Systematics of the genus Scleroplax Rathbun, 1893 (Crustacea: Brachyura: Pinnotheridae)

The taxonomic status of the monotypic genus Scleroplax Rathbun, 1893, is evaluated and separated from other genera of the Pinnixa White, 1846, complex. Distinguishing characters of Scleroplax are a hard, subheptagonal and dorsally, highly convex carapace, and a third maxilliped with a propodus that extends to the end of the dactylus. The genera Scleroplax, Pinnixa, Austinixa Heard & Manning, 1997, Glassella Campos & Wicksten, 1997, Indopinnixa Manning & Morton, 1987, and Tetrias Rathbun, 1898, share a carapace than is wider than long and a distinct lateral exopod lobe on the third maxilliped, all of which may represent monophyletic characters. Updated information on the distribution and hosts of S. granulata Rathbun, 1893, indicate that the species now ranges from Vancouver Island, British Columbia, Canada to El Coyote estuary, Punta Abreojos, Baja California Sur, México. It inhabits burrows of the echiuroid Urechis caupo Fisher & MacGinitie, 1928, and the mud shrimps Neotrypaea californiensis (Dana, 1854), N. gigas (Dana, 1852) (new host record), Upogebia pugettensis (Dana, 1852), and occasionally U. macginiteorum Williams, 1986 (new host record).

Effects of metabolite uptake on proton-equivalent elimination by two species of deep-sea vestimentiferan tubeworm,Riftia pachyptilaandLamellibrachiacfluymesi: proton elimination is a necessary adaptation to sulfide-oxidizing chemoautotrophic symbionts

SUMMARYIntracellular symbiosis requires that the host satisfy the symbiont's metabolic requirements, including the elimination of waste products. The hydrothermal vent tubeworm Riftia pachyptila and the hydrocarbon seep worm Lamellibrachia cf luymesi are symbiotic with chemolithoautotrophic bacteria that produce sulfate and protons as end-products. In this report, we examine the relationship between symbiont metabolism and host proton equivalent elimination in R. pachyptilaand L. cf luymesi, and the effects of sulfide exposure on proton-equivalent elimination by Urechis caupo, an echiuran worm that lacks intracellular symbionts (for brevity, we will hereafter refer to proton-equivalent elimination as `proton elimination'). Proton elimination by R. pachyptila and L. cf luymesi constitutes the worms' largest mass-specific metabolite flux, and R. pachyptilaproton elimination is, to our knowledge, the most rapid reported for any metazoan. Proton elimination rates by R. pachyptila and L.cf luymesi correlated primarily with the rate of sulfide oxidation. Prolonged exposure to low environmental oxygen concentrations completely inhibited the majority of proton elimination by R. pachyptila,demonstrating that proton elimination does not result primarily from anaerobic metabolism. Large and rapid increases in environmental inorganic carbon concentrations led to short-lived proton elimination by R. pachyptila, as a result of the equilibration between internal and external inorganic carbon pools. U. caupo consistently exhibited proton elimination rates 5-20 times lower than those of L. cf luymesi and R. pachyptila upon exposure to sulfide. Treatment with specific ATPase inhibitors completely inhibited a fraction of proton elimination and sulfide and inorganic carbon uptake by R. pachyptila, suggesting that proton elimination occurs in large part via K+/H+-ATPases and Na+/H+-ATPases. In the light of these results, we suggest that protons are the primary waste product of the symbioses of R. pachyptila and L. cf luymesi, and that proton elimination is driven by symbiont metabolism, and may be the largest energetic cost incurred by the worms.

Neuromuscular sensitivity to hydrogen sulfide in the marine invertebrate Urechis caupo.

Hydrogen sulfide (HS) is a well-known inhibitor of aerobic respiration via its reversible binding of mitochondrial cytochrome c oxidase, but recent studies have suggested that HS may have other non-respiratory actions. We have studied the effects of HS on spontaneous and evoked contractions in vitro under hypoxic and anoxic conditions in nerve-muscle preparations from the echiuran worm Urechis caupo. Contraction amplitude in response to electric field stimulation under anoxic conditions was completely abolished by HS within minutes in a classic dose-response relationship (Kd=31 mmol l-1, r2=0.86). Exposure of body wall and esophagus to HS in vitro for up to 6 h demonstrated that the contraction amplitude and frequency of spontaneous activity were relatively insensitive to anoxia, but that the sensitivity to HS was similar to that seen in field-stimulated muscle (Kd=2.7-32 mmol l-1). The toxic effects of HS were reversible, with almost complete recovery under anoxic conditions within the first hour. These data indicate that HS at millimolar concentrations can directly inhibit muscle contraction. Although the mechanism of this action is unknown, it does not appear to involve metabolic pathways or oxygen transport.