and bars; larger juveniles and adults plain except for white margins on fins and a black caudal fin tip; males mature at ~ 900 mm TL, females at ~ 1000 mm TL. This species superficially closely resembles other members of this genus, H. abdita, H. complicofasciata, H. falcata, H. leucoperiptera and H. japanica. From H. abdita and H. complicofasciata, it is distinguished by its lower vertebral counts (precaudal count 105–122 vs. 124–131) and from H. leucoperiptera by its higher vertebral counts (precaudal count 105–122 vs. 94–96). From H. japanica, it differs in number of monospondylous centra (35–38 vs. 39–43) and structure of the cytochrome oxidase 1 (CO1) gene. It is most similar to H. falcata, but differs in colour of late-term embryos and newborns (complicated pattern of bars, lines and rings over body and fins vs.
a series of dusky saddles), second dorsal fin height (6.5–7.1 vs. 5.9–6.5% TL), narrower eye (height 0.8–1.2 vs. 1.3–1.6% TL) and shorter mouth (length 1.9–2.2 vs. 2.2–2.6% TL).
Description. Proportional dimensions as percentage of total length (FAO abbreviations from Compagno, 2001) for type series, listed in Table 1.
Body elongate and slender, trunk circular to subtriangular in cross section at first dorsal-fin base, length of trunk from fifth gill openings to vent 1.33 (1.24–1.35) times head length. A low interdorsal ridge on midline of back between dorsal fins, and a very low postdorsal ridge, but without predorsal ridges; lateral ridges absent from body. Caudal peduncle slender, cylindrically tapering and without lateral keels, caudal peduncle height at upper caudal origin 1.14 (1.02–1.16) its width, 4.32 (3.72–4.68) in dorsal–caudal space. Precaudal pits absent.
Head short, its length 0.87 (0.84–0.93) in pectoral–pelvic space; fairly narrow and flattened, roughly trapezoidal in cross-section at eyes. Outline of head in lateral view nearly straight to convex dorsally, slightly convex ventrally along lower jaws and nearly flat beneath gills; in dorsoventral view head anteriorly parabolic and posteriorly tapering along branchial region. Preoral snout long, 1.15 (0.96–1.07) in mouth width. Snout tip narrowly rounded to acutely pointed in dorsoventral view, with shallow indentations anterior to nostrils; snout bluntly pointed in lateral view, convex above and below.
External eye opening with prominent posterior notch but no anterior one; eyes large and elongate-oval in shape, eye length 7.08 (5.98–7.12) in head length, eye length 2.25 (2.54–4.20) times eye height. Eyes dorsolateral on head, with lower edges well medial to horizontal head rim in dorsal view, subocular ridges prominent. Nictitating lower eyelids external in young and adults, with deep but entirely scaled subocular pouches and secondary lower eyelids.
Spiracles small, length 4.42 (5.45–6.63) in eye length, spiracles 0.34 (0.27–0.33) eye lengths behind and below posterior eye notch. First four gill openings subequal in height; fifth shorter than third, height of fifth 0.77 (0.65–0.84) of third; third 8.75 (8.60–9.73) in head, 0.81 (0.61–0.83) of eye length. All gill openings very slightly concave to nearly straight, gill filaments not visible from outside; upper ends slightly below lower edges of eyes.
Nostrils with large oval to subcircular incurrent apertures lacking posterolateral keels, rounded anterior nasal flaps with rounded tips, prominent mesonarial flaps, small oval excurrent apertures, and very small posterior nasal flaps. Nostrils well in front of mouth; width 2.26 (2.05–2.34) in internarial space, 1.72 (1.69–1.93) in eye length, 1.34 (1.04–1.48) in third gill opening height.
Mouth broadly arched, moderately large, and short, mouth width about 0.67 (0.61–0.77) of head width at mouth corners, 3.48 (2.83–3.66) in head length; mouth length 2.90 (2.80–3.26) in mouth width. Tongue large, flat and broadly rounded, filling floor of mouth. Maxillary valve narrow, width slightly less than one fifth of eye diameter; valve covered with small papillae. No buccal papillae on floor of mouth and palate behind maxillary valve; maxillary valve smooth and covered with buccopharyngeal denticles. Labial furrows long, uppers 1.69 (1.51–1.71) times lowers, anterior ends of uppers under first quarter of eye length and reaching virtually to symphysis of upper jaw. Labial cartilages large.
