Bursa scrobilator

ACERCA DE Bursa scrobilator






                  About  Bursa  scrobilator  Linné,1758



                                      Jose F. Verdejo Guirao



Keyword:  Bursa, scrobilator, Mediterranean, Canary Is.,Tenerife, coriacea






Abstract



Nowadays, Bursa scrobilator Linné,1758 is, in general sense, one of the most uncommon Mediterranean molluscs. After several years of observation and researching, I can provide some data and references about its location in the Mediterranean sea and the Atlantic Ocean, as well as put forward some hypotheses about its current presence in these areas and about the larval stage of the specie. Finally, I give my personal opinion about the differences between the typical Mediterranean form and the Atlantic ones.




             

          Fig.1.- B. scrobilator from  Alboran sea (59x31mm) and Canary Is (60x35 mm and 67x38 mm)
 

Introduction

     For more than ten years, I have been able to get some data about Bursa scrobilator Linné, 1758. I have now some information about more than seventy specimens obtained from the Mediterranean and Atlantic areas.

     The difficulty in establishing the areas where this specie lives lies in its rarity and in the poor knowledge that we have about its habitat. In the last few years, this evasive specie could be observed in its real environment, in Tenerife (Canary Is), where it was occasionally collected alive.
    After carrying out a comparative study between the Mediterranean specimens and the Atlantic ones (from the Canary Islands and the African coast), it is possible to reach to some conclusions about the varieties or different geographical races of this scarce specie. Some authors such as BARBERINI (1985) have recently considered different the Atlantic and the Mediterranean races in general sense. They think that the atlantic's scrobilator shows some different characteristics.

    In the last revision to the Bursidae family, COSSIGNANI (1994) rejects the pustulosa and the atlantica varieties. On that point he agrees with POPPE (1991) and G.D. SAUNDERS (1981), but his proposal is against the existence of the B. scrobilator coriacea Reeve, 1844. Cossignani considers it as a simple form distributed along the Senegal coast up to the Tunisian coast in the Mediterranean Sea. From my point of view, the presence of this variety in Tunisian waters is very uncertain, and there is no news about typical scrobilator in any case. However, I would thank any information about it.
    According to my information on the subject, the range of the coriacea variety goes from the Senegal Coast to the cold and turbulent Angola waters. Including Cape Verde Is BURNAY&MONTEIRO (1977) and Gabon, BERNARD (1984).The Guinea Gulf is in doubt.


Material  and methods:



   In the last few years, the information about live specimens collected in the Mediterranean Sea has been scarce. Beached shells have been, more frequently, collected in the Melilla area, Granada and Málaga coast and the Morocco Atlantic coast.

   However, in the Canary Islands, the species is more often present. It can be found in Tenerife, La Palma, Fuerteventura and Gran Canaria. Nowadays it is possible to collect alive specimens in Tenerife, although it is more usual to collect dead ones.



                    Fig.2 Likely range and last collecting areas
 
      The map shows the Mediterranean localities (red points) and the atlantic areas (red and light blue) where alive specimens, shell fragments and dead shells have been collected in the last few years. It also shows other areas (pink and dark blue) where it would be theoretically possible to find them. 

Most of the Mediterranean specimens were collected in the beach (Melilla, Alicante, Almeria) and by dredging (Melilla area, Granada, Malaga all localities in Alboran Sea). Those shells from the Canary Is. were collected by scuba-diving (the author got a specimen with a hermit crab  Pagurus anachoretus Risso,1827 in the Gran Canary Island in 1989) and the rest were collected by dredging.

       
     In the Canary Islands it has been possible to observe some specimens eating coralline polyps and sea urchins, their favourite preys, with a fast execution (observations made in an aquarium for Vega Luz). B. scrobilator probably uses the prosbicis and some kind of toxic substance as self-defence or to paralyse its victims (Houbrick and Fretter et al.1969).



      The natural habitat of B. scrobilator are crevices under rocks that are not shifted by storms. For it is a nocturnal mollusc, its diurnal activity is very limited. It has been possible to observe up to three alive specimens, not being together, in a two or three square meter area.

