Planonasus
Creators: name: Weigmann, Simon
name: Stehmann, Matthias F. W.
name: Thiel, Ralf
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Elasmobranchii
Carcharhiniformes
Pseudotriakidae
Planonasus

description: Genus Planonasus g. n. Weigmann, Stehmann and Thiel
Diagnosis. Deep-water carcharhiniform sharks with a soft, rather deep, and stout to slender and elongated body; head long, length 24.3–26.7% of TL; snout moderately long and bell-shaped, flattened, preorbital length 8.3–8.5% of TL; spiracles large, nearly vertical, their length 4–6 (longitudinally) and 2–5 (vertically) times in eye length; mouth very large, angular; commissural upper teeth comb-like, others tri- to pentacuspidate, whereas nearly all lower jaw teeth comb-like; labial furrows short; anterior nasal flaps short; internarial space broad, 1.5–1.7 times nostril width; no dermal gill rakers; entire roof of mouth densely set with oral papillae of distinct size; first dorsal fin forming a long and low triangle with rounded upper and narrowly pointed rear apex; no interdorsal ridge; first dorsal-fin base totally in front of pelvic-fin base; second dorsal fin origin over pelvic-fin insertions, much higher than first dorsal fin, forming an uneven triangle with narrowly rounded upper apex; interdorsal space 11.8–14.5% of TL; anal fin small and low, origin behind that of second dorsal fin; no precaudal pit; caudal peduncle relatively short, 5–6% of TL, axis raised upwards; dorsal caudal margin short, 22–23% of TL, not undulated, with a keel of somewhat enlarged denticles at front edge.
Type species. Planonasus parini sp. n.
Remarks. Planonasus differs from the three proscylliid genera Eridacnis Smith, Proscyllium Hilgendorf and Ctenacis Compagno in having a longer and bell-shaped snout in dorsolateral view, whereas the snout is shorter and more evenly rounded in the Proscylliidae. Further differences are the lack of gill rakers, a broader internarial space, a closer to pectoral than to pelvic bases placed first dorsal fin, and the absence of color patterns on the body as well as the fins in Planonasus. Compared to the two other pseudotriakid genera Gollum and Pseudotriakis, the new genus has oral papillae and no nicitating eyelids (vs. oral papillae absent and nicitating eyelids present), a longer head, an intermediate prenarial snout length, an intermediate number of tooth rows per jaw, a first dorsal fin of intermediate height and length and with white free rear tip, a caudal peduncle of intermediate length, and fewer vertebrae. In contrast to Gollum, Planonasus has a softer body, larger spiracles, longer gill openings, a larger mouth, stronger heterodonty, less densely set lateral dermal denticles, a non-falcate second dorsal fin, plain body and fin color, a shorter interdorsal space, and a strongly differing distribution. Compared to Pseudotriakis, the new genus has a much smaller body size, a longer preorbital snout, longer eyes, more vertically oriented spiracles, a shorter first dorsal fin, and a more rectangular anal fin.
Pseudotriakidae gen. sp. n.: Timokhin and Usachev, 1993.
Holotype. ZMH 25895, female 534 mm TL fresh, 516 mm TL 70% ethanol preserved, R/V Vityaz, cr. 17, sta. 2565, 28 October 1988, 12°22’8”N, 53°02’7”E – 12°21’2”N, 53°01’3”E, 1000–1120 m depth, 29 m shrimp trawl, trawl # 5, on the bottom for 62 minutes, off Socotra Islands.
Additional material (2). YugNIRO uncatalogued, juvenile female, 378 mm TL, F/V Dmitry Stephanov, cr. 3, sta. 32, 24 December 1988, 12°16’N, 53°03’E, 560–635 m depth, bottom trawl, collected by S.I. Usachev from YugNIRO, off Socotra Islands; YugNIRO uncatalogued, juvenile male, 339 mm TL, F/V Dmitry Stephanov, cr. 5, sta. 13, 23 October 1989, 12°36’N, 53°09’E, 710–730 m depth, bottom trawl, collected by S.I. Usachev from YugNIRO, off Socotra Islands.
