Bioacoustics of Ventojassa frequens

Remarks . Ventojassa frequens does not exhibit sexual dimorphism in the antenna 2 but does in the gnathopod 2 and enlargement of pereopods 5 and 6 relative to 7. The pereopod enlargement is particularly pronounced in large females though large males show this enlargement to a lesser extent. Chilton recognized two male morphs based on the male’s thumb shape and the expansion of the pereopods 5 and 6 (especially pereopod 6): conical thumb with “stout” pereopods 5 and 6 in his then named Podocerus frequens Chilton, 1883 and cubic thumb with “much expanded” pereopods 5 and 6 in his then named Podocerus latipes Chilton, 1884 . However, Chilton (1884) had reservations about the two forms being different species, stating that Podocerus latipes “...may prove to be only a variety of P. frequens .” Chilton (1921) added some collecting information for these specimens, stating that they were fairly common in Lyttelton Harbour at the roots of Macrocystis and other seaweeds above low-water level. Chilton (1921) also pointed out that Stebbing (1906) had synonymized the two species as Jassa frequens ( Chilton, 1883 ) , regarding the cubic thumbed morph illustrated by Chilton (1884) to be the male and seemingly ignoring the conical thumbed male illustrated earlier by Chilton (1883) . Chilton’s type material listed in Shaw & Poore (2016) were kindly lent by the Canterbury Museum along with material from other locations listed above. The single male specimen that Chilton (1883) illustrated in his type description and Plate III, Fig. 2 was of a very small conical thumb (his Fig. 2b ) and this drawing does not correspond with the long conical thumb borne by the male slide mounted and designated type CMNZ 2015.149.86 ( Fig. 8 ). Chilton (1883) did note in his new species description that “The process on the propodos of second gnathopoda of male varies in size in different specimens, and is often longer and more distinct than shown in fig. 2b.” The other two type slides CMNZ 2015.149.84 and 85 are whole body mounts of adult females, but neither corresponds with Chilton’s (1883) Fig. 2 , either. Chilton’s label on CMNZ 2015.149.84 states that the specimen is a male but it is actually an adult female with setose brood plates. Chilton (1921) also illustrated the cubic thumbed type of male gnathopod 2 in Fig. 4A, p . 228 and this drawing matches the slide mounted male gnathopod 2 on Chilton’s slide CMNZ 2015.149.2161 from Brighton, Otago , New Zealand , collected Jan. 1890 . Chilton’s (1921) Figs 4B, C correspond to dissected appendages of a female from Stewart Island, collected by H. B. Kirk (CMNZ 2015. 149.2116). Chilton’s (1921) Fig. 4D appears to be a pereopod 5 (not 6 as stated in the figure caption) but does not exactly match the pereopods on either of these slide mounts, showing fewer spines on the anterior margin of the basis. Jassa barnardi Stephensen, 1949 from Tierra del Fuego ( type shown in Figs 10 and 11 ) is clearly the same as Chilton’s conical thumbed male ( type male shown in Fig. 8 ). It has the same slender antennae, slender propodus of gnathopod 1, conical thumb on the propodus of gnathopod 2, minimal overlap of the merus over the carpus on pereopods 3 and 4 and wide merus and carpus on pereopods 5–7 with strong spination on the posterior margins. The same features of the urosome, not visible on Chilton’s slide mount of the type is evident in his un-mounted specimens preserved in alcohol (CMNZ 2015.149.575...604). This forces its synonymy under Ventojassa frequens . Additional illustrations of specimens from more recent collections are given here for comparison ( Figs 12–15 ). Fig. 16 shows a graph of thumb length relative to body length in the conical thumbed and cubic thumbed males. The majority of specimens were taken from recent collections in New Zealand but they correspond well with specimens from Chilton’s collection. The contrast between the two morphs is shown in the much longer thumb in the conical thumbed males compared to the cubic thumbed males of the same body length. Within the longer conical thumbed group, there is no marked transition in thumb length, suggesting that thumb production