Holohalaelurus melanostigma Norman 1939

Brett A. Human, 2006, A taxonomic revision of the catshark genus Holohalaelurus Fowler 1934 (Chondrichthyes: Carcharhiniformes: Scyliorhinidae), with descriptions of two new species., Zootaxa 1315, pp. 1-56: 28-36

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z01315p001

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scientific name

Holohalaelurus melanostigma Norman 1939
status

 

Holohalaelurus melanostigma Norman 1939 

(Figs. 8-9, Table 3)

Scyliorhinus (Halaelurus) melanostigma Norman, 1939  ZBK  : 9.

Holohalaelurus punctatus  : Bass et al., 1975: 23 (in part); Springer, 1979: 93 (in part); Bass, 1986: 93 (in part); Compagno et al., 1989: 54 (in part); Compagno et al., 1991: 80 (in part).

Holohalaelurus regani  : Bass et al., 1975: 25 (in part); Bass, 1986: 93 (in part); Compagno, 1988: 156 (in part); Compagno et al., 1989: 54 (in part); Compagno et al., 1991: 81 (in part).

Type Series and Locality. Holotype, BMNH 1939.5.24.2 (Fig. 8), adolescent male originally recorded as 330mm TL, (measured as 335mm TL in this study), collected at John Murray station 115 , 05°05’18”S 39°22’12”E to 05°01’00”S 39°24’12”E, in 640-658m of water off Zanzibar, Tanzania, in very good condition.GoogleMaps 

Paratypes, four specimens in three lots, one specimen lost, incorrectly identified and originally labelled as syntypes (see Remarks below). BMNH 1939.5.24.3 and BMNH 1939.5.24.4 (Fig. 9), adolescent male 330mm TL (size not reported in Normans’ description), and juvenile male originally recorded as 265mm TL, (measured as 267mm TL in this study), collected at John Murray station 115 , both in very good condition.GoogleMaps  It was not recorded in the original description, or on the labels accompanying the specimens, which catalogue numbers correspond to which specimens.

BMNH 1939.5.24.5 (Fig. 15), immature female originally recorded as 205mm TL (measured as 206mm TL in this study), referable to H. grennian  sp. nov. (see account for H. grennian  ), collected at John Murray station 105 (probably sta. 105b (see account for H. grennian  )), 5°34’24”S 39°13’12’E to 5°37’00”S 39°14’36”E, in 238-293m of water off Zanzibar, Tanzania, and is in very good condition. Another female specimen (190mm TL) collected at station 105 with BMNH 1939.5.24.5 was not catalogued, may have been discarded and is lost.GoogleMaps 

Diagnosis. Holohalaelurus melanostigma  is a moderately sized Holohalaelurus  ZBK  shark, distinguished from other Holohalaelurus  ZBK  sharks by: denticles on dorsal midline slightly enlarged beginning from a point level to the pectoral origin on the dorsal midline, to the first dorsal origin; enlarged denticles not present on the dorsal surface of the pectoral fin; club-shaped papillae not present on the distal tip of the clasper; buccal papillae in mouth inconspicuous; moderate to high vertebral count, 121 total vertebrae in the holotype (paratypes 119, 115, mean 116.8); relatively high tooth counts, 57 upper teeth in total in the holotype (paratypes 54, 59, mean 57.8), 50 lower teeth in total in the holotype (paratypes 49, 63, mean 55.8). Large brown spots, stripes and blotches on a dull greybrown background; characteristic tear line marking from the anterior of the orbit to the lateral margin of the snout; white spots never present.

