#annelida

northern feather duster worm, eudistylia vancouveri

Neoleanira

A genus of marine bristle worms found in the Atlantic and Pacific Oceans.

Worm time. This is Proceraea okadai, a segmented worm from the family of Syllidae. They can grow up to 1.3 cm in length [1].

Like other syllid worms, P. okadai reproduce by epitoky, which is a process whereby they modify parts of their body to become suitable for reproduction and these parts (called stolons) then split off from their main body to go off and find an oppositely sexed stolon to reproduce. P. okadai does indeed have two sexes, and it is possible to distinguish male and female stolons. What exactly P. okadai does with the eggs and larvae after fertilisation has not been studied, but similar species have been known to either have the female carry them or to lay them onto hydroids, where they would feed and develop [1].

They were initially discovered in Japan, but seemed to have drifted across the Pacific, as they were found on the North American coast near Washington and San Francisco in the USA in the early 2000s [1]. Their genetic material has also been recorded to be in the Salish Sea, an area in the Northeastern Pacific, as recently as 2018 [2].

As can be seen by their distribution, they mostly inhabit temperate waters in intertidal zones. While their dietary habits haven’t been studied directly, all other species in their subfamily (Autolytinae) are carnivorous, feeding on hydroids and perhaps bryozoans, so it is a fair guess to say that they are too [1].

I'll do typical earthworms, Order: Crassiclitellata.

Rhynchelmis

An genus of aquatic marine worms from the northern hemisphere.

A bit different from our vertebrates over the last few days, today we’re looking at Allonais inaequalis, a species of aquatic freshwater worm [1], whose main reason for appearing in the scientific literature is researchers liking to poison them (more on that later).

They are around 3-9 mm long, colourless, and mostly reproduce asexually [2]. They have been found on decomposing lotus plants, as well as on filamentous algae within the state of São Paulo [3]. They have been recorded across North America, South America, Africa, Australia, South East Asia [4], and China [5].

As they are rather easy to collect and keep in lab conditions, this has led to them being considered a good candidate as a toxicity test organism, meaning we can purposefully fuck up their water quality in a controlled setting to see how that may impact them, which can indicate what effects may befall ecosystems more broadly. From the studies that proposed them as candidates, we know that half of them will die at KCL solutions of 3.5 g/L and ZnCl₂ solutions of 0.16 g/L [4], and their growth starts being inhibited at CuSO₄ concentrations of 0.247 mg/L, ZnCl₂ solutions of 2.7 mg/L, and KCl solutions of 1.36 g/L [2].

Since then we’ve had actual experiments intending to measure water quality tell us that at metal salt levels of 10 mg/L, copper and mercury cause many of them to die, cadmium reduces their growth, and honestly they’re chill with manganese exposure (even at 100 mg/L of MnSO₄). The pesticide Carbofuran also messes with their growth, but Diuron seems to be fine, at least at the concentrations tested in the study [6]. Antibiotics can negatively affect their reproduction, even after a 10 day recovery period [7], but they’re okay with eating polyethylene microplastics (at least in concentrations of up to 320 mg/L) [8].

Their use as a lab test organism has meant that more research has been done as well. They were originally made a species just based on their outside appearance, but after some genetic testing, it appears there may be a cryptic species situation going on, where some of the worms, especially comparing populations in China vs Peru, may not be the same species after all [5]. The fact that A. inaequalis may be multiple species feels particularly ironic since their first description in 1911 didn’t even frame them as their own species, but rather just a variation of Nais pectinata [9].