Holotype Non-type female Non-type male ......continued on the next page
Holotype Non-type female Non-type male ......continued on the next page
TABLE 1. (continued) Diagnosis. A small deep-water pseudotriakid species with the following combination of characters: body soft; head bell-shaped with a broadly parabolic snout; preorbital snout length 1.5–1.9 times the eye length; preoral length 0.7–0.8 times the mouth width, 1.4–1.5 times the prenarial snout length; eye length 1.9–2.3 times the nostril width; head relatively broad, head width at middle gill slits 10–16% of TL; preorbital snout length 1.0–1.7 times the interorbital space (integumental) and 2.1–2.3 (skeletal), respectively; head length 2.0–2.5 times the mouth width, 9.8–10.9 times the nostril width, 2.8–3.3 times the length of preventral caudal-fin margin; length of pectoral-fin anterior margin 2.1–2.2 times the pectoral base length; length of first dorsal-fin inner margin 0.4–0.5 times the pectoral-fin base length; second dorsal-fin base length 13% of TL; coloration plain dusky with fins and ventral snout somewhat darker, free rear tip of first dorsal fin marked white; each jaw with about 110–120 rows of very small tri- to multicuspidate teeth; monospondylous trunk vertebrae centra 50–52, diplospondylous precaudal centra 41, total centra about 115–140.
Description of the holotype (Figs. 2–20). Values of non-type specimens differing from holotype are presented in parenthesis where applicable. More complex differences between holotype and non-type specimens are described separately. Morphometric measurements and meristics are given in Table 1.
External morphology (Figs. 2–18). Body soft, rather deep, and stout (more slender and elongated in the nontype specimens), with long abdominal and caudal sections (Figs. 2–8). No predorsal or interdorsal ridges, lateral keels or precaudal pits. Head broad and strongly depressed, its length 1.0 (1.2) times the pectoral-pelvic space; large eyes long slit-like and low (Figs. 9–10). Preoral snout moderately elongated, its length 0.8 (0.7–0.8) times the mouth width. Snout in front of strongly oblique and large nostrils very flat and soft, rapidly narrowing at level of nostrils, so that snout marked off bell-shaped and of even parabolic shape with broad, bluntly rounded tip. Eyes dorsolaterally on head, very large, strongly elongated, their length 0.2 times the head length, 3.9 (2.9–4.2) times the eye height; cartilaginous interspace rather narrow and only about as wide as eyeball length; inner three-fourths of eyeball widely overlapped by scaled orbital skin in dorsal view. Spiracles large, subquadrangular, spiracle length 3.8 (4.4–6.2) (longitudinally) and 2.4 (3.6–4.7) (vertically) times in eye length, 0.8 (0.9–1.0) (longitudinally) and 1.2 (1.1–1.2) (vertically) of distance from eye to spiracle. Gill openings moderately long, well separated, gill filaments not visible externally; their upper ends slightly below lower edge of eye, not becoming more elevated distally; first four gill openings subequal in height, fifth shortest; height of first about 1.5 times the height of fifth (all five gill openings subequal in height in the non-type specimens); height of first gill slit 0.7 (0.3–0.4) of eye length. Nostrils figure eight-shaped, with nearly equally sized, circular in- and excurrent apertures separated by infused, bluntly triangular, short flaps at anterior and posterior nostril margins, which are narrowly edged blackish like the nasal flaps; prenarial snout length 0.7 of preoral snout length, nostril width 1.7 (1.5) times in internarial space, 2.0 (1.9–2.3) times in eye length, 0.7 (1.3–1.5) times the height of first gill opening. Mouth very large in length and width, jaws strongly angled at about 100–110°; mouth width about 0.8 (0.8–1.0) of head width at middle gill slits, 2.5 (2.1–2.5) times in head length (Fig. 11); symphysis of upper jaw slightly anterior to fore end of eye slit, jaw angles posterior to rear ends of eyes and about level with anterior spiracle margins; upper and lower labial furrows short, subequal in length; entire roof of mouth densely set with oral papillae of distinct size.
