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Linopherus sp. Quatrefages, 1866

Leo Chiu-Leung 2016


This specimen is an annelid polychaete, and is believed to be a part of Genus Linopherus (Quatrefages 1865). It is a small segmented, free living, cryptic, benthic and part of the Amphinomidae family. It has 13 segments, with lateral parapodia on each segment. There are 3 principle forms of the setae; Harpoon, long and short bifurcate structures. Linopherus has a southern hemisphere distribution, and are not threatened under current conservation standards. 

Physical Description


The specimen showed color changes that can be attributed to the preservation process where 4% paraformaldehyde with MOPS fixation buffer (4% PFA) was used. The state prior to preservation is shown below; red coloration is present on the prostomium and pygidium segments as well as on the branchiae on each segment. Dark coloration is present in the center of the specimen, in a line; likely indicating the intestinal system. A blue sheen is also observed on the cuticle. The rest of the body coloration was lightly colored, including the setae; which were clear. 

Figure 1


The prostomium is composed of plate segments, split down the middle and the largest plates at the head of the specimen; furthermore it is sunken into the first segment of the polychaete. It has 6 stubby antennae lining the edges of the prostomium; visible in the figure below, with a further 2 antennae located on the underneath. The caruncle is not immediately obvious and is a small protrusion located underneath the prostomium that does not extend past the prostomium onto the segments. 2 dark red eye spots were also visible prior to preservation.  The caruncle is not obvious, as it is does not extend past the segmentation or outward. It should also be noted that the prostomium is visually similar to the posterior segment in the preserved state but not immediately obvious prior to preservation. 
Figure 2


Metamerism is exhibited with 13 segments on the specimen including the segments that the prostomium and pygidium segments are sunken into. The prostomium and pygidium are different for the obvious reasons. The body dimensions of the specimen are long in terms of the anterior-posterior and compacted in the dorsal-ventral to make an oval.

A ridge is visible running the dorsal of the segments as part of the structural support of the cuticle, visible in the title image. The setae are located on the lateral tufts along the body, both the dorsal and ventral surfaces are clear of structures. Prior to preservation the chaeta held the typical fan shaped formation, as to maximize the size that was present of the neuropodia. This was also likely to aid the locomotion, as the ventral tufts did not contain clear locomotor structures.

The chaetae are also used as a defense mechanism which is covered in the Life History and Behavior section below. 

Figure 3


Prior to preservation, the posterior end was much thinner than the medial and anterior segments as the body thinned down closer to the posterior end. There were also more particles attached to the posterior pre-preservation, likely linked to biological functions. In the preserved state, the pygidium that looks similar to the prostomium; it is also recessed into the last segment this is due to contraction of the entire body into a defensive posture. 


The niche that the specimen best fits in would be of the cryptic benthic predator.

Like most other polychaetes in the Amphinomidae, the body form of the suggests that it is benthic and free living due to being compacted in the dorsal-ventral axis but protruding setae. From examples in the family, the specimen is also likely an omnivore.

Life History and Behaviour

In terms of reproduction, the specimen is likely dioecious, but also able to reproduce asexually by regeneration or fission.

As mentioned before the setae are the defense mechanism for Polychate; they curl as to present their setae outwards at potential predators. The harpoon structures that are part of the composition of the setae aid this, making it difficult to remove and inflicting more damage on the recipient. The setae are longer at either end of the polychaete, as to better protect the respective body part. 

Anatomy and Physiology

General information

Polychaetes do not have a diverse array of body plans. Thus, the minute of differences in setae across species aid in their identification. For example; E. laevisetis is noted to not have any harpoon structures in their chaetae (Arias et al., 2013).

The internal organization is typical of polychaetes and is supported by the cuticle acting as an anchor for the muscles and other organs. Cephalization is exhibited at the anterior prostomium, to aid the sensing as it moves through the environment. The digestive system typical of Amphinomidae is described in Beesley and Glasby(2000) and consists of 5 regions: the buccal organ, mouth , esophagus, long intestine, rectum forming a through gut.

On the Linopherus sp. specimen the setae were examined in detail on the anterior, medial, and posterior sections; with both dorsal and ventral tufts being examined. The findings of the examination are presented below.

Chaeta Structures

Short bifurcate: The most robust structures, they are larger and thicker than most of the other structures.
Long bifurcate: These structures were smaller than the short bifurcate setae, and also containing joints as seen above in drawing. 

Harpoon: This is clearly a defense mechanism, with directional hooks as to make removal difficult.

Fleshy structure: These structures are likely cirri; functioning in a chemosensory capacity. They are by far the largest structures that occurred in the setae. 

Spine structure: This structure was only observed in a single sample at the ventral posterior, it is uncertain if it is a spicule or contamination.

Figure 4

Location of Setae

  • Anterior Ventral: Harpoon, long bifurcate
  • Anterior Dorsal: Harpoon, long and short bifurcate
  • Medial Ventral: Harpoon, short bifurcate, fleshy structure.
  • Media Dorsal: short bifurcate, fleshy structure. 
  • Posterior Ventral: Harpoon, long and short bifurcate, spine structure
  • Posterior Dorsal: Harpoon, long and short bifurcate, fleshy structure

 Table 1. Arrangement of setae structures on the specimen of polychaete. 
Dorsal Ventral
Anterior Harpoon, long and short bifurcate Harpoon, long bifurcate
Medial Short bifurcate, fleshy structure. Harpoon, short bifurcate, fleshy structure.
Posterior Harpoon, long and short bifurcate , fleshy structure Harpoon, long and short bifurcate, spine structure

There are a few trends that can be seen in this examination. Harpoon structures are likely common to all setae tufts on the specimen and likely only serve a defensive purpose for the specimen. Bifurcate structures were the most common occurring setae structure. No long bifurcate setae were present in the medial parapodia. Fleshy structures; cirri or branchiae structures etc. appeared after the anterior setae.