Teeth relatively few, in 36/33 rows. Teeth not arranged in diagonal files, no toothless spaces at symphysis. Teeth weakly differentiated in upper and lower jaws and along jaws, with well defined medials and weakly differentiated anterolaterals and posteriors. Tooth formulae (counts combined for both sides) are: upper = M3, AL10-12, P5-6; lower = M5, AL9-10, P4-5. Upper anterolateral teeth higher-crowned than lowers, both with well-developed distal cusplets and oblique cusps, cusps somewhat higher and more erect on upper teeth than lowers; medial teeth smaller than anterolaterals, with more erect cusps, higher crowns, and both mesial and distal cusplets; anterolaterals gradually become lower crowned and lower-cusped along the dental band, and grade into keel-like posterior teeth which are very low-crowned, lack cusps, and have a broad convex edge.
Lateral trunk denticles of holotype with elongated, teardrop-shaped crowns about 1.5 times as long as wide, closely imbricated; interspaces between ridges, including that between medial ridges, covered with reticulated depressions; crown with prominent paired longitudinal ridges that diverge and then converge posteriorly to end at the medial cusps; medial cusp relatively long and strong, a third to half length of crown; a pair of strong lateral ridges on crown, terminating in strong but short lateral cusps. Denticles of adult male paratype (CSIRO H 5873–05) with more teardrop-shaped crowns than smaller types, with lateral cusps much less developed.
Pectoral fins narrow and very weakly to semi-falcate; anterior margin broadly convex; apex narrowly rounded; posterior margin nearly straight (smaller paratypes) to moderately concave (largest paratypes); free rear tips broadly rounded, inner margins convex; bases narrow; anterior margin 1.61 (1.43–1.64) times pectoral length; slightly larger in area to first dorsal; origins under fourth gill openings; apex posterior to its free rear tip when fin is elevated and adpressed to body.
Pelvic fins broadly triangular and not falcate; pelvic anterior margins 0.46 (0.45–0.51) of pectoral anterior margins; slightly larger in area to anal fin; anterior margin nearly straight; apex bluntly pointed to angular; posterior margin nearly straight in smaller types, becoming slightly concave in larger types; free rear tips pointed, inner margins straight.
Claspers of adult male paratype (CSIRO H 5873–05) relatively long and basally stout, convex and strongly tapering on lateral edge, and with a convex, blunt-tipped clasper glans. Claspers extending well behind pelvic free rear tips, by distance about 1.1 times pelvic inner margin, but falling in front of anal origin by about length of anal base. Most of clasper except dorsal surface of glans covered with small clasper denticles with blunt, rounded crowns and no cusps. Exorhipidion, envelope and pseudopera absent, clasper groove open. Rhipidion present and very large, extending over most of length of clasper glans, formed as a flat, convex-edged blade with posterior end far behind cover rhipidion. Cover rhipidion very low, hardly differentiated from medial edge of clasper groove, extending from apopyle to apex of rhipidion. Pseudosiphon very short and slit-like, extending opposite the posteriormost third of the cover rhipidion.
First dorsal fin high, apically narrow and falcate; anterior margin basally concave and distally convex; apex narrowly rounded (moderately rounded in paratype CSIRO H 6817–02); posterior margin slightly convex near apex, nearly straight for most of upper two thirds, then broadly concave; free rear tip acutely pointed, inner margin nearly straight; origin about level or slightly anterior to free rear tips of pectorals, midpoint of base 1.62 (1.26–1.55) times closer to pectoral insertions than pelvic origins; insertion and free rear tip well anterior to pelvic origins; insertion over or slightly posterior to level of dorsal apex; base 2.50 (2.08–2.71) in interdorsal space, 2.09 (1.96–2.38) in dorsal caudal margin; first dorsal height 1.15 (1.04–1.23) in first dorsal base; first dorsal inner margin 2.11 (2.07–2.28) in first dorsal height, 2.42 (2.29–2.62) in first dorsal base.
