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Purple shore crab
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Purple shore crab
The purple shore crab (Hemigrapsus nudus or the naked shore crab) is a common crab of the family Varunidae that is indigenous to the west coast of United States, Canada, and Mexico. H. nudus was first described in 1847 by Adam White, and in 1851, James Dwight Dana formally classified the species. H. nudus is a small, amphibious crab that is similar physically and behaviorally to Pachygrapsus crassipes and Hemigrapsus oregonensis. The purple shore crab is generally a dark purple color with olive green, red, and white spots. Mating season for H. nudus begins in mid-winter and larval crabs undergo 5 zoeal stages and a juvenile stage. Adult crabs mainly feed on algae but will occasionally scavenge other animals. H. nudus prefers inter-tidal and sub-tidal zones, and it can oftentimes be found sheltering under rocks or other debris. H. nudus demonstrates complex compensatory mechanisms to counteract fluctuating salinity and water oxygen concentrations, permitting it to live in a variety of different environments.
Hemigrapsus nudus is a true crab within the Hemigrapsus genus and Varunidae family. The first documentation of H. nudus occurred in 1847 when zoologist Adam White described the species as Grapsus marmoratus, a name that was not accepted taxonomically and declared a nomen nudum. The purple shore crab was properly classified by James Dwight Dana in 1851. Dana originally described the species as Pseudograpsus nudus, with Hemigrapsus being used as the parent species. Dana also described similar specimens as Heterograpsus nudus, with this name later being classified as synonymous. In 1853, H. Milne Edwards independently described the species as Heterograpsus marmoratus, a name that is not considered taxonomically valid. Another synonym for H. nudus is Brachynotus nudus.
The body of the purple shore crab is divided into two major components, the cephalothorax and the abdomen. A small crab, H. nudus reaches sizes of approximately 4.0–5.6 centimetres (1.6–2.2 in) in width and approximately 4.8 centimetres (1.9 in) in length. Beneath the thorax, there are five pairs of thoracic appendages and three pairs of maxillipeds that fold ventrally. The eyestalks are angled outwardly. The mouth is compositely made of six pairs of appendages, which include one pair of mandibles located on either side of the mouth. Additionally, it is made up of two pairs of maxillae and three pairs of maxillipeds that attach posteriorly to the mouth and cover the mandibles.
The dorsal shell (carapace) is flat, smooth, and has a square-like shape. The antero-lateral margins are rounded and the carapace lacks transverse lines. Its carapace is generally a dark purple in color, although it may be olive green or red, with white or cream markings. The color of the legs matches the color of the carapace but the white-tipped claws (chelipeds) are a lighter color with purple or red spots – these spots allow H. nudus to be distinguished from a similar looking crab, the lined shore crab, Pachygrapsus crassipes, whose chelipeds lack spots. Furthermore, the purple shore crab is generally less aggressive and slower moving compared to the genus Pachygrapsus. While uncommon, fully white and yellow coloration has also been noted in some specimens, which has been observed throughout the Hemigrapsus genus. The chelipeds are smooth, equal in size, and are curved inward. The legs of H. nudus lack setae, a distinguishing feature of the otherwise similar H. oregonensis and P. crassipes.
Hemigrapsus nudus displays sexual dimorphism and females are generally smaller than the males. Male carapaces can grow to a width of 2.2 inches (5.6 cm) while females grow to a smaller 1.3 inches (3.3 cm). The male abdomen is narrow and triangular, with an exposed sternum. The females' abdomen is wide and flap-like, which fully covers the sternum. The center of the chelipods on males is covered in a patch of fine, long hair while this hair is largely absent in females.
Hemigrapsus nudus begins mating between December and January. The mating process is considered very similar to pachygrapsus species, save for that pachygrapsus breed in the summer and not the winter. Mating occurs when a male holds the female by her chelipeds, and guides her via his walking legs. The male will use his swimming legs (first pleopods) to move his sperm to the female. Females become gravid (egg bearing) during January to mid-July, most commonly in April. Samples taken from Puget Sound, Washington have shown that roughly 70% of females are carrying fertilized eggs by late January and 99% are gravid by April. Females lay between 400 and 36,000 eggs annually, and second broods are rarely observed. Embyo crabs begin at a size of 380 μm and grow to 450 μm prior to hatching. Hatching typically occurs between May and July, but is highly dependent on water temperature. Broods in Monterey Bay, California, have been observed hatching between October and May; broods in British Columbia, Canada, hatch between April and May; and Friday Harbor, Washington, broods hatch in July. After hatching, the crabs proceed through 5 zoeal stages and one magalopa (post larval) stage prior to achieving juvenile stage.
Larval H. nudus in the first zoeal stage have lateral projections along their second and third abdominal segments. The first stage zoea are planktotrophic with four spines and compound eyes. The rostrum and distal spines are equal length but the two dorsal spines are shorter. The exospine is 1.2 millimetres (0.047 in) in length. The zoea of H. nudus differ from H. oregonensis and P. crassipes in their body and eye size. When transitioning to a successive stage, the zoea will undergo a molt. Juvenile H. nudus presents with a shallow depression along the frontal carapace and the spines are generally rounded. The eyes are larger and the dactyls are short and flat. The abdomens of males and females are identical at this stage.
Following the juvenile stage, growth will continue through molting. Pre-molting involves the epidermis separating from the cuticle. This is also punctuated by an increase in epidermal cell replication. Post-molt crabs have a soft shell that will gradually harden and will also involve the regeneration of previously amputated limbs.
