Pachygrapsus Crassipes Class: Multicrustacea, Malacostraca, Eumalacostraca
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Phylum: Arthropoda, Crustacea Pachygrapsus crassipes Class: Multicrustacea, Malacostraca, Eumalacostraca Order: Eucarida, Decapoda, Pleocyemata, Brachyura, The lined shore crab Eubrachyura, Heterotremata Family: Majoidea, Epialtidae, Epialtinae Taxonomy: Until recently the brachyuran Cephalothorax: family Grapsidae, the shore crabs, was very Eyes: Eyes present at anterolateral large with several subfamilies and little taxo- angle and eyestalks of moderate size with nomic scrutiny. Based on molecular and orbits deep and oblique (Fig. 2). morphological evidence, authors (von Stern- Antenna: berg and Cumberlidge 2000; Schubart et al. Mouthparts: The mouth of decapod 2000; de Grave et al. 2009; Schubart 2011) crustaceans comprises six pairs of appendag- elevated all grapsid subfamilies to the family es including one pair of mandibles (on either level, reducing the number of species for- side of the mouth), two pairs of maxillae and mally within the Grapsidae. Although recent three pairs of maxillipeds. The maxillae and molecular evidence suggest that maxillipeds attach posterior to the mouth and Hemigrapsus is no longer within this family, extend to cover the mandibles (Ruppert et al. Pachygrapsus remains one of the few 2004). The third maxilliped in P. crassipes members of the Grapsidae sensu stricto has merus, lobate and at an angle (Wicksten based on morphological evidence from 2011). adults, larvae and molecular data (Schubart Carapace: Nearly square in shape and 2011). a little broader than long, transverse lines or grooves on anterior. Lateral margins are Description most broad posterior to orbit (Wicksten 2011). Size: Carapace approximately 40 mm in Carapace sides nearly parallel, but arched width and males are larger than females (Fig. 1). (Hiatt 1948) (Fig. 1). Mature individuals Frontal Area: Broad margin that is weighed 15 g. (Gross and Marshall 1960) smooth, slightly arched and half as wide as and measure 48 mm in width (Puls 2001). carapace. Four slight lobes present below Color: Dark green carapace, with dark red margin with small lobes at outer corners (Fig. or blue transverse lines and some light 2). markings (Plate 21, Kozloff 1993). Chela Teeth: One strong lateral carapace white ventrally and bright red dorsally tooth (below the orbital tooth) (Fig. 2). (males) (Wicksten 2011). Pereopods: Merus of each leg broad General Morphology: The body of decapod and bearing a single tooth at each postero- crustaceans can be divided into the cepha- distal angle, except the fifth (last) pair smooth lothorax (fused head and thorax) and abdo- at distal end, and no sharply distinct teeth men. They have a large plate-like carapace (Fig. 3) (Wicksten 2011). Leg shape broad, dorsally, beneath which are five pairs of tho- compressed and bristled (Rathbun 1918). racic appendages (see chelipeds and pere- Dactyls spinulose (Wicksten 2011). opods) and three pairs of maxillipeds (see Chelipeds: Usually subequal and mas- mouthparts). The abdomen and associated sive. Chela almost smooth with arm and wrist appendages are reduced and folded ventral- striated (Rathbun 1918). Male chela broad ly (Decapoda, Kuris et al. 2007). 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. Pachygrapsus crassipes. 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, Charles- ton, OR. with raised line present on propodus, fingers other species of Pachygrapsus, the smaller P. spooned. Female chela, on the other hand, transversus, occurs only as far north as less broad. California. The only other locally occurring Abdomen (Pleon): Females with wide ab- member of the Grapsidae, Planes cyaneus, is domen and male H. oregonensis have nar- a pelagic species that is only found washed row abdomens that exposes the sternum at ashore on drift logs with gooseneck barnacles the base (see Sexual Dimorphism, see Fig. (Kuris et al. 2007). Rhithropanopeus harrisii, 3, Hemigrapsus oregonensis). an introduced xanthid (Panopeidae) mud Telson & Uropods: crab, occurs locally with shore crabs. It has a Sexual Dimorphism: Male and female slightly convergent sides, strong dorsal ridges brachyuran crabs are easily differentiable. on its carapace and three sharp carapace The most conspicuous feature, the abdo- teeth. men, is narrow and triangular in males while Ecological Information it is wide and flap-like in females (Brachyura, Range: Type locality is probably Oregon Kuris et al. 2007). Male P. crassipes