Teeth tiny, strong heterodonty between upper and lower jaw; teeth in upper jaw set in quincunx pavement pattern of about 110 (about 115) rows (Fig. 12 A), teeth nearly triangular in cross-section of root, tri- to pentacuspidate, median main cusp conically elongated and pointed, lateral cusplets weak (Fig. 13 A), only few posterior to commissural rows with weakly comb-like, multicuspidate teeth with nearly equally sized cusplets each; teeth in lower jaw regularly arranged in about 120 (about 115) strongly oblique, diagonal parallel rows (Fig. 12 B), teeth at symphysis and in few anterior rows of similar shape as the typical upper jaw teeth, but lateral cusplets more distinct, lateral and commissural teeth different, broad, low, comb-shaped, multicuspidate with usually five cusps (Fig. 13 B) (possibly two cusps in the non-type male).
Lateral trunk denticles rather loosely set with distinct interspaces and their tips mostly not overlapping; semierect, tip bent rearward, shape slenderly leaf- to spearhead-like with solid, pointed median main cusp and a weakly developed, very short lateral cusplet at lower level, upper half of most denticles dusky (Fig. 14 A). Lateral trunk denticles in non-type specimens slender, needle-like without lateral cusplets, with four-ray low base and nearly vertically erect long, fine and pointed tip, which slightly curved rearward giving the skin a velvet-like touch. Dermal denticles on top of head and underside of snout very different from lateral trunk denticles, teardrop- to leaf-shaped, strongly inclined rearward, not erect, mostly not overlapping, structured by three longitudinal ridges (Fig. 14 B).
Fifth gill slit over pectoral origin; pectoral fins rather small, subtriangular, non-falcate; anterior margin convex, its length 2.1 (2.1–2.2) times pectoral base length and 1.1 (1.4–2.1) times the length of slightly concave posterior margin, the almost straight inner margin much shorter than the posterior margin (about equal in length in non-type specimens); pectoral base narrow, about as long as inner margin, but only about half as long as anterior and posterior margins (in non-type male base about as long as inner and posterior margins and about half as long as anterior margin, in non-type female base much shorter than inner and posterior margins and about half as long as anterior margin); outer and inner pectoral corners sharply angular at about right angle. Posterior pectoral margins about level with origin of first dorsal fin when pectoral fin elevated and adpressed to body.
First dorsal fin a nearly even semicircle with anterior, upper, and posterior margins forming a continuous arc, lower and longer than second dorsal fin (lower and about equal in length in non-type female, lower and shorter in non-type male); first dorsal fin’s inner margin short, free rear tip pointed and marked white; maximal height of first dorsal fin at about half base length, height 0.3 times base length, 1.7 (1.7–2.0) times inner margin length; first dorsal-fin base 5.5 (4.9–5.9) times the inner margin, 0.6 (0.4–0.5) times the dorsal caudal margin (Fig. 15). First dorsal fin placed half way between pectoral-fin insertions and pelvic-fin origins. Interdorsal space 1.1 times first dorsal-fin base length.
Second dorsal fin a high uneven triangle with long anterior margin, a rounded apex, and nearly vertical, weakly concave posterior margin; inner margin short, free rear tip pointed, not marked white; maximal height of second dorsal fin at about base end, height 0.6 (0.4–0.5) times the base length, 3.0 (2.3–3.0) times the inner margin length; second dorsal-fin base 5.0 (5.4–5.6) times the inner margin, 0.6 times the dorsal caudal margin (Fig. 16). Second dorsal-fin origin over pelvic-fin insertions, base end slightly posterior to anal-fin base end. Interdorsal space 1.2 (0.9–1.0) times second dorsal-fin base length.
Pelvic fins narrowly triangular with long, straight anterior, shorter straight posterior, and even shorter straight inner margins; length of anterior margin 0.6 of length of pectoral-fin anterior margin; outer pelvic corner angular at about 100° (110°), inner corner pointed at about 60° (60–80°). Claspers of non-type male totally immature, hardly exceeding pelvic insertion. Pelvic posterior tips below origin of first dorsal fin. Interspace between pelvic tips and anal origin short, 5.5% (5.7–5.8%) of total length.
