The Ribbonfish Genus Desmodema, with the Description of a New Species (Pisces, Trachipteridae)
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THE RIBBONFISH GENUS DESMODEMA, WITH THE DESCRIPTION OF A NEW SPECIES (PISCES, TRACHIPTERIDAE) RICHARDH. ROSENBLATT~AND JOHNL. BUTLER^ ABSTRACT The genus Desmodema is unique within the Trachipteridae in that the upper caudal lobe, borne on the second ural centrum, is not upturned. and the lower caudal lobe, borne on the first ural centrum in other trachipterids, is absent, and in that there are seven dorsal pterygiophores before the first neural spine. Desmdema lorum n.sp. can be distinguished from D.polystKtum (Ogilby)on the basis of having more vertebrae, fewer caudal rays, a longer tail, and the snout longer than the eye diameter. Desmodema polystictum is probably circumtropical; D.lorurn is restricted to the North Pacific Ocean. The species cf Desmodemo have a distinctive prejuvenile phase characterized by polka dots on the sides, long pelvic fins, a relatively short tail, and elongation of the first six dorsal rays. Metamorphosis is abrupt and involves loss of the pelvic fins, elongated dorsal rays and polka dots, and a great lengthening of the tail. It is suggested that metamorphosis accompanies movement to a deeper habitat. The elongated tail is related to extension of the lateral-line sensory system. On the basis of joint possession of a dermal tubercle and pore system and an abruptly constncted body, Desmdema and Zu are regarded as related. Desmodema, but not Zu. agrees with Regolecus in the arrangement of the dorsal pterygiophores. The genus Desmodema was erected for the recep- material list the first length measurement is the tion of Trachypterus jacksoniensis polystictus snout-vent length (SV), the second the standard Ogilby (Waltersand Fitch 1960). Fitch (1964)sub- length (SL). A single value indicates snout-vent sequently redescribed Desmodema polystictum, length of a broken specimen. mainly utilizing material from the northeast Because of the delicacy of the species, most ofthe Pacific, and placed Trachypterus misakiensis specimens were damaged in some way, and not all Tanaka, 1908 and T. deltoideus Clark, 1938 in its counts and measurements were made on all synonymy. Our interest arose from the observa- specimens. In particular, fin lengths represent tion that two recently collected specimens had minimum measurements, since all fins seem to what appeared to be anomalously low vertebral have been broken to some degree. No specimen counts. This initiated the present study, which has appeared to have unbroken pelvic fins. Measure- revealed the existence of two species, one of them ments are self-explanatory and were taken with undescribed. In addition to distinguishing and de- flat-point dividers or dial calipers. Vertebral scribing the species, our material has allowed us to counts were taken from radiographs or cleared amplify the generic description of Desrnodema and and stained material. Dorsal rays could be enum- to detail some of the remarkable ontogenetic erated on only a few specimens. changes undergone by its species. RESULTS MATERIALS AND METHODS Desinodeinu Walters and Fitch Specimens used in this study are housed in the following institutions: California Academy of Sci- Desmodema Walters and Fitch 1960. Type-species ences (CAS),Department of Biology, University of Trachypterus jacksoniensis polystictus Ogilby California, Los Angeles (UCLA),Natural History 1897, by original designation. Museum of Los Angeles County (LACM), and Scripps Institution of Oceanography (SIO). In the Diagnosis.-A trachipterid with 4-10 caudal rays, the caudal on the same axis as the caudal peduncle, all caudal rays borne on terminal cen- 'Scripps Institution of Oceanography, La Jolla, CA 92093 trum, no lower caudal lobe. Seven dorsal 5outhwest Fisheries Center, National Marine Fisheries Ser- me, NOAA, P 0 Box 271, La Jolla, CA 92038 pterygiophores before first neural spine. Body con- Manuecn t accepted March 1977 843 FISHER#BULLETlN VOL (5, NO 4. 1977 FISHERY BULLETIN VOL 75. NO 4 stricted behind anus, tail exceedingly elongated in Two nostrils in prejuveniles, the posterior just juveniles and adults. Young with numerous dark before anterior margin of eye: posterior opening round spots. Skin of adults pierced by numerous obliterated in juveniles and adults. Nasal pores. epithelium without ridges or folds at all sizes. Head bones cancellous and ridged. Mouth strongly Description-Body strongly compressed later- oblique. Teeth restricted to one to four in each ally, postanal portion of body narrowing into a prernaxilla and two enlarged, recurved fangs on whiplike tail in juveniles and adults (posterior mandible, one on either side of symphysis. Gill vertebrae about four times as long as 14th ver- rakers 12-31 4 (9-10)usually 3 + 9, fleshy, distally tebra). Posterior region of hody of larvae and pre- expanded and leaflike. Rakers ofupper limb with a juveniles narrow, but not exceedingly elongate few teeth. Pseudobranch well developed. Gas (posterior vertebrae shorter than 14th vertebra). bladder present in smalljuveniles (to about 30 mm Seven pterygiophores before first neural spine, SV).rudimentary or absent in large juveniles and one or two pterygiophores between first and sec- ad u 1 ts . ond neural spines. First pterygiophore closely Very young silvery, prejuvcniles silvery with applies to back of skull, no predorsal bones. An- profuse dark spotting. adults without spots. terior five or six dorsal rays elongated in larvae and prejuveniles to form a dorsal pennant: these Growth i,h(iriges.