occurs gradually over several molts rather than at the terminal molt as in Jassa ( Conlan, 1989 ) . For the cubic thumbed group, the largest specimen showed a longer thumb than the others, but more specimens are needed to determine variation. Chilton’s two morphs may indeed be separate species, but this requires DNA analysis as no non-sexually dimorphic characters could be found that separated the two morphs. While large males could be distinguished based on thumb morphology (conical vs cubic), and large females found with the cubic thumbed males had grossly enlarged pereopods 5 and 6 while large females found with conical thumbed males had less enlarged pereopods 5 and 6, smaller females and thumbless males could not be assigned to the two morphs. In addition, the two morphs appeared to co-occur, as evidenced by Chilton’s collection from Lyttelton, New Zealand (CMNZ 2015.149.575...604), which contained 3 conical thumbed males and 2 cubic thumbed males, as well as adult females with a range of moderately to grossly enlarged pereopods 5 and 6. There was also a juvenile Jassa gruneri Conlan, 1990 mixed in. One of the two cubic thumbed males in this collection is the one likely used by Chilton (1884) to illustrate the second gnathopod of the male Podocerus latipes in his type description, as this appendage had been torn off from the right side and the left gnathopod 2 corresponded with his Plate XIX, Fig. 2b. K. H. Barnard (1932) illustrated a conical thumbed male gnathopod 2 of a specimen named “ Jassa pusilla ” captured at Tristan da Cunha 30 Jan. 1926 at 40–46 m on a R. S. S. Discovery expedition. Stephensen (1949) noted that this was the same as his new species Jassa barnardi (herein transferred to V. frequens as stated above). He listed additional specimens to those examined for this study collected at Tristan da Cunha , Nightingale and Inaccessible Islands at 0–40 m depth. The specimens listed by Schellenberg (1931) from Valparaiso and Iquique, Chile (just south of Caleta Bruna) were possibly those examined for this paper and listed above. Schellenberg (1953) illustrated a cubic thumbed male gnathopod 2 and the urosome of a female from L̹deritz bay, Namibia (not seen). In his New Zealand study, J. L. Barnard (1972) collected V. frequens from washes of mixed species of low intertidal algae at stations in Dunedin, Lyttelton, Kaikoura, Wellington , and Leigh in addition to the cubic thumbed morph he illustrated from Huaroa Point and examined for this paper. These have not been seen but are likely to be the same cubic thumbed morph as otherwise, J. L. Barnard would likely have remarked on the difference. Additional unexamined collections of V. frequens from the Bay of Islands, Waitemata Harbour, Leigh, Hahei, and the Chatham Islands , New Zealand ( 0–12 m depth) are held at the Auckland Museum (AuM). Griffiths (1975) recorded two collections of V. frequens from False Bay, South Africa . No station number was given, so it could not be determined whether either of these corresponded to a single False Bay collection (station FAL 604G) that was lent by Griffiths for this study. This collection held a cubic thumbed morph. There are eight species of Ventojassa currently known (ordered by date of description and collection location): V. ventosa (J.L. Barnard, 1962 ) from California, V. crenulata Ledoyer, 1979 from Madagascar , V. dentipalma Kim & Kim, 1991 from Korea , V. helenae Vader & Myers, 1996 and V. zebra Vader & Myers, 1996 from Australia , V. beagle Alonso, 2012 from Argentina and V. palauensis Myers, 2013 from Palau . Of these, V. frequens may be closest to the Australian V. helenae and V. zebra which share the broad merus and carpus on pereopod 5. However, V. frequens has a narrower palm of gnathopod 1, a different ornamentation of the palm of gnathopod 2, pereopod 5 is without stridulating ridges, and pereopod 6 is more spinose and (especially in larger males and females) markedly stouter than pereopod 7. Common to other species of Ventojassa , V. frequens has a strongly produced interramal spinous process underlying the rami of uropods 1 and 2 but this is almost as long as the rami, where in other species it is typically shorter.