Author: (Eliot, 1903)

Order: Nudibranchia  Family: Aegiridae

Maximum Size: 95 mm

Sightings: Sunshine Coast, Capricorn/Bunker Group GBR, Whitsundays

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Aegires gardineri (Eliot, 1903)

Aegires are phanerobranch dorid nudibranchs. The phanerobranchs are unable to retract their gill into a distinct pocket below the surface of the mantle. This is considered a primitive feature. The Aegires, along with the Hexabranchus, are the only phanerobranchs that feed upon sponges.

Aegires gardineri is a large nudibranch recorded up to 95 mm in length. The body is high in profile, firm and stiffened with small spicules. There is no distinct notal margin. The dorsal surface bears blunt nodules or pustules of varying size. These pustules may form a number of ridges by virtue of their proximity and alignment. The ridges, if present, are most noticeable upon the anterior half of the animal. There may be up to five; a midline ridge running from anterior to and between the rhinophores posteriorly to the gill-shield and another two on each side, one from the rhinophores posteriorly to the gill-shield and the other more laterally but tending to also join up with its opposite ridge around the anterior of the rhinophores. A posterior ridge on the midline of the tail is sometime observable. There are also other pustules of irregular distribution. The tail, extending posteriorly from the gills is bluntly rounded and comprises half the animal’s length. The unmarked sole of the foot covers the entire ventral surface.

The rhinophores are small, tapered, smooth and retractable with pockets that have raised rims and are protected laterally by a large raised prominence comprised of fused pustules, more distinct in some specimens than others. Early workers referred to these as valves or flaps indicating they might seal the pocket when the rhinophores are retracted but I have never observed this occurring. The numerous finely-branched gills are located midway down the length of the body and are shielded anteriorly by three large elevated lobes. These lobes, forming a gill-shield, also carry pustules, and are directed posteriorly to partially cover the gill branches. The gills are not retractable but can contract somewhat under the overhanging shield.

The basic colouration is yellow and black but the percentages of each varies. The background colour is yellow, that may range from vivid to “washed-out”, overlaid with large patches and smaller spots of black but their number and size vary greatly. The black may be solid or in some specimens less so, such that the underlying yellow shows through as a reticulation, the black in these instances appearing more brownish. The anterior surface of the gill-shield invariably carries one of the black patches as a transverse bar. Variations include specimens with almost no black pigment (rarely none), specimens that are almost entirely black and specimens where the yellow is replaced by a greyish white (that may possibly be just a complete lack of yellow pigment). The rhinophores are yellow, at times with a black tip. The gills are a translucent yellow.

Juvenile specimens may have completely black rhinophores that eventually change to all yellow in the adult. It has also been suggested that the amount of black covering over the body may increase with the maturity of the animal.

Although Aegires gardineri may at times appear stiff and almost lifeless in situ it can, when searching for a food source, be seen moving slowly across the substrate.

Distribution is broadly the Indian and western Pacific oceans.

Aegires gardineri preys upon sponges of the Leucettidae family with species of Pericharax and Leucetta genera being reported.

The spawn is laid as a coil, on edge, as a bright yellow wavy ribbon.

– Originally described as: Notodoris gardineri
– Notodoris megastigma Allan, 1932 is a synonym described from specimens collected at North West Island, Capricorn Group, GBR.
– Notodoris gardineri form nigerrima is a variation described by Yonow, 1994. Variety names such as this have no official standing in taxonomic nomenclature. It is interesting to note however that this almost entirely black form is only recorded from the Maldives.

Other described species of similar size and appearance include: Aegires minor, however that species has black lines rather than patches of black; Aegires citrinus, however that species is uniformly yellow without any black patches, spots or lines and is more elongate in shape.

Comment about Aegires – Notodoris
Some of the literature uses Notodoris for certain species. Some workers follow the latest published names slavishly. Rudman is of the opinion that: “Part of the scientific method is to test hypotheses. If we just accept things as soon as they are proposed, we miss out a vital step in the scientific method.”

Fahey & Gosliner, 2004 synonmyised Notodoris with Aegires.