Second dorsal fin high, apically narrow and falcate, slightly smaller than first dorsal fin; height 1.28 (1.23–1.34) in first dorsal-fin height, base 0.90 (0.86–0.98) of first dorsal-fin base; anterior margin basally concave and apically convex; apex narrowly rounded (moderately rounded in paratype CSIRO H 6817–02); posterior margin slightly convex near apex, nearly straight for most of upper two thirds, then broadly concave; free rear tip acutely pointed, inner margin straight or very slightly concave; free rear tip extending slightly behind anal free rear tip but far in front of upper caudal-fin origin; insertion over or slightly posterior to fin apex; base 1.30 (1.12–1.37) in dorsocaudal space, second dorsal height 1.32 (1.20–1.39) in second dorsal base, second dorsal inner margin 2.27 (1.94–2.27) in second dorsal height and 2.99 (2.33–2.85) in second dorsal base.
Anal fin low, apically narrow, semi-falcate, and much smaller than second dorsal; height 0.48 (0.46–0.59) times second dorsal-fin height, anal base 0.83 (0.73–0.85) times second dorsal-fin base; anterior margin concave basally and distally convex; apex narrowly rounded to somewhat angular; posterior margin broadly to deeply concave; free rear tip acutely pointed, well in front of lower caudal origin, inner margin nearly straight; base with short, very low preanal ridges less than 1/3 of rest of base; origin slightly behind second dorsal origin by 0.18 (0.21–0.30) of second dorsal base; insertion slightly behind or opposite second dorsal insertion and slightly anterior to apex; base 1.24 (1.14–1.63) in anal–caudal space, anal height 2.26 (1.83–2.24) in anal base, anal inner margin 1.35 (1.26–1.69) in anal height, 3.05 (2.67–3.20) in anal base.
Caudal fin narrow-lobed and asymmetrical, with short terminal lobe and prominent ventral lobe at all stages; falcate; relatively short, dorsal caudal margin 3.85 (3.63–3.93) in precaudal length; preventral caudal margin 2.25 (2.13–2.45) and terminal lobe length 2.66 (2.59–2.74) in dorsal caudal margin, subterminal margin 1.84 (1.42–1.90) in terminal margin; dorsal caudal margin proximally and distally convex, and mesially concave, without lateral undulations; preventral margin basally straight or concave and apically convex, tip of ventral caudal lobe narrowly rounded to pointed, lower postventral margin nearly straight to slightly concave, upper convex, notch between postventral margins forming angle of 98 (94–115)°; subterminal notch a narrow, deep slot; subterminal margin straight to very slightly concave, terminal margin slightly concave, lobe formed by these margins bluntly angular; tip narrowly rounded to somewhat pointed.
Vertebral counts and ratios listed for holotype and 8 paratypes in Table 2 and summarised as follows: total counts (TC) 147 (143–160), precaudal (PC) counts 109 (105–122), monospondylous precaudal (MP) centra 38 (35–38), diplospondylous precaudal (DP) centra 59 (55–67), diplospondylous caudal (DC) centra 50 (48–57). MP counts 25.9 (22.9–26.6)%, DP counts 40.1 (38.5–41.9)%, and DC counts 34.0 (33.3–35.8)% of TC counts. Ratios of DP/MP counts 1.6 (1.4–1.8), DC/MP counts 1.3 (1.3–1.5). Transition between MP and DP centra over pelvic bases and one or two centra behind pelvic girdle. Last few MP centra before MP–DP transition moderately enlarged, not forming a ‘stutter zone’ of alternating long and short centra.
