Brachiopods – Then and Now
Shellfish, yes, but not molluscs.
They lack the spiral form which characterises the molluscs, but have a hard, usually calcareous, shell form similar to bivalves, but shells are ‘top and bottom’, rather than side by side. The ventral (top) valve shell is larger than the lower, dorsal valve, and the ventral valve base gives out a pedicle anchor for the whole organism. The ventral valve may also be called the pedicle valve, and the dorsal one the brachial valve. Brachiopds belong to a related phylum, Lophophorata, which also contains bryozoa.
Brachiopods are hard shell, filter feeders and are also known as roman lamp shells, or toenails. Generally, brachiopods are not conspicuous as a food source, or as competitors in the marine environment, nor especially plentiful, except in some special locations. However, as a group they have proved to be exceptionally good at surviving. They are known in fossil records from early Cambrian times, some 540 million years ago, appearing along with trilobites and graptolites in the early sedimentary rock layers. At their heights they had some 30 000 species, but only about 300 are left now, globally. They outnumbered molluscs in the Palaeozoic Era. They can be said to be living fossils like tuatara! Thus they are important to palaeontologists throughout fossil history for dating other fossils and rocks.
Lamp shells seem to prefer cooler waters now, in habitats from low tide to 200+ m deep. There are 32 brachiopod species in NZ waters, with only 6 off the Wellington south coast. The black Notosaria nigricans are found with difficulty, as they are only about 12 mm wide, in inter- and subtidal, nutrient poor areas on the protected undersides of boulders or rocky reefs. This is similar to sponges, possibly as the best sites to survive in competition with molluscs and seaweeds for substrate attachment space. Elevation of brachiopods above the substrate by the pedicle may limit non-brachiopod competitors and epibionts, smothering sponges, coralline seaweeds and bryozoans. The moveable pedicle may also allow orientation in currents for better feeding.
Notosaria are found down to 800 m deep in dredgings. Pinkish red Terebratella inconspicua are also found, with T. sanguinea (larger) much less common. The best place to see brachiopods is after southerly storms and Owhiro Bay beach is a good place to fossick. Look especially at kelp holdfasts. Both these species are ribbed, whereas most brachiopods are smooth-valved.
T. sanguinea Photo : Luis Ruiz Berti Terebratulida
Shelly loops are attached to the lower middle interior of the lower valve. These support the branchia or lophophores, which are fleshy, spiralled arms which function for breathing and feeding. Brachiopods are suspension feeders which orient with their shells slightly open to allow the passage of water, and extend their lophophores to produce feeding currents and trap microplankton and organic particles, which are then transported to the mouth.
New Zealand is known as a good place to study brachiopods due to their relative availability in shallow waters. They are hard to find in deeper waters because they are so solidly attached to substrates.
Key areas include sites off the Three Kings Islands; the Kermadec Islands, the Hauraki Gulf and northern offshore islands; Ranfurly Banks beyond East Cape; areas of Cook Strait and the Marlborough Sounds; Lyttelton Harbour; the Otago coast; Otago Harbour; parts of Foveaux Strait; parts of the Chatham Rise; and areas of the Campbell Plateau. The Cook Strait region has a diverse brachiopod fauna that represents the northern limit of several key species (eg, Notosaria nigricans). In the Stewart Island region, the brachiopods of Paterson Inlet represent a major component of the benthic biomass (included in Ulva Island – Te Wharawhara Marine Reserve). Fiordland is regarded as a globally significant area for brachiopods, with a diverse and abundant brachiopod fauna found in shallow water. The Chatham Rise represents a biogeographic limit for many of the southern and Subantarctic species.
Brachiopods, Fiordland Photo: Franz Smith
Terebratella inconspicua, Owhiro Bay, Photo: MH
‘Brachiopods are a declining group of marine organisms, today enjoying little of their former importance in benthonic communities of the continental shelf. With a long and rich fossil history behind them, they have dwindled in numbers through the Mesozoic and Cenozoic Eras until today they are rare or minor elements of the marine fauna. Since they are seldom seen in living communities, and since they are important neither as edible shell-fish nor as destructive pests, brachiopods have received little attention from marine zoologists and often go unrecognised by amateur collectors. However to palaeontologists, such as this writer, the study of living brachiopods is essential to understanding the complex evolution of this interesting group’. Zeddie Paul Bowen, University of Otago, Tuatara 1968
Alan Hoverd, Chapter 24 ‘The Taputeranga Marine Reserve’ Edited by J Gardiner and J Bell, VUW, 2008Tuatara: Volume 16, Issue 2, July 1968