Pugettia producta

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Pugettia producta
commonly known as the Kelp Crab, Northern Kelp Crab, and the Shield-Backed Kelp Crab.

Pugettia producta
P. producta on the Boston Harbor floating docks (Olympia, Washington)
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Subclass: Eucarida
Order: Decapoda
Infraorder: Brachyura
Family: Majidae
Genus: Pugettia
Species: P. producta
Binomial name
Pugettia producta
Randall, 1840

Pugettia productus
Epialtus producta
Epialtus productus

kelp crab on Boston Harbor dock


Description and Phylogeny

Auto-montage image of anterior, ventral side of male P. producta


P. producta has a shield-shaped carapace with a prominent, sharp projection directed outward or slightly forward on both sides of the body near or behind the middle. Unlike most spider crabs within the Majidae family, P. producta has a smooth carapace that is usually free of adornment. The carapace is longer than it is wide and in males, the carapace width is up to 93 mm and in females is up to 78 mm. The rostrum consists of two broad, flattened "points" and the entire rostrum is not more than one third or two fifths the length of the rest of the carapace. The distance between the eyes is described as being less than one third of the greatest width of the carapace. [1] [2]

The coloration is cryptic for protection and can be olive, brown, or even a red-brown as a whole, with red or orange tones on the ventral surface. Young are frequently lighter in color. [3] [1]

Similar Species

Auto-montage image of the eye, dorsal side of male P. producta

Pugettia gracilis could be mistaken for P. producta but it tends to be smaller in size and its legs are more stout rather than slender. [4]

Another similar species is Taliepus nuttallii, but it differs from P. producta in having a more convex carapace and a more prominent rostrum. The rostrum also has a small triangular notch at the tip. T. nuttallii lacks the small tooth in front of the eye that is found in P. producta as well. [1]


Auto-montage image of the mouth parts, ventral side of male P. producta

Crabs appeared in the fossil record early in the Jurassic period of the Mesozoic, which is nearly 200 million years ago. Through the record, crabs seem to continue to shorten the body and reduce the abdomen. Of the living species of crabs that have been described, the cephalothorax is a defining characteristic. This is the fusion of head and thorax, covered by the carapace. The cephalothorax is short and broad, and forms practically the whole body. The Brachyura or “short-tailed” crabs, have an abdomen that has been reduced to a thin, flat plate, tucked forward out of sight below the cephalothorax. They tend to have five pairs of head appendages. These include the first and second antennae and the innermost three pairs of mouthparts; the mandibles and the first and second maxillae. The eight pairs of thoracic appendages include the outermost three pairs of mouthparts (the first, second, and third maxillipeds) and the five pairs of walking legs. The first pair of the walking legs are modified as chelipeds or pincers.

Of the intertidal Brachyura there are three large groups: the spider crabs, the cancroid crabs, and the grapsoid crabs. Additional groups occur in deeper waters off the coasts. The spider crabs, family Majidae, include the decorators, which disguise themselves with bits of hydroids, sponges, and algae, and the kelp crabs, which are usually free of adornment.[1] [5]


Geographic Range
P. producta is found in the subtidal to 73m from Prince of Wales Island (Alaska) to Punta Asuncion (Baja California).[1]

The young crabs are common among rocks or on the brown alga Egregia. In the winter the crabs can be found in the low intertidal zone on pilings, floating docks, and rocky shores of protected outer coasts. In summer, the older crabs migrate to floating kelp like Macrocystis.[1][3]

Natural History and Ecology


Juvenile P. producta Cobble beach, Oregon
Auto-montage image of male pleon
Auto-montage image of the other side of the pleon
Auto-montage image of male pleopods

Crabs often show marked sexual dimorphism. Aside from generally size differences between the sexes, the form of the pleon or abdomen is different from males and females. In most males, the pleon has a narrow and triangular form. In females, the pleon is rounded and broad. This is due to the fact that female crabs brood fertilized eggs on their pleopods. Female crabs possess four pairs of pleopods and males bear two pairs of pleopods, used as copulatory organs.

Breeding in P. producta appears to occur all year round. Females appear to be consistently found in nests of interwoven kelp stipes, but it is unknown if these stripes are woven by the crabs. [6] Females mate while they have a hard shell or exoskeleton, not right after molting. In Monterey Bay, eggs are carried for 28-31 days before hatching. Based on laboratory findings, a female can deposit a new brood of eggs within two days after the hatching of the previous brood. Females also appear to be capable of producing a new crop of offspring approximately every 30 days. The brood size can range from 34,000-84,000, with an average brood size in Puget Sound being about 61,000 for females with a carapace width between 41-56mm.