-Although we have no niate- rays completely lost in adults. Pelvics long and rial smaller than 18.9 mm SV,it appears that fanlike in young, absent in adults. Caudal well development from a silvery or transparent form developed, of 4- 10 unbranched rays. parallel to with a triangular outline with the head deepest, axis of tail. Caudal rays all borne on last ural into the polka-dotted, deep bodied prejuvenile is centrum. no ventral caudal lobe t Fignre 1 ). gradual. The transition from prejuvenile to Fin rays with a lateral row ofsmall spines, these juvenile is probably rapid and can fairly be termed weak or absent on posterior pelvic rays, middle a metamorphosis. There is ;i large-size gap in our caudal rays, and pectoral rays. Each dorsal ray material of D. po/.vsfictrrtn (91-260 mm SV). but anterior to elongated tail portion of body with a our material of D. lorrcrti includes the appropriate single laterally directed stout spine on either side size classes. The difference between the pre- of the base. juvenile and the final body form can be seen in Lateral line ending at caudal base, lateral-line Figure 5. The two specimens are almost identical scales with a pair of spines. Body otherwise scale- in snout-vent length. However, the upper speci- less at all sizes ID.po/.vstic,turri ), or young covered men is essentially a miniature adult. The major with scales, each with a pair of'longitudinal spin- differences are in the change in the ventral profile, ous ridges tD. lorurn ). Skin of adults with cartilag- elongation of the tail, increase in eye size, eruption inous tubercles. and pierced by numerous pores of lower jaw teeth, and loss of the spots, pelvic fins. (Walters 1963). No enlarged tubercles on ventral and posterior nostril. Juveniles, including our midline. largest f 173 mm SV) have an elongate opening not yet covered over by the skin at the position of the pelvic fins, indicating that loss of the pelvics may be rapid, and from the base. LValters (19631indicated that juveniles of,D. /x(>.strc,ttrrtr are scaled. but that adults are scale- less. and have cartilaginous tubercles and a sub- dermal canal system connccted to the surface by nunierous port's. In our material of D. lorurn an 18 5-mm SV hilvery individual lacks both scales and tubercles. An individual 36 mm SV is scaled. hut lacks tubercles. and in another 136.5 mm SV), tubtxrclrs are present ventrally. and on the sides hrhind the head. Our largest polka-dotted pre- FIGURE1.-Caudal skeleton of' De,srriodcrm pu/u!ic,tiirri. SI0 juvc,nile is 95 mm SV. upper sides are scaled: 73-340. Camera lucida drawing at 25 6 mag-nificat~~nOnly Th bases of caudal rays shown. CR, caudal ray; Hy hypural. CJt, the reiiiaindcsr of the body is covered with tuber- first ural centrum: LIZ, second ural centruni and hypural cles and the subcutaneous canal system is well 84'1 ROSENBLATT and BUTLER THE RIBBONFISH GENUS DESMODEMA developed, with surface pores present. A juvenile the largest specimens were taken in purse seines, of 104 mm SV has scales along the dorsal base, and indicating depths of capture of no more than 100 one of 131 mm SV lacks scales and has tubercles m. We have three adult D. polystictuni: two were and pores over the entire body. taken in nets towed in the upper 500 m, and one Desmodema polystictum does not agree with D. was taken in a purse seine. lorum in the course of development of the tuber- Fitch’s (1964) report on stomach contents pro- cles and pore system. None of our specimens has vides equivocal evidence: Idiacanthus is a scales. Instead tubercles are developed in a speci- mr,sopelagic vertical migrator, but Phroninia men of 36 mm SV, and tubercles and pores are svtlentnrin occurs in the upper 300 m (Eric present in an individual of 42 mm SV. Walters Shulenberger. Scripps Institution of Oceanog- (1963) was unaware of the existence of the two raphy. pers. commun.). There is thus no objective species of Desniodema and his figure 1 was un- evidence that either species of Desniodema lives doubtedly based on a juvenile of D. lorum. IxaIow 500 m (although the possibility is not In juveniles the first six dorsal rays are elon- excluded). The species of Drsmodema would seem gated (broken in all our specimens). These rays, to be members of the deep epipelagic group as which are borne on the pterygiophores before the defined by I’arin (1968).