Pseudonereis gallapagensis

Pseudonereis gallapagensis Kinberg, 1865 is a polychaete worm of the family Nereididae, in the order Phyllodocida ^[1]. Like other nereidids, it has a long cylindrical body and a pharynx of two rings with horny or soft papillary structures, whose arrangement provides the diagnostic characters of the family ^[2].

In Peru it has been studied mainly at Los Yuyos beach, in Barranco (Lima), where a team from the Universidad Nacional Federico Villarreal used it as a test organism for the toxicity of a detergent ^[3]. Outside the American Pacific it is reported from the Caribbean, South Africa, Madagascar and the Red Sea ^[4].

The genus Pseudonereis is recognised by the paragnaths of the pharynx, which form comb-like rows in areas II to IV of the maxillary ring, and by the dorsal notopodial ligules, which grow much larger toward the rear of the body ^[4].

In specimens studied on the coast of Pakistan, the body was 5.2 to 6.0 cm long with 72 to 80 chaetigers; it was brown in alcohol, soft and translucent at mid-body, with no pigmentation. The prostomium was as long as wide, with cirriform antennae half its length, and the longest tentacular cirri reached chaetiger 4 ^[4]. In the pharynx, area I bore 2 cones; areas II, III and IV had 3, 4 and 5 comb-like rows; area V had 1 cone; and area VI had 1 large transverse paragnath ^[4]. Colombian specimens showed the same comb-like row counts in areas II to IV ^[2].

It differs from Pseudonereis variegata in having a longer dorsal cirrus and fewer paragnaths in area IV; in areas VII and VIII, Pseudonereis variegata has at least twice as many paragnaths, arranged in a double row ^[4]. The same authors consider that a specimen from Iquique, in northern Chile, described earlier under this name, differs in several characters and probably belongs to another species ^[4]. They also note that cryptic species complexes are very likely within Pseudonereis, something DNA data could help to confirm ^[4].

In the Pacific the species is listed from the Galápagos Islands and Baja California, and it is also reported from the Caribbean, South Africa, Madagascar and the Red Sea ^[4]. A note published in 2012 recorded it for the first time in the southern Colombian Caribbean, in Córdoba department ^[2]. Specimens collected in January 2022 on the Makran coast of Pakistan, on a rocky intertidal shore, were also identified as this species ^[4].

For Peru, those authors recall that a redescription of Peruvian specimens had already been published in 1909 ^[4]. The Peruvian study cited in this account comes from Los Yuyos beach, in Barranco (Lima), at about 12°09' S ^[3]. Elsewhere in its range the habitat described is rocky shore: in Colombia it was collected among red algae mats of the rocky intertidal at 0.1 to 0.2 m depth ^[2], and in Pakistan under stones at low tide ^[4].

The authors of the Lima study describe this worm as benthic and abundant, and as part of the diet of the squid Doryteuthis gahi ^[3]. The study does not measure how much it contributes to the squid's diet ^[3].

The individuals used in the Lima test averaged 20.4 mm in length with a standard deviation of 8.8 mm ^[3]. In Colombia it was collected among red algae of the rocky intertidal ^[2].

Not medical advice. For a sting, a poisoning or an allergy, seek medical care.

In a laboratory test, 120 worms from Barranco were exposed for 24, 48 and 72 hours to a powder detergent whose active ingredient is sodium dodecylbenzene sulfonate, at 5 concentrations from 62.5 to 1000 mg/l ^[3]. The median lethal concentration was 744.45 mg/l at 24 h, 384.38 mg/l at 48 h and 102.48 mg/l at 72 h ^[3]. The authors classed it as slightly toxic (by toxicity units) and, under European regulation 1907/2007/EC, which they used, as not classifiable ^[3].

The worm proved less sensitive than the mussel Semimytilus patagonicus tested in the same study: at 48 h the mussel was affected 6.2 times more, and at 72 h 2.9 times more ^[3]. The authors add that it was also less sensitive than other polychaetes tested in the literature, and link this to the use of adults, since larval or smaller forms are recommended for such tests ^[3].

The authors of the Lima study propose using this worm, together with the mussel, as a tool for assessing the acute toxicity of detergents in the sea, because it is abundant, lives on the bottom and is prey of the squid Doryteuthis gahi ^[3]. This is a research proposal: the article describes no monitoring programme under way, and it notes that no tests of this kind had previously been done in Peru with the species ^[3].

The only Peruvian place with coordinates in the sources for this account is Los Yuyos beach, in Barranco (Lima), at 12°09' S and 77°01' W, where the authors collected the worms with a plastic spatula ^[3]. The article describes neither the microhabitat nor the sampling date, so it does not tell where to look on that beach. In other countries the species was found under stones and among algae of the rocky intertidal ^[4],[2]; that is a habitat pattern, not a guarantee of seeing it at a given site ^[4].