Rosa Rubicondior: Refuting Creationism - Another of Those 'Living Fossils' For Creationists To Misrepresent

Spionid traces on fossilized bivalve shells.

Javier Ortega-Hernandez/Harvard University.

Half-billion-year-old parasite still threatens shellfish | UCR News | UC Riverside

It’s Coelacanth time for creationist disinformers again.

Hilariously, I’ve known creationists claim that the 'fact' that coelacanths haven’t changed for 200 million years somehow proves the “evilutionists” are wrong and that Earth is only 6,000–10,000 years old. How they managed to examine the genome of a 200-million-year-old fossil remains a mystery, but DNA appears to play no part in a creationist’s definition of evolution.

So, for an alternative fallacious argument, here’s an even older fossil that’s still around today, apparently in much the same form as it was almost half a billion years ago. It’s a parasitic worm that attacks oysters. The details have just been published in the journal iScience by scientists led by University of California, Riverside palaeobiologist Karma Nanglu, with colleagues from Harvard.

The parasitic, soft-bodied bristle worm belongs to a group called the spionids. It’s common in today’s oceans and feeds on the shells of mussels and oysters, leaving a characteristic question mark-shaped track in their shells. Their parasitism doesn’t kill the shellfish but probably shortens their lifespan.

Background on the family Spionidae (the “spionids”).

Crassostrea gigas infested with Polydora websteri collected from Blidselbucht at Sylt in the German Wadden Sea. a Inner surface of infested valves of C. gigas showing mud blisters caused by P. websteri; b close up of an opened mud blister inhabited by P. websteri; c overview of a single specimen of P. websteri; and d black lines on the sides of the palps of P. websteri.

© Dagmar Lackschewitz (Waser, A.M., Lackschewitz, D., Knol, J. et al. (2020))

Taxonomy & general morphology

Spionids are marine segmented worms in the phylum Annelida, class Polychaeta (bristle-worms). Within that they belong to the order Spionida and family Spionidae. [1.1]
They typically possess a pair of long grooved feeding palps (tentacle-like appendages arising from the prostomium) which they use to forage. [2.1]
Many spionids live within tubes or burrowed structures in sediment or hard substrates. Their bristles (chaetae) and parapodia (lateral lobes) are used for movement and for boring/anchoring. [3.1]
Example morphological data: for the species Polydora ciliata (a spionid): up to ~3 cm long, ~0.7–1 mm wide, up to ~180 segments, with two long palps and a body that burrows into substrates including mollusc shells. [4.1]

Habitat & ecology

Spionids are cosmopolitan (found globally) and most commonly inhabit soft bottoms (sandy or muddy sediments) in littoral or neritic marine zones. Some species tolerate estuarine/low-salinity environments. [3.1]
Many live in tubes constructed by cementing sediment grains with mucus. Others bore into hard substrates (e.g., calcareous rocks, shell surfaces) particularly some species in the genus Polydora. [3.1]
Feeding modes: deposit-feeders and/or suspension-feeders; some specialise in interface feeding (switching between deposit and suspension). [2.1]

Shell-boring / parasitic behaviour

A subset of spionids are shell-borers: they tunnel into mollusc shells (oysters, mussels), weakening the shell rather than consuming the soft tissue of the host. These tunnels may reduce host fitness, increase vulnerability to predation, or affect commercial value of shellfish. [5.1]
Example: Polydora websteri is recorded as a shell-boring spionid in oyster aquaculture, creating “mud blisters” in shells and thereby affecting marketability. [5.1]
Recent fossil evidence suggests such shell-boring behaviour has deep evolutionary roots: a recent study found “question-mark” shaped burrows in ~480-million-year-old (Early Ordovician) mollusc shells, interpreted as traces of spionid-type worms. [6.1]

Significance of the fossil record & evolutionary implications

The discovery of these trace fossils expands the known antiquity of shell-boring spionid behaviour far beyond previous records. The study suggests that spionid-like worms were parasitising bivalves during the Early Ordovician (~480 Ma). [7.1]
From that paper: “This group of worms hasn’t changed its lifestyle in nearly half a billion years.” [6.1]
For your narrative (and for the creationism-refuting angle): these worms demonstrate continuity of a parasitic ecological strategy through deep time, surviving multiple mass‐extinction events while preserving the shell-boring behaviour.

Relevance for your blog post and book themes

The spionids serve as a strong example of evolutionary continuity: rather than dramatic morphological stasis being a “proof” against evolution (as some creationists argue), here we have a group retaining a successful ecological strategy over ~500 million years — which is entirely consistent with evolutionary theory (i.e., retention of a successful form/behaviour, not “no change at all”).
The shell-boring behaviour is an ecological interaction — host/parasite — which underlines the dynamic nature of evolution over time, rather than a static “creation” snapshot.
The fact that modern aquaculture diseases/parasites have ancient analogues emphasises the evolutionary deep‐time dimension of life and its adaptations.