If it is true that (Saunders et al.1981) these species tolerate cold water better than their congeners, the Mediterranean areas where it would be feasible for them to live would be those which withstand more than 10ºC of seasonal temperature variations. In the areas where alive specimens were collected (Almeria, Palermo,  Messina strait) the depth of the water ranged from six (6) meters to more than thirty-five (35) meters depth. This could mean that the Mediterranean habitat should be similar to that of the Canary Islands where the characteristics of the water coincide. Another important factor to take into account would be the need of areas rich in coralline polyps and powerful marine currents.



Discussion



    After comparing almost forty Atlantic specimens (from Marocco, Canary Is. and from Mauritania to C. Frio), to more than twenty Mediterranean ones, no significant morfological differences has been founded between them. B. scrobilator is a specie scarcely variable which only shows light variations in shape, colouring and granulosity (Figs. 1-M at 12-C on Plate).
In the second and third raw on plate, alive specimens from Tenerife are shown (5-C,8-C, and 11-C). It is possible to appreciate that they are similar to the Mediterranean ones especially in granulosity and nodules. But as those specimens from the Canary Is. were collected alive, they show a brighter coloration close to intense red (except Melilla specimen 10-M). Live taken specimens show a periostracum with light transparency and when they are dried acquire a whitish tone (5-C). To summarize, the light differences observed are within the common variability of the species.




     However, significant differences appear between the B. scrobilator and those specimens from Senegal and Angolan waters. The latter are smaller, have a paler coloration and their habitat is in deeper areas. While in Tenerife, the scrobilator appears in areas 5-25 meters deep (normally 15 meters), in Senegal (Cape de Race) it appears in areas 30 meters deep or deeper. In Angola, where the water is even colder, it appears in areas from 80 meters deep onwards.
Fig. 3



In the Fig.3 is possible to see one fresh specimen from Angola and on the plate can see two from Senegal (14-S and 15-S). Their main morphological differences with the typical  scrobilator can be summed up as follows:



-Smaller, solider and more globose

-Superficial granulosity stronger

-General coloration more homogeneous pale brown



Due to their similarities, we could think that there is an intermediate form between the B. scrobilator and the B. granularis Roding, 1798. But the latter has its northern limit in Guinea Bissau (G. Saunders et al, 1981) so this possibility is very uncertain. Therefore, these specimens probably belong to the subspecies named B. s. coriacea Reeve,1884. whose distribution range goes probably from Angola to Senegal, not having any information of its existence in the Guinea Gulf. (Any information about it would be welcomed).

Finally, in Tenerife Is. a local and deeper (more than 100 meters deep) form of scrobilator appears. It is smaller and it always appears dead. Its coloration is paler. However its characteristics are similar to the typical scrobilator (16-C and 17-C on plate), but always smaller (about 30 mm). Although it is probably a batimetric variation of the specie, it shows some similarities to the B. nodosa Borson, 1823.




Conclusions



Nowadays, B. scrobilator scrobilator has established populations, within its rarity, in the Canary Islands (especially in Tenerife) and in the adjacent Atlantic coasts. It is possible that from in these areas, and with some frequency, some larvas go through the Strait of Gibraltar in the zooplacton and are spread by the currents along the western Mediterranean areas where it has been possible to see them, sporadically, in the last few years (Fig. 5). In my "personal" view its possible that fixed populations don't exist on  the Western Mediterranean. The scrobilator´s larvas could cover this distance between Gibraltar and Sicily in less than four weeks (The Atlantic superficial currents that go trougth the strait of Gibraltar has medium rate to 60 cm/s (Margalef et al.1989), and when they reach the warmer and salty mediterranean waters they prevent many Atlantic species successing.

This chance presence of larvas of Atlantic species, allows sporadic findings of species such as Latiaxis sentix Bayer, 1971, Acrilloscala lamyi De Boury, 1909 (the author had the chance to see a 50 mm specimen caught in Malaga), Cancellaria coronata Scacchi, 1835 or Ampulla priamus Gmelin, 1791, and many other species in the Alboran Sea and in the Tyrrhenian Sea. This species could have not fixed population in this sea and depend on the successful arrival of “veliger”. This could be one explanation of the sporadical presence to B. scrobilator in Mediterranean sea, instead of other opinions about its misspelling.

