Neomysis Mercedis Class: Malacostraca Order: Mysidacea a Mysid, Or Opossum Shrimp Family: Mysidae

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Phylum: Arthropoda, Crustacea Neomysis mercedis Class: Malacostraca Order: Mysidacea A mysid, or opossum shrimp Family: Mysidae

Taxonomy: Neomysis awatschensis, N. Carapace: Not attached dorsally at intermedia, and N. mercedis were considered posterior edge. Anterior lateral angles acute three different species (with distinct (Figs. 1, 3). morphology) from the western Pacific, Rostrum: A short triangle with northwestern Pacific and northeast Pacific obtusely pointed apex, and rounded, “flanged” coasts (Tattersall 1951; Holmquist 1973; corners (Tattersall and Tattersall 1951). A Brand et al. 1993), but have since been medial depression obscures the pointed apex synonymized as N. mercedis (Moldin 2007). (Holmquist 1973). In total size, rostrum is only as long as bases of eyestalks (Tattersall Description and Tattersall 1951) (Figs. 1, 3). Size: Adults range in size from 11 to 17 mm Eyes: On movable stalks and about in length (Banner 1948b). The illustrated 1.5 times as long as broad and with corneas specimens (from the Columbia River estuary) that are expanded, but not separated into two were up to 17 mm long. portions (Fig. 3). Color: Clear body with black Antennae: Long, slender, and multi- chromatophores, although an individual articulate (Fig. 1). caught on eelgrass was yellow green Antennae Scale: (= squama) Long, (Banner 1948b). narrow, about eight times longer than wide General Morphology: Mysids are shrimp- (Banner 1948b; Brandt et al. 1993). The size like crustaceans that are occasionally called of the scale, however, may vary among opossum shrimp due to the female individuals (Holmquist 1973). The scale is marsupium or brood pouch, which is setose all around and is with pointed apex composed of oostegites. Like other pointed (Neomysis, Tattersall 1933; Moldin Peracarida (e.g., cumaceans, isopods, 2007) and an articulated tip (Fig. 3). amphipods, tanaids), their bodies are Mouthparts: For general mouthpart elongated and composed of an anterior morphology for the Mysida see Fig. 3, Meland cephalon and pereon (thorax, covered by a et al. 2015. In N. mercedis, the labrum is carapace), and a pleon (abdomen). At the normal (i.e. not produced posteriorly as a cleft posterior end, they have a telson and plate, and with anterior sharp point, Tattersall uropods. Among the Mysidacea specifically, 1933). Anterior is pointed, but not with long the carapace is attached to the thorax by sharp spine (Holmquist 1973). The anterior segments only and the posterior mandibles are without expanded cutting lobe dorsal edge is free (Banner 1948a) (Fig. 1). (Banner 1948a). Mysid eyes are stalked, antennules are Pereon: Anterior pereonites attached to biramous, antennae have a long scale (or carapace. squama), pleopods are often reduced, Pereopods: First pereopod with thoracic legs bear swimming exopodites and endite of basipodite well developed (Banner uropods are lamellar and form tail fan. 1948b). The endopod has a maxilliped-like Mysids are easily distinguished from other feeding structure. The second, third and Peracardia by the presence of a statocyst on fourth articles have enlarged lobes (Fig. 4) the uropod endopods (see Plate 220, Moldin (Banner 1948b). Legs 3–8 are similar, but 2007; Vicente et al. 2014; Fig. 1, Meland et al. third leg is not copulatory (Banner 1948). 2015). Endopods with 8–10 articles (Fig. 5). Cephalon: Pleon:

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12724 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Pleopods: In males, the first and The third pleopod is more or less reduced and second pleopods are rudimentary, and the only the fourth is biramous (Neomysis, second is uniramous (Banner 1948a) (Fig. 6). Banner 1948b). Furthermore, the fourth pleopod is short and slightly curved in N. Other orders of Peracarida include mercedis (Holmquist 1973; Moldin 2007), with lsopoda, Tanaidacea, and Amphipoda, which shortened, uniarticulate endopodite, long are all fairly easily distinguished from exopodite consisting of two articles, and with Mysidacea. One order that might be two