Species belonging to the genus Lithophaga

Phylum: MOLLUSCA
Classe: BIVALVIA L., 1758
Order MYTILOIDA Férussac, 1822
Superfamily MYTILOIDEA Rafinesque, 1815
Family MYTILIDAE Rafinesque, 1815
Subfamily LITHOPHAGINAE Adams & Adams, 1857
Genus Lithophaga Röding, 1798
Shells modioliform, more or less cylindrical with rounded endings and mostly tapering posteriorly. Umbonal part near the anterior end of the valves. Hinge edentulous. Shell margins smooth. Posterior slope frequently with ridges or radial riblets. Periostracum thick, adherent and generally with hard calcareous incrustations or a precipitation of soft calcareous matter. Adults byssate; shells closing without a byssal gape. Seven subgenera are distinguished on the basis of the presence and structure of calcareous incrustations.
The animals bore in different hard substrates varying from rock to living tissue. Young individuals attach to the substrate with byssus threads after which they chemically bore into the substrate (Kleemann, 1990).

Subgenus Diberus Dall, 1898
Calcareous incrustations clearly present (visible without magnification) and distinctly projecting beyond the valves.

Description (by Merijn Bos)
Dorsal side not always clearly divided in a posterior and an anterior part. Periostracum regular, smooth and light brown. Growth lines fine and evenly distributed. Calcareous incrustation partly covering the valves from the hinge to the posterior end. Irregularly ridged with wavy lines only posteriorly, extending 0.5 to 1.2 mm beyond posterior ends of the valves.

Differentiation
Lithophaga malaccana most closely resembles L. mucronata. The latter species has a smooth calcareous incrustation, without a pattern as clear as in L. malaccana. In both L. malaccana and L. mucronata the incrustations extend considerably beyond the shell rim. L. laevigata and L. lessepsiana can have calcareous incrustations with a pattern of ridges as well, but in contrast to L. malaccana these never extend beyond the shell rim.

Lithophaga (Diberus) mucronata (Philippi, 1846)
Modiola mucronata Philippi, 1846: 4/150, pl. 1, fig. 8; "Java".
Material: Lae Lae W (RMNH 87945/3), Bone Baku W (RMNH 87950).

Found associated with:
Fungia (Verrillofungia) scabra, Fungia (Pleuractis) moluccensis, Heliofungia actiniformis.
Source: Hoeksema & Kleemann, 2002

Description (by Merijn Bos)
Dorsal side divided in a posterior and an anterior part. Periostracum slightly rough, brown. Shell completely covered with little calcareous precipitation, growth lines hardly visible therefore. With a hard calcareous, posterior incrustation, posteriorly tapering and smooth, extending 0.75 to 1.3 mm beyond posterior shell rim.

Differentiation
The most conspicuous diagnostic character on the outside is the absence of any structure in the calcareous incrustation. Lithophaga mucronata resembles L. malaccana most, but in the latter species there is a clear pattern of ridges in the posterior incrustation and the shell surface is much smoother.

Lithophaga (Diberus) lima Lamy, 1919
Lithophaga lima (Jousseaume MS) Lamy, 1919: 256-257; "Djibouti, Aden".
Material: Bone Baku W (RMNH 87942/2), Samalona SW (RMNH 87916).

Found associated with:
Fungia (Verrillofungia) scabra, Fungia (Pleuractis) moluccensis, Lithophyllon undulatum.
Source: Hoeksema & Kleemann, 2002

Description (by Merijn Bos)
Periostracum dark brown and smooth. Calcareous precipitation covering the entire shell, posteriorly forming a crust. Incrustation with chevron-like pattern, extending 0.2 to 0.6 mm beyond shell rim.

Differentiation
Shells more elongate than those of other Lithophaga species. The most typical character of Lithophaga lima on the outside are the chevrons in the calcareous incrustation. In L. malaccana there are vertical ridges.

Remarks
Both specimen were collected dead and heavily damaged. One specimen was apparently killed by a predator that bores through the shell, leaving a small, circular hole. The incrustation of both specimen contained other calcareous elements, among which a small gastropod.

Subgenus Leiosolenus Carpenter, 1856
Calcareous incrustations if present, only posteriorly, thin and not projecting beyond shell rim.

Lithophaga (Leiosolenus) laevigata (Quoy & Gaimard, 1835)
Lithodomus levigatus Qouy & Gaimard, 1835: 464-465, pl. 78, fig. 17-18; "Dorey, Nouvelle-Guinée".
Material: BAL.25 (RMNH .. M5), BAL.23 (RMNH .. M7), Bone Baku W (RMNH 87952).

Found associated with:
Fungia (Verrillofungia) scabra, Fungia (Verrillofungia) spinifer.
Source: Hoeksema & Kleemann, 2002

Description (by Merijn Bos)
Dorsal side only in M5-2 divided in a posterior and an anterior part. Periostracum only rough at posterior end, light brown. At the posterior end a chevron-like pattern is discernible (6 to 12x magnification). Calcareous incrustation without any clear pattern, accumulating on the rough posterior part of the periostracum.

