Family Megachasmidae

1 st specimen found in 1976 off Oahu, HI Castro book written 1982, taxonomy not yet assigned although little known about biology, still high profile species

Family Megachasmidae 37 total recorded sightings

Family Megachasmidae #6 caught in drift net off Dana Point, CA only one tracked and photographed alive

Taxonomy current taxonomy: (has been debated since discovered) Order Lamniformes (Mackerel sharks) Family Megachasmidae (Megamouth shark) Megachasma pelagios mega= greatchasma= cave pelagios= of the sea probably most ancestral lamniform

Morphology Characteristics shared with order: 2 spineless dorsal fins, anal fin cylindrical body with a short snout lack nasoral groove and barbells (Order Orectolobiformes) small spiracle behind eye mouth extends behind eye

Morphology Characteristics shared with order:

Morphology Distinguishing characteristics: large terminal mouth (not ventral)* ~ 50 rows of tiny, hooked teeth, 3 rows functional large gill rakers white “upper lip”- feeding? conspecific detection? dark spots on lower jaw no pigment cells on ventral side soft body, poorly calcified skeleton, soft, loose skin,and soft fins

Morphology Characteristics shared with order:

Morphology white “upper lip”

Morphology Size: TL > 500cm smallest recorded: 190cm (male), #9, Brazil

Morphology Size: TL > 500cm largest recorded: 570cm (female), #37, Japan

Morphology Size: TL > 500cm largest recorded: 570cm (female), #37, Japan largest reported: ~ 700cm!!

Habitat and Distribution details unknown oceanic, coastal and offshore continental shelf: 5-40m offshore: caught in very deep water, 8-166m probably worldwide in tropics and subtropics, most specimens from w. Pacific

Habitat and Distribution

Behavior only 2 observations to provide behavior information #6 (CA), #13 (Indonesia) probably low mobility due to soft body and fins probably undergo vertical migrations following food shark #6 tracked for 2 days deep depths during day midwater/shallow at night

Reproduction size at maturity unknown males: #2 (449cm TL) and 6 (494cm TL)- mature females: #7 immature at 471cm TL #12 mature at 544cm (only mature female) right ovary had a large number of eggs

Reproduction probably viviparous and oophagous ovary structure similar to other lamniforms probably mate in fall off coast of SoCal (October/November) males #2,6- claspers suggested recent mating activity male #6- wounds on jaw similar to other shark species’ mating wounds

Prey/Feeding Habits 1 of 3 of the largest, filter feeding sharks stomach contents: primary prey euphasiid shrimp (krill) some also with copepods and jellyfish details of feeding mechanism unknown filter feeding probably evolved independently from others (morphological differences) more likely evolved from ancestral Odontaspididae

Prey/Feeding Habits

Predators and Parasites sperm whales- seen attacking shark #13 (Indonesia) orcas also seen attacking white shark at Farallon Isl. (CA) within the same year new info on shark/whale relationships? cookie cutter shark- scars on almost every specimen other parasites- similar to other sharks; copepods, cestodes

Population status Human importance: None too rare to be harvested Conservation: Data Deficient on IUCN Redlist

Population status Human importance: None too rare to be harvested Conservation: Data Deficient on IUCN Redlist

Literature Cited and Selected Works Castro, J The sharks of North American waters. Texas A&M Univ. Press, College Station. 180p. Compagno, L.J.V Megachasma pelagios. In: IUCN IUCN Red List of Threatened Species.. Downloaded on 14 October Compagno, L., M. Dando, and S. Fowler Sharks of the world. Princeton University Press, Princeton, NJ. 368p. Ito, H., M. Yoshimoto, and H. Somiya External brain form and cranial nerves of the megamouth shark, Megachasma pelagios. Copeia 1999(1): Martins, C. and C. Knickle Megamouth shark. Florida Museum Natural History, Icthyology Department. University of Florida.. Downloaded on 14 October Nelson, D.R., J.N. McKibben, W.R. Strong, Jr., C.G. Lowe, J.A. Sisneros, D.M. Schroeder, and R.J. Lavenberg An acoustic tracking of a megamouth shark, Megachasma pelagios: a crepuscular vertical migratory. Env. Biol. Fishes 49: Shimada, K Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). J. Vert. Paleontology 27(2):