terminal pincer setae (Banner 1948b) confused is Cumacea, small crustaceans of (Fig. 7). The fifth pleopods are rudimentary. up to ½ inch long, with an inflated, shrimp- In females, all pleopods are small, like carapace (see Cumella vulgaris, this uniarticulate, and rudimentary (Fig. 8). guide), a single compound recessed eye Telson: Short, and about twice as long as (except for some eyeless females of some broad. The tip is broadly triangular and not species), and a flexible, tubular abdomen. cleft (Brandt et al. 1993). The telson bears Mysids characteristically have large, stalked, 12–15 pairs of lateral spines (Holmquist 1973) movable eyes, and well developed exopodites (10 in illustrated specimen). The tip has two on their thoracic legs. Mature females have pairs of spines, the outer pair long and the oostegites forming a marsupium. Additionally, inner pair very small and not setose (Banner northeast Pacific mysids lack thoracic gills, 1948b) (Fig. 9). have reduced pleopods in females (and Uropods: Uropod endopods with about 30 sometimes in males). They also have a close set spines along the inner, ventral edge, statocyst on the inner ramus of the uropod. near the statocyst (Fig. 9). The exopods are The Mysidacea is divided into two undivided, and with setae only (no spines) on suborders, the Mysida (approximately 1,200 both outer and inner margins. species worldwide) and Lophogastrida (58 Statocyst: A balance and light organ found species worldwide) (Vicente et al. 2014; on the uropod endopod that is large, opaque, Meland et al. 2015). The former suborder and white in preservation (Fig. 9). comprises coastal and intertidal species while Sexual Dimorphism: The fourth male the latter includes mostly large, pelagic and pleopod is short, slightly curved and deep-sea mysids. These suborders are easily biramous. Mature females are recognizable differentiable by the presence of branchial by oostegites and two pairs of lamellae, or gills, biramous pleopods and the lack of pleura. The anterior pair is with posterior statocysts in Lophogastrida (branchia are "baling lobe" to assist in aerating embryos absent, pleopods are reduced and statocysts and has a setose ventral edge (Fig. 2). are conspicuous in the Mysida) (Moldin 2007). Neomysis mercedis belongs to the Possible Misidentifications Mysida, lacking gills or branchiae on the Mysidacea and Euphausiacea, being thoracic legs and having rather reduced superficially similar in appearance, are often female pleopods. treated together (e.g. Banner 1948a; Within the Mysicadea locally, there are Mauchline 1980). (They were formerly 15 species comprising the following genera: combined as the Schizopoda.) Both are Acanthomysis and Neomysis (comprising orders of the class Malacostraca, but three species and four species, respectively), euphausiids are in the group (i.e. superorder) and Hyperacanthomysis, Alienacanthomysis, Eucarida with the Decapoda (Martin 2007). Columbiaemysis, Deltamysis, Like the mysids, euphausiids differ from Exacanthomysis, Hippacanthomysis, decapods in having biramous thoracic legs Holmesimysis, and Archaeomysis (each with (Kasaoka 1974). Unlike the mysids, a single species represented locally) (Moldin euphausiids have a carapace that is fused 2007). dorsally with all the thoracic segments. The Alienacanthomysis macropsis is mysid carapace is attached only to the first recognizable by elongated eyestalks and two or three thoracic segments. Furthermore, Deltamysis holmquistae has spines on the mysid females have oostegites, but lateral telson margins, but only distally, where euphausiids do not. other species have spines all over the telson

