Cave Chaetognaths In The Canary Islands (Atlantic Ocean)

5 Pages·1998·1.6 MB·

by  F Hernandez

PROCEEDINGS OFTHE BIOLOGICAL SOCIETY OF WASHINGTON
lll(4):916-920. 1998.
Cave chaetognaths in the Canary Islands (Atlantic Ocean)
F. Hernandez and S. Jimenez
Museo de Ciencias Naturales (Dpto. de Biologia Marina), Apto. 853. 38080,
Santa Cruz de Tenerife, Islas Canarias
—
Abstract. Morphological and biometric observations ofchaetognaths found
in a submarine cave on the southeast coast of Tenerife (Canary Islands) are
presented. The specimens, that we have called Spadella aff. ledoyeri, differ
notably from the coastal species Spadella cephaloptera, which is a well known
inhabitant of the submerged seagrass beds of the infralittoral areas of the is-
lands. Because the genus Paraspadella was previously described from an an-
chialine cave on the Grand Bahama Island (western Atlantic Ocean), this is the
second record of an Atlantic cave chaetognath and the first for the genus Spa-
della in Atlantic Ocean caves.
The Canary Island benthic chaetognaths, ta Cruz and Candelaria. Two trawls were
unlike the pelagic species, have only rarely carried out, using a 200 |Jim, manual plank-
been studied. Among the few studies done ton net, 12 m from the entrance and a few
are those of Hernandez & Jimenez (1992) cm above the bottom. A total of 42 chae-
and Broerse (1993), which deal with bio- tognath specimens belonging to the genus
metric aspects of Spadella cephaloptera Spadella was obtained.
(Busch, 1851) in the island of Tenerife. The specimens were measured to give
This species has been found in beds of the data on total length, caudal length, ovarian
submerged sea grass Cymodocea nodosa length, and the number of grasping spines
and on patches of the alga Caulerpa proli- and teeth. For comparison, we used speci-
fera in shallow infralittoral areas of the is- mens ofSpadella cephaloptera, which were
lands of Tenerife (Hernandez & Jimenez caught on the same dates as the cave spe-
1992, Broerse 1993) and Gran Canada, es- cies. These were caught in trawls over beds
pecially in areas with a sandy substratum. of sea grass and algae off the islands of
The discovery ofbenthic cave chaetognaths Tenerife and Gran Canada.
in the Mediterranean (Casanova 1986,
1992) and in the Bahamas (Bowman &
Cave Charactedsties
Bieri 1989) has led us to trawl for them in
dark submarine caves. Specimens of these The cave is a volcanic pipe at the bottom
organisms were found, but they were dif- of a submarine canyon. It has a broad en-
ferent from descriptions of the benthic spe- trance and a sandy floor. The cave narrows
cies S. cephaloptera, which is well known close to the entrance and then widens out
in the islands. again after about one m. The back of the
cave is marked by a natural blockage of
m
Materials and Methods sand. The cave is 16 below ground level,
m m
with a slope of 1.3 and is 15 deep.
The material collected comes from a Geological interest in the cave stems from
dark, submarine cave, situated onthe south- the fact that it forms part of the lava fields
east coast of the island of Tenerife (Canary that flowed from the back of La Esperanza
Islands) (Fig. 1), between the towns ofSan- (Tenerife) to the coast and into the sea.
VOLUME 111, NUMBER 4 917
Canary Islands
LaGomera \
o GranCanaria
26" ElHierro
=^
17» 16» IS" 14°O
_J I _J \
Fig. 1. Location ofthe sample station in the southeast ofTenerife (Canary Islands).
Apart from the chaetognaths, other fauna teeth observed. The maximum size for
mm
found in the cave included shrimps (spawn- stage III sexual maturity is 4.5 (4.3
ing females ofPlesionika narvat), tubicular mm, mean) (Table 1). Biometric datais also
Polychaeta, sponges, formations of Nadra- provided for each sexual stage of the spec-
cis asperula (corals), prawns (Lysmata imens of this study (Table 1). These data
grabhami) and echiurids (Bonellia viridis). have been compared with the specimens
corresponding to the Tenerife (Hernandez
Results and Discussion & Jimenez 1992) and Gran Canaria speci-
The chaetognaths studied showedthefol- mens (Table 2).
The specimens collected in the cave be-
lowing taxonomic characteristics (Figs. 2,
long to the genus Spadella, but do not pre-
3): General aspect ofthe body: white, long,
thinner than in Spadella cephaloptera, sent the typical characteristics of Spadella
which is thicker and yellowishbrown. Head cephaloptera. The specimens studied are
square, not oval as in S. cephaloptera (Fig. closer to Spadella ledoyeri, a cave dwelling
2). Short lateral fins (only 50% of the cau- chaetognath of the Mediterranean (Casa-
dal region), wider than in S. cephaloptera, nova 1986). Among the morphological dif-
which start just before the tail. Ocular pig- ferences between our specimens and those
ment present. The ciliata corona is com- of S. cephaloptera, we observed: the shape
