BULLETIN OF MARINE SCIENCE, 70(1): 33–39, 2002 TAXONOMY AND ZOOGEOGRAPHY OF MICRODESMUS CARRI GILBERT (MICRODESMIDAE) Felipe Amaya, Arturo Acero P. and María M. Criales ABSTRACT This contribution describes juvenile specimens of the cienaga wormfish Microdesmus carri (Microdesmidae) collected at the entrance of the estuarine lagoon Ciénaga Grande de Santa Marta on the Colombian Caribbean. This is the first report of M. carri for South American waters and the third of the species since it was originally described from the Caribbean coast of Costa Rica and later reported for Belize and the Gulf of Mexico. Meristic and morphometric data of the Colombian material are similar to those described for Costa Rica but differences from the Belize and Gulf of Mexico material were found in the fin counts. The species is considered here a southern Caribbean endemic, whose distribution may be explained by geological and oceanographic factors. The gobioid fish family Microdesmidae is widespread in marine tropical waters and includes two subfamilies: Microdesminae (wormfishes) and Ptereleotrinae (dartfishes or firefishes) (Nelson, 1994). However, Thacker (2000) excluded the dartfishes from the Microdesmidae. Wormfishes burrow in soft muddy and sandy bottoms in shelf ecosys- tems from coral reefs to estuaries and from tidepools to about 40 m depth (Robins et al., 1986; Nelson, 1994). Seven species of wormfishes have been described for the western Atlantic, two in the genus Cerdale (C. fasciata and C. floridana) (Dawson, 1974) and five in the genus Microdesmus (M. bahianus, M. lanceolatus, M. longipinnis, M. lucus and M. carri) (Gilbert, 1966; Dawson, 1977). The only wormfish previously recorded from the Colombian Caribbean is C. floridana (Acero and Garzón, 1986). Microdesmus carri was originally described by Gilbert (1966) based on 36 specimens collected from Tortuguero, Costa Rica (10∞30'N 83∞30'W), western Atlantic, in May 1963 and August 1963 and 1964. Recently, Smith and Thacker (2000) reported on additional collections of the species from the southwestern Gulf of Mexico and Belize; however, some interesting differences between their material and that from Costa Rica and Colombia merit discus- sion. The objective of this paper is to report M. carri for the Colombian Caribbean and to discuss its zoogeography. Information is also provided about the ecology of the M. carri material captured at the Boca de la Barra, Ciénaga Grande de Santa Marta (CGSM), Colombia. MATERIAL AND METHODS Collections were performed at Boca de la Barra (10∞59'N, 74∞17'W), the connection of the es- tuarine CGSM to the Caribbean Sea, with a moored channel net (800 m) suspended 50 cm below the surface. The cod end of the net was set up at sunset and retrieved after dawn for two consecutive days during the full and the new moon monthly from February 1998 to February 1999 (Criales et al., 2002). Fish larvae and juveniles were sorted and identified to the lowest possible taxon. Fin elements were counted on 34 specimens following Gilbert (1966) and using an ocular micrometer in a stereomicroscope. Measurements were made on 15 specimens, which were cleared and stained using the Smith and Richardson (1979) technique (Table 1). Descriptive information about the species is included based on Colombian material and the original description. 33 34 BULLETIN OF MARINE SCIENCE, VOL. 70, NO. 1, 2002 RESULTS AND DISCUSSION Microdesmus carri Gilbert, 1966 (Fig. 1, Table 1) Material Examined.—A total of 112 specimens were collected at the Boca de la Barra, of which a peak of 98 juveniles were collected in July and the remaining specimens in March, June, August and September. Specimens are kept at the fish collection of the Instituto de Investigaciones Marinas y Costeras (INVEMAR 2409), Santa Marta, Colom- bia. All specimens were of uniform size ranging between 27 and 30.5 mm standard length (SL), precluding analysis of migrations or structural development of the growth of indi- viduals. Diagnosis.—M. carri can be separated from all other Microdesmus from the western Atlantic by the following combination of counts: dorsal fin with 25–26 (modally 25) spines and 67–71 (modally 69) total elements, anal fin with 33–37 (modally 35 and 36) rays and originating between verticals from dorsal-fin elements 33/34 and 36/37 (mod- ally 35/36), total dorsal and anal fin elements 100–107 (modally 104), and 36–38 (mod- ally 37) precaudal vertebrae (Table 1). The material from Belize and the Gulf of Mexico reported as M. carri by Smith and Thacker (2000) has generally higher fin counts. Description.