Bioacoustics of Trizocheles moosai

Trizocheles albatrossi and T. laurentae are also rather similar to T. moosai . Trizocheles albatrossi is readily distinguished from T. moosai by the more slender ocular peduncle (the corneal diameter is about 0.20 of the ocular peduncle length versus 0.35–0.50), shorter antennal peduncle (falling short of the lateral base of the cornea versus distinctly overreaching it) and fewer stridulatory rods or ridges on the mesial faces of propodi of the second pereopods (Forest 1987a; Komai 2013). Trizocheles laurentae differs from T. moosai in the less dilated cornea being subequal to the basal width of the ocular peduncle and in having a broad median indentation on the terminal margin of the sixth pleomere (Forest 1987a; McLaughlin & Lemaitre 2009). In T. moosai , the cornea is wider than the base of the ocular peduncle and the terminal margin of the sixth pleomere is entire.

Remarks . Trizocheles moosai was known only from the male holotype, and thus intraspecific variation was unknown. The present specimens are referred to T. moosai because of the following characters: ocular peduncle stout, with corneal diameter 0.35–0.50 of length of ocular peduncle; chelipeds equal and similar in size and armature, palms bearing rows of spines; dactyli of second and third pereopods unarmed on dorsal margins; propodi of second pereopods each without dorsodistal spine or dorsal row of spines, but with numerous stridulatory rods or tubercles on mesial face; and carpi of third pereopods each with only small dorsodistal spine. In the present specimens, slight degree of intraspecific variation is seen in the following particulars: the ocular peduncle is 0.5– 0.6 times as long as the shield; the antennular peduncle overreaches the distal corneal margin by the entire to 0.9 length of the ultimate segment when fully extended anteriorly; the antennal peduncle falls slightly short of or just reaches the distal corneal margin. In the holotype, the ocular peduncle is 0.5 times as long as the shield; the antennular peduncle overreaches the distal corneal margin by the entire length of the ultimate segment; the antennal peduncle just reaches the distal corneal margin (Forest 1987a). The holotype differs from the present specimens in having more elongate terminal spine of the ocular acicle and the presence of two spinules on the lateral margin of the shield located posterior to the midlength. In the present specimens, each lateral margin of the shield is unarmed or armed with one minute tubercle or granule. On the other hand, the arrangement of the stridulatory rods or ridges on mesial faces of propodi of the second pereopods seems to be consistent between the holotype and the present specimens. Trizocheles moosai is morphologically very similar to T. boasi . McLaughlin & Lemaitre (2009) distinguished the two species by the extension of the antennular peduncle, but the present study demonstrates that this character is not reliable owing to variation, as noted above. Nevertheless, T. boasi can be distinguished from T. moosai by the slender propodi of the second pereopods (4.0–5.0 times as long as wide versus less than 3.5 times as long) with mesial faces unarmed or armed with only a few stridulatory rods or tubercles (Forest 1987a; McLaughlin & Lemaitre 2009).