pletely circular and different from that ofS. of the ciliata corona, shape and position of
cephaloptera studied in Tenerife and Gran seminal vesicles, shape, position and exten-
Canaria, where it is more flattened and bi- sion of the lateral fins, shape and general
lobed (Fig. 3). Caudal fin completely tri- aspect of the body, shape and size of the
angular; in S. cephaloptera, it is spatula collarette and the aspect ofthe eye pigment.
shaped. Triangular seminal vesicles, sepa- Although the shape ofthe ciliata coronacan
rated from the lateral and caudal fins. In S. vary (Ghirardelli 1968), the characteristics
cephaloptera, the seminal vesicles touch are valid and have a high taxonomic value.
both fins. Caudal region strong and broad. Concerning Atlantic cave-dwelling chae-
Cephalic tentacles and intestinal diverticu- tognaths, the only other species on record
lae were not observed. Ovaries with large, is Paraspadella anops, described from a
rounded ovules. Ten or eleven reddish-light single specimen from Sagittarius Cave near
brown grasping spines. Only 3-4 anterior Gran Bahama Island (Bowman & Bieri
918 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
1 i:.* 'c*
A :# *
,#*^
M
11
1 m
I'
2 mm 2.4 mm
B
Fig. 2. Selected specimens from the samples. A, Spadella aff. ledoyeri; B, Spadella cephaloptera.
1989). This species, as in the case of our Mediterranean from submergence during
specimens of Spadella ledoyeri, is clearly the most recent ice age, or alternatively,
the descendent of Paraspadella schizop- from the deep water species, Spadella bi-
tera, the common neritic species of the re- rostrata, isolated in cavities ofdeepercaves
gion, from which it differs in only a few flooded during a prior glaciation (Casanova
characteristics. 1992).
Likewise, Spadella ledoyeri is believed For the first time in the Atlantic Ocean,
to have evolved from either Spadella ce- benthic chaetognaths of the genus Spadella
phaloptera, isolated in the caves of the from underwater caves are described. Inthe
—
Table 1. Biometric characteristics of stage III specimens ofSpadella aff. ledoyeri on Tenerife. TL = total
length, CL = caudal length, %C/T = relative tail length in relation to total length.
TL(mm) CL(ram) %C/T
Stage I 3.0 1.5 50.0
n = 1
Stage II 3.0^.5 1.5-2.5 42.9-55.6
n = 23 average: 3.9 average: 2.0 average: 50.0
Stage III 4.0-^.5 2.0-2.5 44.4-55.6
n = IS average: 4.3 average: 2.2 average: 51.5
VOLUME 111, NUMBER 4 919
B
Fig. 3. Spadella aff. ledoyeri. A, caudal fin; B, seminal vesicle; C, ocular pigment; D, head and neck.
Spadella cephaloptera. E, caudal fin; F, seminal vesicle; G, head and neck.
—
920 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON
—
Table 2. Comparisonoftotallength(TL)forstage Acknowledgments
III specimens ofSpadella aff. ledoyeri from GranCa-
naria and Tenerife. Our sincere thanks go to Dr. Stephen
Gardiner (Associate Editor) and to the col-
TL(mm) Island Month Habitat lector, Alfredo Lainez, who sent us the
5.5 Gran Canaria April seagrass specimens, together with collection data.
4.0 Tenerife April seagrass
3.5 Tenerife December seagrass Literature Cited
4.5 Tenerife April cave
Bowman,T E., &R. Bieri. 1989.Paraspadellaanops,
new species, from Sagittarius cave Gran Ba-
hama—island, the second troglobitic chaeto-
gnath. Proceedings of the Biological Society
Canary Islands, therefore, as is the case in ofWashington 102:586-589.
the Mediterranean (Casanova 1992, genus Broerse,A.T C. 1993. BiometricvariationinSpadella
Spadella) and the Bahamas (Bowman & cephalop—tera on the Canary islands (Chaeto-
gnatha). Beaufortia43(6):101-113.
Bieri 1989, genus Paraspadella), these an-
Casanova, J. P. 1986. Spadella ledoyeri, chaetognathe
imals exist in the biotope of submarine nouveau de la grotte sous-ma—rine obscure des
caves, where, according to the above men- Tremies (CalanquedeCassis). RapportsCom-
tioned authors, there are original popula- mision international Exploration Mer Mediter-
ranee 30,2:196.
tions.
New collections will be done, at different M.ed1i9t9e2r.raLneese cnhoaredt-oocgcniadtehnstaclea:vemaidcapotlaetsiodnes leat
times of the year, extending the study to speciation, comparaison avec I'Atlantique.
other caves in the islands, in order to in- Bulletin Institute Oceanographique Monaco 9:
83-100.
vestigate the biological cycle and to clarify
Ghirardelli, E. 1968. Some aspects of the biology of
certain aspects, which are debated in the the Chaetognaths.—Advances in Marine Biol-
Mediterranean, of the origin of the cave ogy 6:271-375.
dwelling species and make accurate com- Hernandez, F, & S. Jimenez. 1992. Primeras obser-
parisons between Spadella aff. ledoyeri and vaciones sobre la presencia del genero benton-
the coastal species Spadella cephaloptera ierciofeSp(aCdanealrliaas()C.h—aeAtcotgansatdheal)VenSilmapoissliaodIebeTreinc-o
from waters surrounding the Islands. de Estudios del Bentos Marino 2:95-102.