120 — Mottled brittle star, Ophionereis fasciata

Mottled brittle star, Ophioneries fasciata,
Pilot Bay, Mt. Maunganui, July 2018.

Mottled brittle star, Ophionereis fasciata,
Pilot Bay, Mt. Maunganui, April 2018.

The same brittle star, curled up in a
?defensive ball, Pilot Bay, Mt. Maunganui,
July 2018.

Mottled brittle star, O. fasciata,
Pilot Bay, Mt. Maunganui, July 2018.

Mottled brittle star, O. fasciata,
Pilot Bay, Mt. Maunganui, July 2018.

Mottled brittle star, O. fasciata,
Pilot Bay, Mt. Maunganui, July 2018.

The mottled brittle star, Ophionereis fasciata *, is probably the New Zealand brittle star that people will mostly likely encounter. They are endemic to New Zealand and live under stones at low tide; but have also been found down in much deeper water (~300m).

An interesting thing about this brittle star is that it can produce bioluminescence in the form of blue flashes. It is thought that they use the bioluminescent flashes to ward off potential predators. Also, the chemical pathway for their bioluminescence is similar to that used by deep-sea lantern sharks (Claes et al., 2011).

Another possible defensive technique is shown on the left, where one has curled up into a tight ball with it's tube feet facing outwards. This brittle star reacted this way after encountering a crab.

However, these defensive techniques don't always work, as mottled brittle stars are eaten by a variety of fishes, particularly: red moki, porae, spectacled and variable triple-fins, and Sandagar's wrasse (Russell, 1983).

Now I know about the bioluminescence (I didn't before I researched this post), I'm going to plan a night expedition to see it...


* Hutton, 1872


































More info:

Claes, J. M., Krönström, J., Holmgren, S. & Mallefet, J. 2011. GABA inhibition of luminescence from lantern shark (Etmopterus spinax) photophores. Comp. Biochem. Physiol. C, 153, 231–236.

Mills et al. (2017). Extraordinary echinoderms. A guide to the echinoderms of New Zealand.

NIWA: Critter of the week.

Russell, B. C. (1983). The food and feeding habits of rocky reef fish of north-eastern New Zealand. The New Zealand Journal of Marine and Freshwater Research, 17, 121–145.

119 — Hutton's brittle star, Ophioceres huttoni

Ophioceres huttoni, from under a rock at low tide,
Pilot Bay, Mt. Maunganui, July 2018.

This little brittle star was named after the prominent 19th century New Zealand naturalist Frederick Wollaston Hutton. Ophioceres huttoni (Farquhar, 1899), is a small and little-known brittle star. It's endemic to New Zealand and appears to have a distribution limited to the North Island.

They live under stones in sandy areas and are only about 3cm across (including tentacles), so are easily missed.

The brittle stars pictured here were found at low tide under turnable rocks in Pilot Bay, Mt. Maunganui during July 2018 (there were some 0.0 low tides). There were several under each rock I turned. They co-occur with other brittle stars and I have seen them under the same rock with Ophionereis fasciata Hutton, 1872 and Ophiopteris antipodum E. A. Smith, 1877.

Ophioceres huttoni, under rocks in Pilot Bay,
Mt. Maunganui, 16/7/2018.

Ophioceres huttoni, oral view. This is the same
example as above and is about 2cm across.

Ophioceres huttoni, same location as above,
17/7/18. This one is about 3cm across.

Ophioceres huttoni, same location as above,
17/7/18. This one is about 1cm across.

More info:

Mills et al. (2017). Extraordinary echinoderms. A guide to the echinoderms of New Zealand.

118 — Sea hare, Aplysia juliana

 

Aplysia juliana. feeding on Ulva,
Pilot Bay, Mt. Maunganui, January 2016.

This post leads on from my last post regarding sea hares. Aplysia juliana * is a large sea hare (to ~45cm), which is found circumglobally in warm-temperate waters. They come in a variety of colours, from blotchy light brown to an even dark brown.

Aplysia juliana. feeding on Ulva,
Pilot Bay, Mt. Maunganui, January 2016.

Aplysia juliana, feeding on Ulva,
Pilot Bay, Mt. Maunganui, January 2016.