Anal fin a long and low, uneven triangle, with long straight anterior margin, outer corner angular at about 110°, shorter and weakly concave posterior, and even shorter, straight inner margins; posterior tip pointed at about 70°; anal-fin height 2.4 (2.2–2.6) in second dorsal-fin height, anal-fin base length 1.5 (1.5–1.9) in second dorsal-fin base length; anal-fin height 0.4 (0.3–0.4) times base length, 1.6 (1.3–1.4) times inner margin length; anal-fin base 4.0 (3.6–4.4) times inner margin, 1.3 (1.3–1.6) times anal-caudal space. Anal-fin origin slightly posterior to second dorsal-fin origin, base end slightly anterior to second dorsal-fin base end (Fig. 16). Distance pelvic insertion to anal origin 0.4 (0.5) times interdorsal space, about equal to distance anal insertion to lower caudal origin and distance second dorsal-fin base end to upper caudal-fin origin.
Caudal fin short, narrow-lobed, and strongly asymmetrical; dorsal caudal margin biconvex, mesially concave before subterminal notch, no lateral undulations, length 1.5 (1.8–2.0) times the interdorsal space; upper caudal lobe very low, lower caudal lobe several times deeper, with short, straight preventral and about twice as long, weakly concave postventral margins, ventral corner bluntly angled at about 145°; subterminal notch distinct; terminal caudal margin short, almost vertical and frayed (Fig. 17). Enlarged denticles at anterior two-thirds of upper caudal margin (Fig. 18), no enlarged denticles at lower caudal margin (no enlarged denticles at upper and lower caudal margins in non-type specimens).
Skeletal meristics (from radiographs, Table 1) (Fig. 19). Vertebral counts for holotype: monospondylous trunk centra 52 (50–52), diplospondylous precaudal centra 41, caudal centra about 47 (about 24–28), total centra about 140 (about 115–121, but probably more centra, because caudal centra not clearly visible on radiographs).
Coloration. When fresh (holotype only) (Fig. 2): plain dusky grayish-brown with darker sides and underside of head as well as dusky edged fins; free rear tip of first dorsal fin distinctly marked white.
Color in preservative: plain medium grayish-brown dorsally on head and along back and flanks; fins with bases in body ground color, but outer parts dusky; free rear tip of first dorsal fin marked pale; gill region dusky; underside of head (especially on throat) darker than body ground color. Jaws, gums, and anterior area at symphysis creamy white, but most of mouth cavity dark gray. Nostrils narrowly edged dark gray.
Size. Small shark reaching at least 534 mm TL and 0.56 kg. Magnetic Resonance Imaging (MRI) pictures of the holotype indicate that it is immature or at most adolescent due to small and compact ovaries (Fig. 20). A maturing size of 490 to 560 mm TL is specified by Compagno et al. (2005) for their probably different but closely related, undescribed “Pygmy False Catshark”.
Distribution. Known from off the Socotra Islands (northwestern Indian Ocean south of Yemen and east of the Horn of Africa); collected from the insular slope at about 1000–1120 m depth (holotype) and between 560 and 730 m depth (non-type specimens). The probably closely related, undescribed “Pygmy False Catshark” was found around the Maldives (Anderson and Ahmed 1993; Compagno et al. 2005).
Etymology. Planonasus g. n. (masculine) refers to the flat snout of these sharks (lat. planus = flat, nasus = nose). The species is named in honor of the late Prof. Dr. N.V. Parin, chief scientist of the memorable cruise 17 of RV ‘Vityaz’ in 1988/89, when the holotype was sampled as one highlight among many more chondrichthyans along the deep western Indian Ocean.
