#ostreida

[uncharismatic-fauna]

Uncharismatic Fact of the Day

Get ready, get set, filter! Oysters are masters of removing algae, detritus, and plankton from the water, and none do it faster than the Hong Kong oyster. Despite reaching only 20 cm (7.8 in) in length, each individual is capable of filtering up to 30 L (7.9 gal) of water every hour!

(A Hong Kong oyster (Magallana hongkongensis) reef by Marine Thomas)

[alphynix]

Strange Symmetries #09: Not Toeday, Satan

The shells of bivalve molluscs are formed on the left and rights sides of their bodies, and so are usually roughly bilaterally symmetric.

But some bivalves break that arrangement, developing asymmetrical valves that can be massively different in size and shape.

Gryphaea arcuata was an oyster that lived during the Early Jurassic, about 200-174 million years ago, in the warm shallow seas that covered what is now Europe and eastern Greenland. Around 6cm long (~2.4"), its left valve was thick and strongly convex and curled, while the right valve was relatively thin and slightly concave forming a "lid".

The gnarled curled claw-like shape of Gryphaea fossils led to them being colloquially known as "devil's toenails" in some of the regions where they're commonly found, with folk beliefs that they had the power to prevent joint pain.

Their shape was actually an adaptation to living on very soft seafloor sediments. The larger curled valve acted sort of like a boat on the soupy mud, supporting the Gryphaea's weight and preventing it from sinking.

———

NixIllustration.com | Tumblr | Twitter | Patreon

[animalids]

Cockscomb oyster (Lopha cristagalli)

Photo by Nick Hobgood

[fossilroulette]

Name: Cubitostrea perplicata Age: 41-56 million years ago, Paleogene Period (Eocene Epoch) Location: Alabama, USA, Tallahatta Formation

Sometimes the details of a body plan are highly regular, organized, and built from a blueprint of specific genetic pathways. The ridges on this shell of Cubitostrea perplicata are just the opposite. The waves are the result of chance and the physical properties of oysters.

Some species have highly regular shapes and the same number of ridges on every shell. Other, like Cubitostrea perplicata, are irregular. Different shells have different number of ridges with different shapes. Each shell is disorganized with ridges starting and ending randomly throughout each shell.

When scientists investigated how such patterns were formed, they found an answer in the animals' soft parts. Shells of oysters and other related animals are laid down layer by layer. An organ called the mantle sits where each new layer will be. It lays down the biominerals that become the shell.

Researchers linked the irregular growth of oysters like Cubitostrea to the shape of the mantle. In an oyster like the one in the photograph, the mantle stretched much longer than the edge of the shell it grew on, making the surface ripple and fold like loose cloth. When the mantle started each new layer, it stretched over the old layer of shell. Researchers realized that instead of being purposefully organized, the ridges are just the results of layers after layers of oversized mantle.

References: Checa, Antonio G., and Antonio P. Jimenez-Jimenez. "Rib fabrication in Ostreoidea and Plicatuloidea (Bivalvia, Pteriomorpha) and its evolutionary significant." Zoomorphology 122(2003):145-159.

Where are similar fossils found?

[fossilroulette]

Name: Cubitostrea lisbonensis

Location: Texas, USA, Weches Formation

Age: 40-48 million years ago, Paleogene Period (Eocene Epoch)

The two halves of this shell of Cubitostrea might get mistaken for different species, but unlike other seashells with halves that are mirror images of each other, Cubitostrea and other oysters break the rules of symmetry.

Scientists are working to discover how oyster shells became so lopsided. They’ve already noticed that when an oyster hatches, it starts off with two mirror-imaged, symmetric shell halves like other seashells. Shell growth goes off-track later, when the left half starts to grow more domed than the right. Then, the oyster settles down and begins to cement the left half to a hard surface. From then on, the left half grows to fit that surface, giving it a lumpy, irregular shape.

Because oysters grow into all kinds of different, asymmetric shapes, scientists suspect that instead of following rules to grow into a new, specific shape, the rules for growing a shell have probably been relaxed in oysters. Growth rules are normally dictated by genes and gene regulators.

The next step in the puzzle is to find the right combination of genes and regulators that make oyster shells special. That search could take decades. So far, scientists have looked in one species of oyster for all of the genes related to shell growth. They found 196 genes. Each of those genes is itself a puzzle to solve.

Specimen Number: BEG 36189 and BEG 21387

References:

Seilacher, A. “Constructional morphology of bivalves: Evolutionary pathways in primary versus secondary soft-bottom dwellers.” Palaeontology 27(1984):207-237.

Waller, Thomas R. “Functional morphology and development of veliger larvae of the European oyster, Ostrea edulis Linné.” Smithsonian Contributions to Zoology 328(1981):1-70.

Zhang, Guofang, Xiaodong Fang, Ximing Guo, Li Li, Ruibang Luo, Fei Xu, Pengcheng Yang, Linlin Zhang, Xiaotong Wang, Haigang Qi, Zhiqiang Xiong, Huayong Que, Yinlong Xie, Peter W. H. Holland, Jordi Paps, Yabing Zhu, FucunWu, Yuanxin Chen, JiafengWang, Chunfang Peng, Jie Meng, Lan Yang, Jun Liu, Bo Wen, Na Zhang, Zhiyong Huang, Qihui Zhu, Yue Feng, Andrew Mount, Dennis Hedgecock, Zhe Xu, Yunjie Liu, Tomislav Domazet-Lošo, Yishuai Du, Xiaoqing Sun, Shoudu Zhang, Binghang Liu, Peizhou Cheng, Xuanting Jiang, Juan Li, Dingding Fan, WeiWang, Wenjing Fu, Tong Wang, BoWang, Jibiao Zhang, Zhiyu Peng, Yingxiang Li, Na Li, Jinpeng Wang, Maoshan Chen, Yan He, Fengji Tan, Xiaorui Song, Qiumei Zheng, Ronglian Huang, Hailong Yang, Xuedi Du, Li Chen, Mei Yang, Patrick M. Gaffney, Shan Wang, Longhai Luo, Zhicai She, Yao Ming, Wen Huang, Shu Zhang, Baoyu Huang, Yong Zhang, Tao Qu, Peixiang Ni, Guoying Miao, Junyi Wang, Qiang Wang, Christian E. W. Steinberg, Haiyan Wang, Ning Li, Lumin Qian, Guojie Zhang, Yingrui Li, Huanming Yang, Xiao Liu, Jian Wang, Ye Yin, and Jun Wang. “The Oyster Genome reveals stress adaptation and complexity of shell formation.” Nature 490(2012):49-54.

Where are similar fossils found?