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Taxon profile

family

Solemyidae Gray, 1840

kingdom Animalia - animals »  phylum Mollusca - mollusks »  class Bivalvia - bivalves »  order Solemyida »  superfamily Solemyoidea

Scientific synonyms

incl. Solemyinae J. Gray, 1840
Acharacinae Scarlato & Starobogatov, 1979
Solenomyadae Gray, 1840

Description

Shell aragonitic, with outer prismatic and inner homogeneous layers. Shell inequilateral, anteriorly elongate, weakly calcified and dominated by thick, glossy periostracum, which extends beyond shell margins. Sculpture absent, or limited to low wide radial ribs or furrows. Umbones small. Lunule absent; escutcheon weak or absent. Hinge plate weak, edentate; tubercles and thickened props usually present. Ligament parivincular, opisthodetic, sunk in groove posterior to umbones and attached to nymph. Adductor muscle scars paired, subequal. Pedal muscle scars prominent. Pallial line obscure, entire. Mantle lobes with hypertrophied margins extensively fused, leaving large anteroventral and small posterior openings. Hypo-branchial gland developed. Foot elongate with discoidal sole. Gills protobranch, large; filaments thickened, dark colored. Labial palps minute. Alimentary canal reduced to simple tube with two ducts to small digestive diverticula and narrow intestine passing through ventricle of heart. In some representatives, the entire alimentary system is absent. Larva a pericalymma.
This family, known as early as the Lower Ordivician, comprises two living genera, containing approximately 30 species that are shallow infauna of soft substrata. A complex Y-shaped burrow, with no direct communication with the surface may be constructed by smaller species, but large individuals appear to lie at an oblique angle just below the sediment surface, usually in a small depression in the sediment. The vernacular name, "awning clams," refers to the periostracal fringe projecting beyond the shell margins and usually divided into triangular sections covering the wide, muscular, fused mantle margins. The calcareous portion of the shell is weak and contains a large amount of organic matrix. The result is that the solt parts are enveloped in a largely periostracal flexible tube, stiffened along the dorsal margins by the shell valves. The high solubility of calcium carbonate in the deep ocean means that even recently dead specimens are represented by the periostracum only. All species observed appear to be active, vigorously burrowing through the substratum, and even capable of undirected swimming by adduction, although this has been observed only in specimens artificially displaced from their burrows. The powerful pumping action is probably associated with clearing the burrow.
Source: Coan, E. et al., 2000. Bivalve Seashells of Western North America. Marine bivalve mollusks from Arctic Alaska to Baja California.
The solemyid shell is small to medium-sized (to 100 mm), thin-walled, and anteroposteriorly elongated with parallel dorsoventral margins and rounded ends. It is EQUIVALVE, compressed, and narrowly gaping at both ends. It is INEQUILATERAL (umbones far posterior), with ORTHOGYRATE UMBONES. Shell morphology is highly derived—the shell is weakly calcined especially at the ventral margins, allowing the animal to act as a "flexible tube" that can bend and contract in many directions during burrowing. Shell microstruc-ture is ARAGONITIC and two-layered, with a PRISMATIC outer layer and a HOMOGENOUS inner layer; the inner layer is absent anterior to the umbones, and only the outer layer persists near the margins. Organic content of the shell is very high, comprising two types of conchiolin. TUBULES are apparently absent. Exteriorly solemyids are whitish but covered by a thick, four-layered, glossy, dark brown to greenish PERIOSTRACUM in alternating thin and thick rays or pleats that project beyond the ventral shell margins to form a frill or awning (hence the common name). The periostracum is usually frayed and very brittle when dried. Sculpture is smooth or with irregular, low radial furrows corresponding to the periostracal rays. LUNULE and ESCUTCHEON are absent. Interiorly the shell is non- NACREOUS. The PALLIAL LINE IS EN¬TIRE. The inner shell margins are smooth. The HINGE PLATE is weak and EDENTATE in adults, but thick¬ened buttresses or "horns" are usually present interiorly near the umbones. The LIGAMENT is PARIVINCULAR, set in NYMPHS, and is functionally OPISTHODETIC, but appears AMPHIDETIC by the anterior extension of its outermost layer.
Mikkelsen, P.M. & Bieler, R. 2003, Seashells of Southern Florida. Living Marine Mollusks of the Florida Keys and Adjacent Regions: Bivalves.

Ecology

The family appears to favor regions of reduced oxygen, usually with high organic content. While the majority of species have a normal functioning alimentary canal, an outstanding feature is the reduction of the gut to a simple tube with barely distinguishable stomach, or its entire loss in species belonging to two genera. It has recently been shown that nutrition is obtained from chemoautotrophic bacteria mostly housed in the thick gill filaments. The bacteria utilize hydrogen sulfide to fuel the production of carbohydrates and are able to exist in oxygen-poor environments. The clams live symbiotically with the bacteria and are able to colonize environments with decomposing organic remains, high in hydrogen sulfide and poor in oxygen. The typical location for awning clams in the northeastern Pacific is in basins on the continental shelf and nearshore where there is an accumulation of plant debris. One species is opportunistic and is able to colonize the shallow water around sewage and debris from log storage areas. Those species with stomachs have a less restricted habitat and arc generally absent from such polluted habitats.
Source: Coan, E. et al., 2000. Bivalve Seashells of Western North America. Marine bivalve mollusks from Arctic Alaska to Baja California.
Author: Jan Delsing

Included taxa

Number of records: 3

subfamily Janacekiinae Růžička & Řehoř in Hajkr et al., 1978

Unplaced taxa

genus Acharax Dall, 1908
genus Solemya Lamarck, 1818

Links and literature

http://www.bagniliggia.it/WMSD/HtmFamily...
LIST OF ALL SPECIES OF THE WORLD (RECENT AND FOSSIL) - World Wide Mollusc Species Data Base
EN The Interim Register of Marine and Nonmarine Genera [114907]

Rees, T. (compiler): The Interim Register of Marine and Nonmarine Genera [http://www.irmng.org] [as Solemyidae Gray, 1840]
Data retrieved on: 30 November 2019
EN Australian Faunal Directory [6793ce79-e873-4f69-b00c-72816dded9b7]

ABRS (2009-2019): Australian Faunal Directory [https://biodiversity.org.au/afd/home], Australian Biological Resources Study, Canberra [as Solemyidae J. Gray, 1840]
Data retrieved on: 22 July 2015
CZ Pfleger V. (1999): České názvy živočichů III. Měkkýši (Mollusca), Národní muzeum, (zoologické odd.), Praha, 108 pp. [as Solemyidae]
Data retrieved on: 11 November 2013
EN Carter J. et al (2011): A Synoptical Classification of the Bivalvia (Mollusca), Paleontological Contributions 4 [as Solemyidae J. Gray, 1840b]
Data retrieved on: 6 April 2014
EN Carter J. et al (2011): A Synoptical Classification of the Bivalvia (Mollusca), Paleontological Contributions 4 [as Solemyinae J. Gray, 1840b]
Data retrieved on: 6 April 2014

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