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Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Bivalvia
Order:	Venerida
Superfamily:	Mactroidea
Family:	Mesodesmatidae
Genus:	Paphies
Species:	P. subtriangulata
Binomial name
Paphies subtriangulata (William Wood (Zoologist)
Synonyms
Erycina subangulata Gray, 1825 Mactra subtriangulata W. Wood, 1828 Mesodesma cuneata Hanley, 1842 Mesodesma reentsii Römer, 1862 Mesodesma spissa Reeve, 1854 Paphies porrecta (Marwick, 1928) [1]

Paphies subtriangulata is a species of edible bivalves clam known as Tuatua in the Māori language, a member of the family Mesodesmatidae and endemic to New Zealand. It is found on all three of the main New Zealand islands, buried in fine clean sand on ocean beaches.Tuatua are a very common shellfish, bivavles species, that live in the littoral zone and the sublittoral zones of open New Zealand coasts. They are one of the most abundant species on beaches including the Chatham islands. ^[2]. Tuatua are Part of the Mollusc family which also includes animals such as snails, limpets, sea slugs, and octopuses. ^[3].

The clam burrows beneath the sand, and does so very quickly, making it a challenge to dig for at times. It also squirts water when threatened. All Tuatua are protected with legal limits on their capture. In some areas, one digger may bag no more than 50 to 150 Tuatuas per day, depending on location. ^[4]. Tuatua can easily be found in the knee deep and lower water at low tide. By curling your toes down and wiggling them into the sand, you will feel the top of the shell. All that's left to do once you feel them is to get your hands in the sand and pull them out. Leaving the Tuatua to sit for a few hours after collecting or leaving them til the next day, is recommended so they arent as sandy. They should be stored in fresh ocean water, in a spot out of the direct sun, in a cool spot. ^[5]

Description

The large Tuatua shell is asymmetrical, with the hinge at one side. Its closest relative, the pipi ( Paphies Australis), has a symmetrical shell. ^[6].

Tuatua are shells that are thick and heavy with unequal sides that are curved like a trianlge. The key distinction between pipi and Tuatua is the location of the hinge, which can be commonly confused. Unlike pipi, the Tuatua has a prominent posterior ridge with a hinge that runs one third of the way along the dorsal border. Tuatua have a yellow coloured periostracum and a white shell that can get stained a rusty or black colour. They also can look a creamy grey colour. The size of Tuatua is between 48-80mm and ^[7] and they can reach a shell length of 40-70mm in only 3 years. ^[8] Tuatua have two shells also known as bivalves. In order to survive the two shells pull together tightly when the tide goes out. ^[9]. Tuatua have pointier and more angular shoulders compared to other Paphies shell species. ^[10]. Tuatua feed on organic matter in the water by sucking it up through their short siphons. ^[11].

The soft parts of the animal are an edible delicacy, made into fritters or boiled and served on the shell. Historically the species has been used as a food source by the Māori, and its shell is a common component of excavated Māori middens.

Distribution

Tuatua bury themselves slightly beneath the sand on open beaches from low tide to 4 meters deep. On Auckland's west coast, they are hard to come by. ^[12]. Breaking surf is the most common area to find Tuatua, they are surf clams that like to wedge themselves in water that is four meters deep to around half a meter at low tide. Tuatua prefer to keep part of their shell out of the sand or full coverage with a slight amount of sand on the truncated end. ^[13]. People gather them out of the sand at lowtide when the water is about knee-deep. ^[14]. Migriating down the beach is usually where you will find Tuatua as they grow larger at a rapid pace. ^[15]