Hiebert, T.C. 2015. Neomysis mercedis. 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. margins or in proximal groups. as broad, an articulated distal tip, and a Alienacanthomysis macropsis, has a broadly broadly triangular telson (Moldin 2007). triangular rostrum with long acute lateral Neomysis integer is an Atlantic species that carapace spines and its telson has a fringe of has also been found in plankton in Puget small spines. It is abundant in San Francisco Sound (Kozloff 1974). It has a long pointed Bay and becomes rarer farther north antennal scale, a long telson with a narrow, (Holmquist 1979). It has been reported from truncate apex and long dense lateral spines, Yaquina Bay to lower Columbia River and in there are about 15 spines near the statocyst. Puget Sound in bays amongst Ulva and in Neomysis kadiakensis is a large species (20 plankton (Kozloff 1974). to 23 mm long) (Banner 1948b), with over 40 Archaeomysis grebnitzkii has spines spines near the statocyst. Its telson is long along the lateral margins of uropod exopods, and narrow with 20 or more pairs of lateral which is not seen in other species. Of the spines (Banner 1948b), each spine is longer species without lateral exopod spines, than the distances between their bases. The Hippacanthomysis platypoda has a flattened eyes have corneas larger than their stalks exopod of fourth pleopod (males). and the rostrum is bluntly triangular. Holmesimysis costata and E. davisi have Neomysis kadiakensis ranges from British distinctly segmented pleonites, the former has Columbia, Canada to San Francisco Bay, a broadly triangular telson while the latter has California. Although considered a neritic a telson that is sharply triangular. species, it is possibly more common inside Holmesimysis was extracted from bays and inlets than outside (Banner 1948b). Acanthomysis (Holmquist 1979). Its members Neomysis rayii (=franciscorum, = toion) has a have fourth male pleopods with only two telson at least 2 ½ times longer than wide and segments and a tip that bears two spiny peg- the truncate telson tip is very narrow. There like structures (Mauchline 1980). are 10 to 12 pairs of lateral telson spines Holmesimysis costata, the type species for present and, near the statocyst, are 20 to 50 the genus, has a short, bluntly rounded spines. This is a large species (18 to 65 mm antennal scale. long, Banner 1948b). It ranges from Alaska Columbiaemysis, Acanthomysis, to San Francisco Bay and occurs in the Neomysis and Hyperacanthomysis species plankton in Puget Sound, Washington (Kozloff have pleonites that are smooth and without 1974) and has also been collected in Yaquina distinct folds or segments. Neomysis species Bay and the lower Columbia River, Oregon. have a pointed distal tip of the antennal scale Neomysis awatschensis and N. intermedia (Fig. 3) and members of the remaining genera have been synonymized with N. mercedis have a distal antennal scale tip that is (Moldin 2007). None of the preceding rounded (Tattersall 1951; Moldin 2007). aforementioned Neomysis species, has the Columbiaemysis ignota has been described short, curved male pleopod with its proximal from female specimens only, and only from article 4x the length of its distal article. Also British Columbia. Its antennal scale is long, distinctive in N. mercedis is the antennal setose all around, and has a suture. Its scale, which is 8x longer than wide (Banner telson is tongue shaped, with spines 1948b; Brandt et al. 1993). becoming dense at the tip, and two long spines at the rounded apex. There are four Ecological Information spines on the lower edge of the statocyst. Range: Type locality and namesake There are several northeast Pacific presumably Lake Merced, California (Holmes species in the genus Neomysis (all with 1897 in Tattersall 1951). Known range from pointed apex on the antennal scale, two pairs Prince William Sound, southern Alaska, to of female oostegites, statocyst on the uropod San Francisco Bay area and possibly south to endopod, and male fourth pleopods Pt. Conception, California (Orsi and Knutson biramous). Neomysis japonica is a Japanese 1979). Washington in Puget Sound and species introduced and first collected from inland lakes. Oregon sites include Fletcher San Francisco Bay, California in 2004. It has Lake, rivers and coastal waters and California a long antennal scale that is 10 times as long sites at Lake Merced, Lake Merritt, and the

