Matsui: Description of young platytroctids from northeastern Pacific Ocean 



217 



YS 15 30 40 50 60 70 80 200 

 SL(mm) 



Figure 3 



Length-frequency distribution of Holtbyrnia 

 latifrons in SI0 collections, 1950-73. 



30 



n p i i w i  i p V pi 



YS 15 30 40 60 80 100 120 140 160 180 >200 



SL(mm) 



Figure 4 



Length-frequency distribution of Sagamichthys abei in SIO collections, 1949-79. 



(GO]), located just behind the mandibular symphysis, 

 and the pectoral organ (PO) on the pectoral fins, ap- 

 pear by 75 mm. The anal organ (AO), located just before 

 the anus, appears in large adults. 



Remarks Some young specimens of//, latifrons and 

 S. abei with nearly exhausted yolksacs retain char- 

 acteristics of the earliest stages, i.e., fragile mouth, 

 short head, and toothless mouth. Only the fin rays are 

 relatively well developed. They appear to be starved 

 in spite of the presence of yolk material and may in- 

 dicate that they need to feed while the yolk is present. 

 The severely underdeveloped head and mouth indicate 

 that development either lagged from the very early 

 stages or had regressed from a more advanced stage. 

 These larvae were assumed to be atypical, and were 

 not included in the larval description. 



Distribution 



In SIO samples, H. latifrons larger than 30 mm are rare 

 and individuals >50mm are nearly absent (Fig. 3); 

 relatively small H. latifrons may avoid nets as large 

 as a 3-m IKMT. Decline in size of S. abei in our samples 

 is more gradual. The collection contains a number of 

 individuals as large as 80 mm and a few even larger 

 (Fig. 4). These results point to the inadequacy of nets 



4- 



JUN 



JUL 



> 16 

 Q 



-, APR 



MAY 8 



AUG 



SEP 



OCT 



NOV 



DEC 



T~1 



YS 15 30 40 50 60 YS 15 30 40 50 60 



SL(mm) 



Figure 5 



Length-frequency distribution of Holtbyrnia latifrons in SIO 

 collections, 1950-73, presented by month of capture. 



as large as 3-m IKMT in sampling larger juveniles of 

 both species. 



The presence of individuals smaller than 20 mm dur- 

 ing most of the year is interpreted as year-round 

 spawning (Figs. 5, 6). These figures represent samples 

 collected over many years pooled by month. 



Depth distribution for both species is estimated to 

 be 300-1000 m (Matsui and Rosenblatt 1987). On 

 MLRG-SIO cruises, 63 opening-closing Leavitt net 

 tows made in this depth zone collected 12 specimens 

 of H. latifrons and 3 of 5. abei. Fourteen net tows 

 sampling shallower than 300 m and 30 tows sampling 

 deeper than 1000 m on these cruises failed to catch 