Comparisons. References used for comparisons are Last and Gaudiano (2011) for characters of Gollum attenuatus and G. suluensis, as well as Yano and Musick (1992) for characters of Pseudotriakis microdon, if not otherwise stated. Planonasus parini differs from the species of Gollum and Pseudotriakis in having numerous tiny oral papillae on roof and floor of mouth. Contrary to the other pseudotriakid species, P. pa r in i also has no nicitating eyelids and a white free rear tip of the otherwise plain-colored first dorsal fin. In P. p a r i n i, the head length is 24.3–26.7% of TL, whereas in G. attenuatus it is 21.6–22.5% of TL, in G. suluensis it is 21.5–23.0% of TL, and in P. microdon it is 16.1–23.5% of TL. The prenarial snout length is 4.9–5.6% of TL in P. p a r i n i, 7.4–7.8% of TL in G. attenuatus, 5.9–6.5% of TL in G. suluensis, and 2.6–4.8% of TL in P. microdon. The base length of the first dorsal fin is 10.5–13.1% of TL in P. p a r i n i, 10.3–11.1% of TL in G. attenuatus, 9.3–10.0% of TL in G. s u l u e n s i s, and 15.5–36.3% of TL in P. microdon. The first dorsal-fin height is 3.5–4.1% of TL in P. parini, 6.1–6.5% of TL in G. attenuatus, 5.5–6.4% of TL in G. suluensis, and 2.3–3.9% of TL in P. microdon. The anal-caudal space is 5.0–6.3% of TL in P. p a r i n i, 7.7–9.4% of TL in G. attenuatus, 7.7–10.1% of TL in G. suluensis, and 1.4–4.7% of TL in P. microdon. The total vertebral centra count is 115–140 in P. parini, 162–168 in G. attenuatus, 151–154 in G. suluensis, and 183–189 in P. microdon. P. parini has about 110–115 tooth rows in upper and about 115–120 rows in lower jaw, G. attenuatus has (after Compagno 1973) 96–99 rows in upper and 108–114 in lower jaw, G. suluensis has about 94 rows in upper and about 81 rows in lower jaw, and P. microdon has (according to Compagno 1984b) 202–294 rows in upper and 258–335 in lower jaw.
Compared to the species of Gollum, Planonasus parini has a softer body. In P. p ar i ni and G. attenuatus, only the teeth at symphysis and in few anterior rows are tri- to pentacuspidate with long median main cusp, whereas the lateral and commissural lower jaw teeth are comb-like and arranged in strongly oblique diagonal parallel rows. In G. suluensis (immature male paratype CSIRO H 7193–01), the symphyseal and most lateral teeth are tri- to pentacuspidate with long median cusp, whereas only the posterolateral and commissural teeth are comb-like and arranged in strongly oblique diagonal parallel rows. The lateral trunk denticles of P. parini are set relatively loosely with large interspaces, whereas they are densely set like roof tiles in Gollum. The second dorsal fin of P. parini is non-falcate with nearly straight margins, whereas it is falcate with concave posterior margin in Gollum. In P. parini and G. suluensis, the anal fin is non-falcate with nearly straight margins, whereas it is falcate with concave posterior margin in G. attenuatus. P. parini has a plain medium grayish-brown color with only underside of head and outer parts of fins being dusky, and the free rear tip of first dorsal fin is marked white; jaws, gums, and anterior area at symphysis are creamy white, but most of mouth cavity is dark gray. G. attenuatus has an abrupt lateral demarcation of relatively dark dorsal surface and whitish ventral surface and white posterior margins at all fins. G. suluensis has a distinctly brighter coloration than P. p a r i n i, with plain brown color dorsally and dusky ventrally with some whitish patches, a brownish and white speckled mouth cavity, and dorsal and anal fins with translucent dusky posterior margins. In P. parini, the spiracle length is 1.2–1.8% of TL, in G. attenuatus it is 1.0% of TL, and in G. suluensis it is 0.4–0.8% of TL. The height of the first gill slit is 1.7–3.1% of TL in P. parini, 1.3–1.7% of TL in G. attenuatus, and 1.5–2.2% of TL in G. suluensis; the fifth gill-slit height is 1.8–2.0% of TL in P. parini and 1.1–1.4% of TL in both species of Gollum. The mouth width is 9.8–12.8% of TL in P. parini, 7.6–8.0% of TL in G. attenuatus, and 8.8–9.7% of TL in G. suluensis. In P. parini, the interdorsal space is 11.8–14.5% of TL, in G. attenuatus it is 19.4–20.1% of TL, and in G. suluensis it is 19.3–21.1% of TL. Although Compagno (1973) defined the presence of an interdorsal ridge for Gollum, both its species—like P. parini —actually do not have an interdorsal ridge (J. Pogonoski, CSIRO, pers. comm.). The distribution of P. p a r i n i appears to be confined to the northwestern Indian Ocean, G. attenuatus is known only from off New Zealand, New Caledonia, and the Norfolk Ridge, G. suluensis is known only from off Palawan Island (Philippines).