abdo- (erroneously Hawaii, Hiatt 1948; Wicksten men is narrow and triangular, exposing ster- 2011). Known range includes Oregon to Gulf num at sides (as in Hemigrapsus nudus and of California, however there is significant ge- H. oregonensis.) Female abdomen is round- netic structuring between populations north ed, wide and hiding sternum in the adult. and south of Pt. Conception, California Dimorphism obvious when animals only 6 (Cassone and Boulding 2006). mm wide (Hiatt 1948). Local Distribution: Northernmost boundary Possible Misidentifications is 45° N (Newport, Oregon), probably due to Pachygrapsus species are members cold winter temperatures found on protected of the Grapsidae, a family characterized by rocky beaches and in southern Oregon estu- the carpus of the third maxilliped not articu- aries. lating near the anterior merus angle and by Habitat: Prefers hard substrates, especially lateral mouth margins that are parallel or rocks, jetties and boulders with crevices and convergent (Wicksten 2011). There is only crannies covered in algal growth. Also occurs one local Pachygrapsus species, but it may in Salicornia marshes where Salicornia roots be confused with other grapsid crabs from provide burrows. the family Varunidae, characterized by che- Salinity: Most aspects of the biology of P. lae morphology, gaping third maxillipeds and crassipes, in the following categories, were setose walking legs (Ng et al. 2008). Pach- described by Hiatt (1948). Osmoregulatory ygrapsus crassipes is superficially similar to adaptations indicate movement toward terres- the slower Hemigrapsus nudus, but the latter trial habitat and can regulate against salt con- has obvious red spots on its chelipeds, and centrations in the body during periods of ex- lacks the dark green color and transverse posure, and thus maintain a constant body striations of P. crassipes. Furthermore, the salinity (Jones 1941). Occurs less frequently frontal margin of P. crassipes is straight and in brackish water than does Hemigrapsus it has one lateral tooth, not two (Symons (Hiatt 1948). 1964). Two similar shore crabs in the genus Temperature: Northern limit of range appar- Hemigrapsus are H. oregonensis, which is ently determined by low winter temperatures smaller, and H. nudus, with two lateral teeth and individuals can tolerate greater tempera- and a smooth, square carapace. The only ture fluctuation than can Hemigrapsus (Hiatt 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] 1948). nia, Hiatt 1948) and May to November (Sea Tidal Level: Lives over an extensive vertical Beach, California, Schlotterbeck 1976; Puls range from mean low water to + 2.5 m. 2001), but off-season mating occurs (Ricketts Pachygrapsus crassipes is found highest in and Calvin 1971). Most breeding, however, intertidal of all Pacific Northwest crabs and is takes place in summer months (Boolootian et especially abundant at the higher levels al. 1959). Impregnation to extrusion of eggs (upper intertidal, Schmitt 1921) progressing takes 16–25 days with incubation period ave- toward terrestrial habitat (Hiatt 1948). How- raging 29 days. Mating generally occurs once ever, as blood concentrations of potassium, a year and occasionally second broods are calcium, and magnesium increase more produced (Hiatt 1948). Upon hatching em- than sodium when animal is desiccated, ter- bryos are deep purple brown in color restrial adaptation may be inhibited. Also, (Schlotterbeck 1976). The reproduction and efficiency of the animal's vascular system, life-cycle of the parasitic nemertean, C. epialti affected by osmotic stress, further limits eco- is dependent on and corresponds to that of its logical range (Gross 1959). host species. However, this nemertean is not Associates: Pachygrapsus crassipes oc- host specific (unlike Carcinonemertes errans curs with Hemigrapsus oregonensis in bays, on Cancer magister) and occurs amongst egg and with H. nudus on rocky outer shores. , It masses of other species including H. nudus, competes with both for shelter (Hiatt 1948), H. oregonensis (Kuris 1993; Roe et al. 2007; but not for food. Fucus (alga) and Salicornia Kuris et al. 2007). (pickleweed) often provide protection. Larva: Larval development in P. crassipes Individuals can be infested by bopyrid proceeds via a prezoea and a series of zoea isopods (Southern California, Schmitt 1921). (five total) and megalopa stages, each Hemigrapsus oregonensis, H. nudus and P. marked by a molt with total larval duration (to crassipes can be all be host to the fifth zoea, as measured