Anterior Ventral setae

Types of Setae present: Harpoon, long bifurcate

Figure 5

Anterior Dorsal setae

Types of Setae present: Harpoon, long and short bifurcate

Note: that there seems to be two versions of the short bifurcate setae, as seen in the figure above. There is a smaller bifurcate in comparison requiring an x40 microscope to image as opposed to the x10 on the top. These smaller bifurcate setae were also found much more commonly with a longer stalk than the large versions. 

Figure 6

Medial Ventral Setae

Types of Setae present: Harpoon, short bifurcate, fleshy structure. 

The fleshy structure are likely cirri, as other structures such as the branchiae would need to be more suited towards exchange of oxygen such as increased surface area that the structure does not contain. 

Note: clear size difference between the harpoon structures and the biramous setae - zoom diff is x10 and x40 respectively. 

Figure 7

Media Dorsal setae

Types of Setae present: short bifurcate, fleshy structure. 
Figure 8

Posterior Ventral setae

Types of Setae present: Harpoon, biramous short, long, spine structure 

Note: fewer short biramous structures, more long biramous

Figure 9

Posterior Dorsal setae

Types of Setae present: Harpoon, biramous short, long, fleshy structure

Note: roughly equal amounts of both short and long biramous structures. 
Figure 10
Figure 11

Biogeographic Distribution

There are very few geographical limits to the polychaete habitable range. They occur globally, with species found within the Antarctic Circle. As such, the living ranges are polychaete genus and species are not well defined. Beesley and Glasby (2000) notes that members of Amphinomidae are most commonly occurring in nearshore areas as cryptic species. However, species of Amphinomidae were also noted to occur in marine debris, sediments as well as commensal and parasitic forms living within the mantle cavity of stalked barnacles, and in sea urchin guts.

The above Linopherus specimen was noted to have been collected from within reef rubble. Stored in the University of Queensland biological aquarium, but originating from Heron Island on the Great Barrier Reef. In literature, Linopherus is noted to be occurring in the waters off New Zealand (JERRY D. KUDENOV, 1993). This proximity with the Australian Great Barrier Reef is challenged by the overall eastward current following the south pacific gyre. However, their presence in the correct geographical location means that it is possible that members of the genus could be found on the East Australian Seaboard and the Great Barrier Reef following the return of the south pacific gyre.

Evolution and Systematics

In the world register of Marine Species (WoRMS) (Read and Bellan, 2016), Linopherus is classified as Kingdom Animalia : Phylum Annelida :  Class Polychaeta : Subclass Errantia : Order Amphinomida : Family Amphinomidae : Subfamily Amphinomidae : Genus Linopherus.

While there has been some uncertainty, the general consensus among literature is the family Amphinomidae is situated within Order: Amphinomida (Beesley and Glasby, 2000). It should be noted that however, the Genus: Linopherus has previously been labeled as Genus: Pseudeurythoe in Fauvel, 1932 before reverting to Linopherus under Quatrefages, 1866.

Conservation and Threats

Due to their cryptic nature and diversity of forms, the conservation status of polychaetes; especially the specimen is not well understood. However, it is unlikely that Linopherus sp. and in general family Amphinomidae are threatened at this point, their reproductive ability; supported also by the ability to asexually reproduce means that polychaetes in general have a high fecundity and ability to replace population quickly. However, being a benthic species, the formation of dead zones would likely dramatically affect polychaete populations in general, as they do not possess the capability to quickly evacuate areas that have become anoxic, thus possibly eliminating populations.  

Additionally, as they are connected to the low levels of the trophic chain, they are potential sources of arsenic bioconcentration in the environment(Joel Waring et al., 2005). This is due to their feeding behavior exposing them to arsenic in the environment; in sediments or other smaller filter feeding animals, and they retain the arsenic concentrations even after removal and purification allowing it to be passed up the trophic levels.


Arias, A.,Barroso, R., Anadón, N., Paiva, P., 2013. On the occurrence of the firewormEurythoe complanata complex (Annelida, Amphinomidae) in the Mediterranean Seawith an updated revision of the alien Mediterranean amphinomids. ZooKeys 337,19–33. doi:10.3897/zookeys.337.5811

Beesley, P.L., Glasby, C.J., 2000. Polychaetes & Allies: TheSouthern Synthesis, Fauna of Australia. Canberra : Environment Australia.

Fauchald, K., 1977. THE POLYCHAETE WORMS: Definitions and Keys to theOrders, Families and Genera, Science. NATURAL HISTORY MUSEUM OF LOS ANGELESCOUNTY.


Joel Waring, William Maher, Simon Foster, Frank Krikowa, 2005.Occurence and Speciation of Arsenic in Common Australian Coastal PolychaeteSpecies. Enviromental Chem. 108–118. doi:10.1071/EN05027

Read, G., Bellan, G., 2016. Linopherus Quatrefages, 1866. In: Read,G.; Fauchald, K. (Ed.) (2016). World Polychaeta database. [WWW Document].Linopherus Quatrefages 1866. URL on 2016-05-31