Chondrocranium studied by dissection of a paratype (CSIRO H 6817–01) and checked on radiographs of other specimens. Rostral cartilages elongated, slender, cylindrical-compressed, and not hypercalcified in adults. Medial rostral cartilage 2.2 in nasobasal length (NBL, length 46% NBL), distance between bases of lateral rostral cartilages 1.7 in medial rostral cartilage. Medial rostral cartilage narrow-based and arched dorsally, lateral rostrals horizontal. Rostral node formed as a broad anteriorly divergent plate with a rostral fenestra. Nasal capsules large, high, transversely elliptical and somewhat wider than long, width across them 1.3 in NBL (75% NBL), length of capsule 1.2 in its width. Anterior margins of nasal capsules nearly straight, transverse to the cranial axis. Nasal apertures on ventrolateral faces of capsules, separated from large nasal fontanelles by a broad channel. Ectethmoid chambers inside nasal cavities, at posterior edges of nasal fontanelles and not visible ventrally. Subnasal plate in the form of irregular medial extensions of the lateral capsule wall, and broad lateral extensions of the narrow, high internasal septum bordering the wide nasal fontanelles. Strong ectethmoid condyles on posteroventral edges of nasal capsules, separated by a broad arcuate subnasal fenestra. Anterior fontanelle transversely oval, length about 1.2 times in its width and about 4.3 in NBL (23% NBL). Dorsal lip of fontanelle not flared but with an epiphysial notch. Cranial roof broadly arched, about level with supraorbital crests but not dome-like. Parietal fossa deep. Orbital notches deep. Basal plate nearly flat from orbital notches to occipital centrum, without keels. Internal carotid foramina slightly closer to each other than to the stapedial foramina. Edge of supraorbital crests deeply arcuate in dorsal view, with short, prominent triangular preorbital processes and laterally directed, ventrally hooked, triangular postorbital processes. Width across preorbital processes 1.4 in NBL (71% NBL), width across postorbital processes 1.3 in NBL (77% NBL), least width across supraorbital crests 1.8 in width across postorbital processes. Orbits horizontally subrectangular in lateral view. No ledge between suborbital shelves and nasal capsules. Suborbital shelves broadly convex, extending well lateral to the supraorbital crests in dorsal view. Width across suborbital shelves 1.5 in NBL (65% NBL). Otic capsules not greatly expanded or inflated, their lengths about 3.5 in NBL (29% NBL) and greatest width across them 2.0 in NBL (50% NBL). Sphenopterotic ridges diagonally arched in dorsal view, without a distinct pterotic horn in lateral view. Opisthotic ridges high, extending laterally to edges of sphenopterotic ridges. Hyomandibular facets large, wedge-shaped, extending across rear half length of otic capsules and slightly exserted posteriorly. Occipital condyles broad and slightly exserted from occiput, with a single occipital centrum between them.
Colour. In alcohol: larger types (> 55 cm TL) are greyish-brown above, lighter below, with prominent whitetipped dorsal, pectoral, pelvic, and caudal fins. Dorsal and pectoral fins with white apical region which extends along posterior margin becoming narrower towards the free rear tip; abruptly dusky below their white tips which highlights these markings. Pelvic and anal fins with less well demarcated white margins, but still evident. Caudal fin with white apical region on lower ventral lobe, extending as a narrow margin along postventral margins; subterminal margin dusky anteriorly, white-tipped apically; terminal margin white-edged for lower half to two thirds; tip distinctly blackish, extending as a blackish margin down dorsal third to half of terminal margin. Paratype CSIRO H 6817–02 (497 mm TL) with more prominent dusky margins on fins and with faint dark bars and blotches evident on dorsal and lateral surfaces of head and body (Fig. 1 c). Late-term embryos with a consistent, bold colour pattern of dark brownish bars and rings on a pale brown background; pattern dominated by a series of somewhat complicated saddle markings, each made of medium brown bars with narrow, dark brown edges; 10 saddle markings evident between snout and tail tip, 1st over eyes, 2nd and 3rd predorsal, 4th and 7th below dorsal fins, 5th and 6th over interdorsal region, 8th at caudal-fin origin and last two on caudal fin upper lobe; a series of rings and short bars present on snout tip anterior to eyes, below and just posterior to spiracles, along body below lateral midline and between saddles on caudal fin; dorsal fins with dark markings including a dark central blotch (sometimes formed as a ring); pectoral fins with a dark ring marking distally and sometimes with other dark markings basally; caudal-fin terminal lobe with a dark ring or blotch terminally.
