Amphioxus lanceolatum Pallas, 1774

Synonyms: Branchiostoma lanceolatum Pallas, 1744

Common names: Engl: Lancelet; Bulg: Lantsetnik, Russ: Lantsetnik, Ukr: Lantsetnyk

Order: AMPHIOXI

Family: BRANCHIOSTOMIDAE

Taxonomic description: Amphioxus lanceolatum belongs to the higher cord animals, that do not have a spinal column, but rank right below the vertebrates in the taxonomy. The cord is clearly differentiated and runs through the whole body length. The body is segmented, dorso-ventrally flat, spindle-shaped, pointed at both ends. Colour is pink, semi-transparent. There is a membranous flipper along the dorsal side. The caudal end of the body has a lance-like flipper, where the name of the animal originates from. Cranium and head are not differentiated as well as central nervous system. There is no heart either but pulsating blood vessels instead. The length of the body reaches usually up to 3-5 cm and rarely - up to 8 cm.

Amphioxus lanceolatum arealIUCN Status:
    World level:
    Black Sea Regional level:
    Subregion level: VU

Distribution:

Habitats type, Critical habitats, Limiting factors: Amphioxus lanceolatum inhabits the sandy sublittoral zone at depths down to 28-30 m. It is accompanied by some specific Polychaeta species (e.g. Staurocephalus keffersteini) forming together the biocenoses “Amphioxus sand”. It prefers sand mixed with shells. It is very rare on muddy bottoms because it is not adapted to penetrate ground with small particles.

Biology: A. lanceolatum feeds on: microalgae, infusoria, crustaceans, etc. Its behavior differs according to the ground structure. In coarse sand, where water is rich in oxygen and food particles circulate freely, it buries itself entirely. In fine sand only half of the body is buried and half of it emerges from the ground. In muddy ground it does not bury itself at all because it can neither feed nor breathe there. The animal is more active during the night. It reproduces during the summer. It lives for to 4 years.

Population trends: Muddy areas have expanded during the last decade as a result of the intensive dumping of dead organic matter. It is unfavourable for the Amphioxus lanceolatum because a change in the ground results in a considerable decrease in its abundance. In the 1960s the species was quite common along the Bulgarian coast with the highest abundance recorded north of Cape Maslen Nos at 21 m depth (1130 ind/m2). In 1981 it was still encountered in Varna bay but in 1991 the species did not occur in seasonal investigations in the same region. Separate individuals of A. lanceolatum were found in the southern region (Sozopol) in autumn1996.

Threats: The main threat is the reduction in areas with coarse sand as a result of eutrophication and organic pollution.

Conservation measures taken: No measures have been taken so far.

Conservation measures proposed: Reduction in pollution and eutrophication on global scales.

References:

  1. Jizn jiwotnih. 1983. v.IV, Moskow “Proswestenie”, pp. 9-11.
  2. Kaneva-Abadjieva, V., T. Marinov. 1966. Razpredelenie na zoobentosa na piasachnata biocenoza pred balgarskia chernomorski briag. Izv. NIORS, Varna, v.7, pp. 69-95.
  3. Cherno more. Sbornik. 1978. “G.Bakalow”, Varna, pp. 123-124.
  4. Marinov, T. 1990. Zoobentosat ot balgarskia sector na Cherno more” BAN, p. 195.
  5. Konsulova, Ts. 1992. Seasonal structure and ecological status of Varna Bay (Black Sea) sandy and muddy macrozoobenthic coenoses. Rapp. Comm. int Mer Medit., v.33, p. 42.

Compiled by: T.Konsulova