Hermilius longicornis Bassett-Smith 1898
Creators: name: Boxshall, Geoff
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Maxillopoda
Siphonostomatoida
Caligidae
Hermilius
Hermilius longicornis

description: Hermilius longicornis Bassett-Smith, 1898
(Fig. 65)
Material examined. 3♀♀ from Netuma proxima (Ogilby, 1898) (TC16993) 11 January 2016, QM Reg. No. W53119; 12♀♀ (TC16997) 11 January 2016, 6♀♀ QM Reg. No. W53120, 6♀♀ NHMUK Reg. Nos 2017.334– 339.
Site on host. Gill filaments.
Differential diagnosis. Cephalothorax well developed with lateral zones folded ventrally (Fig. 65A, B) and supported by prominent ribs; outer margins of lateral zones provided with marginal membrane. Frontal plates with marginal membrane, lacking lunules. Fourth pedigerous somite forming narrow “waist” region; fourth legs concealed by genital complex. Genital complex large and dorsoventrally flattened, with wide wing-like lateral extensions reaching to base of free abdomen (Fig. 65A, C); genital complex about 1.76 times longer than wide, with rounded posterolateral corners. Abdomen indistinctly subdivided by constriction at mid-length (Fig. 65C); about 1.4 times longer than wide and shorter than genital complex. Caudal rami longer than wide, armed with short setae. Antenna comprising short unarmed first segment, lacking any process, slightly longer second segment and well developed subchela forming large apical hook with conspicuous accessory hook (Fig. 65D); subchela with single seta on proximal part and subapical seta on accessory hook. Tine of post-antennal process vestigial; papillae on vestigial process bisensillate; no papilla found on adjacent body surface. Maxillule with long slender posterior process. Maxilla with robust calamus and canna fused to basis. Maxilliped very slender. Sternal furca with short blunt tines, box of furca largely incorporated into ventral cephalothoracic surface. Leg 1 (Fig. 65E) with short sympod bearing enlarged outer basal seta and hirsute vestigial endopod; spines 1 to 3 on distal exopodal segment of leg 1 extremely developed, as long as (spine 3) or markedly longer than segment (spines 1 and 2); seta 4 short and naked: posterior margin with 3 short plumose setae. Leg 2 biramous, with 3-segmented rami: outer spines on exopodal segments aligned close to longitudinal axis of ramus; proximal outer spine on third segment similar in length to spine on second segment (Fig. 65F). Leg 3 with indistinctly 3-segmented exopod (Fig. 65G); first segment bearing weakly curved spine but lacking inner seta; second segment incompletely separated from third, armed with outer spine and inner seta; third segment with 3 spines and 4 setae; endopod 2-segmented; first segment forming small rounded velum and bearing inner seta; compound distal segment with 6 plumose setae. Leg 4 uniramous, indistinctly segmented (Fig. 65H); exopod with 1 lateral spine and 3 distal spines; outer and middle distal spines about equal in length. Body length of female 7.36 mm, range 7.0 to 7.36 mm (based on 10 specimens).
Remarks. This species can be characterized by the lack of any transverse suture line located distal to the accessory hook on the subchela of the antenna, combined with the setiform state of the caudal setae. According to the most recent key to species of the genus Hermilius produced by Ho & Kim (2000), these two character states are shared by H. longicornis, H. alatus Hameed, 1981, H. ariodi Prabha & Pillai, 1986 and H. youngi Kabata, 1964. Two of these species have markedly reduced setation on the exopod of leg 3: H. ariodi has a total of only 5 setal elements on the compound distal exopodal segment while H. youngi has 6 elements (cf. Fig. 66G). In H. longicornis the second and third exopodal segments of leg 3 are incompletely separated and have a setal formula of I-I; III,4 (Fig. 65G). In contrast, the second and third segments are clearly separated in H. alatus and exhibit reduced armature: the second segment has a long outer spine but lacks an inner seta, while the third carries 3 long naked spines plus a single plumose seta around its distal margin (Hameed, 1981: Fig 3a).
Hermilius longicornis was previously reported from Sri Lanka (Bassett-Smith, 1898b; Kirtisinghe, 1964), Trivandrum, India (Pillai, 1963), Malaysia (Leong, 1985) and Kuwait (Ho & Kim, 2000). This is the first report from Australian waters. Previously recorded hosts include the ariids Arius acutirostris Day, 1877, Plicofollis dussumieri (Valenciennes, 1840) (as A. dussumieri) and A. thalassius (Ho & Kim, 2000). The host in Moreton Bay, Netuma proxima, is a new host record.
description: Published as part of Boxshall, Geoff, 2018, The sea lice (Copepoda: Caligidae) of Moreton Bay (Queensland, Australia), with descriptions of thirteen new species, pp. 1-172 in Zootaxa 4398 (1) on page 139, DOI: 10.11646/zootaxa.4398.1.1, http://zenodo.org/record/1202953