94 — Siphon whelk, Penion sulcatus

Penion sulcatus, Enclosure Bay,
Waiheke Island, in ~1m, Feb 2015.

The siphon whelk, Penion sulcatus (Lamarck, 1816) is a moderately large whelk (~170mm), endemic to New Zealand and found from low-tide down to depths of ~100m. They like areas of medium wave exposure where there is a mixture of sand and rock. However, they can also be found in muddy inshore habitats and also off exposed sandy beaches, so they seem indifferent to the sediment type. They are not what you would call common, but you will occasionally see them washed up after a storm with ostrich foot shells (Struthiolariidae).

Siphon whelks are very easily confused with P. cuvierianus, which is a deeper-living species (although the deep end of P. sulcatus' distribution overlaps the shallow end of the distribution for P. cuverianus). Their shell morphology overlaps as well, but generally speaking, P. sulcatus has coarser sculpture and the shell is of a heavier build than P. cuvierianus.

Penion sulcatus are thought to feed on bivalves (particularly Dosina spp. and Condylocardia crassicosta Bernard, 1897—but probably others, depending on habitat). This is another species I've seen live amongst the low-tidal rocks along Tamaki Drive in central Auckland.

Penion sulcatus, Enclosure Bay,
Waiheke Island, in ~1m, Feb 2015.

Penion sulcatus, ex-harbour dredge, Tauranga
Harbour, 1970's. Ex-Cath Fletcher collection.

Penion sulcatus, ex-harbour dredge, Tauranga
Harbour, 1970's. Ex-Cath Fletcher collection.

More info:

3D model:
http://www.nzfauna.ac.nz/penions

More pictures: http://www.mollusca.co.nz/speciesdetail.php?speciesid=1124&species=Penion%20sulcatus

93 — Small lined whelk, Buccinulum vittatum

Buccinulum vittatum, Lion Rock, Piha, 2015.
The shell in the middle has a polychaete
tube-worm attached to it.

Buccinulum vittatum, Lion Rock, Piha, 2015.

Endmic and found throughout New Zealand, Buccinulum vittatum * is a small whelk, reaching about 33mm. They are extremely variable in shape and colour and many species were originally described based on these variations. These days the number of species has been reduced, so at present there is one variable species and a regional sub-species from the Chatham Islands.

They are common under rocks at low tide and down to a few metres. The examples pictured here are a form called motutaraense (Powell, 1929) and was originally described from the west coast of Auckland. These ones were found living in deep rock pools on the south side of Lion Rock, Piha, an area with very high wave exposure.

* (Quoy & Gaimard, 1833)





More info:

More images: http://mollusca.co.nz/speciesdetail.php?speciesid=1080&species=Buccinulum%20vittatum

92 — Cushion star, Patiriella regularis

Many Patiriella regularis disappearing into the
harbour channel depths, Pilot Bay
Mt. Maunganui, 2015.

An unusual four-sided Patiriella regularis,
Pilot Bay, Mt. Maunganui, 2015.

The cushion star, Patiriella regularis (Verril, 1867) is probably the most common sea star in New Zealand waters, and is found throughout. It is also believed to be an invasive species in southern Australia. In Tasmania it was thought that it was introduced in the 1930's on the shells of imported oysters.

They can get up to about 70mm across and can be many colours: from red to orange to greeny-blue, and combinations in between. Most commonly they have five arms, but occasionally they can be seen with six or four.

They prefer shores with moderate to low wave exposure (although I have seen them on rock pools at Piha, which is very exposed) and will eat pretty much anything slow enough to catch.





More info:

NIWA's echinoderm guide

91 — Crab megalopa

Crab megalopa (live), Piha, 2/05//15.

Crab megalopa (live), Piha, 2/05//15.

Crab megalopa (dead), Piha, 2/05/15.

The lifecycle of a crab is really interesting and larval crabs are quite different from adults. In fact larval crabs were considered to be different species, until it was shown that they were just juvenile forms.

After a crab larvae hatches, it joins the plankton. Then, as they grow they go through several developmental stages, shedding their exoskeleton between each stage. Some of these stages bear very little resemblance to the adult crab. The megalopa stage is the last planktonic stage, during which the crab settles and then later moults and emerges as a small version of the adult form.

The cues controlling where and when a megalopa will settle are very important to the crab's survival, as various crab species are adapted to survive in particular habitats. Ambient sound is believed to be an important settling cue, with some crab species being more sensitive than others. For example, megalopae of the mud crab, Austrohelice crassa (Dana, 1851), are not very sensitive to sound cues and it is thought that this could be related their choice of habitat: soft sediments with little wave action (low ambient noise). Conversely the megalopae of the rocky-reef crab, Leptograpsus variegatus, (Fabricius, 1793) are quite sensitive to sound cues and their preferred habitats are rocky reefs with moderate to high wave exposure (high ambient noise).

These two megalopa were found in the cove at south Piha 2/05/15 and are probably (educated guess here) L. variegatus. They were about 1 cm across.