After a female carries the fertilized eggs for about 30 days, they hatch into protozoea larvae and immediately molt to zoea larvae. The zoea larvae are more like shrimp in appearance than adult crabs. During this stage, the zoeal period, they exist as part of the plankton. Periodically they molt their larval exoskeletons, the body enlarging and undergoing some change in form at each molt. The stages between molts are called instars, and different species of crabs exhibit one to five zoeal instars. The last zoeal instar is followed by a molt and metamorphosis to the megalops stage. At this stage they resemble a small crab. Their abdomen is somewhat flattened and can be folded forward below the cephalothorax, allowing them to sit on the substratum like an adult, and can be extended posteriorly, allowing it to swim by the beating of its pleopods. Once the megalops molts, it is in the first juvenile crab instar. As a juvenile crab, they remain on the bottom and commences like adults. Molting occurs less frequently as crabs get larger and older. Some species cease molting on becoming sexually mature; others continue to molt throughout life. In P. producta, there are no further molts after maturity. [7] [1] [6]

Foraging Behavior

P. producta is generally an herbivore on larger brown algae. Near California the crabs prefer Macrocystis, Egregia, and Pterygophora. In the Puget Sound areas of Washington the diet varies throughout the year. In summer, their diet consists of brown algae like Fucus, Sargassum, and Nereocystis. In the winter months, individuals change to a carnivorous diet which may consist of barnacles, hydroids, and bryozoans. This occurs because they are found on pilings and floating docks where the normal plant foods are not available. In the zoeal period, they eat metazoans, larval forms, and protozoa even smaller than themselves. [1]


P. producta are found to be parasitized by a nermertean worm and a rhizocephalan barnacle. The nermertean, Carcinonemertes epialti, is a small worm that is about 1-2mm long. It is found among the eggs and is found in 66 percent of the ovigerous females examined. The barnacle is Heterosaccus californicus and it is a specialized barnacle which occupies the entire region between the abdomen and the sternal surface of the thorax. H. californicus inhibits host reproduction and feminizes male hosts. This parasite affects adult host size by the host having passed though less instars before the molt of puberty. [8] [6]

Conservation Status

Pugettia producta has not been evaluated by the International Union for Conservation of Nature (IUCN).[9]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Garth, John, and Donald Abbott. "Brachyura: The True Crabs." INTERTIDAL INVERTEBRATES OF CALIFORNIA. Stanford, California: Stanford University Press, 1980. 592-599. Print.
  2. Kozloff, Eugene N., and Linda H. Price. "19. Phylum Arthropoda: Subphylum Crustacea: Class Alacostraca: Subclass Eucarida." Marine invertebrates of the Pacific Northwest . Seattle: University of Washington Press, 1996. 413. Print.
  3. 3.0 3.1 Kozloff, Eugene N.. "On and Around Floating Docks and Pilings." Seashore life of the northern Pacific coast: an illustrated guide to northern California, Oregon, Washington, and British Columbia. Seattle: University of Washington Press, 1993. 78. Print.
  4. Cowles, Dave . "Pugettia producta." WWU: On Campus. N.p., n.d. Web. 1 Feb. 2011. <http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Majidae/Pugettia_producta.html>
  5. Schram, Joel W.. "On the Origin of Decapoda." Decapod crustacean phylogenetics . Boca Raton: CRC Press, 2009. 3-13. Print.
  6. 6.0 6.1 6.2 Boolootian, R. A., A. C. Giese, A. Farmanfarmaian, and J. Tucker. "Reproductive Cycles of Five West Coast Crabs." Physiological Zoology Volume 32.No. 4 (1959): 213-220. JSTOR. Web. 5 Feb. 2011.
  7. Fincham, A. A., P. S. Rainbow, Richard Hartnoll, and Peter Gould. "Brachyuran life history strategies and the optimization of eff production." Aspects of Decapod Crustacean biology: the proceedings of a symposium held at the Zoological Society of London on 8th and 9th April 1987. Oxford [Oxfordshire: Published for the Zoological Society of London by Clarendon Press ;, 1988. 1-9. Print.
  8. O'Brien, Jack . "Precocious Maturity of the Majid Crab, Pugettia producta, Parasitized by the Rhizocephalan Barnacle, Heterosaccus californicus." Bio. Bull. 166 (1984): 384-395. Print.
  9. [eol],"Pugettia producta (J. W. Randall, 1840) - Encyclopedia of Life." Encyclopedia of Life. N.p., n.d. Web. 18 Jan. 2011. <http://www.eol.org/pages/1024220



P. producta video

juvenile P. producta video