The researchers identified similar tracks in fossil shells dated to about half a billion years old. Their research is explained in a UC Riverside news release by Jules Bernstein.

Half-billion-year-old parasite still threatens shellfish
Half-billion-year-old parasite still threatens shellfish
A new study has unexpectedly discovered that a common parasite of modern oysters actually started infecting bivalves hundreds of millions of years before the dinosaurs went extinct.

The research, published in iScience, used high-resolution 3D scans to look inside 480-million-year-old shells from a Moroccan site known for its exceptionally well-preserved sea life. The scans revealed a series of distinctive patterns etched both on the surface of the fossils and hidden inside them.

The marks weren’t random scratches. We saw seven or eight of these perfect question mark shapes on each shell fossil. That’s a pattern.

Karma Nanglu, lead author.
Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology
Harvard University
Cambridge, MA, USA.

It took us a while to figure out the mystery behind these peculiar-looking traces. It was as if they were taunting us with their question mark-like shape. But as often happens, we came across the answer while deep in obscure literature before our eureka moment.

Javier Ortega-Hernandez, co-author
Museum of Comparative Zoology and Department of Organismic and Evolutionary Biology
Harvard University
Cambridge, MA, USA.

The research team determined the marks are the work of a soft-bodied marine bristle worm, still common in today’s oceans. The worms, which belong to a group called the spionids, live and feed on mussels and oysters without killing them, though they are still destructive.

They parasitize the shells of bivalves like oysters, not the flesh of the animals themselves. But damaging their shells may increase oyster death rates.

Karma Nanglu.

The shells examined in the study belonged to an early relative of modern clams that thrived during the Ordovician, a period of rapid ecological change.
This is a time when ocean ecosystems got more intense. You see the rise of mobility, predation, and, clearly, parasitism.

Karma Nanglu.

The researchers considered the possibility that the question marks on the fossils were made by the shellfish themselves or by some other kind of organism. But the evidence was strongest for the spionid explanation.
There’s one image in particular, from a study of modern worms, that shows exactly the same shape inside a shell. That was the smoking gun.

Karma Nanglu.

Beyond the thrill of identification, the discovery offers a rare evolutionary insight.

This group of worms hasn’t changed its lifestyle in nearly half a billion years. We tend to think of evolution as constant change, but here’s an example of a behavior that worked so well, it stayed the same through multiple mass extinction events.

Karma Nanglu.

To get a look inside these question mark-shaped traces, the researchers used a method similar to a medical CT scan but much more detailed, called micro-CT scanning. This revealed another discovery, that more bivalves with more parasites were hidden from view inside the rock, where the fossil layers were stacked like a multilayered cake.
We never would’ve seen this without the scanner.

Karma Nanglu.

The parasite’s life cycle also offered a key clue to its identity. It appears to have followed a consistent pattern: beginning life as a larva, settling onto a host shell at a specific time and place, then dissolving a small area to anchor itself. As it grew, it burrowed farther into the shell, forming the distinctive question mark shape.

No other known animal creates this exact pattern.

If it’s not a spionid, then it’s something we’ve never seen before, but it would have to have evolved the same behavior, in the same place, in the same way.

Karma Nanglu.

The same shell-burrowing behavior seen in the fossils still affects oysters today. Though spionid worms don’t feed on the animals directly, the structural damage they cause can lead to higher mortality in commercial fisheries.

This parasite didn’t just survive the cutthroat Ordovician period, it thrived,” Nanglu said. “It’s still interfering with the oysters we want to eat, just as it did hundreds of millions of years ago.

Karma Nanglu.

The fossil site in Morocco is renowned for offering snapshots of long-lost behavior. Other finds include animals on the remains of squid-like creatures, providing rare evidence of ancient inter-species interactions frozen in time.
You’re lucky to get any record of an animal from that long ago, but to see evidence of two animals interacting? That’s gold.

Karma Nanglu.

Publication:
Nanglu, Karma; Waskom, Madeleine E.; Losso, Sarah R.; Ortega-Hernández, Javier
A 480-million-year-old parasitic spionid annelid
iScience (2025) 28(11); DOI: 10.1016/j.isci.2025.113721.

Highlights

The first evidence of parasitism from best preserved Ordovician fossil site, Fezouata
Parasitic spionids occurred ∼100 million years older than previously known
Life history strategy of these worms has remained stable for 480 million years

Summary
The Paleozoic fossil record provides unique insights into the evolution of life history traits through the direct preservation of interspecific interactions in deep time. However, evidence of direct interactions between different species is relatively rare even among localities with exceptional soft-tissue preservation. Here we provide evidence of parasitic organisms from the Fezouata Shale biota of Morocco. Seven specimens of the bivalve mollusk Babinka show highly characteristic, question mark-shaped shell borings consistent with those produced by modern and fossil parasitic spionid polychetes. This suggests that the spionid polychetes, or polychetes with behavior consistent with spionids, were present in the Early Ordovician, a significant biostratigraphic shift in their temporal origins from their accepted Devonian occurrence. Many unique life history strategies which were significant components of the Fezouata Shale biota remain undiscovered, despite the high concentration of taxonomic attention on the site.