Description. Morphometric and meristic data are given in Table 3. Holotype, adolescent male 335mm TL (paratypes, adolescent male 330mm TL, juvenile male 267mm TL, mean of all specimens examined in Table 3, including the type series, see Study material): body slender and elongate; head compressed, head width 2.56 (2.67, 3.33, 2.85) times its height at the posterior margin of the orbit, and head width 2.27 (2.50, 3.03, 2.35) times its height at the pectoral fin origin; trunk depressed, trunk width 1.63 (1.25, 2.04, 1.55) times its height; abdomen slightly depressed, abdomen width 1.40 (0.96, 1.78, 1.30) times its height; tail slightly compressed, tail width 0.87 (0.79, 1.09, 0.91) times its height; caudal peduncle compressed, caudal peduncle height 1.60 (1.41, 1.60, 1.56) times its width; ventral sensory pores not conspicuously black in preserved specimens, although likely to be so in fresh or live specimens; head moderately long, head length 0.21 (0.22, 0.22, 0.22) times the precaudal length; snout relatively long, rounded and coming to a point, preoral length 0.32 (0.32, 0.30, 0.30) times the snout to first gill slit distance; mouth short and narrow, moderately arched, buccal papillae in mouth inconspicuous, mouth width 2.09 (2.73, 2.68, 2.50) times its length; eye slit like, eye length 2.40 (1.67, 2.0, 2.06) times its height, distance from snout to the anterior origin of the orbit 0.66 (0.63, 0.64, 0.65) times the snout to spiracle length; spiracle length 0.11 (0.14, 0.18, 0.17) times the eye length; area around gill slits naked, lacking denticles; distance from snout to first dorsal fin origin 0.67 (0.68, 0.62, 0.67) times the distance from the snout to the second dorsal fin origin; denticles slightly enlarged on the dorsal midline beginning from a point level to the pectoral origin on the dorsal midline, to the first dorsal origin; first dorsal fin length 1.94 (2.33, 2.57, 2.32) times its height, length of the base of first dorsal fin 0.61 (0.55, 0.68, 0.65) times the length of the base of second dorsal fin; second dorsal fin length 2.13 (2.45, 2.46, 2.48) times its height; snout to pectoral origin length 0.51 (0.46, 0.48, 0.50) times the snout to pelvic fin origin length; pectoral fin large and winglike, no enlarged denticles on the dorsal surface in adults, pectoral fin length 1.36 (1.59, 2.01, 1.57) times its height; height of the pectoral fin 3.21 (2.93, 2.23, 2.71) times the height of the pelvic fin; distance from pectoral insertion to pelvic origin 0.99 (0.98, 0.77, 0.94) times the distance between the insertion of the second dorsal fin and the caudal fin dorsal origin; pelvic fin long and low, pelvic fin length 4.36 (4.37, 3.87, 4.0) times its height, pelvic fin free rear tips variably fused, but never completely fused; claspers elongate without papillae on the distal tips, clasper inner margin length 8.33 (8.56, 8.0, 6.73) times their base; snout to anal origin length 4.26 (4.27, 4.50, 4.56) times the distance between the anal fin insertion and the origin of the ventral caudal fin; anal fin long and low, anal fin length 5.85 (6.11, 7.0, 5.89) times its height; length of anal fin base 1.93 (1.82, 1.98, 1.94) times the length of the second dorsal fin base; caudal dorsal margin length 1.53 (2.30, 2.17, 2.13) times the interdorsal space, caudal ventral lobe weakly developed. Vertebral counts: 28 (31, 28, 28.8) monospondylous, 57 (51, 55, 53.0) precaudal diplospondylous and 36 (37, 32, 35.0) caudal diplospondylous vertebrae. Dental formula: upper jaw (left) 27 (24, 28, 27.0), symphyseal 2 (5, 2, 3.0), (right) 28 (25, 29, 27.8); lower jaw (left) 25 (22, 31, 26.8), (symphyseal) 4 (5, 2, 3.8), (right) 21 (22, 30, 25.3).

Size and Sexual Maturity. The largest specimen referrable to H. melanostigma  is 384mm TL, and the smallest recorded size is 267mm TL (Fig. 1 and Table 3). Males are immature at 267mm TL, adolescent at 330mm TL and 335mm TL, and mature at 384mm TL. Females of this species are unknown.

Colouration. Holohalaelurus melanostigma  has a dull grey brown background dorsal colouration, with many relatively large dark brown spots covering the entire dorsal surface and frequently fusing together to form short to long stripes, blotches, reticulations and rings (Fig. 8-9), extending posteriorly to the origin of the caudal epaxial fin web, fusion of spots apparently becomes more extensive as the animal gets larger, and the largest specimen had spots fused into lines and large rings extending from the posterior of the eye to the first dorsal fin; a characteristic marking found on this species is the conspicuous line from the anterior margin of the eye to the lateral margin of the snout, giving the appearance of a tear line; spots extending on to pectoral fins, but not pelvic fins; spots on bases of dorsal fins, rest of dorsal fin dull grey brown; dusky patches on hypaxial caudal fin web and terminal lobe; white spots absent, no white spot above pectoral base or white spot at dorsal fin origins. Ventral colouration uniform dull grey brown, without markings, sensory pores may be black on live and fresh specimens, but are not observed on preserved animals.

Comparison with other species. Holohalaelurus melanostigma  has slightly enlarged denticles on the dorsal midline, less so than in H. favus  and H. regani  , about equally developed in H. grennian  , and more so than in H. punctatus  . There are no enlarged denticles on the dorsal surface of the pectoral fins in adults, a trait common with H. grennian  and H. punctatus  . Buccal papillae are inconspicuous, as in H. favus  and H. grennian  , and less developed than in H. punctatus  and H. regani  . Fusion of the spots into bars and reticulations is more evident than in H. favus  , H. grennian  and H. punctatus  , and differs from H. regani  in that spots are more often fused into long lines, as opposed to horseshoe shaped markings. No white spots present. Holohalaelurus melanostigma  grows to a larger size than H. grennian  and H. punctatus  , is equivalent in size to H. favus  before becoming fully mature, but is smaller than H. favus  adults, and all maturity stages of H. regani  . Holohalaelurus melanostigma  is closest to H. regani  in overall morphology and colouration.