More info:

Stanley JA, Radford CA, Jeffs AG 2011. Behavioural response thresholds in New Zealand crab megalopae to ambient underwater sound. PLoS ONE 6(12): e28572. doi:10.1371/journal.pone.0028572

90 — Another deep-water volute, Alcithoe jaculoides

Alcithoe jaculoides (johnstoni form).

Alcithoe jaculoides (johnstoni form).

Alcithoe jaculoides, Powell 1924 is another one of those little-known New Zealand sea shells. It's a large shell (~180m) with a distribution limited to the north of North Island, on the continental shelf down to at least 450m. However, recent work has inferred that a closely related southern species (Alcithoe calva, Powell, 1928), is actually a smooth form of A. jaculoides. Just to complicate matters the specimen shown here is the 'johnstoni' form, which has a large flared aperture and shorter spire than typical jaculoides.

Closely related shallow water species are known to feed on bivalves, so it is likely that A. jaculoides does also. I was given this shell as part of a collection when I was about 16. The collection had been accumulated by a fisherman in the 1960's and that's all I can remember. Sadly, I have no locality data for this shell. However, chances are this came from the Bay of Plenty.

89 — Eleven-armed starfish, Coscinasterias muricata

Coscinasterias muricata, Piha, 9/2/15.

Coscinasterias muricata, Piha, 9/2/15.

Coscinasterias muricata, Piha, 9/2/15,
macro shot showing the pedicellariae.

Coscinasterias muricata Verrill, 1870, is a large sea star (~20cm across). They are found throughout New Zealand and southern Australia where they are inter-tidal to sub-tidal. Although they are known as eleven-armed sea stars, this number can vary. For example, the one pictured her only has ten arms.

They are especially common under mussel farms, where they prey on fallen mussels. Elsewhere, they are reported to feed on gastropods and bivalves, particularly (again mussels and) oysters.

In the third picture below you can see the small upward-facing wrench-like appendages called pedicellariae, in a ring around white-coloured spines. These guard against ant attempts by encrusting organisms to settle. Encrusting organisms could reduce the flexibility and mobility of the starfish and therefore reduce its chances of survival.















More info:

Morton, J. E., Miller, M. C. 1968. The New Zealand Sea Shore. Collins.

NIWA sea star identification guide:
https://www.niwa.co.nz/static/extraordinary_echinoderms.pdf

88 — Depressed olive, Amalda depressa

Amalda (B.) depressa, Devonport,
Auckland, 17/6/18.

Amalda (B.) depressa, Devonport,
Auckland, 17/6/18.

The depressed olive, Amalda (Baryspira) depressa * is a small (~18mm) and attractive olive species. Its name derives from its squat shape, not any perceived snail-mood. They are endemic to New Zealand and are found down to the top of South Island.

Amalda (B.) depressa, Devonport,
Auckland, 2016.

Amalda (B.) depressa, Devonport,
Auckland, 2016.

Amalda (B.) depressa, Mount Beach,
Mt. Maunganui 14/11/16.

Amalda (B.) depressa, Mount Beach,
Mt. Maunganui, 14/11/16.

They prefer fine sandy sediments in areas of moderate shelter; essentially similar habitat to the southern olive (A. (B.) australis). However, A. (B.) depressa is less common.

Behaviourally, they are very fast burrowers and will re-bury themselves in about a minute if disturbed. This is yet another small species for which there is very little ecological knowledge available.


* (G.B.Sowerby II, 1859)

87 — Lemon nudibranch, Dendrodoris citrina

Dendrodoris citrina, Tamaki Drive, 2016.

Dendrodoris citrina, under Ngapipi Bridge,
Tamaki Drive, 2016. The chiton in the
top right is Acanthochitona zelandica
(Quoy & Gaimard, 1835).

Dendrodoris citrina, Takapuna Reef, 2015.

Dendrodoris citrina, under Ngapipi Bridge
Tamaki Drive, 2016.

The lemon nudibranch, Dendrodoris citrina * is found throughout New Zealand waters and are endemic. They are frequently seen around the low tide mark, amongst coraline algae and in pools.

Dendrodoris citrina is one of the most silt-tolerant of New Zealand's nudibranchs and is one of the most common nudibranchs seen off Auckland's Tamaki Drive. However, they are also found on more exposed coasts and are supposedly nocturnal.

They are thought to feed on the orange solitary ascidian (Microcosmus sp.), but they may also feed in sponges. For such a common species I was surprised at how little information I could find regarding their ecology. The individuals pictured below were found in less than half a metre of water and ranged in size between ~50–70mm.

* (Cheeseman, 1881)

Two Dendrodoris citrina,  mating,
Mission Bay, Tamaki Drive, 2016.

More info:

http://www.seaslugforum.net/find/dendcitr

Willan, R.C.; Morton, J.E. 1984. Marine Molluscs Part 2: Opisthobranchia. University of Auckland, Leigh Marine Laboratory, Leigh, New Zealand. 106 Pp.