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 Ellis, 2005) produced by the mother. The thresher sharks (Alopiidae) and the mackerel sharks sensu stricto (Lamnidae) are further described below.
REFERENCES: Compagno, 1990, 2001; Kim et al., 2013; Musick, 2011; Musick and Ellis, 2005; Shimada, 2005; Shimada et al., 2009.
LAMNIFORMES : ALOPIIDAE—Thresher Sharks
DIVERSITY: 1 genus, 3 species
REPRESENTATIVE GENUS: Alopias
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; neritic to epipelagic
REMARKS: Thresher sharks use their long, whip-like caudal fin to disable small pelagic fishes and squids during feeding (Kim et al., 2013). Like mackerel sharks, at least one species (Alopias vulpinus) has the ability to maintain a higher body temperature than ambient seawater (Sepulveda et al., 2005). Thresher sharks are oophagous (Musick, 2011; Musick and Ellis, 2005), giving birth to small numbers of relatively large pups. These sharks support limited commercial fisheries.
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; Kim et al., 2013; Musick, 2011; Musick and Ellis, 2005; Sepulveda et al., 2005.
ALOPIID CHARACTERISTICS:
1) upper lobe of caudal fin long and whip-like, equaling length of body
2) mouth subterminal, relatively small
3) second dorsal fin and anal fin small, pectoral fins large
4) caudal peduncle with a precaudal pit
5) gill slits small, fourth and fifth above pectoral-fin base
ILLUSTRATED SPECIMEN:
Alopias vulpinus, SIO 64–804, 1,448 mm TL
LAMNIFORMES : LAMNIDAE—Mackerel Sharks
DIVERSITY: 3 genera, 5 species
REPRESENTATIVE GENERA: Carcharodon, Isurus, Lamna
DISTRIBUTION: Atlantic, Indian, and Pacific oceans
HABITAT: Marine; tropical to temperate; neritic to epipelagic
REMARKS: Mackerel sharks are strong-swimming, large-bodied predators that prey mainly on fishes, birds, marine mammals, and cephalopods. These sharks are one of a few groups of fishes known to have body temperatures higher than their surroundings, allowing them to remain active in very cold water (Bernal et al., 2001). Mackerel sharks are oophagous (Musick, 2011; Musick and Ellis, 2005) and give birth to large, well-developed pups. For example, newly born White Shark pups can be up to 1.3 m long (Domeier, 2012). The White Shark is responsible for a number of attacks on humans each year (Domeier, 2012). Some laminid species support commericial fisheries.
REFERENCES: Bernal et al., 2001; Compagno, 2001; Compagno, in Carpenter, 2003; Compagno, in Carpenter and Niem, 1998; Compagno et al., in Fischer et al., 1995; Compagno et al., 2005; Domeier, 2012; Musick, 2011; Musick and Ellis, 2005.
LAMNID CHARACTERISTICS:
1) second dorsal fin much smaller than first dorsal fin
2) caudal fin nearly symmetrical (approaching lunate)
3) caudal peduncle strongly depressed with a lateral keel and precaudal pit
4) mouth large, extending past level of eyes
5) gill openings large
6) teeth large
7) gill rakers absent
ILLUSTRATED SPECIMEN:
A) Isurus oxyrinchus, SIO 55–85, 875 mm TL (dorsal view)
B) head of Isurus oxyrinchus, SIO 55–85 (lateral view)
LAMNIFORM DIVERSITY:
A) PSEUDOCARCHARIIDAE—crocodile sharks: Pseudocarcharias kamoharai, SIO 97–221, 952 mm TL
B) MEGACHASMIDAE—megamouth sharks: Megachasma pelagios, SIO 07–53, 2,150 mm TL
C) MITSUKURINIDAE—goblin sharks: Mitsukurina owstoni, SIO 07–46, 1,150 mm TL
CARCHARHINIFORMES—Ground Sharks
The ground sharks comprise the most speciose order of sharks, with eight families, approximately 50 genera, and at least 287 species. More than half of the species are small-bodied cat sharks (Scyliorhinidae and Proscylliidae), named for their horizontally elongate eyes. The false cat sharks (Pseudotriakidae) are characterized