Remarks. The holotype for H. melanostigma  is labelled with a tag tied around the caudal peduncle clearly identifying that specimen as the “type” (Fig. 8), and the specimen is readily identifiable from a reference made to it in the description by Norman (1939). However, all other type specimens were originally labelled as syntypes, when they are in fact paratypes (due to the presence of a readily identifiable holotype). Eschmeyer (1998) correctly listed them as paratypes, and the labels have been corrected by an unknown source.

The type series contains multiple species, as Bass et al. (1975) reasoned (see below). The type series includes two female specimens, only one of which is still in existence, and the other was presumably identical in appearance to the remaining specimen. The remaining specimen, BMNH 1939.5.24.5, is not H. melanostigma  and belongs to the new taxon, H. grennian  sp. nov. Norman most likely included these specimens in the H. melanostigma  type series, although very different to the holotype and other paratypes, because both are female and smaller than the other specimens in the type series and Norman presumably attributed these differences to sexual and ontogenetic dimorphism. Norman also notes differences in the proportions of some measurements for “young” specimens compared to adult specimens, which is most likely in reference to the small female specimens. Furthermore, Norman uses the “narrow elliptical dark spot… on each dorsal fin” (1939: 10) as a diagnostic feature for the “young” of H. melanostigma  . This is incorrect and these dorsal fin markings are a character referable to H. grennian  . Holohalaelurus melanostigma  does not have any markings on either dorsal fin (Fig. 8-9). Male Holohalaelurus  ZBK  (SAM 36077 and SAM 36078) that most closely match BMNH 1939.5.24.5 in colouration, morphology and size have since been collected and justify the exclusion of the two female specimens from H. melanostigma  , and the erection of a new species.

Bass et al. (1975) examined the entire H. melanostigma  type series and synonymised specimens BMNH 1939.5.24.2-4 with H. regani  , which they deemed to be indistinguishable from the Natal specimens of H. regani  . Specimen BMNH 1939.5.24.5 was synonymised with H. punctatus  , although in this case, they acknowledged the colour pattern differences and noted the possibility that it was a distinct species. This arrangement was followed by Compagno (1984b, 1988, and subsequent publications).

Fowler (1941), Smith (1949) and Bass (1986) list H. punctatus  and H. regani  , however make no mention of H. melanostigma  . Springer (1979) apparently did not examine any of the H. melanostigma  material and followed Bass et al. (1975) with their synonymy of H. melanostigma  with H. punctatus  and H. regani  . Compagno (1984b, 1988) also followed the synonymy of Bass et al., and reported the collection of the two male SAM specimens referable to H. grennian  in both works.

Although not observed on preserved specimens (Fig. 8), it is likely that H. melanostigma  has black sensory pores on the ventral surface, as these markings have been observed to fade in specimens of H. punctatus  and H. favus  (under the name of H. regani  ) once preserved (Bass et al., 1975).

Compagno et al. (1989, 1991) refer to Holohalaelurus  ZBK  occurring in Kenya and Tanzania, but do not specifically mention H. melanostigma  . Compagno (1999) refers to dwarf H. regani  from Kenya and Tanzania as being possibly referable to H. melanostigma  , however the dwarf Holohalaelurus  ZBK  from this region is H. grennian  sp. nov. Holohalaelurus melanostigma  is a moderately sized member of the genus and the confusion with dwarf Holohalaelurus  ZBK  from the area is an error stemming from the presence of multiple species in the type series.

Distribution. Holohalaelurus melanostigma  is a regional endemic and its known range is extremely limited (Fig. 10). It is confined to the deep tropical waters of northern Tanzania and southern Kenya, within one degree of latitude, in the western Indian Ocean. The type specimens referable to H. melanostigma  , as defined here, were taken in 640-658m of water and the Kenyan specimen was taken in 607-612m of water.

Although the type locality was recorded as being “Zanzibar, Tanzania”, the actual station was closer to Pemba Island. The collection of further specimens of this species will most probably require deep sea exploratory research cruises, because it is unlikely that fishing activities in the region occur at such depths.

Etymology. Although not specified in the original account (Norman, 1939), the species name most likely derives from the Greek melano, meaning black, and stigma, Greek for mark or spot, and is reference to the dark coloured spots on the dorsal surface of this species.

Common name. Norman did not give a common name for this species. The common name crying Izak was recently coined (Compagno & Human, 2003), and is in reference to the characteristic tear line markings, akin to those seen on the cheetah ( Acinonyx jubatus  ), projecting from the anterior of the eye to the edge of the lateral surface in dorsal aspect.

Study material. BMNH 1939.5.24.2 holotype of H. melanostigma Norman 1939  , see under Type Series and Locality for details; BMNH 1939.5.24.3 and BMNH 1939.5.24.4 paratypes (not syntypes) of H. melanostigma Norman 1939  , see under Type Series and Locality for details; RUSI 14114, previously PCH 80-15, mature male 384mm TL, Fridtjof Nansen station 854 , 4°27’S 39°50’E, off Shimoni, Kenya.GoogleMaps 

To the authors knowledge, these specimens are all of the known specimens referrable to this species. Females are unknown.