Compared to Pseudotriakis microdon, Planonasus parini has more rectangular anal fins, whereas in P. microdon the outer corner is situated more posteriorly compared to the total length of the fin. The spiracles of P. parini are oriented almost vertically to body axis, in P. microdon they are aligned diagonally to body axis. In P. parini, the preorbital snout length is 8.3–8.5% of TL, in P. microdon it is 3.7–7.3% of TL. P. p a r i n i has an eye length of 4.4–5.5% of TL, P. microdon has an eye length of 2.3–4.1% of TL. Furthermore, P. p ar i ni is much smaller: the largest known specimen of P. parini is the female holotype with 534 mm TL. Considering the smallest known specimen of 339 mm TL and the maturing size of 490 to 560 mm TL in the closely related, undescribed “Pygmy False Catshark”, a maximum size below 1000 mm TL is assumed for P. parini. In contrast, P. microdon grows up to 2950 mm TL in males and 2960 mm TL in females (Yano and Musick 1992) and has a maturing size of more than 2000 mm (Compagno 1988) with the smallest confirmed mature female having 2565 mm TL (Forster et al. 1970) and the largest immature male having 2500 mm TL (Yano 1992). Taking into account the largest known near-term embryos of P. microdon with 1120–1380 mm TL (Taniuchi et al. 1984; Yano 1992; Stewart 2000), the assumed maximum size of P. parini is well below the size at birth of P. microdon.
Remarks. There are a few morphometric and morphological differences between the non-type specimens and the holotype that might be of ontogenetic nature but eventually instead caused by individual variation or artificial effects due to the condition of the specimens. 1) the relative lengths of the first dorsal fin and its base increase with the size of the specimens, 2) in the juvenile non-type specimens all five gill openings are subequal in height whereas the fifth one is distinctly shorter than the first four openings in the holotype, 3) the nostril width is 1.3 to 1.5 times the height of the first gill opening in the non-type specimens but only 0.7 times the height of the first gill opening in the holotype, 4) the lateral trunk denticles are nearly vertically erect without lateral cusplets in the nontype specimens, whereas they are semi-erect with a short lateral cusplet at lower level in the holotype, 5) there are no enlarged denticles at upper caudal margin in the non-type specimens, whereas there are enlarged denticles at the anterior two-thirds of upper caudal margin in the holotype (Fig. 18).
Additionally, the preorbital snout length is 1.0 times the integumental interorbital space in the female specimens, whereas this ratio is 1.7 in the male. Secondly, the comb-like lateral and commissural lower jaw teeth usually have five cusps in the females, but possibly only two cusps in the male.
The biology of Planonasus parini is unknown, but possibly similar to other pseudotriakid sharks. The soft fins, skin and musculature are suggestive of a sluggish and inactive shark of nearly neutral buoyancy similar to Pseudotriakis microdon (Compagno 1998). The low-angle caudal fin with no ventral, but large longitudinal and subterminal hypochordal lobes and the moderately elongated, not fusiform body of P. parini are typical for slowswimming demersal and benthic sharks with anguilliform motion according to Thomson and Simanek (1977) and Webb and Keyes (1982). This development in caudal-fin design and body shape is adapted for near-bottom living and low swimming speeds when effective cruising is more important than high vertical mobility (Thomson and Simanek 1977). Other pseudotriakids are yolk-sac viviparous and oophagous like P. microdon (Yano 1992) and Gollum attenuatus (Yano 1993a), but no information is available for P. p a r i n i. Other pseudotriakids feed predominantly on bony fishes plus sharks and cephalopods like P. microdon (Yano and Musick 1992) or sharks plus bony fishes, crustaceans, and mollusks like G. attenuatus (Yano 1993b), but again no information is available for P. parini.
description: Published as part of Weigmann, Simon, Stehmann, Matthias F. W. & Thiel, Ralf, 2013, Planonasus parini n. g. and n. sp., a new genus and species of false cat sharks (Carchariniformes, Pseudotriakidae) from the deep northwestern Indian Ocean off Socotra Islands, pp. 163-181 in Zootaxa 3609 (2) on pages 164-179, DOI: 10.11646/zootaxa.3609.2.3, http://zenodo.org/record/219134