Size. Type material ranged from late-term embryos 178–260 mm TL, to an adult male of 947 mm TL. White (2007) reported basic biological data for 380 individuals of H. indroyonoi (as H. sp. 1): females and males ranged from 506–1152 and 544–1200 mm TL, respectively; males mature at ~ 900 mm TL; females have litters of 6–11; reproductive mode is viviparous, with histotrophy (no yolk-sac placenta); size at birth ~ 280–300 mm TL. White (2007) also provides length-weight relationships for females and males.
Distribution. Known only from off the islands of Bali and Lombok in eastern Indonesia. No information on capture depth is known but typically caught with squalid dogsharks (Squalus) so presumably occurring on the outer continental shelf and upper slope.
Etymology. Named in honour of Dr Indroyono Soesilo, who has provided a great deal of support for shark research in Indonesia and was a strong advocate for the production of the field guide to sharks and rays of Indonesia (White et al., 2006).
Comparisons. Compagno (1970, 1979, 1984, 1988) noted that Hemitriakis is readily distinguished from other triakid genera but that the species of Hemitriakis are morphologically very similar in external appearance. Subtle differences in external morphology between these species are masked by inadequate series of specimens, by considerable growth changes in proportions and fin and body shape between juveniles and adults, and by considerable variation in some characters within individuals of the same maturity class. There are few morphometric and external morphological characters that separate the species in our limited sample. Compagno & Stevens (1993) provide detailed morphometrics of H. falcata, H. abdita, H. japanica and a New Caledonian Hemitriakis, and Takahashi & Nakaya (2004) also provide detailed morphometrics for H. complicofasciata.
The Hemitriakis species are most clearly separable by vertebral counts, as are certain other triakids and some carcharhinids which are externally similar but differ sharply in numbers of vertebrae and in ratios of vertebral groups. For example, closely related Mustelus species in the Gulf of Mexico and the Gulf of California (Heemstra, 1973), sympatric species pairs within Carcharhinus such as C. amboinensis + C. leucas and C. dussumieri + C. sealei (Garrick, 1982), and some allopatric species of Rhizoprionodon (Springer, 1964). Hemitriakis abdita and H. complicofasciata are clearly separable from other members of the genus in having higher vertebral counts, i.e. precaudal counts 124–131 vs. 101–122 in H. falcata, H. indroyonoi and H. japanica, and 94–96 in H. leucoperiptera (Compagno & Stevens, 1993; Takahashi & Nakaya, 2004). Although H. indroyonoi and H. japanica have similar precaudal and total vertebral counts, they do differ slightly in number of monospondylous centra, i.e. 35–38 vs. 39–43, respectively. Hemitriakis falcata has very similar vertebral counts to H. indroyonoi, but on average has more caudal centra (mean 57.6 vs. 52.6).
Young Hemitriakis are more boldly patterned than adults, as in many other carcharhinoid sharks (Compagno, 1988), but juvenile colour patterns differ greatly between some species. Young H. japanica have a dark upper terminal tip (Fig. 5 d) and young H. leucoperiptera have obscure saddles on their caudal peduncles, and dusky epichordal caudal lobes and terminal lobe bases (Fig. 5 e). Juvenile H. abdita differ in having a black snout tip and black bar on the underside of the snout and a dark bar beneath the eye. Young H. falcata have a series of dusky saddles on back and over gills, dark spots or bars over eyes and on caudal fin margins (Fig. 5 b). In strong contrast, young of H. complicofasciata, H. indroyonoi and H. sp. A [sensu Compagno et al., 2005] have a complicated pattern of bars, lines and rings over body and fins (Figs 5 a, c, f). Takahashi & Nakaya (2004) stated that late-term embryos and juveniles between 385–604 mm TL possessed the complicated colour pattern. In contrast, this colour pattern appears to be less persistent in H. indroyonoi, with a juvenile paratype of 497 mm TL with only faint dark banding still evident, and without the complicated colour pattern of the late-term embryos (Figs 1 c, 5c).
Hemitriakis indroyonoi and H. falcata have a similar cytochrome oxidase 1 (CO1) gene structure, but they differ markedly from H. japanica from Taiwan (B. Ward, unpubl. data).
