Trachinus LINNAEUS, 1758

Přikryl, Tomáš, 2009, A Juvenile Trachinus Minutus (Pisces, Perciformes, Trachinidae) From The Middle Oligocene Of Litenčice (Moravia, Czech Republic), Acta Musei Nationalis Pragae Series B 65 (1 - 2), pp. 3-8 : 4-5

Genus Trachinus LINNAEUS, 1758

Trachinus minutus ( JONET, 1958) Figs 2, 3A

1958 Megalolepis minutus JONET, Pl. 8, Fig. 5

1968 Trachinus minutus (JONET) Jerzmańska, Pl. 6, Fig. 1; Text fig. 20

1991 Trachinus minutus (JONET) Pharisat , Figs 44, 45

The body is elongated, with a large head. Although the total length is only 16.5mm, most of the bones are well ossified. The caudal penducle depth is about 28 % of the body depth. The head is almost triangular in shape and its length exceeds the depth of the body. The head length is 29.3 % of standard length (SL). The maximal body depth was 6.4 times the SL. Measurements of the specimen and percentages of the standard length and head length are given in Table 1.

S k u l l: The ratio of the head length to the head depth equals 1.09. The eye is quite large and it is placed in the anterior part of the head (preorbital length is 27.4 % of the head length). The diameter of the orbit is about 25 % of the head length. The mouth is moderately large and elevated. The neurocranium is relatively deep (34.7 % of head depth). The parasphenoid is exposed in the middle part of the orbit as a slender shaft. Infraorbital bones are poorly preserved. The praemaxilla has an ascending process probably fused with the processus articularis. The praemaxilla bears small conical teeth which are arranged in several rows. The maxilla is relatively narrow and has a distinct articular head. The attachment between dentary and angulo-articular is not obvious. The teeth preserved in the dentary are small, sharp and conical. The lower jaw articulation is under the anteriormost part of the orbit. The quadrate has a triangular corpus quadrati and along its anterodorsal edge the corpus quadrati articulates with the ectopterygoid. The praeoperculare ( Text-fig. 3A ) is sickle shaped. The anterior part of the ramus horizontalis is not preserved. The outer margin of the praeoperculare has 5 spiny projections. The operculare is a thin broad plate. The posterior part of the operculare is not preserved. There are 5 branchiostegal rays preserved.

A x i a l s k e l e t o n: There are 23 caudal vertebrae (including urostyle) and most probably 7 abdominal vertebrae. The first two abdominal vertebrae are covered by the dorsal part of the operculare. The ribs are not preserved. The vertebral column is S bent and slightly elevated dorsally in the anterior part of the body. The ratio of vertebra length to its maximum depth is 1.34 (measured at the first caudal vertebra). The neural spines are long and slender in the first half of the body, in the second half of body they are shorter than the haemal spines. The haemal spines are relatively long and slenderand slightly curved (straight in the posterior half of the caudal part of the body).

The dorsal fin is preserved directly behind the head. There are 5 spines preserved in the anterior dorsal fin. Other rays and spines are not preserved.

The anal fin is poorly preserved and it is impossible to determine the number of fin rays.

The pectoral fin has 13 rays. The fin base is positioned under the third abdominal vertebra. The ventral fin has one spine and probably six rays. Its base is situated directly behind the head in the ventral part of body.

The caudal fin has 16 preserved rays.

Scales are absent.

Figures

Text-fig. 3. Trachinus minutus, praeopercular shape, lateral view. A – Litenčice specimen (Czech Republic). B – Froidefontaine specimen (France). C – Specimen from Jamna Dolna (Poland). Scale bar represents 1mm. According Pharisat (1991) and Jerzmańska (1968), modified.