Moro & Ortega, 2015 attempt to reinstate Notodoris on the basis of (a suggested translation from the Spanish follows) “…the shape of the radicular teeth (acicular or hooked) and the mandibular (thickened or folded) architecture is so different in the species of both genera that we understand that the synonymy is unjustified and must be kept separate,…”

However Fahey & Gosliner were most careful in proposing the synonym. In their 2004 paper: A Phylogenetic Analysis of the Aegiridae Fischer, 1883 (Mollusca, Nudibranchia, Phanerobranchia) with Descriptions of Eight New Species and a Reassessment of Phanerobranch Relationships, they undertook a phylogenic analysis using no less than 64 characters. The results indicated that: “Notodoris is nested in Aegires.” and “Notodoris clusters together in a monophyletic clade that is basally situated to the Indo-Pacific Aegires. Synapomorphies that unite the Notodoris clade are the presence of large, firm gill protective structures (#19), radular teeth that have one spur below the main cusp (#31) and reduced eyes (#46). In all analyses performed for the present study, the Notodoris clade is nested within the Aegires sharing multiple synapomorphies with Aegires.”

So Fahey & Gosliner do agree that there is a difference and in fact refer to all those species previously known as Notodoris as a distinct clade but nevertheless still nested within the Aegires.

The upshot here is that the structure of the radula is but a single character that Moro & Ortega use, and place undue emphasis upon, in attempting to reinstate Notodoris. This would appear to be mediocre taxonomy at best.

Fahey & Gosliner based their findings on a phylogenetic analysis. GenBank DNA sequences point to exactly the same outcome – a clade within Aegires. Separating that clade out of Aegires as Notodoris involves a decision regarding the degree of difference, but not only that, if that decision is made it then leaves behind another group in the Aegires that would then be considered, using the same argument, different to both – and Aegires therefore paraphyletic when it is monophyly that is strived for and is widely accepted as the only criterion for grouping of taxa.

David A. Mullins – April 2022

References:
– Eliot, C. N. E. (1903). Nudibranchiata, with some remarks on the families and genera and description of a new genus, Doridomorpha. In: The Fauna and Geography of the Maldive and Laccadive Archipelagoes, Being the Account of the Work carried on and the Collections made by an Expedition during the years 1899 and1900. Vol 2. Part 1. 540-573. Gardiner, J. S. (Ed.). Cambridge: at the University Press.

– O’Donoghue, C. (1924). Report on Opisthobranchiata from the Abrolhos Islands, Western Australia, with descriptions of a new parasitic Copepod. Zoological Journal of the Linnean Society 35:521–579, pls.27–30.

– Allan, J. (1932). Australian Nudibranchs. The Australian Zoologist. Vol. 7-Part 2: 87-105.

– Thompson, T. E. (1975). Dorid nudibranchs from eastern Australia (Gastropoda, Opisthobranchia). Journal of Zoology, London, 176: 477-517

– Willan, R. C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 16-17

– Gosliner, T. M. & Behrens, D. W. (1997). Description of four new species of phanerobranch dorids

(Mollusca: Nudibranchia) from the Indo-Pacific, with a redescription of Gymnodoris aurita (Gould, 1852). Proceedings of the California Academy of Sciences 49(9):287–308.

– Rudman, W. B. (1998). Family Aegiretidae. Pages 995–996 in P.L. Beesley, G.J.B. Ross, and A. Wells, eds., Mollusca: The Southern Synthesis. Fauna of Australia. 5, Part B. CSIRO Publishing, Melbourne.

– Marshall, J. G. & Willan, R. C. (1999). Nudibranchs of Heron Island, Great Barrier Reef. A survey of the Opisthobranchia (Sea Slugs) of Heron and Wistari Reefs. Backhuys Publishers, Leiden, The Netherlands, 257 pp.

– Rudman, W. B., (2003, July 11) Notodoris gardineri Eliot, 1906.. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/notogard and associated messages.

– Fahey, S. J. & Gosliner, T. M. (2004). A Phylogenetic Analysis of the Aegiridae Fischer, 1883 (Mollusca, Nudibranchia, Phanerobranchia) with Descriptions of Eight New Species and a Reassessment of Phanerobranch Relationships. Proceedings of the California Academy of Sciences 55(34): 613–689.

– Yonow, N. (2012). Opisthobranchs from the Western Indian Ocean, with Descriptions of Two New Species and Ten New Records (Mollusca, Gastropoda). Zookeys 197: 1-129.

Moro, L. & Ortea, J. (2015).Nuevos taxones de babosas marinas de las islas Canarias y de Cabo Verde (Mollusca: Heterobranchia). Vieraea. 43: 21-86.

– Gosliner, T. M., Valdés, Á. & Behrens, D. W. (2018). Nudibranch and Sea Slug Identification: Indo-Pacific – 2nd Ed. New World Publications, Jacksonville, Florida.