Differentiation
Lithophaga laevigata is not easy to recognise. The calcareous incrustation, if present, covers the rough part of the periostracum which can be chevron-like. This incrustation can consist of ridges like in L. malacccana or L. lima, but it never extends beyond the shell rim.

Lithophaga (Leiosolenus) lessepsiana (Vaillant, 1865)
Lithodomus lessepsianus Vaillant, 1865: (115), 123-124; "dans l'isthme de Suez".
Material: Bone Baku W (RMNH 87944/2), Kudingareng Keke W (RMNH 90181), Bone Tambung SW (RMNH 87941), Lae Lae W (RMNH 87945).

Found associated with:
Fungia (Danafungia) horrida, Herpolitha limax, Halomitra pileus, Lithophyllon undulatum.
Source: Hoeksema & Kleemann, 2002

Description (by Merijn Bos)
Dorsal side divided in a posterior and an anterior part. Smooth periostracum light brown in smaller specimen, dark brown in larger ones, sometimes with lighter bands along growth lines. Almost no accumulation of calcareous matter at the posterior end; if present, then structured with fine, hardly visible (at 6 to 12x magnification), wavy lines.

Differentiation
Lithophaga lessepsiana most closely resembles L. simplex. Shells of both species lack any conspicuous posterior calcareous incrustation on the shell. According to Kleemann (1980), L. simplex is more oval and smaller than L. lessepsiana. In L. lessepsiana sometimes a calcareous pattern of wavy ridges might be discernible at 6 to 12x magnification.

Lithophaga (Leiosolenus) simplex Iredale, 1939
Lithophaga simplex Iredale, 1939: p. 421, pl. 6, fig. 25; "Low Isles".
Material: Kudingareng Keke SW (RMNH 87906, RMNH 87905/2).

Found associated with:
Fungia (Wellsofungia) granulosa, Sandalolitha robusta.
Source: Kleemann & Hoeksema, 2002

Description (by Merijn Bos)
Dorsal side regularly curved. Shell oval. Periostracum light brown, slightly rough at posterior end. Calcareous incrustation soft, not in a particular pattern and not accumulating at specifically the posterior ends of the valves.

Differentiation
Lithophaga simplex most closely resembles L. lessepsiana. In his revision of Queensland Lithophaginae (1979), Wilson even places L. simplex into the synonymy of L. lessepsiana. Kleemann (1980) however, states that L. simplex is more oval than L. lessepsiana. This difference is not quite as obvious as Kleemann states. Samples identified as L. lessepsiana by Hoeksema & Kleemann (2002) are elongate to oval, but on average much larger than L. simplex specimen. Moreover the shells of these specimen have differences in the pigmentation of the periostracum, which is absent in L. simplex specimen.
Within this description of Lithophaga simplex the criterion of total absence of any calcareous incrustation was used as most diagnostic character.

Lithophaga (Leiosolenus) punctata Kleemann & Hoeksema, 2002
Lithophaga punctata Kleemann & Hoeksema, 2002: ; "Spermonde archipelago, SW Sulawesi".
Material: Bone Lola W (RMNH 87886), Kapodasang N (RMNH 87894, RMNH 87895), Kudingareng Keke SW (RMNH 87899, RMNH 87908), Bone Baku W (RMNH 87943, RMNH 87903), Samalona SW (RMNH 87921), Lae Lae W (RMNH 87945/3), Kudingareng Keke W (RMNH 90180), BAL.23 (M6), BAL.25 (M5-1).

Found associated with:
Fungia (Verrillofungia) repanda, Fungia (Verrillofungia) spinifer, Fungia (Pleuractis) paumotensis, Sandalolitha robusta, Halomitra pileus, Lithophyllon mokai.
Source: Hoeksema & Kleemann, 2002

Description (by Merijn Bos)
Dorsal side not divided in a posterior and an anterior part. Periostracum mostly dark brown with light brown patterns parallel to the growth lines. Growth lines fine and evenly distributed, turning rough postero-dorsally. Dark brown band from mid-dorsal to ventro-posterior, often covered by a thin calcareous layer. This layer, if present, covers the valves in a band pattern from mid-dorsal, laterally to posterior end, not projecting beyond posterior ends of the valves. Calcareous incrustation irregularly ridged only posteriorly because of the rough, posterior part of the periostracum. There is a very typical band with regularly distributed dots from the lateral-anterior to the lateral-posterior end, mostly not covered by little calcareous precipitation.

Differentiation
Lithophaga punctata is one of only very few Lithophaga species with a conspicuous structure on the shell and the only one known where the structure consists of dots. Small specimen often are clearly bi-coloured. The dots are less conspicuous at larger specimen and the bi-coloration is less extreme then.