Asterocheres proboscideus Stock, 1966

Bandera, Eugenia & Conradi, Mercedes, 2013, Redescription of five Asterocheres species (Copepoda: Siphonostomatoida) and a description of a new species discovered in the collections of the Zoological Museum of Amsterdam, Journal of Natural History 47 (5 - 12), pp. 597-618 : 612-614

Asterocheres proboscideus Stock, 1966

( Figure 6 )

Material examined

Holotype female (ZMA-Co.100.957a) and six paratype females (ZMA-Co.100.957a and ZMA-Co.100.957b) associated with the calcareous sponge Pericharax heteroraphis Polejaeffin Mauritius (20 ◦ 22 ′ S, 57 ◦ 21 ′ E) at 10–19 m depth collected 10 February 1964 by J.H. Stock.

Description

Female. Body cyclopiform, with cephalothorax nearly circular in outline and occupying distinctly less than half of entire body length and cylindrical urosome (fig. 9A; Stock 1966). Mean body length 720 µm (650–810 µm) and maximum width 370 µm (330–400 µm), based on six specimens. Prosome comprising cephalothorax (fully incorporating first pedigerous somite) and three free pedigerous somites. Cephalothorax and free pedigerous somites with rounded posterolateral angles (fig. 9A; Stock 1966). Urosome four-segmented, comprising leg 5-bearing somite, genital double-somite and two free abdominal somites (fig. 9B; Stock 1966). Genital double-somite about as long as wide; paired genital apertures bipartite, each comprising lateroventral copulatory pore and dorsolateral gonopore; lateral margins with rows of long spinules on distal half and posterior part of somite (fig. 9B; Stock 1966). Each genital area with two smooth setae.

Caudal rami slightly wider than long; with rows of spinules on terminal part; and six setae. Seta I absent. Setae II and VII smooth and displaced onto dorsal surface. Setae III–VI plumose, arranged around posterior margin of segment, middle setae very stout.

Antennule 20-segmented ( Figure 6B ), about 360 µm long. Segmental fusion pattern as follows: 1(I)-2, 2(II)-2, 3(III)-2, 4(IV)-2, 5(V)-1, 6(VI)-2, 7(VII)-1, 8(VIII)-2, 9(IX-XII)-7, 10(XIII)-1, 11(XIV)-1+1 spine, 12(XV)-2, 13(XVI)-2, 14(XVII)-2, 15(XVIII)-2, 16(XIX)-2, 17(XX)-1, 18(XXI)-2+1 aesthetasc, 19(XXII-XXIII)-3 and 20(XXIV-XXVIII)-9. Segment 10(XIII) reduced and partly overlapped by distal expansion of compound segment 9(IX-XII). All setae smooth.

Antenna biramous ( Figure 6E ), about 270 µm long (including terminal claw). Coxa small, unarmed. Basis elongate with spinules on inner distal margin. Exopod one-segmented, 1.5 times longer than wide, with one proximal seta medially, one subterminal seta laterally, and one distal seta twice as long as other two; all setae smooth. Endopod three-segmented; proximal segment elongate, with spinules on inner part; middle segment produced distally on medial side but articulating with distal segment proximally on lateral side, with one smooth subterminal seta, shorter than entire segment; distal segment with row of long setules on inner margin, one smooth lateral seta, one smooth subterminal seta, and terminal claw slightly longer than entire endopod.

Siphon very long, about 600 µm long, with tubiform distal part usually curled; reaching beyond caudal rami.

Mandible ( Figure 6A ) comprising stylet-like gnathobase and one-segmented palp. Palp elongate, with spinules on laterodistal margin and two plumose terminal setae unequal in length.

Maxillule bilobed ( Figure 6C ). Inner lobe 2.5 times longer than outer; with tuft of short spinules on distal half and four distal setae, one of them smooth and short. Outer lobe with one subterminal barbed seta and three plumose terminal setae.

Maxilla ( Figure 6D ) two-segmented. Coxa unarmed and basis claw-like with row of small spinules on outer margin and fan-like tuft of setules medially as figured.

Maxilliped five-segmented (fig. 10E; Stock 1966) as described and illustrated by Stock (1966).

Swimming legs 1–4 biramous, with three-segmented rami and intercoxal sclerite present in all of them. Swimming legs 1–4, fifth and sixth legs as described and illustrated by Stock (figs 9B, 10F, 11A–C; Stock 1966).

Colour ruddy-yellowish.

Male. Unknown.

Discussion

This species, which lives associated with the sponge Pericharax heteroraphis Polejaeff in Mauritius, was collected by Stock in 1964. The discrepancies found in the reexamination of this species are as follows: (1) the antennule has 20 segments in contrast with the 19 segments described by Stock; (2) Stock described the antennary exopod having two terminal setae but this segment has one terminal, one subterminal and one proximal seta; (3) the only segment of the mandibular palp carries two plumose distal setae; (4) the inner lobe of the maxillule (second half) is covered with short and stout spinules; (5) the second segment of the maxilla, the claw, has a fan of spinules at middle length and a row of spinules on the distal margin.

This species belongs to the group of species with a 20-segmented antennule in the female. This group comprises 22 species, however A. proboscideus can be separated from all of the remaining species by the length of the oral cone. This is the only species in the group with a siphon that extends beyond the caudal rami ( Stock 1966).

Figures

Figure 6. Asterocheres proboscideus Stock, 1966, holotype (female). (A) Mandibular palp; (B) antennule; (C) maxillule; (D) maxilla; (E) antenna.