Ooperipatellus nickmayeri

These velvet worms have 14 pairs of legs in both sexes, with the last pair reduced in size but used for walking. Each foot features three complete spinous pads, with the first and third pads smaller than the second. Most legs also feature a fourth fragmented pad. The nephridial tubercle on the fourth and fifth leg pairs is located in the third pad, dividing the pad into two unequal parts. Each foot features paired claws and three distal foot papillae (one anterior, one medial, and one posterior). The males of this species feature crural tubercles on leg pairs 6 through 13. These tubercles are smooth at the base, with no scales, but feature cone-shaped tips with tiny scales.^[1]

These velvet worms vary in color from blue to predominantly orange-brown, with a light blue ventral surface. Each antenna features 30 to 32 rings, with tan or orange bands on every fourth ring starting with the 15th most distal ring and ending with ring 27 or 31. The slime papillae are also tan or orange. A furrow runs down the middle of the back. The dorsal integument features dermal papillae arranged into 12 complete plicae (transverse ridges) per segment. The gonopore in the male is cruciform, with the transverse slit longer than the longitudinal slit. The ovipositor in the females is large and conspicuous, with a genital opening in the form of a longitudinal slit at the distal end. The anus is located at the terminal end of the body in both sexes. The males of this species feature a pair of anal gland openings in front of the anus. The spinous pads, the crural tubercles and the genital pad in males, and the ovipositor in females are all whitish or light orange.^[1]

Notwithstanding the large body size, which distinguishes this species from others in the same genus, this species exhibits many of the traits that characterize this genus. These features include oviparous reproduction, 14 leg pairs in each sex, females with a well-developed ovipositor, males with a cruciform gonopore, and the absence of any modified head papillae or head organ. Phylogenetic analysis based on molecular data confirms the placement of this species in the genus Ooperipatellus.^[1]

This species also exhibits a set of features aside from its large size that distinguish these velvet worms from other species in this genus. These features include a distinctive color pattern, including the sequence of bands on the antennae, the number of plicae per segment, and the form and number of the crural tubercles in males. Furthermore, karyological analysis reveals a distinct karyotype for this species, with a heteromorphic pair of sex chromosomes (XY) and the greatest number of chromosomes (2n = 50 XY) reported to date for a species in the family Peripatopsidae.^[1]

In 2017, a phylogenetic analysis based on molecular data placed O. nickmayeri in a clade with an undescribed Tasmanian species (Ooperipatellus sp. 5), indicating that O. nickmayeri is more closely related to this Tasmanian species than to two other Tasmanian species (O. cryptus and O. decoratus) and the mainland Australian species O. insignis, three species that together form a separate clade in the same genus.^[1] In 2025, the specimen providing the molecular data for Ooperipatellus sp. 5 was identified as a specimen of O. spenceri,^[3] suggesting that O. nickmayeri and O. spenceri are closely related. The type localities of O. spenceri and O. nickmayeri are more than 88 km apart, and the molecular evidence separates these two velvet worms on relatively long branches in a phylogenetic tree, suggesting that these two close relatives are distinct species.^[1]

Distinguishing these two close relatives based on morphology requires more information from a comprehensive revision of O. spenceri. These species might be distinguished based on the spinous pads on the feet, for example, which are whitish or pale orange in the species O. nickmayeri.^[1] In the species O. spenceri, these pads are mostly brownish yellow, but the distal pad and the distal and lateral edges of the middle pad are blue.^[4] Furthermore, the slime papillae are orange or tan in O. nickmayeri but white in O. spenceri.^[1][4] Little is known, however, about intraspecific variation in these color patterns in O. spenceri.^[1]