Hemitriakis indroyonoi is morphologically similar to H. falcata, but they differ in the following characters (based on specimens> 400 mm TL; Compagno & Stevens, 1993): second dorsal fin taller (height 6.5–7.1 vs. 5.9–6.5% TL); slightly longer prenarial length 4.5–5.1 vs. 3.7–4.5% TL in H. falcata; narrower eye (height 0.8–1.2 vs. 1.3–1.6% TL); slightly shorter mouth (length 1.9–2.2 vs. 2.2–2.6% TL).
Although H. indroyonoi and H. falcata are very similar in morphology and meristics, they do differ significantly in size. Compagno & Stevens (1993) examined seven adult males of H. falcata between 695 and 773 mm TL, whereas White (2007), based on a large sample size, recorded that all males of H. indroyonoi <810 mm TL possessed non-calcified claspers. Males with fully calcified claspers were typically> 900 mm in length, with males attaining 1200 mm TL. Chen & Mizue (1973) stated that male H. japanica mature at about 850 mm TL and reach 1100 mm TL which is close to this new species, but a specimen from Taiwan was adult (or nearly so) at only 675 mm. Takahashi & Nakaya (2004) stated that females and males of H. complicofasciata mature at 760 and 805 mm TL, respectively, which is considerably smaller than that recorded for H. indroyonoi, i.e. ~900 and> 1000 mm TL, respectively.
There are very little differences in morphology and number of teeth in members of this genus, with the counts for each species generally overlapping. Hemitriakis complicofasciata and H. indroyonoi both lack an accessory cartilage at the symphysis of the upper jaw, whereas H. abdita has an accessory cartilage present (see Fig. 10 in Takahashi & Nakaya, 2004).
The chondrocrania of Hemitriakis indroyonoi, H. falcata and H. japanica are generally similar but differ in some minor details. The chondrocrania of H. indroyonoi is morphologically closer to that of H. falcata than that of H. abdita and H. japanica. For example, the former species have a much shorter medial rostral cartilage, indicating a shorter rostrum, than the two latter species (45–46 vs. 59–63% of nasobasal length). The crania of H. indroyonoi and H. falcata are similar, but differ in several subtle characters including: lateral rostrals horizontal (vs. arched ventrally), nasal capsules slightly smaller (width 75 vs. 82% of nasobasal length) and otic capsules slightly larger (length 29 vs. 25% of nasobasal length).
Some ontogenetic differences in morphology were evident from the measured type specimens of H. indroyonoi. The single late-term embryo measured (CSIRO H 6818–01, male 254 mm TL) differed from the measured post-natal types (> 497 mm TL) in a number of proportional characters including: longer preoral length (8.3 vs. 6.1–7.3% TL); longer prespiracular length (12.5 vs. 9.4–10.9% TL); longer prebranchial length (17.1 vs. 14.2–15.9% TL); longer head (length 21.3 vs. 17.8–19.8% TL); longer predorsal length (28.7 vs. 24.1–26.2% TL); larger eyes (length 5.0 vs. 2.7–3.3% TL); larger spiracle (1.1 vs. 0.5–0.6% TL); smaller first dorsal fin (length 12.4 vs. 13.0–14.6% TL, height 6.4 vs. 8.2–9.4% TL, posterior margin 5.9 vs. 8.8–10.0% TL).
Hemitriakis sp. A [sensu Compagno et al., 2005] is still problematical because of its inadequate sample of four fetuses (SU 40097). It clearly differs from the sympatric H. leucoperiptera in coloration of the young and vertebral counts. The colour pattern of the young more closely resembles H. complicofasciata and H. indroyonoi, but the vertebral counts (PC = 116, MP = 44) lay between these species. Thus, this is likely to represent another undescribed species of Hemitriakis, but further samples are required, particularly of adult specimens.
description: Published as part of White, William T. & Compagno, Leonard J. V., 2009, Hemitriakis indroyonoi sp. nov., a new species of houndshark from Indonesia (Carcharhiniformes: Triakidae), pp. 41-57 in Zootaxa 2110 on pages 46-55, DOI: 10.5281/zenodo.187881