Hemigrapsus Nudus Class: Multicrustacea, Malacostraca, Eumalacostraca
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Phylum: Arthropoda, Crustacea Hemigrapsus nudus Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Eucarida, Decapoda, Pleocyemata, Brachyura, The purple shore crab Eubrachyura, Thoracotremata Family: Grapsoidea, Varunidae, Varuninae Taxonomy: The brachyuran family Grapsi- men. They have a large plate-like carapace dae, the shore crabs, was a very large fami- dorsally, beneath which are five pairs of tho- ly with several subfamilies and little taxo- racic appendages (see chelipeds and pereo- nomic scrutiny, until recently. Based on mo- pods) and three pairs of maxillipeds (see lecular and morphological evidence, authors mouthparts). The abdomen and associated (von Sternberg and Cumberlidge 2000; appendages are reduced and folded ventrally Schubart et al. 2000; de Grave et al. 2009; (Decapoda, Kuris et al. 2007). Schubart 2011) elevated all grapsid subfam- Cephalothorax: ilies to family level, reducing the number of Eyes: Eyestalks and eyes of moderate species formally within the Grapsidae. Re- size with eyes that are at antero-lateral angles cent molecular evidence has placed Hemi- (Fig. 2). Grapsid species apparently have grapsus species within the Varunidae, but keen vision (Wicksten 2011). this is currently debated and some authors Antenna: still refer to them as members of the Grapsi- Mouthparts: The mouth of decapod dae sensu lato (Ng et al. 2008; Wicksten crustaceans comprises six pairs of appendag- 2011) and others have adopted the new fa- es including one pair of mandibles (on either milial designation (e.g. Kuris et al. 2007). side of the mouth), two pairs of maxillae and Besides the higher taxonomic classifica- three pairs of maxillipeds. The maxillae and tions, the known specific synonym for H. nu- maxillipeds attach posterior to the mouth and dus is Pseudograpsus nudus (Wicksten extend to cover the mandibles (Ruppert et al. 2011), which is not currently used. 2004). Carapace: Flat, smooth, punctate Description (Schmitt 1921) and bears three teeth (two lat- Size: Carapace 56.2 mm in width and 48 eral that are posterior to postorbital) mm in length (Rathbun 1918; Wicksten (Wicksten 2011). Square in shape, with 2011) (Fig. 1). An adult male from Coos rounded antero-lateral margins (Rathbun Bay, was 32 mm in width and weighed 17.5 1918) and no transverse lines (compare to P. g (wet weight). crassipes) (Fig. 1). Posteriorly, carapace is Color: Red, purple, or whitish with chelipeds flat (Wicksten 2011) (Fig. 1). that are red-spotted (compare to H. Frontal Area: Very slightly rounded oregonensis, Plate 21 Kozloff 1993; Kuris et and without prominent lobes (Fig. 2). al. 2007) (Fig. 1). Although coloration is Teeth: Two carapace teeth below the generally species-specific among grapsid orbital tooth, which are lateral, while the last crabs, nearly white or yellow forms of both tooth is small (Fig. 2) (Wicksten 2011). Hemigrapsus species have been reported Pereopods: Naked (without hair) and (Wicksten 2011). rather short (Schmitt 1921) with short dactyls General Morphology: The body of decapod (Fig. 1) (Wicksten 2011). crustaceans can be divided into the cepha- Chelipeds: Smooth, equal or almost lothorax (fused head and thorax) and abdo- A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: https://oimb.uoregon.edu/oregon-estuarine-invertebrates and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Hiebert, T.C. 2015. Hemigrapsus nudus. In: Oregon Estuarine Invertebrates: Rudys' Illustrated Guide to Common Species, 3rd ed. T.C. Hiebert, B.A. Butler and A.L. Shanks (eds.). University of Oregon Libraries and Oregon Institute of Marine Biology, Charleston, OR. equal in size with curved fingers (Wicksten following features are particularly useful in dif- 2011). Chelipeds stout, mottled above, with ferentiating the two Hemigrapsus species: 1) teeth on margins and with small round red H. oregonensis has a marked frontal notch spots (Fig. 1). Male with inflated palms and where H. nudus has a shallow depression, 2) a patch of fine hair on inner surface. the lateral spines of H. oregonensis are sharp Abdomen (Pleon): Females with wide ab- and distinctly separated from the side but H. domen and male H. nudus have narrow ab- nudus spines are not, 3) The dactyls of walk- domens that exposes the sternum at the ing legs 1–3 are long in H. oregonensis and base (see Sexual Dimorphism, Fig. 3). short in H. nudus and 4) the dactyl of the Telson & Uropods: fourth walking leg is round in H. oregonensis Sexual Dimorphism: Male and female and flat in H. nudus (Kuris et al. 2007). The brachyuran crabs are easily differentiable. final varunid crab that occurs locally is the in- The most conspicuous feature, the abdo- troduced Chinese mitten crab, Eriocheir men, is narrow and triangular in males while sinensis, but this species is very large and it is wide and flap-like in females (Brachyura, easily differentiable from either Hemigrapsus Kuris et al. 2007). Male