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12724 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Sacramento-San Joaquin estuary (Holmquist Associates: Sometimes co-occurs with 1973). Archaeomysis grebnitzkii, but more rarely with Local Distribution: Oregon coastal waters Exacanthomysis davisii, Alienacanthomysis including lagoons, inlets, estuaries, and bays macropsis and other mysids (Holmquist (Holmquist 1973). Planktonic in fresh water, 1982). In the Columbia River Estuary, A. but originated in shallow marine bays, from macropsis and N. mercedis females host which it has also moved into fresh water lakes generally inconspicuous ectoparasitic (Banner 1948b). Very sensitive to oxygen copepods (Hansenulus trebax) within their content and does poorly in water that has less marsupium (see Fig. 2, Daly and Damkaer than 8 ppm (Heuback 1969). 1986). Thirty-six percent of brooding females Habitat: Benthic and planktonic in brackish were infected with these copepods, which water and freshwater. Rarely found in strictly feed on developing embryos within the marine habitats except river mouths. Turbid marsupium (Columbia River Estuary, Oregon, to clear water (Orsi 1978). Daly and Damkaer 1986). Salinity: Euryhaline, and tolerates a wide Abundance: Second most common mysid of range of salinities, but becomes stressed with the northeastern Pacific after A. grebnitzkii sudden changes to fresh water (Heuback (Holmquist 1982). In Coos Bay, Oregon, 1969). Although most members of the densities varied from zero to 29 individuals Mysidacea are marine, N. mercedis has per cubic meter (summer, Ziegler 1983). adapted to an estuarine environment, and Abundance peaks were observed on May 26, sometimes occurs in freshwater (e.g. San July 3 (highest) and July 24 and correlated Joaquin Estuary, Moldin 2007). Especially with high temperatures, chlorophyll counts, common in shallow bays with salinities of 10 and possibly reproductive swarming. In the and less (Banner 1948b). Ranges farther California Delta, densities drop off when upstream into fresh water than any other temperatures are over 18°C, light intensity is Neomysis from salinity of 30 (potentially as high, salinities less than 10 and when little high as 32.3, Orsi 1978) to entirely fresh flow reversal occurs at flood tide. Low water. This species is a model estuarine population densities were observed in Lake species for toxicity testing and has been Washington and ranged from 0.1–0.17 reared at salinities as low as 2 at 17˚C on a mysids per cubic meter in 1991 and 1992 diet of Artemia salina (see Brandt et al. 1993). (Chigbu 2004). Temperature: Eurythermic and tolerates temperature ranges from 7–27 °C in summer, Life-History Information but winter temperature range is unknown Reproduction: All mysid development takes (Holmquist 1973). Upper lethal temperature place within the female marsupium, is is 25.5 degrees. Population densities are low lecithotrophic and proceeds through three when temperatures are over 22 degrees, distinct stages: 1) the embryonic stage; 2) especially when combined with low dissolved the first nauplioid stage (eyeless larva); and oxygen (Heuback 1969). 3) the post-naplioid (eyed larva) stage to a Tidal Level: Subtidal, but closer to the juvenile (see Figs. 38.1–38.2, Vicente et al. surface at flood than at ebb tide (Heuback 2014). Neomysis mercedis individuals are 1969). Depth distribution is highly variable reproductive during most of year, but few (e.g. eight to more than 30 meter depths in gravid females are observed in December Lake Washington, Chigbu et al. 1998) but and January (Heuback 1969) and peak individuals tended to be more abundant at reproductive time is in summer months. shallower stations, with some diel vertical Brood size depends on female body size, egg migration observed (deep water during the size, and season (in high and temperate day, surface water at night, Cooper et al. latitudes) (Johnston and Northcote 1989). 1992; Haskell and Stanford 2006). Juveniles Estuarine N. mercedis females 7–17 mm long do not always exhibit the diel pattern of adults had 5–57 eggs per brood (Heuback 1969; and may be present in surface waters during Cooper et al. 1992). The percentage of small the day than mature individuals (Siegfried et gravid females (7–10 mm) was greatest late al. 1979, but see Heuback 1969). summer and fall with most mortality occurring

