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A Morphology of Lepidonotus allmaniella


Aishah Tul-Firdaus Abdul Khalid 2017

Summary

Sub-family of specimen was determined to be Lepidonotinae, based on dichotomous key by Fauchald K. (1977). Determination of genus proved to be difficult due to contradictions between desrcibed traits and those found in specimen. Sub-par quality images of holotype scaleworm specimen obtained further complicates identification of scaleworm species. Hypothesised species will be discussed in Systematics. Due to insufficient knowledge on Lepidonotus Allmeniella, most information provided on this page is based on other similar Polynoidae where possible.


Polynoids are scale-worms that are active carnivores. Their well-developed heads are followed by segmented bodies that each have a pair of well-developed parapodia. They can be free-living or lives commensally with other invertebrates, and are found in various locations worldwide. These scaleworms occupy a wide range of habitats, from intertidal zones to deep sea depths. This particular specimen was found among clumps of bivalves from the reefs of Heron Island. 


Physical Description

Lepidonotus sp. has 12 pairs of elytra (Figure 1), that are partly bordered by branchiae (Figure 3). Its elytra are ornamented by tubercles, macro and micro, in a scattered fashion. Turbercular projections seem to be conical and framed with subtly undulate aureolas. 

Anterior end is equipped with a bilobed prostomium that has two pairs of eyes. A pair of anterior antennae is attached to prostomium by ceratophores. Other projections at anterior end include a median antenna,  a pair of palps, a pair of biramous ventral cirri and uniramous cirri (Figure 4, 5 and 6).

Specimen has a pair of parapodia on each of its 26 segments (Figure 2). Its parapodia are biramous. neuropodia is more outward than notopodia, and both are compound, with numerous setae. notosetae slightly thinner or the same thickness as neurosetae. Each parapodia has a ventral cirrus (Figure 8).

The posterior end of Lepidonotus sp. has a pair of pygidial cirri and flanked by three pairs of shorter dorsal cirri (Figure 7).

1
Figure 1
2
Figure 2
3
Figure 3
4
Figure 4
5
Figure 5
6
Figure 6
7
Figure 7
8
Figure 8

Ecology

Habitat

Similar to how they are found throughout the world, they also occupy a variety of habitats. Namely in marine waters, from intertidal zones and coral reefs to ocean vents in deep water; and communally live with various marine invertebrates such as asteroids, holothurians and sponges.

The specimen was found among a clump of bivalves that were separated. Members of the Polynoidae also favour living amongst algae, rock crevices like in Figure 9, and burrows of other animals (Pamela L., 2000)




9
Figure 9

Communal Living


  In Polynoidae, there are 4 types of communal living. They can behave as ectoparasite of host or feed on food of host if they are carnivores. They can also feed on faecal matter of host. In the case that the host is a deposit-feeder, they can feed on is pseudo-faeces (Pamela L., 2000)

Life History and Behaviour

Reproduction

Harmothoinae, a close taxonomic group to Lepidonotinae are seasonal breeders. Here, the reproduction strategy of Harmothoe imbricata is used as an example.

They reproduce by spawning during the breeding season that takes place in Spring. Most polychaetes do not survive till the next spawning season. Males carry mature sperm throughout the season and only deposit a small proportion of gametes at each spawning. In females, the eggs start maturation in September, and each female releases two batches of spawns. 


They develop under the scales of the female as a mass which is held together by an adhesive layer that surrounds each egg.


The male stays on the dorsal surface of the female while waiting for the female to spawn. When she does, the male deposits its sperm over the eggs. The pair of polychaetes then separate. 

The sperm has an acrosome, which is an organelle that covers the head of  the sperm and contains enzymes that will allow it to breakdown the protective coating of the egg to allow access. The long acrosome of the sperm will penetrate the adhesive layer of the egg to fertilise it (Figure 10).  

The embryos then stay protected under the scales of the mother until they develop into larvae. The trochophore larvae are then released into the sea, where they undergo metamorphosis, and then settle (Garwood, 1980).

Variations in larval development and breeding seasons has been recorded. They might have a planktonic larval phase or that the larva completely develops while it is protected in the female’s body. Also, some breeding seasons extend for two months, some were observed to happen in Winter or that the successive breeding periods happen two months apart (Daly, 1972).

Variations in the breeding periods can be justified by the fact that they are controlled by an internal clock mechanism. This mechanism synchronises the event between the individuals of a population. In turn, the internal clock is affected by changes in the local environment, like temperature and length of daylight (Garwood, 1980).

Settlement is followed by maturation and subsequent breeding when the season comes (Garwood, 1980)

10
Figure 10

Anatomy and Physiology

Due to insufficient knowledge on Lepidonotus Allmeniella, there is no accurate information on the Anatomy and physiology in the species.

Biogeographic Distribution

Presence of Lepidonotinaehas been recorded in various areas worldwide. Among them are the NorthAtlantic Ocean (Bellan, 2001), the MediterraneanSea and South America (José Eriberto De Assis, 2015) , the North Sea (V., 2007).
 