H. nudus have a species. narrow abdomen, exposing the sternum at Pachygrapsus crassipes, a consistent the base (Fig. 3) and the palm of the male member of the Grapsidae, is a dark green cheliped with a patch of long, fine hair. Fe- crab with many transverse dark red striations males have a wide abdomen, hiding the on its legs and carapace (H. oregonensis is sternum (Fig. 3), and only a few isolated smooth), its frontal margin is straight and it bristles on the palm of the cheliped. has one lateral tooth, not two (Symons 1964). The only other, locally occurring grapsid crab, Possible Misidentifications Planes cyaneus, is a pelagic species that is Hemigrapsus species were formally only found washed ashore on drift logs with members of the Grapsidae, a family charac- gooseneck barnacles (Kuris et al. 2007). terized by the carpus of the third maxilliped Rhithropanopeus harrisii, an introduced not articulating near the anterior merus an- xanthid (Panopeidae) mud crab, is sometimes gle and by lateral mouth margins that are found with H. oregonensis and potentially H. parallel or convergent (Wicksten 2011). The nudus. It has a slightly convergent sides, genus Hemigrapsus may now a member of strong dorsal ridges on its carapace and three the family Varunidae (see Taxonomy) char- sharp carapace teeth. acterized by chelae morphology, gaping third maxillipeds and setose walking legs Ecological Information (Ng et al. 2008). Two Hemigrapsus species Range: Type locality is Puget Sound, Wash- occur locally, H. oregonensis and H. nudus. ington (Ricketts and Calvin 1971). Known Hemigrapsus nudus, the purple shore crab, range includes Sitka, Alaska, to Gulf of Cali- is larger than H. oregonensis, is “naked” (i.e. fornia (Rathbun 1918). Uncommon in South- not hairy) on its walking legs and has cheli- ern California (Garth and Abbott 1980; Jaffe peds with conspicuous red spots. Hemi- et al. 1987; Wicksten 2011). grapsus nudus lives mostly on the rocky Local Distribution: Coos, Siletz, and open coast, but is also found in salt marshes Tillamook Bay estuaries (and probably more (Knudsen 1964). Hemigrapsus oregonensis Oregon estuaries) in rocky, brackish habitats. has been called a small, bleached edition of Habitat: Semi-protected and protected rocky H. nudus (Ricketts and Calvin 1971). The coasts and bays. Prefers coarse sand to A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: https://oimb.uoregon.edu/oregon-estuarine-invertebrates and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] gravel substrates overlain with large rock Portunion conformis, occurs in perivisceral cover (Schmitt 1921; Kuris et al. 2007). In cavity of some individuals (Garth and Abbott salt marshes, but not as commonly encoun- 1980). Can be host to nemertean tered as H. oregonensis, and in burrows and Carcinonemertes epialti. Hemigrapsus under driftwood. Less common in California nudus, H. oregonensis and P. crassipes can salt marshes (Kozloff 1993). Hemigrapsus all be host to this nemertean egg predator, nudus is common in mid tide pool regions which can negatively impact brood mortality in (Ricketts and Calvin 1971) and is found in these species (Shields and Kuris 1988). areas of swift water and large boulders These three species can also serve as (Puget Sound, Knudsen 1964). intermediate hosts for a variety of parasites Hemigrapsus nudus can be found in more including trematode metacercariae, larval exposed situations than H. oregonensis and trypanorhynch tapeworms, as well as withstands desiccation better (large Polymorphus acanthocephalan and nematode specimens). The two Hemigrapsus species (Ascarophis) larvae (Kuris et al. 2007). do co-occur, but one usually finds one or the Abundance: Locally abundant (Ricketts and other (Kozloff 1993). Calvin 1971) and less common south (e.g. Salinity: Occurs in outer shore full strength Morrow Bay, California, Kuris et al. 2007). seawater, brackish and hyper-saline Life-History Information (estuarine marsh) waters. Can endure low Reproduction: In Puget Sound, Washington, salinities better at high temperatures (Todd mating occurs between December and Janu- and Dehnel 1960). ary and is similar to Pachygrapsus (Hiatt Temperature: Hemigrapsus nudus individu- 1948; see Fig. 2, 3, Knudsen 1964), however als can tolerate temperatures up to 33.6˚C P. crassipes exhibits peak breeding in but are more tolerant of cold than warm tem- summer months compared to winter months peratures and modify their behavior to regu- in H. nudus (Boolootian et al. 1959). Females late body temperature (McGaw 2003). Sur- ovigerous January through April, 70% vival is most poor with low temperature com- ovigerous in late January and 99% with bined with low salinity, but smallest speci- fertilized eggs early April. Hatching occurs mens are most resistant to temperature ex- between May and June (Puget Sound, tremes (Todd and Dehnel 1960). Washington). This timeline can be earlier Tidal Level: Strictly littoral (Ricketts and (hatching Oct–May in Monterey Bay, Calvin 1971) and found higher than H.