Poroderma Smith, 1837

Brett A. Human, 2006, A taxonomic revision of the catshark genus Poroderma Smith, 1837 (Chondrichthyes: Carcharhiniformes: Scyliorhinidae)., Zootaxa 1229, pp. 1-32: 3-5

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Poroderma Smith, 1837


Poroderma Smith, 1837 

Poroderma Smith, 1837  : 85.

Conoporoderma Fowler, 1934  ZBK  : 234 (as a subgenus of Poroderma  ); Bigelow and Schroeder 1948: 197 (replacement for Poroderma  ).

Type Species. Squalus africanus Gmelin, 1789  ZBK  , through subsequent designation by Fowler 1908: 53.

Diagnosis. See Compagno (1988) for a comprehensive diagnosis of Poroderma  . Poroderma  sharks are scyliorhinids with a stocky build; head slightly depressed; nasal barbels much longer than their basal diameter; mouths with labial furrows on both the upper and lower jaws; 1st dorsal fin larger than 2nd dorsal fin; origin of 1st dorsal fin posterior to the pelvic fin insertion; pelvic fins variably, but never completely, fused in males; claspers short and stubby, outer length three times that of their width at the base.

Common name. Compagno (1988) and Compagno et al. (1989) referred to this genus as the barbeled catsharks.

Remarks. Smith (1837) proposed the genus Poroderma  , without describing it, as a replacement to the generic name Scyllium Cuvier, 1816  ZBK  , for the species Scyllium africanum (Gmelin, 1789)  (wrongly attributed to Cuvier by Smith), Poroderma pantherinum (Smith in Mueller and Henle, 1838)  (given by name only in Smith 1837), P. submaculatum Smith, 1837  ZBK  and P. variegatum Smith, 1837  . Poroderma  remained uncharacterised until Garman (1913) (Compagno 1984b, 1988). Although four species were named for this genus, the type species for Poroderma  was subsequently designated by Fowler (1908) to be Squalus africanum  ZBK  , and placed Scyliorhinus stellaris (Linnaeus, 1758)  in Poroderma  in the same account.

Fowler (1934) proposed Conoporoderma  ZBK  as a subgenus of Poroderma  for P. pantherinum  (the type species for the subgenus) and his new species P. marleyi Fowler, 1934  ZBK  . The subgenus was erected on the basis that the species he placed in this genus had long nasal barbels. Bigelow and Schroeder (1948) synonymised Poroderma  with Scyliorhinus  , and since P. africanum  was the type for Poroderma  , they raised Conoporoderma  ZBK  to the rank of genus for the remaining species P. marleyi  ZBK  and P. pantherinum  ; however, P. africanum  was almost immediately returned to the genus Poroderma  (Smith 1949).

The synonymy of P. marleyi  ZBK  with P. pantherinum  (see Remarks for P. pantherinum  ) dictates that the subgenus Conoporoderma  ZBK  would exist only for P. pantherinum  . However, the relatively long nasal barbels of P. pantherinum  compared to P. africanum  amounts to species differentiation, as determined by this study, and this difference alone is insufficient to justify the existence of a subgenus for P. pantherinum  . Therefore, the author agrees in synonymising Conoporoderma  ZBK  with Poroderma  , following Bass et al. (1975), Springer (1979), and Compagno (1984b, 1988).

Garman (1913), Fowler (1941), Bass et al. (1975), Springer (1979), and Compagno (1984b, 1988) have diagnosed this genus. Günther (1870), Garman (1913), Fowler (1941), Smith (1949), Bass et al. (1975), and Springer (1979) describe Poroderma  as lacking labial furrows on the upper lip. Bass et al. (1975) and Springer (1979) explain that the folds on the upper lip are not true labial furrows. All Poroderma  specimens examined in this study had small to large labial folds present on the upper lip, and skeletonisation by the author of many Poroderma  specimens of both species has shown that a labial cartilage is associated with the upper labial furrow in all instances, which should therefore be considered a true labial furrow. Compagno (1984b) similarly diagnosed Poroderma  as having true upper labial furrows.

Most Scyliorhinus  species, the genus to which Poroderma  is most closely allied to (Springer 1979; Compagno 1984b, 1988), have a nasal barbel, however it is not as well developed as in Poroderma  (Garman 1913; Springer 1979; Compagno 1984b, 1988); in addition, Poroderma  has a true upper labial furrow, whereas Scyliorhinus  does not (Compagno 1984b, 1988).

Two species are recognised in this study, P. africanum  and P. pantherinum  . Both are abundant and endemic to South Africa.

Etymology. The derivation of Poroderma  was not given by Smith (1837). It is possible that the generic name is based on the Greek words poros, meaning hole or passage, and deros, meaning skin or hide. If this derivation is correct, it is unclear what Smith was referring to in these sharks, as they have rather tough hides with pores not enlarged.

Distribution. The genus Poroderma Smith, 1837  is endemic to South Africa and contains two valid taxa as determined by this study, P. africanum (Gmelin, 1789)  , and P. pantherinum (Smith in Mueller and Henle, 1838)  . Both Poroderma  species are largely sympatric and are distributed along the South African coastline: P. africanum  from Saldanha Bay on the west coast to north of East London on the east coast, and P. pantherinum  from Cape Town on the west coast to Durban on the east coast (Bass et al. 1975; Compagno 1984b; current study).

Bass et al. (1975) suggest that the central point of the distribution of P. pantherinum  is Algoa Bay, and Bass (1986) states that this species is less abundant than P. africanum  in shallow waters of the southwest Cape. The author encountered P. pantherinum  and P. africanum  with about equal frequency in Western Cape waters, and the apparent abundance of P. pantherinum  in Eastern Cape waters may be a perceptual artefact due to the decreased abundance of P. africanum  in the Eastern Cape, however it may occupy a niche in the absence of P. africanum  and may explain why the larger specimens of P. pantherinum  are found in the Eastern Cape.

Tagging and anecdotal evidence suggest that Poroderma  sharks have a limited home range and are philopatric. The author attempted a population genetic study on this genus (Human et al. 2001) to address the apparent philopatry of these sharks, and to determine whether the colour pattern variation observed in P. pantherinum  was due to population differentiation. The attempt was unsuccessful and a future study into this aspect of Poroderma  is needed.

Key to the species of the genus Poroderma 

1a. Nasal barbels less than one half the preoral length and not reaching the upper lip; prenarial length less than 0.9 times the mouth length, bold black stripes running parallel from snout tip to tail on the dorsal surface, background colouration pale to dark grey.. ..................................................................................................................... P. africanum 

1b. Nasal barbels greater than one half the preoral length and overhanging the upper lip; prenarial length more than 1.1 times the mouth length, combinations of black rosettes, small to large spots and stripes variably present or absent on the dorsal surface, background dorsal colouration pale grey to glossy jet black .......................... P. pantherinum