Illacme Cook & Loomis, 1928

Marek, Paul E., Krejca, Jean K. & Shear, William A., 2016, A new species of Illacme Cook & Loomis, 1928 from Sequoia National Park, California, with a world catalog of the Siphonorhinidae (Diplopoda, Siphonophorida), ZooKeys 626, pp. 1-43 : 6

Taxon classification Animalia Siphonophorida Siphonorhinidae

Genus Illacme Cook & Loomis, 1928

Family placement.

The genus Illacme is placed in the family Siphonorhinidae based on the following characters: Head pear-shaped (♂) or triangular (♀), not elongate or beak-shaped, as in the Siphonophoridae (Fig. 2 A–F). Antennae elbowed between antennomeres 3, 4 (Figs 2B; 3A, B). Antennomeres 5, 6 with apical dorsal cluster of 7 or 8 basiconic sensilla (Bs2) in slight depression, not in defined circular pits, as in the Siphonophoridae (Figs 2B, D; 3A, B). Antennomere 1 set deep in cranium, not entirely visible dorsally as in Siphonophoridae (Figs 2A, B; 2E; 3C, D). Antennomere 2 longer than wide, conical, not doughnut-shaped and wider than long as typical in Siphonophoridae . Anterior margin of collum straight, not emarginate medially as in Siphonophoridae . Sterna with prominent midline triangular projections, oriented ventrally (Figs 3E, F; 4A, B). Posterior gonopods with distal podomere divided into 2-4 branches with one branch spike-like (Figs 4C, D, E, F; 5 A–D). See also diagnoses of Illacme in Shelley (1996b, pg. 23), Marek et al. (2012, pg. 85), and Enghoff et al. (2015, pg. 386), and of Siphonorhinidae in Shelley and Hoffman (2004, pg. 218), Wesener (2014, pg. 417), and Enghoff et al. (2015, pg. 386).

Diagnosis. Adults of Illacme are distinct from other siphonorhinid genera (and commonly encountered millipedes co-occurring with Illacme tobini sp. n. and Illacme plenipes ) based on the combination of the following characters: Body light cream-colored, thread-like, extremely narrow and long (max. width: ♂ 0.55, ♀ 0.64; max. length: ♂ 28.16, ♀ 40.40). Adult individuals with 84-192 segments, and with 318-750 legs. Body covered with many long delicate setae, imparting a velvety appearance (Figs 5E, F; 6A, B). Antennae elbowed between antennomeres 3, 4 (Figs 2B; 3A, B). Antennomeres 5, 6 enlarged, appearing much larger relative to other articles (Figs 2B, D, 3A, B). Head pear-shaped in males or triangular or chevron-shaped in females, eyeless (Fig. 2 C–F). Genae slightly convex (♂) or straight (♀), not concave (imparting a teardrop-shaped head) as in Nematozonium filum , Siphonorhinus sp. ( Wesener 2014), and the family Siphonophoridae (Shelley 1996, Shelley and Hoffman 2004). Mouthparts (gnathochilarium, mandibles) and labrum tightly appressed, tapered anteriorly to rounded apex-not beak-shaped, as in the Siphonophoridae (Figs 2 A–F; 3C, D). Labrum with a deep medial slit, margins lined with teeth (Figs 6 C–F; 7 A–F). Denticulate shelf-like carina, projecting dorsally from labrum-epistome margin (Figs 6E, F; 7D; 8A, B). 9th and 10th leg pairs modified into gonopods, each comprising 7 podomeres (Figs 4C, D; 8 C–F; 9 A–F). Anterior gonopod thick, bulkier than posterior gonopod (Figs 4C, D; 8 C–F). Anterior gonopodal apex (podomere 7, A7-Fig. 4C, D) spade-shaped; at rest, cupped sheath-like around posterior gonopodal stylets (podomere 7, P7-Figs 4E, F; 9 A–F). Posterior gonopodal podomere 7 deeply divided, comprising a bundle of 3 ( Illacme plenipes ) or 4 ( Illacme tobini sp. n.) stylus-shaped articles; one article spike-shaped (Fig. 4E, F); other siphonorhinid taxa with 2 stylus-shaped articles and a small spine ( Nematozonium filum ) or 2 articles without spine ( Siphonorhinus species and Kleruchus olivaceus Attems, 1938). 2, 3 dorsal-most, longest articles laminate distally and recurved laterally, with denticulate posterior margins appearing saw-like (Fig. 5 A–D). Ventral-most, shortest article acuminate distally, spike-like.