In Australia alone, as much as 22 genera and 81 species of Polynoidae has been recognised. They have been recorded in Western Australia, New South Wales, Queensland and Victoria, among others (Day & Hutchings, 1979).

Evolution and Systematics

Diagnostic features used to distinguish between genera of Polynoidae are as follows:

  • number of pairs of elytra
  • coverage of dorsum by elytra
  • point of insertion of lateral antennae
  • compared thickness of notochaetae and neurochaetae
  • chaetal ornamentation

(Pamela L., 2000)

Using the dichotomous key from Fauchald, K. (1977) of the following features: 

  1. Neurosetae unidentate without accessory teeth.
  2. Has ventral cirrus and smooth ventrum.
  3. Palps well developed
  4. lateral antennae attached to prostomium distally by ceratophores (Figure 11). 
  5. Parapodia bilobed with compound setae
  6. notosetae thicker than neurosetae
  7. neuropodia longer than notopodia.
  8. Prostomium anteriorly produced and forms large bilobes with antenna distally attached.
This led to the classification Allmaniella of Lepidonotinae. 

According to the mentioned book, a feature of Allmaniella is that it has between 15 to 30 pairs of elytrae. However, the specimen in figure 1 only has 12 pairs of elytrae. 

Other genuses that are characterised by 12 pairs of elytrae includes Chaetacanthus and Euphione.  Both genuses would correspond with the specimen in that it has 26 segments. But The former would differ in that it has coarsely spinose neurosetae and it is not confirmed that the prostomium belonging to the latter genus would be bilobed like the prostomium of the specimen.

Assuming that discrepancies are due to shortcomings on my part, I decided that the first hypothesis, that the specimen is a Lepidonotus Allmaniella, is most correct. 

Following that, the genus Allmaniella is not a well-studied taxonomic group. Some species of Harmothoe are synonymous to Lepidonotus sp. For example Harmothoe imbricata and Lepidonotus cirratus; and Harmothoe impar and Lepidonotus impar (Kluijver, n.d.).

With the exception of several species of Polynoidae; namely Harmothoe imbricata and Lepidonotus squamatus, the Family is not yet well-studied. There is still revising and redescription of classifications that are unresolved. Similarly, the genus Allmaniella is not a well-studied.  

Thus, most information on this page will not be specifically on Allmaniella, but instead on close Polynoidae taxonomic groups.




11
Figure 11

Conservation and Threats

Due to insufficient knowledge on the diversity and biology of Lepidonotus allmaniella, there is no data on existing threats and conservation efforts towards this species.

References

Bellan, G., 2001. European registerof marine species: a check-list of the marine species in Europe and abibliography of guides to their identification.. In: M. e. al., ed. Polychaeta,in: Costello. s.l.:Collection Patrimoines Naturels, pp. 214-231. Available online at http://www.vliz.be/imisdocs/publications/77636.pdf.[Accessed June 2017].

Daly,J. M., 1972. The maturation and breeding biology of Harmotho~ imbricata(Polychaeta: Polynoidae). Marine Biology, Volume 12, pp. 53-66.

Day,J. H. a. P. A. H., 1979. An annotated check-list of Australian and New ZealandPolychaeta, Archiannelida and Myzostomida. Records of the Australian Museum,32(3), pp. 80-161. Available online at https://australianmuseum.net.au/uploads/journals/17532/203_complete.pdf [Accessed 2 June 2017].

Fauchald,K., 1977. THE POLYCHAETE WORMS . In: R. E. Ostermeyer, ed. Definitions andKays to the Orders, Families and Genera. Los Angeles: Natural HistoryMuseum of Los Angeles County, pp. 55-65.

Garwood,P. R., 1980. THE ROLE OF TEMPERATURE AND DAYLENGTH IN THE CONTROL OF THEREPRODUCTIVE CYCLE OF HARMOTHOE IMBRICATA (L.) (POLYCHAETA: POLYNOIDAE). Journalof Experimental Marine Biology and Ecology, Volume 47, pp. 35-53.

JoséEriberto De Assis, R. J. d. B. M. L. C. a. J. R. B. d. S., 2015. A catalogue ofthe scaleworm genus Lepidonotus (Polynoidae, Polychaeta) from South America,with two new records for Brazilian waters. Zookeys, Volume 533, pp.63-98. doi: 10.3897/zookeys.533.6184 Availableonline at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4669924/ [Accessed 2 June 2017].

Kluijver,M. d., n.d. Marine Species Identification Portal. [Online]
Available at: http://species-identification.org/search.php?search_for=lepidonotus&x=0&y=0
[Accessed 2 June 2017].

PamelaL., B. G. J. B. R. a. C. J. G., 2000. POLYCHAETES AND ALLIES: THE SOUTHERNSYNTHESIS.. In: P. R. Jones, ed. FAUNA OF AUSTRALIA. POLYCHAETA,MYZOSTOMIDA, POGONOPHORA, ECHIURA, SIPUNCULA.. Canberra: CSIRO, pp.152-157.

V.,Z., 2007. Biodiversity of shipwrecks from the Southern Bight of the North Sea.In: PhD Thesis. s.l.:University of Louvain, Department of Biology, p.343.