Aplysia juliana is particularly fond of sea lettuce (Ulva sp.) (Fring & Fring 1965). The ones pictured here feeding on sea lettuce and you can see the sea hare in the video devouring a piece.

Aplysia juliana moving over shell hash,
Pilot Bay, Mt. Maunganui, January 2016.

This species is also unusual in that it doesn't produce ink, but instead produces opaline: a white milky secretion. Opaline fulfils a similar defensive role to the ink produced by other sea hares and has been shown to protect sea hares from predation by spiny lobsters (Kicklighter et al., 2005).



Aplysia juliana is unusual amongst sea hares in that the posterior end of it's foot can act as a sucker. What this means is that it can inch it's way along a bit like a leech: reaching the head out and placing it down, then lifting up the posterior end of the foot and bringing that forward, which most other sea hares don't do. This form of motion can be seen the video on the right.

Given the abundance of sea lettuce in Tauranga Harbour in summer during recent years it would be interesting to see if there has been a corresponding increase in this species of sea hare. That's a research project for some one :)

* Quoy & Gaimard, 1832




More info

Sea slug forum: What are sea hares?

Sea slug forum: Aplysia juliana

Fring, H., Fring, C., 1965. Chemosensory bases of food-finding and feeding in Aplysia juliana (Mollusca, Opisthobranchia). Biological Bulletin, 128(2), 211–217.

Kicklighter C. E., Shabani, S., Johnson, P. M., Derby, C. D., 2005. Sea hares use novel antipredatory chemical defenses. Current Biology, 15, 549–554. doi:10.1016/j.cub.2005.01.057

Willan, R. C., Morton, J. E. 1984. Marine molluscs part 2: Opisthobranchia. University of Auckland, Leigh Marine Laboratory, Leigh, New Zealand. 106 pp.

117 — Sea hare, Aplysia keraudreni

Aplysia keraudreni, Warrior Rocks,
Mt. Maunganui, July 2018.

Sea hares are large sea slugs which can reach sizes of up to half a metre in length. They get their name from a superficial appearance to actual hares. There are several species of sea hare found in New Zealand and although they are not considered to be rare, they tend to be what known as locally common. What this means is that if conditions are right you can get loads of them, but otherwise you won't see them at all.

Aplysia keraudreni Rang, 1928, is found in northern New Zealand and there is a similar species found in Australia. From what I can gather, sea hares (and particularly this species) are not that well-described, so it may turn out that this is a different species than previously thought. A. keraudreni has also been recorded from Chile and it is considered to have a south Pacific distribution (Medina et al., 2005; Uribe et al., 2013).

Aplysia keraudreni, Warrior Rocks,
Mt. Maunganui, July 2018.

Egg mass of A. keraudreni, Warrior Rocks,
Mt. Maunganui, July 2018.,

Aplysia keraudreni, expelling ink.

Once they reach adult size, sea hares don't appear to have many natural predators—but when they're disturbed can release clouds of toxic liquid. The colour of these inky clouds can go some way to helping identify the species: Aplysia keraudreni releases a purply-coloured ink, while the ink of A. dactylomela is wine-red coloured, and A. juliana doesn't release ink of any kind. The video below shows A. keraudreni expelling ink.

The sea hare pictured here (~25cm in length) was part of a mating pair and sea hares are known for forming-up into long chains of mating pairs. They then lay eggs in long gelatinous noodle-like structures, which can look a lot like a pile of instant noodles. However, if you look closely you can see the individual eggs.

The eggs hatch to release a tiny planktonic veliger larvae, which then live in the plankton for some time and then settle. This would also appear to be one part of sea hare biology that is not that well-known for many species.


More info

Sea slug forum: What are sea hares?

Medina, M., Collins, T., & Walsh, P. J. 2005. Phylogeny of sea hares in the Aplysia clade based on mitochondrial sequence DNA data. Bulletin of Marine Science 76(3), 691–698.

Uribe, R. A., Nakamura, K., Indacochea, A., Pacheco, A. S., Hooker, Y., & Schrödl, M. 2013. A review on the diversity and distribution of opisthobranch gastropods from Peru, with the addition of three new records. Spixiana, 36(1), 43–60. 

Willan, R. C., Morton, J. E. 1984. Marine molluscs part 2: Opisthobranchia. University of Auckland, Leigh Marine Laboratory, Leigh, New Zealand. 106 pp.