Life cycle

A study around the 1980s looking at larval shell development, showed that Northern Tuatua ( paphies subtriangulata) adults spawned at 15-20 degrees celsius. The spawning has been monitored and linked to "warm spring sunny days and relatively cool water temperatures. ^[16]. "Tuatua have separate sexes (1:1 sex ratio) and reproduce by spawning." ^[17]. A quick change in water temperature has also been associated with tutua spawning. Eggs came out as a sphere shape and a diameter of 56-61 micrometers which includes 2 micrometer vitelline membrane According to the the same research tuatua sperm were as long as 48 micrometers; the head of the sperm was 3.5 micrometers long, 2.2 micrometers in diameter at the widest point, and the tail measuring 44 micrometers long. Studies showed that after the tuatua went through the larval development stage it goes through the straight-hinge stage. The Veliger can be completed 24-48 hours after being fertilised and the development stage after that is the settlement stage, which occurs within a further 17-18 days. Further along the research they discovered that the Tuatua grew an average of 8 micrometers a day. As the Tuatua grow gradually they become more asymmetrical longways and the long front shoulders and ends lengthen more than the posterior shoulders and ends. ^[18]. Notes from a study in November 1993 looked at the reproductive cycle of the Paphies subtraingulata and showed that Tuatua reproduce annually. From samples being reviewed monthly, they found that there are four gemetogenic stages of reproduction. Three of the distant phases of the Tuatua reproductive cycle, are as follows. February up until April the Tuatua are found spawning, in May to late August they go through regeneration of gonad, as from September to November they show more spawning activity. In the study Tuatua gonads often showed different stages at the same time and there was a slow paced advancement in the dominating stages. From the observation in the field, looking at natural spawning, eight occurrences proved that the "spawning times deduced from histological sections". This proof outlined that the proportion sizes of populations spawning at one time, were very small and that tuatua engage in spawning activity daily. An interesting fact is that the related species Paphies australis spawned at the same periods as Paphies subtriangulata. ^[19]. The juvenile Tuatua are very mobile, they let themselves be taken by the waves like the more mature Tuatua then bury themselves into the sand quickly after. If not collected by humans for a feed, the maximum age for a Tuatua to survive, is around five or so years, however natural mortality levels are found to be high too. ^[20]

Interactions

Both the Northern Tuatua and the Southern Tuatua can be found living together on some beaches, with a possibility that they could interbreed. However, this is not certain. ^[21]. Because the Tuatua are such close relatives, they are found in similar areas. Tuatua have also been found spawning as close as centermeters away from Pipi. ^[22]. Tuatua love ocean beaches with sand so they are a good indication of where the "fine, clean, and fluid sands are. Tuatua move about by the waves and are redistributed by backwash. ^[23]. In 2013 a Managment plan of protecting Tuatua and other bivalves at Pegasus Bay, outlined a "positive linear relationship between the number of vehicle passes and Tuatua mortality". This outlines motor vehicle as a threat to the abundance of Tuatua. Horses also were reported as a threat and made up 36.9% of Tuatua mortalities from just a hoof print breaking the shell. In the long run this is is seen as exceedingly harmful to the bivalves species. ^[24].

Further information

Paphies subtriangulata are known as Northern Tuatua, in New Zealand there are also Southern Tuatua Paphies donacina. ^[25].This relative is more commonly found on Aucklands west coast and at more southern points. ^[26]. Between the Southern tuatua and the Northern tuatua, it is quite hard to tell the difference due to their overlap of similar features. The Southern island beaches tend to have bigger Tuatua. Growing between 8 - 10cm. ^[27]. For many years when Tuatua were first discovered, there was confusion of some Tuatua having different traits to each other, which Richardson et al (1982) linked to the existence of not one type of Tuatua but the two. ^[28]. Comparing Tuatua to other shellfish and common types of fish, Tuatua are known to have a good amount of charbohydrates and protein, and an easily accessible food if you go to a beach that has them. ^[29]

Subspecies

Three subspecies have been recognised:

• Paphies subtriangulata subtriangulata (Wood, 1828)
  Distribution: throughout North and South Islands
  Maximum length is 76 millimetres (3.0 in), height 48 millimetres (1.9 in), and thickness 28 millimetres (1.1 in).
• Paphies subtriangulata porrecta ( Marwick, 1928)
  Distribution: Chatham Islands
  Maximum length: 93 millimetres (3.7 in), maximum height: 57 millimetres (2.2 in).
• Paphies subtriangulata quoyii ( Deshayes, 1832)
  Distribution: throughout North and South Islands
  Size: Thicker relative to length - Maximum length is 86 millimetres (3.4 in), height 65 millimetres (2.6 in), and thickness 38 millimetres (1.5 in).

References

Category:Commercial molluscs Category:Bivalves of New Zealand Category:Endemic fauna of New Zealand Category:Mesodesmatidae Category:Bivalves described in 1828 Category:Taxa named by William Wood (Zoologist) Category:New Zealand seafood Category:Māori cuisine