—The head is somewhat depressed anteriorly, with a blunt tip, 10.8–12.2 % SL; the eyes are lateral on the highest part of the head, their diameter 20.3–25.4 % of the head length, the lips are fleshy but not very large (Fig. 1, Table 2). The lower jaw has only one row of short, strong, pointed, conical, and backward oriented teeth, which de- crease in size posteriorly. Gill openings are somewhat long, beginning immediately be- fore the insertion of the first pectoral-fin ray; the opercular margin runs vertically to- wards the isthmus. The body is elongated and tubular. The dorsal fin originates after the beginning of the pectoral fin; the predorsal fin length is 17.9–20.5 % SL. The dorsal fin is not confluent with the caudal fin and has XXV or XXVI spines and 42–46 rays, with XXV, 44 as the modal count. The total number of vertebrae ranged between 66 and 70, modally 68 (Table 1). All specimens were naked. In general our specimens coincide with the original description of the species, but Smith and Thacker’s (2000) material from Belize and the Gulf of Mexico tends to differ from the southwestern Caribbean speci- mens. The main differences based on Smith and Thacker’s (2000) description of their specimens, are centered on the higher counts of the northern material, i.e., anal-fin rays 35–39, mean close to 37, and counts in one specimen of XXVI, 46 dorsal-fin elements and anal fin originating at vertical of dorsal-fin elements 38/39. The total of 110 elements in the specimen reported by Smith and Thacker (2000) is well over 107, the upper limit of the Costa Rican and Colombian material. It may seem that the northern population is more elongated, i.e., it has higher number of dorsal and anal fin elements; nevertheless, it does not seem to clearly have higher vertebral counts than the southern population. Gil- bert (1966: 527) reported that “M. carri and M. suttkusi share the following characters, the combinations of which are unique among the species of Microdesmus: total dorsal elements 67 to 71; total anal elements 33 to 37 (33 to 36 in M. carri); origin of anal fin beneath 33rd ro 37th dorsal elements.” Dawson (1977), in his key to western Atlantic species of Microdesmus, reported that M. carri has 24–27 dorsal fin spines and 34–40 AMAYA ET AL: STATUS OF MICRODESMUS CARRI 35 Table 1. Meristic data of southwestern Caribbean specimens of Microdesmus carri. Data from Costa Rica were taken from Gilbert (1966). Tsotal dorsal fin elements Anal fin element 687 69607173343536373 C150osta Rica 1741-791- C774olombia 16- 1151341 Total dorsal and anal fin elements 1100 120 130 140 150 160 170 10 C1--10osta Rica 1474 C18265855olombia Position of anal-fin origin in relation to dorsal-fin elements 353/34 364/3 375/3 36/3 C1695osta Rica C190olombia 24 Precaudal and caudal vertebrae 36+360 3 +361 3 +372 3 +370 3 +371 3 +382 3 +380 3 +381 3 +32 C123263-1-osta Rica C-212521-1olombia (modally 37) anal fin rays. Those ranges are very wide, even including the northern ma- terial. We do not have an explanation for such discrepancies. Pigmentation.—Specimens of M. carri kept in alcohol after several days of being cap- tured were relatively unpigmented. The most conspicuous pigmentation was a row of small and elongated melanophores from throat to level of pectoral-fin base, diverging into a paired series to a point slightly behind half-way between pelvic-fin base and anal- fin origin. There was also a paired series of melanophores located at both sides of the base of each anal-fin ray. Medially on the caudal peduncle there is an elongated melano- phore and on the caudal-fin base one or two additional melanophores. Specimens de- scribed by Gilbert (1966) were separated into two distinct morphological types. Two large individuals (36.0 and 53.0 mm SL) were well pigmented on body and fins, with a rounded caudal fin, the dorsal and anal fins adnate to caudal. The other 34 smaller indi- viduals (28.0 to 33.5 mm SL) were almost completely devoid of pigment on body and fins with an emarginate caudal fin and the dorsal and anal fins not adnate to caudal. M. carri from Colombia corresponds to the postlarval or juvenile stage described by Gilbert (1966). The shape and development of the anal fins also correspond to Gilbert’s descrip- tion. Gilbert (1966) found that the Tortuguero specimens collected at midday were heavily pigmented in contrast to those collected during the night,which were unpigmented. Be- cause we did not collect during daylight light hours we can not add to this discussion. Common Name.—Herewith we propose for M. carri the official common name of cienaga [pronounced sjé-na-ga] wormfish, from the Spanish ciénaga meaning shallow lagoon or swamp, which is the kind of environment in Colombia and Costa Rica where the species has been found. Ecology.—Almost nothing is known about the life history, habits or behavior of these fishes.