Graphical abstract

Introduction
Evidence of parasitic ecological interactions in the fossil record is critical for understanding how the life history strategies of animals have evolved and to unveil the full complexity of the ecosystems in which they lived.¹ Despite evidence for instances of ancient parasitism among broad taxonomic groups² across the Phanerozoic, it is significantly rarer in sites of exceptional soft-tissue preservation.^1,3,4,5 Here, we report an exceptionally preserved instance of a distinctive shell boring parasitic behavior between a spionid-like polychete worm and the bivalve mollusk Babinka from the Early Ordovician (ca. 480 million years ago) Fezouata Shale biota in Morocco. The discovery of this shell boring association carries three main implications for understanding the evolutionary history of parasitism. The morphology of the fossilized borings indicates behavioral complexity previously unknown from Paleozoic polychetes.⁵ The presence of boring traces in Babinka documents the first evidence of parasitic behavior from the Fezouata Shale biota,.⁶ and the earliest instance of shell boring parasites on mollusks in the fossil record.^1,5,7 Finally, the boring traces extend the earliest evidence for the polychete order Spionida into the late Tremadocian.^1,5,8

Figure 1 Fossiliferous slab with specimens of the bivalve mollusk Babinka from the Fezouata Shale biota (Early Ordovician) showing evidence of fossilized spionid-like borings

(A) Babinka cluster; from left to right, MCZ.IP.202859, MCZ.IP.202860, and MCZ.IP.202861.
(B) Tomographic reconstruction of fossiliferous slab showing additional evidence of spionid-like borings preserved as iron oxides within the rock matrix.
(C) Magnification of spionid-like borings within rock matrix. MCZ.IP.202862 (left) and MCZ.IP.202863 (right).

Figure 2 Specimens of the bivalve mollusk Babinka from the Fezouata Shale biota (Early Ordovician) showing evidence of fossilized spionid-like borings

(A) From left to right, MCZ.IP.202864 and MCZ.IP.202865.
(B) Tomographic reconstruction of fossiliferous slab spionid-like boring preserved as iron oxides in MCZ.IP.202864.
(C) Tomographic section of boring specimen showing high density of iron oxides relative to aluminosilicate matrix.
(D) Magnification of isolated spionid-like boring in MCZ.IP.202864.

Figure 3 The extant spionid genus Polydora and biostratigraphic distribution of spionid-like borings during the Paleozoic

(A) Polydorid U-shaped shell borings on Pacific oyster Magallana gigas (image courtesy of V. Radashevsky; see Radashevsky et al.¹⁶).
(B) Adult of the spionid polychete Polydora hoplura (image courtesy of V. Radashevsky; see Radashevsky et al.¹⁶).
(C) Simplified geological timescale of evidence for bivalve shell parasitism during the Paleozoic^1,5,19; fossil traces in Babinka from the Fezouata Shale represent the earliest example of shell boring on bivalve mollusks to date, and the oldest record of spionid-like borings.

Nanglu, Karma; Waskom, Madeleine E.; Losso, Sarah R.; Ortega-Hernández, Javier
A 480-million-year-old parasitic spionid annelid
iScience (2025) 28(11); DOI: 10.1016/j.isci.2025.113721.

Copyright: © 2025 The authors.
Published by Elsevier Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

Spionids are a family of marine bristle worms (Annelida: Spionidae) that have been quietly doing their thing for almost half a billion years. These soft-bodied worms are still common in today’s seas, living in tubes or burrows and using a pair of long, grooved palps to feed. Some species are “shell-borers”, tunnelling into the shells of oysters and mussels and leaving the same question mark-shaped scars now as they did hundreds of millions of years ago.

Creationists love to claim that when a species appears “unchanged” in the fossil record, it somehow disproves evolution. Yet the persistence of spionid worms is a textbook example of why that claim is nonsense. Evolution doesn’t demand that every species must constantly change its appearance — only that it must remain well adapted to its environment. When a design works, natural selection favours keeping it. These worms found an effective niche early on and have simply carried on exploiting it.

In other words, their long survival isn’t evidence against evolution, but a triumph of it. What creationists see as “stasis” is really evolutionary success: a strategy so efficient it has withstood half a billion years of shifting oceans, climate change, and mass extinctions. The spionids aren’t fossils that refused to evolve — they’re survivors that got evolution right the first time.

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