Fishes: A Guide to Their Diversity. Philip A. Hastings

      HETERODONTIFORM CHARACTERISTICS:

      1) five external gill slits, two to three behind pectoral-fin origin

      2) two dorsal fins, each with a broad-based spine

      3) crests above eyes

      4) eyes without a nictitating membrane

      5) spiracles small

      6) nostrils and mouth connected by a groove

      ILLUSTRATED SPECIMEN:

      Heterodontus francisci, SIO 64–33, 765 mm TL

      INSET: Lower jaw of Heterodontus francisci (SIO 60–23, 865 mm TL) showing anterior rows of pointed teeth and posterior rows of pavement-like teeth.

      ORECTOLOBIFORMES—Carpet Sharks

      The carpet sharks comprise seven families, 14 genera, and 42 species of mostly benthic sharks, noted for sitting perfectly still on the bottom of the ocean. Their nostrils have barbels and are connected to the relatively small mouth by a groove. The wobbegongs (Orectolobidae) are sit-and-wait predators and have a head covered in skin flaps, cryptic coloration, large spiracles, and large fang-like teeth. Their phylogenetic relationships were studied by Goto (2001) and Corrigan and Beheregaray (2009). Two families (Ginglymostomatidae and Rhincodontidae) are described in more detail below. The remaining families (Parascyliidae, Brachaeluridae, Hemiscyliidae, and Stegostomatidae) include relatively few species and occur in the tropical Indo-West Pacific.

      REFERENCES: Corrigan and Beheregaray, 2009; Goto, 2001.

      ORECTOLOBIFORMES : GINGLYMOSTOMATIDAE—Nurse Sharks

      DIVERSITY: 1 family, 3 genera, 3 species

      REPRESENTATIVE GENERA: Ginglymostoma, Nebrius, Pseudoginglymostoma

      DISTRIBUTION: Atlantic, Indian, and Pacific oceans

      HABITAT: Marine; tropical to subtropical; continental shelf, benthic on shallow reefs and adjacent sandy areas

      REMARKS: Nurse sharks are characterized by their brownish coloration and by dorsal fins located far back on the body. They are generally nocturnal and can be observed resting in small groups on the reef or sandy surfaces during the day. The small mouth with a large oral cavity is capable of suction-feeding benthic invertebrates and small fishes. Nurse sharks are yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005).

      REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005.

      GINGLYMOSTOMATID CHARACTERISTICS:

      1) five small gill openings (slits), fifth slit nearly overlapping fourth

      2) dorsal fins without spines, positioned posteriorly on body

      3) mouth short, subterminal, not extending to level of eyes

      4) eyes without nictitating membrane

      5) spiracles small, located just behind eyes

      6) nostrils with barbels

      ILLUSTRATED SPECIMEN:

      Ginglymostoma cirratum, SIO 64–229, 521 mm TL (dorsal view)

      ORECTOLOBIFORMES : RHINCODONTIDAE—Whale Sharks

      DIVERSITY: 1 genus, 1 species

      REPRESENTATIVE GENUS: Rhincodon

      DISTRIBUTION: Atlantic (absent from Mediterranean), Indian, and Pacific oceans

      HABITAT: Marine; tropical to warm temperate; usually epipelagic but occasionally mesopelagic or neritic

      REMARKS: While the Whale Shark is distinguished by its huge size (the largest fish on Earth), it feeds on planktonic organisms and fish eggs, using its long, thin gill rakers for filter feeding. Its brain anatomy was studied by Yopak and Frank (2009). The Whale Shark is yolk-sac viviparous (Musick, 2011; Musick and Ellis, 2005), but, curiously, produces keratized egg capsules that hatch within the female. These enormous fishes are highly fecund compared to other members of the Chondrichthyes; one female caught by fishermen held 300 pups. In many areas, the Whale Shark has been overfished; it is considered “vulnerable” by the IUCN (2013) and it has been given protected status by many nations.

      REFERENCES: Compagno, 2001, 2005; Compagno, in Carpenter, 2003; Compagno, Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Musick, 2011; Musick and Ellis, 2005; Yopak and Frank, 2009.

      RHINCODONTID CHARACTERISTICS:

      1) body covered in yellow or white spots

      2) head broad and flattened

      3) snout short, mouth nearly terminal, anterior to small eyes

      4) mouth and gill openings especially large

      5) spiracles small

      6) longitudinal ridges on body of adults

      ILLUSTRATED SPECIMEN:

      Rhincodon typus, SIO 85–20, 601 mm TL (dorsal and lateral views)

      LAMNIFORMES—Mackerel Sharks

      The mackerel sharks have two dorsal fins without spines, an anal fin, five gill slits (the last two often above the pectoral fin), eyes without a nictitating membrane, a large mouth that extends well behind the eyes, and small spiracles usually present behind the eyes. This distinctive lineage includes only 15 species, classified in ten genera and seven families, indicating a high level of morphological diversity among a small number of closely related species. For example, the Basking Shark (Cetorhinidae) and the Megamouth Shark (Megachasmidae) are large-bodied filter feeders, while the White Shark (Lamnidae) is one of the ocean’stop predators. The Goblin Shark (Mitsukurinidae), characterized by an elongate snout, and the Crocodile Shark (Pseudocarchariidae), which has extremely large eyes, are generally found in deeper water. The sand tiger sharks (Odontaspididae) are some of the few sharks that have exposed teeth when the mouth is closed, giving them a ferocious appearance. In contrast with the otherwise similar Carcharhiniformes, members of the Lamniformes do not have a nictitating membrane protecting the eyes. The phylogenetic relationships of lamniforms have been studied by a number of workers (e.g., Compagno, 1990; Naylor et al., 1997; Shimada, 2005; Shimada et al., 2009), while variation in their caudal-fin anatomy was documented by Kim et al. (2013). Lamniforms have an unusual reproductive mode in which developing embryos eat eggs (oophagy) and sometimes other embryos (Musick, 2011; Musick and

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