Finally, the geographical variety known as Bursa scrobilator coriacea Reeve,1844, may be limited  from Senegal to Angola showing morfological shell characters  differents to typical scrobilator..



Acknowledgements



         I would like to thank my wife Julia, her patience and  inestimable help for years making possible this work.  I would like also to thank to Emilio Rolán for his critical revision of the manuscript and his valuable help. Also to Ricardo Vega Luz for the informations and help. I would like to dedicated this work to my very good friends Carmela and Giovanni Buzzurro. 





REFERENCES



Anonymous, 1758.- La Conchiglia. XV (170-171): 15.

Abbot, R .T.& Dance, P. 1980.- Compedium of Seashells. Dutton.N.Y 411 pp.

Barberini, L. 1985.- La familia Bursidae Thiele,1925 nel mar Mediterráneo.Argonauta I (2/3): 39-45.

Bozzetti, L. 1991.- Bursa nodosa Borson,1823. survives in Australia. La Conchiglia., (260) :2.

Consolado, M.C. M. 1998.- Seashell of Portugal. Verbo. 516 pp

Cossignani, T. 1994.- Bursiade of the World. Ed. L’Imformatore Piceno.Ancona. 119 pp

Franchini, D. 1974.- Mediterranean Conchology. Famiglia BURSIDAE. La Conchiglia. VI (62): 3-5.

Giannuzzi-Savelli, R. & Pusateri, F. & Palmeri, A. & Ebreo, C. 1996.-Atlante delle Conchiglie Marine del Mediterraneo.Ediz. La Conchiglia. Roma.

Houbrick, J. & Fretter,Vera, 1969.-Some aspect of the functional anatomy and biology of Cymatium and Bursa.Proc. Malac. Soc. LONDON,38:415-429

Martinez Rueda, J. 1996.- Nuevos hallazgos de Bursa scrobilator Linné.,1758. Malakos Boletín informativo.nº1 Marzo

Nordsieck, F. & Garcia-Talavera, F. 1979.- Moluscos marinos de Canarias y Madera (Gastropoda).Aula de Cultura de Tenerife. 208 pp, 44 pls,

Poppe, G. & Goto, Y. 1991.-European Seashells.Vol I.Verlag C. Hemmen. 352pp, 40 pls.

Russo, G. F. 1981.-Prima descrizione di un esemplare vivente di Bursa scrobilator Linné,1758. La Conchiglia. XIII (152-153): 20-21

Sabelli, B. & Spada, G. 1982.-Guida illustrata all’identificazione delle conchiglie del Mediterraneo.Supplemento a Bollettino Malacologico XVIII (5/6).

Saunders, G. D. 1981,.-Confronto dei dati disponibili sulla Superfamiglia CYMATIACEA nei mari europei, nel Mediterraneo e nell¨atlantico orientale. La Conchiglia. XIII (146-147) :3-6.

Settepassi, F. 1967.- Atlante Malacologico. Molluschi Marini Viventi Nel Mediterraneo. Vol I. Ed.Settepassi.Roma    

Vega Luz, R. & Vega Luz, R. 1996.-The family Bursidae Thiele,1929 (Gastropoda) of Tenerife (Canary Is.).Malakos Boletin informativo.nº1 Marzo

Wickstead, J. 1979.- Zooplancton marino. Ediciones OMEGA. BARCELONA. 70 pp





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7 comments:

Anonymous said...

Yo he recogido la concha de un ejemplar hoy, 6 de febrero de 2011, tiene unos 56 mm, está algo desgastada pero es inconfundible. La he recolectado en un tramo de costa entre la ensenada de Bolonia y la de Valdevaqueros, cerca de Punta Paloma, término de Tarifa.

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Anonymous said...

En Febrero 2011 recogí 14 ejemplares de B. scrobilator en Playa Arenas Blancas, El Hierro (hasta 60 mm). Acabo de volver de allí con 8 ejemplares (hasta 59 mm), uno recogido vivo, opérculo ovalado excéntrico. Todos típicos, de color rojo oscuro. Saludos de Alemania.

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Anonymous said...

may be that Bursa nodosa is still live?