122 — Feathered hydroid, Pennaria disticha

A colony of Pennaria disticha, underneath
Ngapipi Bridge, Tamaki Drive,
Auckland, 18/5/18.

Under Ngapipi Bridge, Tamaki Drive, 18/5/18.

Under Ngapipi Bridge, Tamaki Drive, 18/5/18.
This could be a different species.

Under Ngapipi Bridge, Tamaki Drive, 9/4/16.

I think it would be a safe to say that most people don't notice hydroids when they visit the sea shore, and if they do they assume that they're some kind of seaweed. However, although they look like plants, hydroids are actually carnivorous animals. They belong in the phylum Cnidaria, in which you'll also find jellies, sea anemones, and corals.

The feathered hydroid, Pennaria disticha*, is what's known as an athecate hydroid. Athecate essentially means without a cup, and this refers to the flowery red bit of the hydroid (called a hydranth). In athecate hydroids, the hydranth sit out by itself and is not protected by a sheath or cup. The hydranths shown here are ~3–5mm in size. Colonies can form clumps and get to around 20x20x20cm.

Feathered hydroids are fouling organisms and have been transported all over the world attached to the bottom of ships. It was thought that they originated in the Atlantic and spread from there. However, a recent genetic study found that instead of one cosmopolitan species, Pennaria distcha is probably several genetically distinct cryptic species^1.

If you happen across a colony like the one pictured here it's best not to touch it, as the colonies are venomous. You can be stung and apparently it's quite painful. Their venomous nature means that these hydroid colonies are considered to be a bit of a nuisance when they grow on aquaculture facilities ^{2, 3.}

*(Goldfuss, 1820)




More info:

^1. Miglietta, M. P., Odegard, D. Faure, B., Faucci, A. (2015). Barcoding techniques help tracking the evolutionary history of the introduced species Pennaria disticha (Hydrozoa, Cnidaria). PlosOne, 10(12), e0144762. doi:10.1371/journal.pone.0144762

^2. Bosch-Belmarab, M., Azurro, E., Pulis, K., Milisenda, G., Fuentes, V., Ons, K-D., Micallef, A., Deidun, A., Piraino, S. (2017). Jellyfish blooms perception in Mediterranean finfish aquaculture. Marine Policy, 76, 1–7. doi.org/10.1016/j.marpol.2016.11.005

^3. Tezcan, Ö. D., Sarp, S. (2013). An unusual marine envenomation following a rope contact: A report on nine cases of dermatitis caused by Pennaria disticha. Toxicon, 61, 125–128. http://dx.doi.org/10.1016/j.toxicon.2012.10.019

121 — Resilient brittle star, Ophiactis resiliens

Ophiactis resiliens, from under a road bridge
along Tamaki Drive, Auckland, 12/9/18.
This is at half speed.

O. resiliens, from under a road bridge
along Tamaki Drive, Auckland, 12/9/18.

O. resiliens, from under a stone,
Tamaki Drive, Auckland, 2017.

O. resiliens, from under a road bridge
along Tamaki Drive, Auckland, 12/9/18.

As above, this example is about 40mm across.

O. resiliens, from under a turnable rock,
Bowentown, Bay of Plenty, 6/11/17. This
example is only ~15mm across.

The resilient brittle star Ophiactis resiliens* is another small brittle star and one without a common name But, apparently, resiliens means rebounding or resilient, so I'm calling it the resilient brittle star.

They can be found at low tide around northern New Zealand and southern Australia down to reasonable depths (Mills et al., 2017). At low-tide you can find them under and between rocks; and sometimes along with other common intertidal brittle stars (mottled, oar, and Hutton's brittle stars).

Ophiactis resiliens is what’s called a suspension feeder: feeding on small organic particles in the water around it. It does this by waving its arms around in the water directly above it. The arms have little tube feet, which the brittle star uses to collect its food.

They have separate sexes and in Australian waters spawn during the winter months.**


*Lyman, 1879















































More info:

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

**Faulkner, I., Byrne, M., (2003). Reproduction of Ophiactis resiliens (Echinodermata: Ophiuroidea) in New South Wales with observations on recruitment. Marine Biology, 143(3), 459–466.

**Selvakumaraswany, P., Byrne, M. (2000). Reproduction, spawning, and development of 5 ophiuroids from Australia and New Zealand. Invertebrate Biology, 119(4), 394–402.