Pseudoscopelus scriptus, Lutken, 1892 Pseudoscopelus scriptus Lutken, 1892

Melo, Marcelo R. S., 2019, A revision of the genus Pseudoscopelus Lütken (Chiasmodontidae: Acanthomorphata) with descriptions of three new species 2710, Zootaxa 2710 (1), pp. 1-78 : 13-14

Pseudoscopelus scriptus species group

Composition. The Pseudoscopelus scriptus species group is composed of six species: P. cephalus , P. cordilluminatus , P. obtusifrons , P. pierbartus , P. sagamianus , and P. scriptus .

Diagnosis. The Pseudoscopelus scriptus species group is diagnosed from its congeners by unique configuration of supraorbital canal pores and photophore pattern: supraorbital canal pores modally five, small pore of supraorbital canal, medial to supranasal pore usually absent, with the exception of the holotype of P. cephalus and a few specimens of P. cordilluminatus (vs. supraorbital canal pores six, the small pore of supraorbital medial to supranasal pore always present in all other species of Pseudoscopelus ); luminescent tissue present as discrete photophores (vs. completely absent in P. aphos and represented as vestigial white lines in P. parini ); mxf arranged in an elongate continuous row that extends from level of posterior margin of eye to the angle between preopercle and dentary, and apf absent (vs. mxf and apf absent in the species of the P.scutatus species group; mxf absent and apf present in P. lavenbergi ; mxf short, not connected posteriorly with apf present in the P. astronesthidens species group; and mxf irregular, with widely spaced photophores anteriorly, and connected with apf posteriorly in the P. altipinnis species group); if and prvf continuous (vs. if and prvf disconnected at level of cleithrum in all other species of Pseudoscopelus ); trf in a single row of closely spaced photophores, with a medial, circular cluster (vs. trf absent in the P. astronesthidens and P. scutatus species groups; trf arranged in a broad band of three or four photophores in P. lavenbergi ; and in a single row of widely spaced photophores without the medial cluster in the P. altipinnis species group).

Ontogenetic changes and the identification of juveniles. Characteristics of dentition are of great importance to diagnose the species of the Pseudoscopelus scriptus species group; however, they are not completely developed in specimens less than 45.0 mm, with the exception of P. obtusifrons . Ontogenetic changes in dentition are best understood in P. scriptus , because it is very well represented in scientific collections in a wide range of sizes.

Juveniles of Pseudoscopelus scriptus have teeth arranged similar to P. pierbartus , the premaxilla is not very wide (10–12% in length) and dentition arranged in three series of a single row of teeth each, with the mesial series having few teeth. Because the distribution of P. scriptus and P. pierbartus overlaps, the juveniles cannot be separated easily, but in P. pierbartus the saf extends a little more anteriorly, reaching the level of anus, than in P. scriptus . This allows making tentative identifications. The number of rows of teeth in the mesial series of the premaxilla increases with size, starting in specimens of about 31.0–32.0 mm SL and reaching full development by 45.0 mm SL. Teeth of the mesial row in a specimen of 31.0 mm SL (MCZ 68463) are externally developed, but are not attached to the bone; in a 31.8 mm SL specimen (UF 19987), the teeth of the left side of the premaxilla has the adult arrangement and are completely attached to bone, but in the left side it is as juvenile. A 44.5 mm SL specimen (MCZ 101790) is the smallest specimen examined with fully developed dentition on the premaxilla and dentary. Pseudoscopelus cephalus , P. cordilluminatus , and P. sagamianus are not common in scientific collections and a good series of juveniles is not available. A 24.4 mm SL specimen (USNM 200533), tentatively identified as P. cordilluminatus , has some growing teeth under the skin. In P. obtusifrons the diagnostic hooked teeth flared outwards are developed in a 16.8 mm SL specimen (USNM 200535).

Pseudoscopelus scriptus and P. obtusifrons have allometric, statistically significant growth of the pectoral fin: in P. scriptus the growth is positive (p=0.001); in P. obtusifrons , it is negative (p=0.042); this explains the large standard deviation variation found for both species (SD= 5.3 and 3.2, respectively).