Hiebert, T.C. 2015. Neomysis mercedis. 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. thereafter; remaining females lacked the California Delta, but 80% of energy came marsupium in winter. Females 11–12 mm from rotifers and copepods (Kost and Knight long were gravid most of year, and produced 1975; Siegfried and Kopache 1980). the most eggs in early summer months. Neomysis mercedis is not an active predator Large females (over 13 mm), were gravid in and captures prey in a self-generated current. late winter and spring (California Delta, Adults feed continuously, especially at night Heuback 1969). Females may produce 1–5 and juveniles eat rotifers when available, but broods per year (Daly and Damkaer 1986; not copepods. Individuals will eat Artemia Johnston and Northcote 1989). Coos Bay salina nauplii in the lab (Siegrdied and brood time is probably 5 weeks (Ziegler Kopache 1980; Brandt et al. 1993). In the 1983). Fraser River, British Columbia, N. mercedis Larva: The first nauplioid stage has eats harpacticoid copepods (Johnston and appendages that resemble the typical Lasenby 1982) and in Lake Washington, the nauplius larva (e.g. see Balanus glandula, this cladoceran Daphnia (Murtaugh 1981a, 1981b; guide), but lacks an eye or swimming setae. Chigbu and Sibley 1994; Chigbu 2004). In The next post-nauplioid stage has all adult the lab, N. integer consumed on average of appendages, carapace and eyes. Both over 1 million cells, and maximum of 6 million stages are non-motile and lecithotrophic. cells, of the diatom, Nitzschia, per hour (See Ultimately, the post-nauplioid molts into a Lucas in Tattersall and Tattersall 1951). free-living juvenile (Vicente et al. 2014). Although N. mercedis is also a food source Newly hatched individuals are approximately for juvenile salmonids and other fishes (see 1 mm in cephalothorax length (Figs. 1–2, predators below), this mysid is also a Brandt et al. 1993). competitor that consumes the same Juvenile: Juvenile N. mercedis range in size zooplankton prey as several common pelagic from 1–3 mm in length (Siegfried et al. 1979; fish (e.g. sockeye salmon, Cooper et al. 1992; Brandt et al. 1993). Hyatt et al. 2005; American shad and chinook Longevity: Neomysis integer lifespan is salmon, Haskell and Stanford 2006). probably 12 to 18 months, but lives are Predators: A primary food for fishes of upper shorter in dense cultures of diatoms and bays and the principal food source of young diatom-free water (see Lucas in Tattersall and of the year striped bass in the California Delta Tattersall, 1951) or in the lab (e.g. 150 days, (Murtagh 1981a). Also eaten by American Brandt et al. 1993). shad, white sturgeon, white catfish, caridean Growth Rate: Growth among mysids occurs shrimp and juvenile Chinook salmon (Tiffan et in conjunction with molting where the al. 2014) and striped bass (Siegfried and exoskeleton is shed and replaced. Post-molt Kopache 1980). Longfin smelt may regulate individuals will have soft shells as the cuticle the abundance of N. mercedis, according to a gradually hardens. During a molt, arthropods study from Lake Washington from 1988 to have the ability to regenerate limbs that were 1992 (Chigbu and Sibley 1998; Chigbu et al. previously autotomized (Kuris et al. 2007). In 1998). Additional predators include the Japanese Neomysis, the May generation carnivorous shrimp, Crangon franciscorum matured in 1 ½ months and the August and Palaemon macrodactylus (Sacramento- generation matured the following April San Joaquin River Delta, California, Siegfried (Tattersall and Tattersall 1951). After 1982). hatching, individuals are 1 mm (cephalothorax Behavior: In sea water, individuals tend to length) and grow to 3.5 mm after 60 days avoid light when in dense diatom cultures (see Fig. 1, Brandt et al. 1993). Size at (Tattersall and Tattersall 1951). sexual maturity ranged from 9–20 mm in two Canadian lakes (Kennedy and Muriel Lakes, Bibliography respectively, Cooper et al. 1992). 1. BANNER, A. H. 1948a. A taxonomic study Food: Mysids are generally omnivorous and of the Mysidacea and Euphausiacea eat detritus, algae and zooplankton by (Crustacea) of the northeastern Pacific. filtration (Siegfried and Kopache 1980; Moldin Part I. Mysidacea, from family 2007). Individuals preferred large diatoms in Lophogastridae through tribe Erythropini.

