Hemigrapsus Nudus Class: Malacostraca Order: Decapoda Section: Brachyura the Purple Shore Crab Family: Varunidae
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Phylum: Arthropoda, Crustacea Hemigrapsus nudus Class: Malacostraca Order: Decapoda Section: Brachyura The purple shore crab Family: Varunidae Taxonomy: The brachyuran family Cephalothorax: Grapsidae, the shore crabs, was a very large Eyes: Eyestalks and eyes of family with several subfamilies and little moderate size with eyes that are at antero- taxonomic scrutiny, until recently. Based on molecular and morphological evidence, lateral angles (Fig. 2). Grapsid species authors (von Sternberg and Cumberlidge apparently have keen vision (Wicksten 2011). 2000; Schubart et al. 2000; de Grave et al. Antennae: 2009; Schubart 2011) elevated all grapsid Mouthparts: The mouth of decapod subfamilies to family level, reducing the crustaceans comprises six pairs of number of species formally within the appendages including one pair of mandibles Grapsidae. Recent molecular evidence has (on either side of the mouth), two pairs of placed Hemigrapsus species within the maxillae and three pairs of maxillipeds. The Varunidae, but this is currently debated and maxillae and maxillipeds attach posterior to some authors still refer to them as members the mouth and extend to cover the mandibles of the Grapsidae sensu lato (Ng et al. 2008; (Ruppert et al. 2004). Wicksten 2011) and others have adopted the Carapace: Flat, smooth, punctate new familial designation (e.g. Kuris et al. (Schmitt 1921) and bears three teeth (two 2007). Besides the higher taxonomic lateral that are posterior to postorbital) classifications, the known specific synonym (Wicksten 2011). Square in shape, with for H. nudus is Pseudograpsus nudus rounded antero-lateral margins (Rathbun (Wicksten 2011), which is not currently used. 1918) and no transverse lines (compare to P. crassipes) (Fig. 1). Posteriorly, carapace is Description flat (Wicksten 2011) (Fig. 1). Size: Carapace 56.2 mm in width and 48 mm Frontal Area: Very slightly rounded in length (Rathbun 1918; Wicksten 2011) (Fig. and without prominent lobes (Fig. 2). 1). An adult male from Coos Bay, was 32 mm Teeth: Two carapace teeth below the in width and weighed 17.5 g (wet weight). orbital tooth, which are lateral, while the last Color: Red, purple, or whitish with chelipeds tooth is small (Fig. 2) (Wicksten 2011). that are red-spotted (compare to H. Pereopods: Naked (without hair) and oregonensis, Plate 21 Kozloff 1993; Kuris et rather short (Schmitt 1921) with short dactyls al. 2007) (Fig. 1). Although coloration is (Fig. 1) (Wicksten 2011). generally species-specific among grapsid Chelipeds: Smooth, equal or almost crabs, nearly white or yellow forms of both equal in size with curved fingers (Wicksten Hemigrapsus species have been reported 2011). Chelipeds stout, mottled above, with (Wicksten 2011). teeth on margins and with small round red General Morphology: The body of decapod spots (Fig. 1). Male with inflated palms and a crustaceans can be divided into the patch of fine hair on inner surface. cephalothorax (fused head and thorax) and Abdomen (Pleon): Females with wide abdomen. They have a large plate-like abdomen and male H. nudus have narrow carapace dorsally, beneath which are five abdomens that exposes the sternum at the pairs of thoracic appendages (see chelipeds base (see Sexual Dimorphism, Fig. 3). and pereopods) and three pairs of Telson & Uropods: maxillipeds (see mouthparts). The abdomen Sexual Dimorphism: Male and female and associated appendages are reduced and brachyuran crabs are easily differentiable. folded ventrally (Decapoda, Kuris et al. 2007). The most conspicuous feature, the abdomen, 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. A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12710 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to [email protected] is narrow and triangular in males while it is has one lateral tooth, not two (Symons 1964). wide and flap-like in females (Brachyura, The only other, locally occurring grapsid crab, Kuris et al. 2007). Male H. nudus have a Planes cyaneus, is a pelagic species that is narrow abdomen, exposing the sternum at the only found washed ashore on drift logs with base (Fig. 3) and the palm of the male gooseneck barnacles (Kuris et al. 2007). cheliped with a patch of long, fine hair. Rhithropanopeus harrisii, an introduced Females have a wide abdomen, hiding the xanthid (Panopeidae) mud crab, is sometimes sternum (Fig. 3), and only a few isolated found with H. oregonensis and potentially H. bristles on the palm of the cheliped. nudus. It has a slightly convergent sides, strong dorsal ridges on its carapace and three Possible Misidentifications sharp carapace teeth. Hemigrapsus species were formally members of the Grapsidae, a family characterized by Ecological Information the carpus of the third maxilliped