Spirobranchus bakau sp. nov. from Singapore: yet another species of S. kraussii-complex (Polychaeta: Serpulidae)

Elevated temperatures increase abnormalities in embryos and reduce larval survival in serpulid polychaetes

Environmental temperature is one of the most significant factors influencing the developmental rate and survival of embryos and larvae of many marine animals, including polychaetes. The aim of this study was to experimentally evaluate the effect of temperature increase on the embryonic development and larval survival of Spirobranchus incrassatus and S. cf. corniculatus. Adult worms of both species were collected from the western margin of the Gulf of Tehuantepec, Mexico. Embryos and larvae were obtained from these worms and exposed to four temperature treatments (28, 30, 32 and 34°C). The optimal temperature for embryonic development of S. incrassatus and S. cf. corniculatus was 30 and 28°C, respectively. For both species, the maximum critical temperature was 32°C and the lethal temperature was 34°C. The embryonic stages of S. cf. corniculatus were most negatively affected by elevated temperatures. Larval survivorship of S. incrassatus and S. cf. corniculatus was higher at 30°C and 28°C (76.2±2.8%; 72.6±4.2%) and lower at 34°C (28.9±2.6%; 26.3±2.9%), respectively. These results suggest that S. cf. corniculatus has the lowest thermal tolerance. Both Spirobranchus species already live near their upper limit of thermal tolerance in the study region (30°C). In the near future, under a global warming scenario, the distribution of both species could be modified, causing a loss of biodiversity, changes in the trophic chain, and alterations in the water column, such as excess organic matter.

A new species of the Spirobranchuskraussii complex, S.akitsushima (Annelida, Polychaeta, Serpulidae), from the rocky intertidal zone of Japan

A new species of Spirobranchus (Annelida: Serpulidae) is described based on specimens collected at the coastal Shonan area of Sagami Bay and the adjacent areas of Honshu, Japan. Spirobranchusakitsushima sp. nov. forms large aggregations in the intertidal rocky zone of warm-temperate Japanese shores. This species was referred to as Pomatoleioskraussii (Baird, 1864) until the monotypic genus Pomatoleios was synonymized with Spirobranchus. This new species is formally described based on morphologically distinct Japanese specimens with supporting DNA sequence data. The calcareous opercular endplate of Spirobranchusakitsushima sp. nov. lacks a distinct talon, but some specimens have a slight rounded swelling on the endplate underside, while in other species of the S.kraussii complex a talon is present, usually extended, and with bulges. We examined sub-fossil tube aggregations of the new species and suggest that such aggregation stranded ashore is a good indicator of vertical land movements (uplift and subsidence) resulting from past events, such as earthquakes, in Honshu, Japan.