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Purple shore crab
The purple shore crab (Hemigrapsus nudus or the naked shore crab) is a common crab of the family Varunidae that is indigenous to the west coast of United States, Canada, and Mexico. H. nudus was first described in 1847 by Adam White, and in 1851, James Dwight Dana formally classified the species. H. nudus is a small, amphibious crab that is similar physically and behaviorally to Pachygrapsus crassipes and Hemigrapsus oregonensis. The purple shore crab is generally a dark purple color with olive green, red, and white spots. Mating season for H. nudus begins in mid-winter and larval crabs undergo 5 zoeal stages and a juvenile stage. Adult crabs mainly feed on algae but will occasionally scavenge other animals. H. nudus prefers inter-tidal and sub-tidal zones, and it can oftentimes be found sheltering under rocks or other debris. H. nudus demonstrates complex compensatory mechanisms to counteract fluctuating salinity and water oxygen concentrations, permitting it to live in a variety of different environments.
Hemigrapsus nudus is a true crab within the Hemigrapsus genus and Varunidae family. The first documentation of H. nudus occurred in 1847 when zoologist Adam White described the species as Grapsus marmoratus, a name that was not accepted taxonomically and declared a nomen nudum. The purple shore crab was properly classified by James Dwight Dana in 1851. Dana originally described the species as Pseudograpsus nudus, with Hemigrapsus being used as the parent species. Dana also described similar specimens as Heterograpsus nudus, with this name later being classified as synonymous. In 1853, H. Milne Edwards independently described the species as Heterograpsus marmoratus, a name that is not considered taxonomically valid. Another synonym for H. nudus is Brachynotus nudus.
The body of the purple shore crab is divided into two major components, the cephalothorax and the abdomen. A small crab, H. nudus reaches sizes of approximately 4.0–5.6 centimetres (1.6–2.2 in) in width and approximately 4.8 centimetres (1.9 in) in length. Beneath the thorax, there are five pairs of thoracic appendages and three pairs of maxillipeds that fold ventrally. The eyestalks are angled outwardly. The mouth is compositely made of six pairs of appendages, which include one pair of mandibles located on either side of the mouth. Additionally, it is made up of two pairs of maxillae and three pairs of maxillipeds that attach posteriorly to the mouth and cover the mandibles.
The dorsal shell (carapace) is flat, smooth, and has a square-like shape. The antero-lateral margins are rounded and the carapace lacks transverse lines. Its carapace is generally a dark purple in color, although it may be olive green or red, with white or cream markings. The color of the legs matches the color of the carapace but the white-tipped claws (chelipeds) are a lighter color with purple or red spots – these spots allow H. nudus to be distinguished from a similar looking crab, the lined shore crab, Pachygrapsus crassipes, whose chelipeds lack spots. Furthermore, the purple shore crab is generally less aggressive and slower moving compared to the genus Pachygrapsus. While uncommon, fully white and yellow coloration has also been noted in some specimens, which has been observed throughout the Hemigrapsus genus. The chelipeds are smooth, equal in size, and are curved inward. The legs of H. nudus lack setae, a distinguishing feature of the otherwise similar H. oregonensis and P. crassipes.
Hemigrapsus nudus displays sexual dimorphism and females are generally smaller than the males. Male carapaces can grow to a width of 2.2 inches (5.6 cm) while females grow to a smaller 1.3 inches (3.3 cm). The male abdomen is narrow and triangular, with an exposed sternum. The females' abdomen is wide and flap-like, which fully covers the sternum. The center of the chelipods on males is covered in a patch of fine, long hair while this hair is largely absent in females.
Hemigrapsus nudus begins mating between December and January. The mating process is considered very similar to pachygrapsus species, save for that pachygrapsus breed in the summer and not the winter. Mating occurs when a male holds the female by her chelipeds, and guides her via his walking legs. The male will use his swimming legs (first pleopods) to move his sperm to the female. Females become gravid (egg bearing) during January to mid-July, most commonly in April. Samples taken from Puget Sound, Washington have shown that roughly 70% of females are carrying fertilized eggs by late January and 99% are gravid by April. Females lay between 400 and 36,000 eggs annually, and second broods are rarely observed. Embyo crabs begin at a size of 380 μm and grow to 450 μm prior to hatching. Hatching typically occurs between May and July, but is highly dependent on water temperature. Broods in Monterey Bay, California, have been observed hatching between October and May; broods in British Columbia, Canada, hatch between April and May; and Friday Harbor, Washington, broods hatch in July. After hatching, the crabs proceed through 5 zoeal stages and one magalopa (post larval) stage prior to achieving juvenile stage.
Larval H. nudus in the first zoeal stage have lateral projections along their second and third abdominal segments. The first stage zoea are planktotrophic with four spines and compound eyes. The rostrum and distal spines are equal length but the two dorsal spines are shorter. The exospine is 1.2 millimetres (0.047 in) in length. The zoea of H. nudus differ from H. oregonensis and P. crassipes in their body and eye size. When transitioning to a successive stage, the zoea will undergo a molt. Juvenile H. nudus presents with a shallow depression along the frontal carapace and the spines are generally rounded. The eyes are larger and the dactyls are short and flat. The abdomens of males and females are identical at this stage.
Following the juvenile stage, growth will continue through molting. Pre-molting involves the epidermis separating from the cuticle. This is also punctuated by an increase in epidermal cell replication. Post-molt crabs have a soft shell that will gradually harden and will also involve the regeneration of previously amputated limbs.