107 — Cheeseman's trophon, Paratrophon cheesemani

Paratrophon cheesemani, Maori Bay,
west coast of Auckland, March 2011.

Paratrophon cheesemani, between green-lipped
mussels, Maori Bay, west coast of Auckland,
March 2011.

Cheeseman's trophon, Paratrophon cheesemani (Hutton, 1882), is a small gastropod (~14mm) named after Thomas Frederic Cheeseman (1845–1923), an ex-curator at Auckland Museum. It's endemic to the northwest coast of North Island, where it lives in the lower intertidal zone of exposed coasts. There is a transition zone around Port Waikato where this form is replaced by the predominantly southern P. cheesemani exsculptus Powell, 1933.
Once these two forms are genetically analysed* they may turn out to be separate species.

Very little appears to be known regarding their ecology. However, Cheeseman's trophon is a muricid whelk and these whelks feed by boring through the shells of other animals (typically other gastropods, bivalves, and barnacles). My observations suggest that this species possibly fulfils a similar role to that of the oyster borer (Haustrum scobina (Quoy & Gaimard, 1833)), but lower on the shore, especially since vertical distributions of these two species don't appear to overlap. I suspect that this small gastropod is easily overlooked and the exposed nature of its habitat makes working on it difficult in situ.

*Barco et al. (2015) looked at P. cheesemani exsculptus but not P. cheesemani cheesemani, so no comparison was made between the two forms.



More info:

Barco A, Marshall B, Houart R, Olivero M. 2015. Molecular phylogenetics of Haustrinae and Pagodulinae (Neogastropoda: Muricidae) with a focus on New Zealand species. Journal of Molluscan Studies, 81(4): 476–488.

Paratrophon cheesemani http://www.mollusca.co.nz/speciesdetail.php?speciesid=1000&species=Paratrophon%20cheesemani

Paratrophon cheesemani exsculptus http://www.mollusca.co.nz/speciesdetail.php?speciesid=1001&species=Paratrophon%20cheesemani%20exsculptus

106 — Asian paddle crab, Charybdis japonica

Asian paddle crab, Long Bay marine reserve,
Auckland, 24/3/17.

The Asian paddle crab, Charybdis japonica * is a medium-large green-coloured crab (to ~12cm carapace width), which has become established in northeastern New Zealand. At present they are known from the Waitemata Harbour north to Whangarei Harbour, and Opua/Waitangi in Northland.

Asian paddle crabs were first detected in the Waitemata Harbour near the end of 2000. They prefer sheltered estuarine conditions and are very aggressive, with a strong and painful nip (personal experience). They reach maturity at around ~46 mm carapace width (for females) and can reproduce frequently, possibly several times a year, meaning they could become established in a new area quite quickly. However, they need the water temperature to be at least 20˚C to breed and this will probably limit their southward advance.

The invasive asian paddle crabs are of a similar size to the commercially exploited local species of paddle crab (Ovalipes catharus).  Asian paddle crabs feed on a variety of benthic species including gastropods, bivalves, and other crabs; so there is the potential for competition with local species for resources. Recently I was told that in areas where these two species co-occur, asian paddle crabs now predominate: having out-competed the local species.

* (A. Milne-Edwards, 1861)

Asian paddle crab, from under a rock,
Musick Point, Tamaki Estuary, 14/1/17.

Asian paddle crab, from under a rock,
Musick Point, Tamaki Estuary, 14/1/17.

A smaller Asian paddle crab, from under a
different rock, Musick Point, Tamaki
Estuary, 14/1/17.

And less than half a second later...

More info:

http://www.biosecurity.govt.nz/pests/asian-paddle-crab

http://www.cabi.org/isc/datasheet/89054

https://researchspace.auckland.ac.nz/bitstream/handle/2292/6659/whole.pdf?sequence=8

105 — Spotted whelk, Cominella maculosa

Cominella maculosa, low tide at Devonport,
Auckland 2015.

Cominella maculosa, Sumner, Christchurch, 1993.

The spotted whelk, Cominella maculosa * is another small to middle-sized snail (~45mm) endemic to New Zealand. It's very similar to it's near relative the speckled whelk (C. adspersa). However, spotted whelks have a slightly different distribution, tending to occur in shallower, more sheltered waters and harder substrates. They are found throughout North Island and down to at least Christchurch in the south. South Island forms are smaller and more compact than those from the north.

These two Cominella species are thought to be predator/scavengers and can often be found around carrion. Graham (1941) reported C. maculosa as feeding on the rock oyster **  and cockle *** in Manukau Harbour. However, those observations were published before the advent of the Pacific oyster #, which now dominates much of that habitat. It would be interesting to find out if C. maculosa preys on the Pacific oyster.


* (Martyn, 1784)
** Saccostraea glomerata (Gould, 1850)
*** Austrovenus stutchburyi (Wood, 1828)
# Crassostraea gigas (Thunberg, 1793)



More info:

http://www.mollusca.co.nz/speciesdetail.php?speciesid=1088&species=Cominella%20maculosa

Donald K. M. , Winter, D. J., Ashcroft, A. L., Spencer, H. G. 2015. Phylogeography of the whelk genus Cominella (Gastropoda: Buccinidae) suggests long-distance counter-current dispersal of a direct developer. Biological Journal of the Linnean Society, 115, 315–332.

Graham DH 1942. Breeding habits of twenty-two species of marine Mollusca. Transactions and Proceedings of the Royal Society of New Zealand, 71, 152–159.