not Range: Type locality is Puget Sound, articulating near the anterior merus angle and Washington (Ricketts and Calvin 1971). by lateral mouth margins that are parallel or Known range includes Sitka, Alaska, to Gulf convergent (Wicksten 2011). The genus of California (Rathbun 1918). Uncommon in Hemigrapsus may now a member of the Southern California (Garth and Abbott 1980; family Varunidae (see Taxonomy) Jaffe et al. 1987; Wicksten 2011). characterized by chelae morphology, gaping Local Distribution: Coos, Siletz, and third maxillipeds and setose walking legs (Ng Tillamook Bay estuaries (and probably more et al. 2008). Two Hemigrapsus species occur Oregon estuaries) in rocky, brackish habitats. locally, H. oregonensis and H. nudus. Habitat: Semi-protected and protected rocky Hemigrapsus nudus, the purple shore crab, is coasts and bays. Prefers coarse sand to larger than H. oregonensis, is “naked” (i.e. not gravel substrates overlain with large rock hairy) on its walking legs and has chelipeds cover (Schmitt 1921; Kuris et al. 2007). In with conspicuous red spots. Hemigrapsus salt marshes, but not as commonly nudus lives mostly on the rocky open coast, encountered as H. oregonensis, and in but is also found in salt marshes (Knudsen burrows and under driftwood. Less common 1964). Hemigrapsus oregonensis has been in California salt marshes (Kozloff 1993). called a small, bleached edition of H. nudus Hemigrapsus nudus is common in mid tide (Ricketts and Calvin 1971). The following pool regions (Ricketts and Calvin 1971) and is features are particularly useful in found in areas of swift water and large differentiating the two Hemigrapsus species: boulders (Puget Sound, Knudsen 1964). 1) H. oregonensis has a marked frontal notch Hemigrapsus nudus can be found in more where H. nudus has a shallow depression, 2) exposed situations than H. oregonensis and the lateral spines of H. oregonensis are sharp withstands desiccation better (large and distinctly separated from the side but H. specimens). The two Hemigrapsus species nudus spines are not, 3) The dactyls of do co-occur, but one usually finds one or the walking legs 1–3 are long in H. oregonensis other (Kozloff 1993). and short in H. nudus and 4) the dactyl of the Salinity: Occurs in outer shore full strength fourth walking leg is round in H. oregonensis seawater, brackish and hyper-saline and flat in H. nudus (Kuris et al. 2007). The (estuarine marsh) waters. Can endure low final varunid crab that occurs locally is the salinities better at high temperatures (Todd introduced Chinese mitten crab, Eriocheir and Dehnel 1960). sinensis, but this species is very large and Temperature: Hemigrapsus nudus easily differentiable from either Hemigrapsus individuals can tolerate temperatures up to species. 33.6˚C but are more tolerant of cold than Pachygrapsus crassipes, a consistent warm temperatures and modify their behavior member of the Grapsidae, is a dark green to regulate body temperature (McGaw 2003). crab with many transverse dark red striations Survival is most poor with low temperature on its legs and carapace (H. oregonensis is combined with low salinity, but smallest smooth), its frontal margin is straight and it 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. specimens are most resistant to temperature and the production of second brood is rare. extremes (Todd and Dehnel 1960). Embryos are approximately 380 µm in Tidal Level: Strictly littoral (Ricketts and diameter and become 450 µm upon hatching Calvin 1971) and found higher than H. (Jaffe et al. 1987). The reproduction and life- oregonensis, but both species are found from cycle of C. epialti is dependent on and high to low levels (Todd and Dehnel 1960). corresponds to that of its host species. Occurs is the rockweed belt, underneath However, this nemertean is not host specific rocks and is commonly found just below high- (unlike Carcinonemertes errans on Cancer tide level (Monterey, California, Hiatt 1948). magister) and occurs amongst egg masses of Hemigrapsus nudus is often found with other species including Hemigrapsus Pachygrapsus, which extends higher into the oregonensis, Pachygrapsus crassipes (Kuris intertidal and prefers larger rocks. 1993; Roe et al. 2007; Kuris et al. 2007). Associates: Territory overlaps with Larva: Larval development in H. nudus Pachygrapsus crassipes over whom it is proceeds via a series of zoea (five total) and dominant (Hiatt 1948) and occasionally with megalopa stages, each marked by a molt. H. oregonensis. Parasitic castrating isopod, The zoea are planktotrophic and have large Portunion conformis, occurs in perivisceral compound eyes and four spines: one each cavity of some individuals (Garth and Abbott dorsal and rostral and two lateral (see Fig. 32, 1980). Can be host to nemertean Puls 2001; Fig. 54.5, Martin 2014). The Carcinonemertes epialti. Hemigrapsus rostrum and dorsal spines are of equal length nudus, H.