Sphaerobelum aesculus Rosenmejer & Enghoff & Moritz & Wesener 2021, sp. nov.

Sphaerobelum aesculus Rosenmejer & Wesener sp. nov.

urn:lsid:zoobank.org:act: 84D3714E-5CF8-4063-8A4D-40BF8CBEBFB0

Figs 2A, 3–5, 6A

Diagnosis

Differs from all other species of the genus Sphaerobelum in the shape of the posterior telopod, where there is a swelling at the tip of the immovable finger, but the swelling does not extend above the margin (Fig. 5B arrow). Such a swelling is currently unknown from any other giant pill-millipede species.

Derivatio nominis

Named after the horse chestnut tree Aesculus hippocastanum L., for the resemblance of the rolled-up female to a horse chestnut. Noun in apposition.

Material examined

Holotype THAILAND • ♂; Phuket Island, Forest in Kathu district; 14 Feb.1989. M. Andersen and A.R. Rasmussen leg.; in and under old logs; NHMD 621693.

Other material

THAILAND • 1 ♀; Nakhon Si Thammarat Prov., Khao Luang NP; 8°43′25.2″ N, 99°40′7.7″ E, 355 m a.s.l.; 10–12 Oct. 2003; ATOL Expedition 2003 leg.; NHMD 621694.

Description (based on holotype)

SIZE. Length 23.8 mm. Width of thoracic shield 10.5 mm, of widest segment (9) 11.1 mm. Height of thoracic shield 6.2 mm, Height of highest segment (7) 7 mm.

COLOUR. Head, antenna, legs and tergites golden light brown. Posterior margin of tergites and paratergite tips medium brown. Anal shield medially brown, with lighter colour at edges (Fig. 2A). HEAD. Number of ommatidia 55. Antennae (Fig. 3A–C): Antennomere lengths: 6>1>2=3=4=5. Antennae short, barely reaching first leg pair. Sixth antennomere apically slightly swollen (Fig. 3A), number of apical cones 52/56 (Fig. 3B). Mandible: not dissected. Gnathochilarium: lingual lamella with numerous long setae, medially glabrous.

COLLUM. With few setae spread thinly along borders.

THORACIC SHIELD. Thoracic shield grooves wide and deep, with 3 sclerotized ledges along inner ridge.

TERGITES. Paratergite tips on posterior half projecting backwards. Tergites glabrous with dull leather-like surface (Fig. 3D–E). At high magnification tiny setae become visible.

ENDOTERGUM (Fig. 6A). With a regular flat margin. Outer zone with two rows of irregular

MARGINAL SETAE. Not extending beyond posterior margin, but reaching ⅔ of the outer area. Anterior part of marginal ridge flat. Intersegmental membrane smooth, without cones and with a row of setae with large glabrous gaps.

FIRST STIGMATIC PLATE (Fig. 4A). With a well-rounded apex.

PLEURITES. Pleurite 1 projecting posteriorly with sharp apex. Pleurite 2 with rounded apex projecting slightly.

LEGS. Ventral spines on leg 1 4/4, on leg 2 3/5, on leg 3 3/4. Apical spine absent on leg 3. Three apical and 4 or 5 ventral spines on midbody legs (Fig. 4C). Inner margin of femur with 8–12 small teeth, but not excavated. Femur 2, tarsus 4 times as long as wide.

ANAL SHIELD. Well-rounded and glabrous. Ventral side with a single small locking carina, placed ⅓ from pleurite.

MALE GONOPORE. Located at mesal margin of coxa (Fig. 4B), large, covered by a membranous plate.

ANTERIOR TELOPODS (Fig. 4D–F). Podomere 1 rectangular, as long as wide, covered with setae anteriorly, with extra long setae medially, and posteriorly glabrous. Podomere 2 with long immovable finger visible laterally in anterior view. Finger curving inwards against podomere 3. Podomere 3 cylindrical twice as long as wide. Suture between podomere 3 and 4 barely visible in posterior and lateral views. Podomere 4 very short, just ¼ of length of podomere 3, with one short and dark spine on apex.

POSTERIOR TELOPODS (Fig. 5A–B). Podomere 1 as long as wide, covered in setae anteriorly, and nearly glabrous posteriorly. Podomere 2 with wide immovable finger. Immovable finger straight, only slightly tapering towards apex, bearing an oval membranous spot on posterior side. The membrane between podomere 2 and 3 with single membranous lobe, angled. Podomere 3 with sparse setation. Podomere 3 ca 3 times longer than wide, towards immovable finger with membranous ledge, a single spine, posterior side with row of 9 or 10 crenulated teeth. Podomere 4 short, straight, ca 2.5 times as long as wide, with a short membranous ledge and 2 spines towards immovable finger.

Female from Khao Luang NP Length 45 mm. Width of thoracic shield 23 mm, of widest segment (9) 24.6 mm. Height of thoracic

shield 12.6 mm, of highest segment (8) 15.2 mm.Antennae reaching leg pair 2. Apical cones on antennae 43/34. Subanal plate well rounded. Vulvae (Fig. 5C): small, with a narrow operculum (Op), only reaching bottom part of prefemur. External lateral plate (EP) and inner mesal plate (IP) almost completely fused.

Distribution

If the female from Khao Luang (Fig. 2A) is indeed conspecific with the male holotype, the species appears to have a wide area of distribution stretching from Phuket Island at least 160 km to the east (Fig. 2). Unpublished data from a larger inventory project (see, e.g., Wesener et al. 2021) of giant pill-millipedes in the surroundings of Krabi, half way between Phuket Island and Khao Luang, did not recover this species among the numerous specimens, hinting at a patchy distribution and specific microhabitat requirements of S. aesculus sp. nov.