A publication of the University of Oregon Libraries and the Oregon Institute of Marine Biology Individual species: http://hdl.handle.net/1794/12724 and full 3rd edition: http://hdl.handle.net/1794/18839 Email corrections to: [email protected] Transactions of the Royal Canadian mercedis Holmes (Crustacea, Mysidacea) Institute. 26. from the Fraser River Estuary, British 2. ——. 1948b. A taxonamic study of the Columbia. Canadian Journal of Zoology. Mysidacea and Euphausiacea (Crustacea) 60:813-824. of the Northeastern Pacific. Part II: 10. KOZLOFF, E. N. 1974a. Keys to the marine Mysidacea from tribe Mysini through invertebrates of Puget Sound, the San Juan subfamily Mysedellinae. Transactions of Archipelago, and adjacent regions. the Royal Canadian Institute. 27:65-125. University of Washington Press, Seattle & 3. HAIR, J. R. 1971. Upper lethal temperature London. and thermal shock tolerances of the 11. MAUCHLINE, J. 1980. The biology of opossum shrimp, Neomysis mysids and euphausiids, p. 681. In: awatschensis, from the Sacramento-San Advances in marine biology. Vol. 18. J. H. Joaquin Estuary, California. California Fish S. Blaxter, F. S. Russell, and C. M. Yonge and Game. 57:17-27. (eds.). Academic Press, London; New York. 4. HEUBACH, W. 1969. Neomysis 12. MURTAUGH, P. A. 1981. Selective awatschensis in the Sacramento-San Predation by Neomysis mercedis in Lake Joaquin River estuary. Limnology and Washington. Limnology and Oceanography. Oceanography. 14:533-546. 26:445-453. 5. HOLMQUIST, C. 1973. Taxonomy, 13. ORSI, J. J., and A. C. KNUTSON. 1979. An distribution and ecology of the three extension of the known range of Neomysis species Neomysis intermedia mercedis, the opossum shrimp. California (Czerniavsky), N. awatschensis (Brandt) Fish and Game. 65:127-130. and N. mercedis Holmes (Crustacea, 14. SIEGFRIED, C. A., and M. E. KOPACHE. Mysidacea). Zoologische Jahrbücher. 1980. Feeding of Neomysis mercedis Abteilung für Systematik, Ökologie und (Holmes). Biological Bulletin. 159:193-205. Geographie der Tiere. 100:197-222. 15. TATTERSALL, W. M. 1932. Contributions to 6. ——. 1981. The genus Acanthomysis a knowledge of the Mysidacea of California. Czerniavsky, 1882 (Crustacea:Mysidacea). I. On a collection of Mysidae from La Jolla, Zoologische Jahrbücher. Abteilung für California. University of California Press, Systematik, Ökologie und Geographie der Berkeley, Calif. Tiere. 108:386-415. 16. ——. 1933. Euphausiacea and Mysidacea 7. ——. 1979. Mysis costata Holmes, 1900, from Western Canada. Contributions to and its relations (Crustacea, Mysidacea). Canadian Biology and Fisheries. 8:181-205. Zoologische Jahrbücher. Abteilung für 17. TATTERSALL, W. M., and O. S. Systematik, Ökologie und Geographie der TATTERSALL. 1951. The British Tiere. 106:471-499. Mysidacea. Ray Society, London. 8. ——. 1982. Mysidacea (Crustacea) secured 18. TURNER, J. L., and W. HEUBACH. 1966. during investigations along the west coast of Distribution and concentration of Neomysis North America by the National Museums of awatschensis in the Sacramento-San Canada, 1955-1966, and some inferences Joaquin Delta. California Fish and Game. drawn from the results. Zoologische 133:105-112. Jahrbücher. Abteilung für Systematik, 19. ZIEGLER, R. 1983. A study of Neomysis Ökologie und Geographie der Tiere. mercedis in the Coos River., p. 13. 109:469-510. University of Oregon Institute of Marine 9. JOHNSTON, N. T., and D. C. LASENBY. Biology, Charleston, Oregon. 1982. Diet and feeding of Neomysis